Novel Malonate-Containing Coordination Compounds with Ligands

ARTICLE pubs.acs.org/crystal

Novel Malonate-Containing Coordination Compounds with Ligands Having N- and NO-Donors: Synthesis, Structures, and Magnetic Properties Fernando S. Delgado,† Claudio A. Jimenez,‡ Pablo Lorenzo-Luis,§ Jorge Pasan,† Oscar Fabelo,†,^ Laura Ca~nadillas-Delgado,†,^ Frances Lloret,|| Miguel Julve,|| and Catalina Ruiz-Perez†,* Laboratorio de Rayos X y Materiales Moleculares (MATMOL), Departamento de Física Fundamental II, Facultad de Física, Universidad de La Laguna, Avda. Astrofísico Francisco Sanchez s/n, E-38204 La Laguna, Tenerife, Spain ‡ Departamento de Química Organica, Facultad de Ciencias Químicas, Universidad de Concepcion, Edmundo Larenas 129, Barrio Universitario, Concepcion, Chile § Departamento de Química Inorganica, Facultad de Química, Universidad de La Laguna, Avda. Astrofísico Francisco Sanchez s/n, E-38204 La Laguna, Tenerife, Spain Instituto de Ciencia Molecular (ICMol)/Departament de Química Inorganica, Universitat de Valencia, Polígono La Coma s/n, E-46980 Paterna, Valencia, Spain

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Crystal Growth & Design 2012.12:599-614. Downloaded from pubs.acs.org by MIDWESTERN UNIV on 01/24/19. For personal use only.

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bS Supporting Information ABSTRACT: In our efforts to tune the structures of mixed-ligands malonate-containing coordination compounds, four copper(II) and two high-spin cobalt(II) complexes of formulas [Cu(mal)(H2O)(dpo)]n (1), [Cu2(mal)2(H2O)2(dpp)]n 3 7nH2O (2), [Cu2(mal)2(H2O)2(bpe)]n 3 2nH2O (3), {[Cu(mal)2(H2O)2][Cu(dien)]}n 3 4nH2O (4) [Co2(mal)2(H2O)6(dpo)] 3 2H2O (5) and [Co(mal)(H2O)(phen)]n 3 2nH2O (6) [H2mal = malonic acid, dpo =4,40 -bipyridine-N,N0 -dioxide, dpp = 2,3-bis(pyridyl)pyrazine, bpe =1,2-bis(4-pyridyl)ethylene, dien = diethylenetriamine and phen = 1,10-phenanthroline] have been synthesized and structurally characterized by X-ray diffraction on single crystals. Complexes 1, 2, 4, and 6 are chain compounds, 5 is a dinuclear species, and 3 has a sheet-like structure. The malonate ligand in this family acts as either a blocking (1 and 5) or bridging ligand (26). The rod-like molecules dpo (1 and 5) and bpe (3) exhibit the bis-monodentate (1 and 3) and monodentate (5) coordination modes, whereas dpp (2), dien (4), and phen (6) act as bis-bidentate (2), tridentate (4), and bidentate (6) ligands. The neutral motifs of 16 are interlinked through hydrogen bonds and weak CH 3 3 3 π and ππ type interactions affording supramolecular three-dimensional networks. Variable-temperature magnetic susceptibility measurements show the occurrence of weak ferro- (2, 3, 5, and 6) and antiferromagnetic (1 and 4) interactions, the exchange pathways being the carboxylatemalonate (36), oxo-carboxylate (2), bis-bidentate (dpp) (2) or hydrogen bonds (1). Remarkably, the equatorial-apical exchange pathway through the carboxylate bridge present in 4 provides the first case of the occurrence of an antiferromagnetic interaction in a malonate-containing copper(II) complex.

’ INTRODUCTION Interest in the design of supramolecular coordination networks has permanently increased during the past decade.1 In this respect, the concept of molecular building block or tecton, in the context of supramolecular synthesis,2 afforded a large number of new coordination topologies with different metrics. The control of the network parameters through a careful selection of the metal ion and the organic bridging ligands offers new possibilities for developing new functional materials with useful properties. Polydentate N- or O-donor ligands are suitable examples of the tectons that are currently employed for the rational design of solid-state functionality.3 The metal assembling into predictable multidimensional structures becomes easier having in mind the structural simplicity and the well-known coordination modes of r 2011 American Chemical Society

these ligands. The control of the metrics of the resulting net arrays and their inherent properties by careful tuning of the tecton structure, donor properties, and mutual spatial alignment of binding sites, seems very attractive. In this context, novel perspectives for the design of coordination polymers may be offered by molecules that have the structural simplicity of the above ligands and special properties such as the ability to form coordination polymers both in neutral and anionic forms and to serve as efficient donors of hydrogen bonds for the effective control of the counterion position and the enclathration of hydrophilic guest species. A suitable strategy to build a spatial well-spanned Received: May 28, 2011 Revised: November 3, 2011 Published: November 10, 2011 599

dx.doi.org/10.1021/cg200675u | Cryst. Growth Des. 2012, 12, 599–614

Crystal Growth & Design

ARTICLE

Scheme 1. Coordination Modes of the Malonate Ligands in Compounds 16

framework is to use certain features of potential ligands, such as the conformational flexibility, diversity of binding modes, and ability to form hydrogen bonds. It is well-known that the carboxylate ligands play an important role in coordination chemistry. However, the rigid rod-like spacer molecules have been useful building blocks for the construction of metalorganic frameworks. The use of organic spacers, particularly the flexible dicarboxylates bridging ligands and rigid nitrogen donors as superexchange pathways between transition metal ions is of growing interest in the field of molecular magnetism. Recently, success has been achieved by combination of the flexible aliphatic dicarboxylates and chelating bridging ligands. Such compounds have either 2D layer-like structures or 3D frameworks.46 A careful selection of ligands, metal center, and reaction conditions can confer control over the topology of the resulting frameworks. In this regard, ligands as the malonic acid (H2mal), 4,40 bipyridine-N,N0 -dioxide (dpo), 2,3-bis(2-pyridyl)pyrazine (dpp), 1,2-bis(4-pyridyl)ethylene (bpe), 1,10-phenantroline (phen), and diethylenetriamine (dien), can be used as useful connectors or blocking ligands, to assemble paramagnetic centers into highdimensional arrangements. The efficiency of these ligands depends on the extent of their rigidity, and this allows a certain degree of control to be exerted over the steric constraints on the assembly process.3 The prediction of the crystal structures is still a difficult task, but their retrospective analysis provides important information for the design of materials with specific properties. For example, we have observed that the flexible malonate group is a dicarboxylate ligand with a singular behavior different from other more extended dicarboxylate-containing ligands. In previous works of its complex formation with first-row metal ions, we observed that it can exhibit different coordination modes such as bidentate [k2O,O0 (1)] and bidentate/monodentate [μk2O:kO0 (2), μ-kO:kO0 :kO00 with anti-anti (3) and anti-syn (46) conformations of the carboxylate bridge] (see Scheme 1).5 More complex bridging modes of the malonate in its complexes with heavier metal ions (4d, 5d, and 4f elements) were reported by other authors,4 but they are less frequent with 3d metal ions. The bis-bidentate behavior analogue to that exhibited by the oxalate is forbidden by geometric reasons and this dramatically affects the structure and properties of the malonate complexes. The malonate ligand occupies one or two coordination positions at a given metal ion and it neutralizes two positive charges from the metal center, allowing the inclusion of other ligands in its coordination sphere. These complementary ligands can act as bridging or blocking ligands contributing to the interconnection or isolation of the spin carriers. Thus, combining the malonate with other bridging and/or blocking ligands we have been able to prepare discrete mono-, di-, tri-, and tetranuclear species as well as infinite nD motifs (n = 13).5,6

Scheme 2

Bis-monodentate ligands such as bpe have been widely used and exploited as building blocks in multidimensional polymers.3 They are linear spacer molecules, but the coordination behavior of the metal ion and the metal/ligand ratio used is crucial. In previous works, it has been shown that dpo is also very interesting in the construction of multidimensional arrays. Dpo is an O-donor ligand, a feature that accounts for its high affinity to various lanthanide cations.7 Three-dimensional (3D) networks can be obtained based on the high coordination numbers of the heavier elements involved (equal or greater than seven).8 Mainly 1D coordination polymers have been obtained with first-row transition metal ions. Only a few examples exist for homoleptic high dimensional polymers.9 The relatively low space-demanding nature of the pyridylN-oxide donor group, combined with the orientation of the lone pairs on the N-oxide atoms, results in a relatively high flexibility regarding its coordination behavior. However, hydrogen bonding, which is the important directional interaction responsible for the supramolecular arrangement and the significant factor in crystal engineering,10 has a drawback in the field of molecular magnetism since hydrogen-bonded systems cannot provide enhanced magnetic interactions to the extent that covalent-bonded systems do. However, the supramolecular assembled networks can be easily manipulated through the adequate coligands to produce extended covalent networks.11 In the light of all of these results, and in the context of our magneto-structural research with malonate-containing homometallic complexes, we extended our work with the design and synthesis of new mixed-ligand coordination compounds. In this workr, we report the synthesis, crystallographic analysis, and magnetic properties of six different complexes by adding specific ligands (see Scheme 2): bis-monodentate (dpo and bpe); bidentate (phen); bis-bidentate (dpp) and tridentate (dien). The compounds are presented and described following the malonate coordination mode shown in Scheme 1: [Cu(mal) (H2O)(dpo)]n (1), [Cu2(mal)2(H2O)2(dpp)]n 3 7nH2O (2), [Cu2(mal)2(H2O)2(bpe)]n 3 2nH2O (3), {[Cu(mal)2(H2O)2] [Cu(dien)]}n 3 4nH2O (4) [Co2(mal)2(H2O)6(dpo)] 3 2H2O (5), and [Co(mal)(H2O)(phen)]n 3 2nH2O (6).

’ EXPERIMENTAL SECTION Materials and Methods. The reagents and solvents used were of commercially available reagent quality, unless otherwise stated. The synthetic procedure to obtain cobalt(II)-malonate can be found elsewhere.5k 600

dx.doi.org/10.1021/cg200675u |Cryst. Growth Des. 2012, 12, 599–614


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Table 1. Crystal Data and Details of Structure Determination for Compounds 16 compound formula M crystal system

1

2

3

4

5

6

C13H12CuN2O7

C20H32Cu2N4O17

C18H22Cu2N2O12

C10H29Cu2N3O14

C16H28Co2N2O18

C15H16CoN2O7

371.79

727.58

585.46

542.44

654.26

395.23

monoclinic

triclinic

monoclinic

monoclinic

monoclinic

monoclinic

C2/c

P-1

P21/n

P21/m

P21/n

P21/n

a, Å

12.918(3)

7.2818(4)

5.3547(3)

7.217(1)

7.308(3)

15.149(3)

b, Å

10.348(2)

11.813(1)

22.517(2)

17.536(2)

32.068(7)

6.620(1)

c, Å

20.404(4)

17.434(1)

9.168(1)

7.963(1)

10.378(2)

15.936(3)

α, deg β, deg

108.09(3)

74.128(8) 82.298(6)

101.346(7)

96.22(1)

93.66(2)

90.62(3) 1598.1(5)

space group

γ, deg V, Å3

86.668(6) 2592.7(9)

1429.4(2)

1083.9(2)

1001.9(2)

2427(1)

8

2

2

2

4

4

T, K

293(2)

293(2)

293(2)

293(2)

293(2)

293(2)

Fcalc (Mg m3)

1.729

1.691

1.794

1.798

1.790

1.643

F(000)

1512

748

596

560

1344

812

0.71073 1.905

0.71070 1.573

0.71073 2.032

0.71073 2.197

0.71073 1.458

0.71073 1.116

no. pars/restraints

256/0

388/0

192/0

145/0

343/0

290/0

goodness of fit (S)

1.100

1.030

0.975

1.077

1.009

1.015

R1, I > 2σ(I) (all)

0.0398 (0.0624)

0.0494 (0.1052)

0.0427 (0.0788)

0.0515 (0.0758)

0.0744/0.1934

0.0448/0.0942

wR2, I > 2s(I) (all)

0.0659/0.0753

Z

λ (MoKα Å) μ (MoKα) (mm1)

0.0792 (0.0858)

0.1212 (0.1420)

0.0933 (0.1014)

0.1167 (0.1250)

0.1220/0.1506

max/min elec den (e/Å3)

0.831/0.504

0.753/0.710

0.521/0.657

1.071/ 0.973

0.641/0.451

0.331/0.339

meas. reflections (Rint)

11416 (0.0338)

16204 (0.0351)

7555 (0.0526)

6152 (0.0310)

16976 (0.0918)

12757 (0.0861)

indep. ref [I > 2σ(I)]

3687 (2872)

7950 (4815)

3037 (2021)

2953 (2219)

6859 (3213)

2759 (1820)

mixture, and air-dried. Yield 238 mg, 60%. (Found: C, 37.16; H, 3.80; N, 4.60%; calcd. for C18H22O12N2Cu2: C, 36.89; H, 3.76; N, 4.78%). {[Cu(mal)2(H2O)2][Cu(dien)]}n 3 4nH2O (4). Compound 4 is obtained by the same procedure as 1 using an ethanolic solution (5 cm3) of diethylenetriamine (21 mg, 0.5 mmol) instead of dpo. Single crystals of 4 as sky blue prisms were grown from the mother liquor by slow evaporation at room temperature within a week. They were collected, washed with a water/ethanol mixture and air-dried. Yield 98 mg, 75%. (Found: C, 22.12; H, 4.71; N, 7.48%; calcd. for C10H29O14N3Cu2: C, 22.12; H, 5.35; N, 7.74%). [Co2(mal)2(dpo)(H2O)6] 3 2H2O (5). An aqueous solution (5 cm3) of 4,40 -bipyridine -N,N 0 -dioxide (140 mg, 0.55 mmol) was added to an aqueous solution (10 cm3) of cobalt(II)-malonate (197 mg, 1 mmol) under continuous stirring. The reddish slurry obtained is filtered and red prisms of 5 were grown by slow evaporation at room temperature within five days. They were collected, washed with a water/ethanol mixture, and air-dried. Yield 273 mg, 80%. (Found: C, 30.02; H, 4.30; N, 4.17%; calcd. for C16H28O18N2Co2: C, 29.35; H, 4.28; N, 4.28%). [Co(mal)(phen)(H2O)]n 3 2nH2O (6). The synthetic procedure followed to obtain 6 is similar to that used for 5 but using a H2O/EtOH 50:50 (v/v) solution (5 cm3) of 1,10-phenanthroline (235 mg, 1 mmol) instead of dpo. Single crystals of 6 as pale red plates were grown from the resulting solution by slow evaporation at room temperature within three weeks. They were collected, washed with a water/ethanol mixture and air-dried. Yield 311 mg, 70%. (Found: C, 45.46; H, 4.11; N, 7.15%; calcd. for C15H16N2O7Co: C, 45.57; H, 4.08; N, 7.09%). Physical Measurements. Magnetic measurements were performed at the “Servicio de Medidas Magneticas” of the University of La Laguna on polycrystalline samples with a Quantum Design SQUID magnetometer working in the temperature range 1.8300 K. The diamagnetic corrections

Elemental analyses (C, H, N) were performed on an EA 1108 CHNS-O microanalytical analyzer of the SEGAI service of the University of La Laguna. Syntheses of the Complexes. [Cu(mal)(dpo)(H2O)]n (1). Solid copper(II) basic carbonate (55 mg, 0.25 mmol) was added to an aqueous solution (15 cm3) of malonic acid (52 mg, 0.5 mmol) under continuous stirring. The suspension was heated at 4050 C, until a blue slurry solution is obtained. This solution was filtered and then mixed with an ethanolic solution (5 cm3) of 4,40 -bipyridine-N,N0 -dioxide (94 mg, 0.5 mmol). Single crystals of 1 suitable for X-ray diffraction as blue prisms were obtained by slow evaporation at room temperature within a week. They were washed with a water/ethanol 50:50 (v/v) solution and air-dried. Yield 160 mg, 80%. (Found: C, 37.44; H, 3.26; N, 7.37; calcd. for C13H12O7N2Cu: C, 41.96; H, 3.23; N, 7.53%). [Cu2(mal)2(dpp)(H2O)2]n 3 7nH2O (2). A similar procedure to that of 1 was followed for the preparation of 2, but a H2O/EtOH 50:50 (v/v) solution (5 cm3) of 2,3-bis(pyridyl)pyrazine was used instead of dpo. The dark green solution resulting from this mixture was filtered and allowed to evaporate at room temperature. X-ray quality green prisms of 2 were obtained within a week, washed with a water/ethanol 50:50 (v/v) solution, and air-dried. Yield 241 mg, 70%. (Found: C, 31.60; H, 4.15; N 7.20%; calc. for C20H32O17N4Cu2: C, 32.99; H, 4.40; N, 7.70%). [Cu2(mal)2(bpe)(H2O)2]n 3 2nH2O (3). Solid copper(II) basic carbonate (110 mg, 0.5 mmol) was added to an aqueous solution (10 cm3) of malonic acid (104 mg, 1 mmol) under continuous stirring. The suspension was heated at 4050 C, until a blue slurry solution is obtained. This solution was filtered and added to one of the arms of an H-shaped tube. An ethanol/water 50:50 (v/v) solution (5 cm3) of 1,2-bis(4-pyridyl)ethylene (182 mg, 1 mmol) was added to the other arm and an ethanol/water 50:50 (v/v) solution was used as diffusive medium. Green rectangular prisms of 3 as unique product were grown after one week at room temperature. They were collected, washed with a water/ethanol 601



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Table 2a. Selected Bond Lengths (Å) and Angles (deg) for 1a Cu(1)O(1)

1.915(2) Cu(1)O(12a)

1.962(2)

Cu(1)O(2)

1.924(2) Cu(1)O(1w)

1.950(2)

Cu(1)O(11)

2.376(2)

O(1)Cu(1)O(2)

96.01(7)

O(1)Cu(1)O(12a) 93.60(7) O(1)Cu(1)O(1w) 169.7(1)

a

O(12a)Cu(1)O(1w)

83.59(8)

O(2)Cu(1)O(12a) O(2)Cu(1)O(1w)

169.39(7) 86.16(8) 95.64(8)

O(1)Cu(1)O(11)

85.73(7)

O(12a)Cu(1)O(11)

O(2)Cu(1)O(11)

89.57(8)

O(1w)Cu(1)O(11) 104.40(9)

Symmetry operations: (a) x, y + 1, z + 1/2.

Table 2b. Relevant Hydrogen Bonds for 1a DH 3 3 3 A

D 3 3 3 A (Å)

H 3 3 3 A (Å)

DH 3 3 3 A (deg)

dpyo synthon C(11)H 3 3 C(18)H 3 3

3 O(12b)

3.362(3)

2.49(3)

174(3)

3 O(11c)

3.325(3)

2.45(3)

176(2)

O(1w)H 3 3 O(1w)H 3 3

3 O(3d)

2.768(3)

2.00(4)

166(4)

3 O(4e)

2.590(3)

1.86(4)

171(5)

3.343(4)

2.36(3)

179(3)

tape pattern

C(2)H 3 3 3 O(4f)

other H-bonds

Figure 1. View of a fragment of the crystal structure of 1 along with the numbering scheme. Ellipsoids of probability are presented at 50%. of all the constituent atoms were evaluated from Pascal’s constants12 as 183 106 (1), 184 106 (2), 141 106 (3), 134 106 (4), 166 106 (5), and 224 106 (6) cm3 mol1 [per mol of Cu(II) (14)/Co(II) ion (5 and 6)]. Experimental susceptibilities were also corrected for the temperature-independent paramagnetism [60 106 cm3 mol1 per one Cu(II) ion] and the magnetization of the sample holder. Crystal Data Collection and Refinement. Suitable single crystals of compounds 14 were mounted on a Bruker Smart CCD diffractometer, whereas those of compounds 5 and 6 were measured on a Bruker Nonius Kappa CCD diffractometer. Diffraction data for all compounds were collected at 293(2) K using graphite-monochromated MoKα radiation (λ = 0.71073 Å). The orientation matrix and lattice parameters for 16 were obtained by least-squares refinement of the reflections obtained by a θχ scan (Dirax/lsq method). Data collection and data reduction were done with the COLLECT13a and EVALCCD13b programs for 16 compounds. Spherical absorption corrections were carried out using SADABS13c for compounds 16. The indexes of data collection were 17 e h e 18, 14 e k e 14, 28 e l e 17 (1), 9 e h e 10, 14 e k e 16, 24 e l e 23 (2), 7 e h e 5, 28 e k e 31, 12 e l e 12 (3), 10 e h e 6, 22 e k e 24, 11 e l e 10 (4), 6 e h e 10, 44 e k e 42, 13 e l e 14 (5), and 18 e h e 17, 7 e k e 7, 18 e l e 18 (6). Of the 3687 (1), 7950 (2), 3037 (3), 2953 (4), 6859 (5), and 2759 (6) measured independent reflections in the θ range 5.0529.98 (1), 6.4330 (2), 6.4130.00 (3), 6.4230.13 (4), 6.4130 (5), and 6.4025.02 (6), 2872 (1), 4815 (2), 2021(3), 2219 (4), 3213 (5), and 1820 (6) have I g 2σ(I). All of the measured independent reflections were used in the analysis. The structure was solved by direct methods and refined with full-matrix least-squares technique on F2 using the SHELXS-97 and SHELXL-97 programs13d included in the WINGX software package.13e All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were located from difference Fourier maps for compounds 1, 3, and 6 and refined with isotropic thermal factors, whereas those of 2, 4, and 5 were set in geometrical positions and

a

C(2)H 3 3 3 O(1 g) C(2)H 3 3 3 O(3 g) C(10)H 3 3 3 O(2e)

3.484(3) 3.420(4)

2.53(3) 2.59(4)

144(2) 131(2)

3.457(3)

2.70(3)

144(2)

C(12)H 3 3 C(16)H 3 3

3 O(3c)

3.610(3)

2.70(3)

167(2)

3 O(1c)

3.269(3)

2.54(3)

132(2)

C(16)H 3 3 C(17)H 3 3

3 O(3c)

3.228(3)

2.33(2)

155(2)

3 O(4 h)

3.553(3)

2.71(3)

152(3)

D and A stand for donor and acceptor, respectively. Symmetry operations: (b) x, y + 1, z; (c) x, y 1, z; (d) x 1/2, y 1/2, z; (e) x + 1/ 2, y + 3/2, z + 1; (f) x + 1, y + 2, z + 1; (g) x, y 1, z; (h) x 1/ 2, y + 3/2, z 1/2.

refined with a riding model. Some disorder was found in the 1,2-bis(4pyridyl)ethylene molecule in 3, where two positions were encountered for the ethylene group, a coupled s.o.f. parameter was refined indicating similar occupation for the two positions. A summary of the crystallographic data and structure refinement is given in Table 1. Selected bond lengths and angles for compounds 16 are listed in Tables 27, respectively. The final geometrical calculations and the graphical manipulations were carried out with PARST9713f and DIAMOND13g programs, respectively. Crystallographic information is deposited in the CCDC database with numbers 294205 (1), 294202 (2), 294206 (3), 294204 (4), 294291 (5), and 294292 (6).

’ RESULTS AND DISCUSSION Description of the Structures. [Cu(mal)(dpo)(H2O)]n (1). The structure of compound 1 is made up of zigzag chains of aqua(malonate)copper(II) units bridged through dpo coligands that grow along the crystallographic b axis (Figure 1). These zigzag chains are pair-wised through a double CH 3 3 3 O synthon (Scheme 1) involving dpo atoms (Table 2b) and parallel displaced ππ interactions between dpo molecules with values of the centroid 3 3 3 centroid separation of 3.8417(9) Å (Py1 3 3 3 Py1) and 3.5152(10) Å (Py2 3 3 3 Py2), those of the centroid to normal of the plane of the aromatic ring being 33.4 (Py1) and 22.8(1) 602



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Figure 2. (a) View along the a axis of a single dpo-bridged regular chain of copper(II) ions in 1. (b) Detail of the double chains running along the b direction and their intertwining.

(Py2). They are in agreement with previously reported ππ interactions14 and form small channels of 6.6 3.5 Å2 along the b axis.15d Even when the ligand is coordinated to metal atoms, its remaining lone pair may form hydrogen bonds with neighboring hydrogen bond donors. These hydrogen bonding interactions are considerably strong due to the participation of the strongly polarized NO group.15b Hydrogen bonds involving malonateoxygen atoms and coordinated water molecules (Tables 2a and 2b) forming a tape pattern extended in the [110] and [110] directions (Figure 2) are responsible for the interlinking of the double chains to form a three-dimensional supramolecular network. Each copper(II) ion is five-coordinated and it exhibits a slightly distorted square pyramidal environment with a τ parameter16 of 0.04. The CuO5 chromophore is formed by two malonate- and one dpo-oxygen atoms and a water molecule in the equatorial plane [the average CuO(eq) bond distance being 1.938(2) Å, see Table 2a], whereas one dpo-oxygen atom occupies the apical position [CuO(ap) being 2.376(2) Å]. The maximum deviation from the mean equatorial plane is 0.084(2) Å at O(1w); however, the metal atom is shifted by 0.1079 Å from the mean equatorial plane toward the apical position. The malonate ligand exhibits a bidentate coordination mode toward the copper(II) ion [through O(1) and O(2)], with the angle subtended at the metal atom being 96.01(7). The sixmembered chelate-ring exhibits a half-chair conformation [θ = 41.6(5) and ϕ = 146.0(1)]17 which is quite unusual in malonate complexes.5,6 The dpo acts as a bis-monodentate ligand [through O(11) and O(12) toward Cu(1) and Cu(1i); (i) = x, y 1, z + 1/2] adopting the trans coordination mode. The two pyridyl rings of the dpo are planar but the ligand as a whole deviates from planarity, the dihedral angle between the two pyridyl rings being 8.85(8). The bond lengths and angles of the dpo ligand are in good agreement with those previously reported in the literature for other dpo-containing copper(II) complexes.9,15 The coppercopper separation through the dpo ligands along the chains is 12.267(2) Å, a value larger than the shortest intermolecular separation of 4.7818(12) Å [Cu(1) 3 3 3 Cu(1j); (j) = x, y + 2, z + 1]. The intermolecular separation between copper atoms in the double chain is 6.587(2) Å [Cu(1) 3 3 3 Cu(1k), (k) = x, y, z + 1/2].

Figure 3. (a) View of a fragment of the crystal structure of 2 along with the numbering scheme. Ellipsoids of probability are presented at 50%. (b) Central projection of a fragment of the copper(II) chain formed by the regular alternation of double-oxo(carboxylte) and dpp bridges.

[Cu2(mal)2(dpp)(H2O)2]n 3 7nH2O (2). The structure of 2 is made up of neutral dinuclear [Cu2(mal)2(dpp)(H2O)] units formed by a central dpp molecule which acts as a bridge between two Cu(mal)(H2O) groups. These units are linked through long double oxo(carboxylate) bridges to form regular chains that run along the [101] direction (Figure 3). These chains are further connected in the ac plane through hydrogen bonds [O 3 3 3 O distances in the range 2.711(7) to 2.876(4) Å] involving coordinated water molecules [O(1w) and O(2w)] and uncoordinated malonate-oxygen atoms [O(3) and O(33)]. These supramolecular layers are regularly alternated along the b direction by a layer of crystallization water molecules. Two crystallographically independent copper(II) atoms are present in 2, both of them being six-coordinated. They exhibit a distorted 4 + 1 + 1 octahedral environment. Each copper atom is surrounded by four practically coplanar atoms [two malonateoxygen and two dpp-nitrogen atoms with average CuO and CuN bond distances of 1.918(2) and 2.001(3) Å (at Cu(1)) and 1.916(2) and 2.004(3) Å (at Cu(2)), respectively] which build the equatorial plane, a water molecule which occupies the closer axial position [2.425(4) Å for Cu(1)O(1w) and 2.423(5) Å for Cu(2)O(2w)] and an oxygen atom from a malonate group of a symmetry-related [Cu2(mal)2(dpp)(H2O)] unit with a longer bond distance [2.751(4) Å for Cu(1)O(1a) and 2.810(5) Å for Cu(2)O(31b); (a) = x +1, y + 2, z; (b) = x, y + 2, z + 1] in the remaining axial site (see Table 3). The equatorial atoms around Cu(2) do not deviate significantly from planarity, whereas the maximum deviation around Cu(1) is 0.021(3) Å for N(11). The metal atoms are shifted by 0.0841(4) [Cu(1)] and 0.1031(4) [Cu(2)] from the mean equatorial plane toward the shorter axial position, indicating the weakness of the linkage between the dinuclear units. 603



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Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2a Cu(1)O(1)

1.931(2) Cu(1)N(11)

2.020(2)

Cu(1)O(2)

1.904(2) Cu(1)N(12)

1.981(3)

Cu(1)O(1w)

2.471(3) Cu(1)O(1a)

2.739(2)

Cu(2)O(31)

1.927(2) Cu(2)N(13)

2.015(2)

Cu(2)O(32) Cu(2)O(2w)

1.905(2) Cu(2)N(14) 2.451(3) Cu(2)O(31b)

1.992(3) 2.810(3)

O(1)Cu(1)O(2)

94.2(1)

N(11)Cu(1)N(12)

O(1)Cu(1)N(11)

171.5(1)

O(2)Cu(1)N(11)

80.3(1) 91.6(1)

O(1)Cu(1)N(12)

93.4(1)

O(2)Cu(1)N(12)

171.25(9)

O(1)Cu(1)O(1w)

97.83(9) N(11)Cu(1)O(1w)

87.73(9)

O(2)Cu(1)O(1w)

95.11(9) N(12)Cu(1)O(1w)

88.1(1)

O(1a)Cu(1)O(1)

80.67(8) O(1a)Cu(1)O(2)

93.20(9)

O(1a)Cu(1)N(11) 92.91(9) O(1a)Cu(1)N(12) O(1w)Cu(1)O(1w) 171.65(8)

83.81(9)

O(31)Cu(2)O(32)

93.6(1)

N(13)Cu(2)N(14)

80.4(1)

O(31)Cu(2)N(13)

171.6(1)

O(32)Cu(2)N(13)

91.8(1)

O(31)Cu(2)N(14)

93.5(1)

Figure 4. View of a fragment of the crystal structure of 3 along with the numbering scheme. Ellipsoids of probability are presented at 50%.

O(32)Cu(2)N(14) 170.4(1)

O(31)Cu(2)O(2w)

98.3(1)

N(13)Cu(2)O(2w)

87.6(1)

O(32)Cu(2)O(2w)

94.5(1)

N(14)Cu(2)O(2w)

90.8(1)

O(31b)Cu(2)O(31)

81.89(9) O(31b)Cu(2)O(32) 92.86(9)

O(31b)Cu(2)N(13) 91.46(9) O(31b)Cu(2)N(14) 81.83(9) O(2w)Cu(2)O(31b) 172.63(8)

Symmetry transformations: (a) x + 1, y + 2, z; (b) x, y + 2, z + 1.

a

Two crystallographically independent malonate groups are present in 2. Both of them act as bidentate ligands through O(1) and O(2) toward Cu(1), and through O(31) and O(32) toward Cu(2) [the angle subtended at the Cu(1) and Cu(2) atoms being 94.22(9) and 94.3(2), respectively] and as monodentate ligands [through O(1) and O(31) toward Cu(1a) and Cu(2b), respectively]. Each malonate group forms a six-membered ring including the copper atoms that exhibit a boat conformation, the geometric values being θ = 90.0(3) and ϕ = 125.3(3) [for Cu(1)] and θ = 91.7(3) and ϕ = 121.2(3) [for Cu(2)].17 The dpp ligand acts as a bis-bidentate ligand [through the pyridyland pyrazine-nitrogen atoms at each side], the bite angles being 80.34(10) [at Cu(1)] and 80.44(10) [at Cu(2)]. The pyrazine (pyz) and the two pyridyl rings (py1 and py2) are essentially planar whereas the ligand as a whole deviates strongly from planarity. The dihedral angles between the two pyridyl rings is 42.81(11) [py1/py2] and those between the mean pyrazine and pyridyl planes are 23.74(11) [py1/pyz], 22.81(10) [py2/pyz]. Bond lengths and angles are in good agreement with those reported for the free dpp18 and for the dpp-bridged dinuclear copper(II) complexes.19 The coppercopper separation within the dinuclear [Cu2(mal)2 (dpp)(H2O)] unit is 6.7215(7) Å [Cu(1) 3 3 3 Cu(2)]. Double oxo(carboxylate) bridges between copper(II) ions connect the units along the chains (Figure 3b), the values of the metalmetal distance within these bridges are 3.5975(6) Å [Cu(1) 3 3 3 Cu(1a)] and 3.6242(6) Å [Cu(2) 3 3 3 Cu(2b)], whereas the CuOCu angles are 99.34(9) [Cu(1)O(1)Cu(1a)] and 98.09(9) [Cu(2)O(31)Cu(2b)]. The shortest intermolecular copper copper separation occurs between adjacent chains of the supramolecular layers in the ac plane [6.5074(7) Å [for Cu(1) 3 3 3 Cu(2c); (c) = x + 1, y, z], a value which is smaller than the shortest

Figure 5. View along the a axis of the two-dimensional network of 3, where the pores are filled with crystallization water molecules.

separation between copper atoms of different layers [10.1865(12) Å for Cu(2) 3 3 3 Cu(2c); (c) = x, y + 1, z + 1]. [Cu2(mal)2(bpe)(H2O)]n 3 nH2O (3). The structure of 3 is a corrugated two-dimensional brick-wall arrangement of copper(II) ions where chains of carboxylate-bridged [Cu(mal)(H2O)] units 604



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Table 4. Selected Bond Lengths (Å) and Angles (deg) for 3a

a

Cu(1)O(1)

1.959(2) Cu(1)O(4a)

1.946(2)

Cu(1)O(2)

1.952(2) Cu(1)N(1)

2.027(2)

Cu(1)O(1w)

2.221(2)

O(1)Cu(1)O(2)

88.44(8)

O(4a)Cu(1)N(1)

89.43(9)

O(1)Cu(1)O(4a) O(1)Cu(1)N(1)

90.74(8) 161.3(1)

O(2)Cu(1)O(4a) O(2)Cu(1)N(1)

173.16(9) 89.18(9)

O(1)Cu(1)O(1w) 104.8(1)

O(4a)Cu(1)O(1w)

93.36(8)

O(2)Cu(1)O(1w)

N(1)Cu(1)O(1w)

93.89(9)

93.41(8)

Symmetry operations: (a) x 1/2, y + 1/2, z 1/2.

which extended in the [101] direction are interlinked by bis-monodentate bpe ligands along the crystallographic b axis (Figure 4). These neutral layers are further held together by means of hydrogen bonds involving water molecules and free malonate-oxygen atoms, which contribute to the formation of the resulting supramolecular three-dimensional network. The packing of the corrugated layers allows the formation of channels of 9 11 Å2, which are filled by the crystallization water molecules [O(2w), Figure 5] forming a hydrogen C2 bonded chain20 [2.890(5) and 2.888(4) Å for O(2w) 3 3 3 O(2wb) and O(2w) 3 3 3 O(2wc), respectively; (b) x, y + 1, z + 1, (c) = x + 1, y + 1, z + 1]. These water chains are linked to the host through H-bonds involving the uncoordinated O(3) malonate-oxygen atom [O(2w) 3 3 3 O(3) = 2.736(4) Å]. The crystallographically independent copper(II) ion in 3 is five-coordinated and it exhibits a distorted square pyramidal environment [τ value16 equal to 0.20]. Three oxygen atoms from two malonate groups [1.952(2) Å for the average Cu(1)O bond distance, see Table 4] and one bpe-nitrogen atom [2.027(2) Å for Cu(1)N(1)] build the equatorial plane around the metal atom, whereas the apical position is filled by a water molecule [the Cu(1)O(w) bond distance being 2.221(2) Å]. The equatorial atoms deviate significantly from planarity, the maximum deviation from the mean equatorial plane being 0.134(2) Å at N(1). The copper(II) ion is shifted by 0.205(2) Å from the mean equatorial plane toward the apical position. The malonate group acts simultaneously as bidentate [through O(1) and O(2) toward Cu(1); the bite angle being 88.44(8)] and monodentate [through O(4) toward Cu(1d); (d) x + 1/2, y + 1/2, z + 1/2] ligand (see Figure 4). The six-membered chelate ring exhibits a slightly distorted twist-boat conformation.17 The bpe ligand exhibits the trans-conformation, acting as bis-monodentate ligand connecting two equatorial sites from the copper atoms that it links. The pyridyl rings of the bpe ligand and the ligand as a whole are practically planar. The geometrical values of the bpe are within the range of other bpe-containing copper(II) complexes.21 The carboxylate group O(4)C(3)O(2) exhibiting the anti-syn conformation connects two equatorial sites of adjacent copper(II) within the chain [Cu(1) 3 3 3 Cu(1d) = 5.0845(7) Å]. The coppercopper distance through the bridging bpe ligand is much larger [13.3768(9) Å for Cu(1) 3 3 3 Cu(1e); (e) = x + 3, y, z + 1] than the shortest intermolecular metalmetal separation [5.3547(3) Å for Cu(1) 3 3 3 Cu(1f); (f) = x + 1, y, z]. Let us finish the structural description of 3 with a comparison with the related compounds {(H2bpe)[Cu(mal)2]}n 3 4nH2O and [Cu4(mal)4(bpe)3]n 3 6nH2O.6 The former complex is a salt of (H2bpe)2+ and [Cu(mal)2]2, where these latter units are


Table 5. Selected Bond Lengths (Å), Angles (deg) and Hydrogen Bond Lengths (Å) for 4a Cu(1)O(1)

1.936(2) Cu(2)O(3)

2.161(3)

Cu(1)O(2) Cu(1)O(1w)

1.944(3) Cu(2)N(21) 2.528(4) Cu(2)N(22)

1.982(5) 1.976(5)

Cu(2)O(1)

2.785(2) Cu(2)N(23)

O(1)Cu(1)O(2)

92.1(1)

2.008(6)

O(1)Cu(2)O(3)

91.4(9) 50.6(8)

O(1)Cu(1)O(1w)

86.9(1)

O(3)Cu(2)O(3)

O(2)Cu(1)O(1w)

86.3(1)

O(3)Cu(2)N(22) 134.2(7)

O(1w)Cu(1)O(1wa) 180.00

O(3)Cu(2)N(21)

95.1(7)

O(1)Cu(2)N(21)

87.2(5)

O(3)Cu(2)N(23)

93.4(7)

O(1)Cu(2)N(22) O(1)Cu(2)N(23)

83.8(5) 91.5(5)

N(21)Cu(2)N(23) 167.8(2) N(22)Cu(2)N(21) 85.1(2)

hydrogen bonds O(1w) 3 3 3 O(4b) O(1w) 3 3 3 O(3wc) O(1w) 3 3 3 O(3w)

2.790(4) O(3w) 3 3 3 O(1w) 2.778(5) O(2w) 3 3 3 O(3wb) 2.792(5) O(2w) 3 3 3 O(2we)

2.792(5)

O(2w) 3 3 3 O(3) O(2w) 3 3 3 O(4d) O(3w) 3 3 3 O(1wc)

2.791(5) O(3W) 3 3 3 N(21f) 3.056(6) N(23) 3 3 3 O(3)

3.082(4)

2.778(5) N(21) 3 3 3 O(3)

3.059(5)

2.776(5) 2.862(5) 3.036(6)

Symmetry operations: (a) x, y + 1, z; (b) x + 1, y + 1, z ; (c) x, y + 1, z 1; (d) x + 1, y + 1, z + 1; (e) x, y + 1/2, z; (f) x, y + 1/2, z. a

linked through long apical to equatorial carboxylate bridges to form a chain. The crystal structure of [Cu4(mal)4(bpe)3]n 3 6nH2O is three-dimensional involving corrugated layers of malonato-bridged copper(II) ions linked by bpe molecules. Compound 3 can be viewed as a condensation of the salt complex, the carboxylate bridged chain being now linked through the bpe ligand, although the number of coordinated malonate groups is reduced since the bpe now fills an equatorial position of the copper(II) environment. {[Cu(mal)2(H2O)2][Cu(dien)]}n 3 4nH2O (4). The crystal structure of 4 consists of zigzag chains of malonate-bridged copper(II) 605



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around the metal atom [average CuO bond distance is 1.940(2) Å, see Table 6], whereas two water molecules [O(1w) and O(1wa); (a) = x, y + 1, z] occupy the axial positions. Cu(1) is shifted by 0.016(2) Å from de mean equatorial plane toward O(1w). Cu(2) lies on a crystallographic reflection plane, it is five coordinated and exhibits a very distorted square pyramidal polyhedron. Three coplanar nitrogen atoms from the dien ligand [N(21), N(22), and N(23); the average CuN bond distance being 1.989(4) Å, see Table 6] fill equatorial positions while the two symmetry related malonate oxygen atoms [O(3) and O(3e); (e) = x, y + 1/2, z] occupy alternatively the other equatorial and apical positions [Cu(2)O(3e) = 2.161(3) Å]. Since the basal atoms deviate significantly from planarity, an alternative description of the Cu(2) environment as a distorted trigonal bipyramid can be envisaged. In this situation, two carboxylate oxygen atoms [O(3) and O(3e)] and one nitrogen atom of the dien ligand [N(22)] would build the trigonal plane, whereas the N(21) and N(23) atoms from the dien ligand would fill the axial positions. Cu(2) would be shifted by 0.0372(4) Å from the trigonal plane toward N(23). The τ parameter16 for the distorted geometry of the CuN3O2 environment of Cu(2) is 0.56 (square pyramidal and trigonal bipyramidal surroundings corresponding to τ = 0 and 1, respectively) indicating a strong distortion of the square pyramidal environment toward the trigonal bipyramidal one. Distorted environments (trigonal and square pyramidal) have been previously reported in other dien-containing copper(II) complexes with carboxylate groups.23 One crystallographically independent malonate group is present in 4, which acts simultaneously as a bidentate [through O(1) and O(2) toward Cu(1)] and monodentate ligand [through O(3) toward Cu(2)]. The six-membered chelate ring formed exhibit a twist-boat [θ = 96.7(4) and ϕ = 9.8(5)] conformation.17 The trans-diaquabis(malonate)copper(II) and (diethylenetriamine)copper(II) units are connected through the O(1)C(1) O(3) carboxylate bridge leading to the zigzag chains that run along the b axis; the separation of the copper(II) ions through this bridge is 4.5955(5) Å [Cu(1) 3 3 3 Cu(2)]. The shortest copper copper interchain separation is 7.2175(10) Å [Cu(1) 3 3 3 Cu(1 g); (g) = x, y, z + 1]. [Co2(mal)2(dpo)(H2O)6] 3 2H2O (5). The structure of 5 consists of neutral malonato-bridged [Co2(mal)2(dpo)(H2O)6] dinuclear units (Figure 7) and crystallization water molecules. These dinuclear units are held together in the ac plane by an extensive network of hydrogen bonds involving crystallization and coordinated water molecules and uncoordinated malonate oxygen atoms [O 3 3 3 O distances in the range 2.580(4) to 3.104(5) Å, see Table 6]. The supramolecular layers are stacked regularly in the b direction where π-type interactions between the dpo molecules take place The two centroid-centroid distances are 3.7573(15) and 3.7987(15) Å, whereas the offset angles are 27.2(1) and 27.8(1) for ππ interactions between adjacent dpo ligands from different layers. The supramolecular three-dimensional network can be viewed as a regular alternation of hydrophobic (ππ interactions between dpo ligands) and hydrophilic layers [those corresponding to the environment of the cobalt(II) ions]. Two crystallographically independent cobalt(II) ions [Co(1) and Co(2)] occur in 5. Both of them are six-coordinated in a slightly distorted octahedral environment [s/h = 1.24 and ϕ = 58.99 for Co(1) and s/h = 1.25 and ϕ = 59.29 for Co(2)].22 Four coplanar malonate-oxygen atoms build the equatorial plane

Table 6. Selected Bond Lengths (Å), Angles (deg) and Hydrogen Bond Lengths (Å) for 5a Co(1)O(1)

2.057(3) Co(1)O(2)

2.044(3)

Co(1)O(11)

2.061(3) Co(1)O(12)

2.044(3)

Co(1)O(1w) O(1)Co(1)O(2)

2.112(4) Co(1)O(2w)

2.118(4)

88.4(1)

O(11)Co(1)O(12)

89.5(1)

O(1)Co(1)O(11)

96.2(1)

O(2)Co(1)O(11)

174.5(1)

O(1)Co(1)O(12)

174.1(1)

O(2)Co(1)O(12)

86.0(1)

O(1w)Co(1)O(1)

90.3(1)

O(1w)Co(1)O(2)

91.1(1)

O(1w)Co(1)O(11) O(2w)Co(1)O(1)

91.8(1) 86.7(1)

O(1w)Co(1)O(12) O(2w)Co(1)O(2)

88.2(1) 89.8(1)

O(2w)Co(1)O(11)

87.6(1)

O(2w)Co(1)O(12)

94.8(1)

O(1w)Co(1)O(2w) 176.8(1) Co(2)O(4)

2.047(3) Co(2)O(21)

2.106(3)

Co(2)O(3w)

2.123(3) Co(2)O(4w)

2.056(3)

2.141(3) Co(2)O(6w)

2.132(4)

Co(2)O(5w) O(4)Co(2)O(21)

88.5(1)

O(3w)Co(2)O(4w) 91.5(1)

O(4)Co(2)O(3w) O(4)Co(2)O(4w)

99.1(1) 169.1(1)

O(21)Co(2)O(3w) 169.5(1) O(21)Co(2)O(4w) 81.3(1)

O(5w)Co(2)O(4)

89.5(1)

O(5w)Co(2)O(21)

97.2(1)

O(5w)Co(2)O(3w) 90.1(1)

O(5w)Co(2)O(4w) 87.9(1)

O(6w)Co(2)O(4)

O(6w)Co(2)O(21)

88.9(1)

O(6w)Co(2)O(3w) 82.2(1)

90.8(1)

O(6w)Co(2)O(4w) 95.1(1)

O(5w)Co(2)O(6w) 171.8(1) hydrogen bonds O(1w) 3 3 3 O(3a) O(1w) 3 3 3 O(14b) O(2w) 3 3 3 O(3c) O(2w) 3 3 3 O(14d) O(3w) 3 3 3 O(2) O(3w) 3 3 3 O(11c) O(4w) 3 3 3 O(13c) O(4w) 3 3 3 O(22e)

2.757(5) O(5w) 3 3 3 O(14d) 2.863(5) O(5w) 3 3 3 O(8w) 2.781(5) O(6w) 3 3 3 O(22f) 2.863(5) O(7w) 3 3 3 O(3) 2.793(4) O(7w) 3 3 3 O(6wg) 2.803(5) O(8w) 3 3 3 O(2wc) 2.580(4) O(8w) 3 3 3 O(6wh)

2.717(4) 2.848(5) 2.671(5) 2.905(5) 3.030(5) 3.104(5) 2.963(5)

2.782(5)

Symmetry transformations: (a) x + 1/2, y + 1/2, z + 1/2; (b) x + 1/2, y + 1/2, z 1/2; (c) x 1/2, y + 1/2, z + 1/2 (d) x 1/2, y + 1/2, z 1/2; (e) x + 1, y + 1, z + 1; (f) x + 2, y + 1, z + 1; (g) x, y, z 1; (h) x 1, y, z.

a

ions with a regular alternation of trans-diaquabis(malonate) copper(II) and (diethylenetriamine)copper(II) units (Figure 6). These neutral chains grow along the crystallographic b axis and the [Cu(mal)2(H2O)2] unit in each chain is linked to two [Cu(dien)] fragments in a bis-monodentate coordination mode through two trans-malonato oxygen atoms. Hydrogen bonds (see Table 5) involving the amino groups [N(21), N(22), N(23)], the coordinated water molecule [O(1w)] and the uncoordinated malonate oxygen atoms [O(3) and O(4)] connect the layers along the a direction to form supramolecular layers on the ab plane. These layers of malonate-bridged copper(II) chains are regularly alternated in the c direction with layers of crystallization water molecules, affording the supramolecular three-dimensional network. Two crystallographically independent copper(II) ions [Cu(1) and Cu(2)] occur in 4. Cu(1) lays on a inversion center, it is sixcoordinated and it exhibits a 4 + 2 distorted octahedral environment with ϕ = 54.16 and s/h = 1.47 (ϕ and s/h being the twist angle and the compression ratio, respectively).22 Four coplanar oxygen atoms [O(1), O(2) and its inversion symmetry related] from two different malonate ligands build the equatorial plane 606



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Table 7a. Selected Bond Lengths (Å), Angles (deg) for 6 Co(1)O(1)

2.066(2) Co(1)O(2)

2.070(2)

Co(1)N(11)

2.121(3) Co(1)N(12)

2.124(2)

Co(1)O(1w)

2.077(3) Co(1)O(3a)

O(1)Co(1)O(2)

85.61(9)

2.117(2)

N(11)Co(1)N(12)

78.1(1)

O(1)Co(1)N(11) O(1)Co(1)N(12)

95.8(1) 173.5(1)

O(2)Co(1)N(11) O(2)Co(1)N(12)

89.29(9) 91.83(9)

O(1w)Co(1)O(1)

93.8(1)

O(1w)Co(1)O(2)

93.2(1)

O(1w)Co(1)N(11) 170.1(1)

O(1w)Co(1)N(12)

O(3a)Co(1)O(1)

85.38(9)

O(3a)Co(1)O(2)

169.94(9)

92.3(1)

O(3a)Co(1)N(11)

87.16(9)

O(3a)Co(1)N(12)

96.64(9)

O(1w)Co(1)O(3a)

91.9(1)

Table 7b. Relevant Hydrogen Bonds for 6a DH 3 3 3 A

a

D 3 3 3 A (Å) H 3 3 3 A (Å) DH 3 3 3 A(deg)

O(1w)H(2w1) 3 3 3 O(1a) O(1w)H(1w1) 3 3 3 O(2wb) O(2w)H(1w2) 3 3 3 O(4c)

2.648(4) 2.694(5)

1.98(4) 1.91(4)

151(4) 169(4)

2.860(4)

2.09(5)

158(5)

O(2w)H(2w2) 3 3 O(3w)H(1w3) 3 3

3 O(4)

2.779(4)

2.00(5)

163(5)

3 O(4d)

3.021(4)

2.33(6)

140(5)

2.814(4)

2.03(6)

170(5)

O(3w)H(2w3) 3 3 3 O(2)

D and A stand for donor and acceptor, respectively. Symmetry code: (a) x + 3/2, y + 1/2, z + 1/2; (b) x, y + 1, z; (c) x + 1, y 1, z + 1; (d) x + 1, y, z + 1.


in 5. L1 acts simultaneously as a bidentate [through O(1) and O(2) toward Co(1)] and monodentate [through O(4) toward Co(2)] ligand, whereas L2 adopts a bidentate coordination mode [through O(11) and O(12) toward Co(1)]. The values of the angle subtended by L1 and L2 at Co(1) are 88.38(12) and 89.49(12), respectively. Both malonate groups form sixmembered chelate rings in a boat [θ = 87.7(4) and ϕ = 122.6 (5)] and twist-boat [θ = 89.74(14) and ϕ = 101.96(13)] conformations for L1 and L2, respectively. The dpo molecule acts as a monodentate ligand through O(1) toward Co(2). This coordination mode has been observed in other structurally characterized dpo-containing cobalt(II) complexes.9,15d,24 The values of the bond lengths and angles of the dpo ligand agree well with those reported for the free ligand.25 The dpo as a whole does not deviates significantly from planarity [the dihedral angle between the pyridyl rings being 2.2(2)]. The maximum deviation from the mean equatorial plane is 0.047(4) Å at O(21). The cobalt(II) ions are linked within the dinuclear unit through a O(4)C(3)O(2) carboxylate group in the anti-syn conformation involving two equatorial sites of the cobalt environments. The intramolecular cobaltcobalt separation is 5.2566(13) Å [Co(1) 3 3 3 Co(2)], a value shorter than the shortest intermolecular metalmetal distance [6.1719(17) Å for Co(1) 3 3 3 Co(1d)]. [Co(mal)(phen)(H2O)]n 3 2nH2O (6). The structure of 6 consists of zigzag chains of malonate-bridged cobalt(II) ions growing along the b axis and crystallization water molecules (Figure 8). Hydrogen bonds involving the crystallization and coordinated water molecules and the malonate oxygen atoms [O 3 3 3 O distances in the range 2.648(4) to 3.021(4) Å; see Tables 7a and 7b] connect the cobalt(II) chains in the [101] direction. Two motifs can be found in these hydrogen bonded


around Co(1) [the average Co(1)O(eq) bond distance is 2.052(3) Å, see Table 6], whereas two water molecules in trans configuration fill the axial positions [2.115(4) Å for the mean Co(1)O(w) bond distance]. The metal ion is shifted by 0.0157(7) Å from the mean equatorial plane toward O(1w). Two water molecules [O(3w) and O(4w)] and two oxygen atoms [O(21) and O(4)] from the dpo and malonate group build the equatorial plane around Co(2) [2.083(3) Å being the mean Co(2)O(eq) bond distance], whereas the axial positions are occupied by two water molecules [O(5w) and O(6w); mean Co(2)O(ax) bond length being 2.136(4) Å]. The Co(2) atom is shifted by 0.0352(7) Å from the mean equatorial plane toward O(5w). Two crystallographically independent malonate ligands noted L1 [C(1)C(2)C(3)] and L2 [C(11)C(12)C(13)] occur 607



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Figure 10. Thermal dependence of the χMT vs T for 2: (O) experimental data and () best fit curve (see text).

Figure 9. Thermal dependence of the χMT product of 1: (O) experimental data and () best-fit curves (see text).

the dpo ligand has been previously reported in the literature for other dpo-bridged copper(II) complexes,15 an inspection of the structure of 1 allow us to appreciate other possible magnetic exchange pathways. First, the aqua(malonate)copper(II) units are also connected through hydrogen bonds involving equatorial oxygen atoms [CuOwH 3 3 3 OCOCu] leading to a ladder-like chain. Second, another exchange pathway between copper(II) ions is possible through hydrogen bonds involving some dpo atoms [CuO(ap) 3 3 3 HCNO(eq)Cu]. In both cases, one can expect weak ferro- or antiferromagnetic interactions. So, we attempted to fit the magnetic data of 1 through a CurieWeiss law, where the θ parameter accounts for all of the possible magnetic exchange pathways. The least-squares fit of the magnetic data through a CurieWeiss law leads to: g = 2.09(3), θ = 1.65(2) K and R = 3.1 103 [R is the agreement factor defined as Σ[(χMT)obs (χMT)calc]2/Σ[(χMT)obs]2] (see blue line in Figure 9). Alternatively, assuming that the exchange pathway through the dpo bridge would be dominant, we analyzed the magnetic data of this compound by using the Bonner and Fisher’s expression for a regular copper(II) chain with an antiferromagnetic interaction between the local spin doublets:28

network, a R42(8) and one R44(12) ring patterns which share one edge (defined by two malonate oxygen atoms).26 The supramolecular layers are linked through weak π-type interactions between the pyridyl rings of the phen ligand [the centroid-centroid separation is 3.7786(6) Å and the offset angle is 23.91(8), in agreement with previously observed values].14 Each cobalt(II) ion in 6 is six-coordinated. Three oxygen atoms from two different malonate ligands [mean CoO(mal) bond distance equal to 2.084(2) Å, see Table 7], a water molecule and two phen-nitrogen atoms [2.123(3) Å for the mean CoN(phen)] build a distorted octahedral environment around the metal ions with geometric values s/h = 1.23 and θ = 54.8.22 The malonate ligand adopts simultaneously bidentate [through O(1) and O(2) toward Co(1); 85.61(9) being the bite angle] and monodentate [through O(3) toward Co(1e); (e) = x + 3/2, y 1/2, z + 1/2] coordination modes. The sixmembered chelate ring formed exhibits a boat conformation [θ = 93.6(3) and ϕ = 125.7(3)].17 The phen molecule is coordinated to the cobalt(II) ion as a bidentate ligand with a bite angle of 78.13(10). This value is far from the ideal value of 90 due to the constrained geometry of the phen ligand.27 The phen molecule is planar [the maximum deviation from the ligand mean plane being only 0.038(4) Å at C(17)]. The cobalt(II) ions are linked within the chain by the O(1)C(1)O(3) carboxylate group exhibiting an anti-syn configuration. The intrachain cobalt 3 3 3 cobalt separation is 5.3482(10) Å [Co (1) 3 3 3 Co(1e)], a value which is much shorter than the shortest interchain metalmetal distance [8.735(2) Å for Co(1)...Co(1d); (d) x + 1, y, z + 1]. Magnetic Properties. [Cu(mal)(dpo)(H2O)]n (1). The magnetic properties of 1 under the form of χMT vs T plot [χMT being the magnetic susceptibility per copper(II) ion] in the 250 K temperature range are shown in Figure 9. The value of the χMT at rom temperature is 0.42 cm3 mol1 K, a value which is near from that expected for a magnetically isolated spin doublet. Upon cooling, χMT remains constant until ca. 50 K and it further decreases to reach a value of 0.21 cm3 mol1 K at 2.0 K. This plot is as expected for a very weak antiferromagnetic interaction between copper(II) ions. The structure of compound 1 consists of uniform copper(II) chains where the aqua(malonate)copper(II) units are bridged by the extended dpo ligand which are further linked through hydrogen-bonds. Although a weak magnetic exchange through

χM ¼

Ng 2 β2 0:25 þ 0:074975x þ 0:075235x2 kT 1:0 þ 0:9931x þ 0:172135x2 þ 0:757825x3

ð1Þ with x = (|J|)/(kT) The best least-squares fit through this expression leads to the following parameters: J = 1.72(1) cm1, g = 2.165(1) and R = 1.7 105 (see green line in Figure 9). The quality of the fit through the Bonner and Fisher expression is very good, but the value of the magnetic coupling J is somewhat larger when compared with those previously published. Therefore, we cannot exclude that other exchange pathways could be operative and the AF behavior observed would be the result of the different magnetic pathways described above. [Cu2(mal)2(dpp)(H2O)2]n 3 7nH2O (2). The thermal dependence of the χMT product in the 2100 K temperature range [χMT being the magnetic susceptibility per two copper(II) ions] for compound 2 is shown in Figure 10. χMT at room temperature is 0.77 cm3 mol1 K, a value which is as expected for two magnetically isolated spin doublets. Upon cooling, χMT continuously increases to reach a value of 0.94 cm3 mol1 K at 2.0 K. This behavior indicates the occurrence of an overall ferromagnetic 608



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coupling. Looking at the structure of 2, two intrachain exchange pathways are possible: the double oxo(carboxylate) bridge and the bis-bidentate dpp ligand (see Figure 3b). Given that exchange coupling between copper(II) ions through the dpp bridge is very weak and antiferromagnetic [values of J ranging from 1.4 to 0.2 cm1],19a,b,e we have analyzed the magnetic data of 2 through the BleaneyBowers expression for dinuclear units,29 considering that the double oxo(carboxylate) bridge is the main magnetic exchange coupling. Least-squares fit leads to the following parameters: J = +2.25(4) cm1, g = 2.003(1), and R = 1.1 105. In order to take into account the magnetic interaction, if any, through the bis-bidentate/dpp bridge we have introduced a θ term in the Bleaney Bowers expression. The fitting leads to a θ value of ca. 0.2 K, this small term supporting the validity of the simple dinuclear model used. The out-of plane exchange pathway through the double oxo(carboxylate) bridge in 2 is responsible for the ferromagnetic coupling observed which is due the accidental orthogonality between the two magnetic orbitals of the pair of interacting copper(II) ions. Finally, the nature and magnitude of the ferromagnetic coupling observed in 2 agrees with that reported for the compound {[Cu(H2O)3][Cu(Phmal)2]}n (H2Phmal = phenylmalonic acid) through the same exchange pathway [J = +1.95 cm1).30 [Cu2(mal)2(bpe)(H2O)]n 3 nH2O (3). The thermal dependence of the χMT product for compound 3 [χMT being the magnetic susceptibility per one copper(II) ion] in the 2300 K temperature range is shown in Figure 11. χMT at room temperature is 0.43 cm3 mol1 K, a value which is close to that expected for a magnetically isolated spin doublet. Upon cooling, χMT continuously increases to reach a value of 1.28 cm3 mol1 K at 2.0 K. This behavior is characteristic of an overall ferromagnetic coupling between copper(II) ions. The structure of 3 consists of regular carboxylate-malonate copper(II) chains which are further linked through the bpe ligands affording corrugated layers (see Figure 5). Of the two possible intralayer exchange pathways, the contribution through the longer bpe bridge [13.3768(9) Å] has to be negligible compared with that of the anti-syn carboxylate bridge [5.0845(7) Å]. So, from a magnetic point of view, 3 can be considered as regular chains of interacting spin-doublets. Consequently, we have analyzed the magnetic data of 3 through the Baker and Rushbrooke expression for a regular chain of ferromagnetically coupled local spin doublets (eqs 25).31 χM ¼ ðN β2 g 2 =4kTÞðA=BÞ2=3

Figure 11. Thermal dependence of the χMT product for 3: (O) experimental data and () best-fit curve (see text).

Figure 12. Thermal dependence of the χMT product for 4: (O) experimental data and () best fit curve (see text). A θ parameter has been included in the refinement to take into account the interchain interactions through hydrogen bonds.

carboxylate(malonate) bridged copper(II) complexes with the same equatorial-equatorial pathway (case of strict orthogonality between the interacting magnetic orbitals).5a,h,i,np,6 {[Cu(mal)2(H2O)2][Cu(dien)]}n 3 4nH2O (4). The thermal dependence of the χMT product for 4 [χMT being the magnetic susceptibility per two copper(II) ions] in the 2300 K temperature range is shown in Figure 12. χMT at room temperature is 0.82 cm3 mol1 K, a value which is as expected for two magnetically isolated copper(II) ion. Upon cooling, χMT smoothly increases to reach a value of 1.18 cm3 mol1 K at 4.5 K, and then it decreases reaching a value of 1.02 cm3 mol1 K at 2 K. This plot indicates the occurrence of a dominant ferromagnetic coupling which could coexist with an antiferromagnetic interaction, this last one accounting for the decrease of χMT in the low temperature range. One can see that the structure of 4 consists of malonatebridged copper(II) chains where one crystallograhically independent anti-syn carboxylate group connect adjacent copper(II) ions (see Figure 6). Within the Cu(1)O(1)C(1)O(3)Cu(2) carboxylate pathway the O(1) occupies an equatorial position of the Cu(1) environment with a short bond distance, however the O(3)Cu(2) separation is longer [2.161(3) Å] and it simultaneously occupies an equatorial and an apical position of the Cu(2)

ð2Þ

A ¼ 1:0 þ 5:7979916y þ 16:902653y2 þ 29:376885y3 þ 29:832959y4 þ 14:036918y5

ð3Þ

B ¼ 1:0 þ 2:7979916y þ 7:0086780y2 þ 8:6538644y3 þ 4:5743114y4

ð4Þ

with y = J/2kT and the spin Hamiltonian being defined as follows: ^ ¼ H

∑i J

Sî 3 Sîþ1

ð5Þ

The best-fit parameters are: J = +3.85(3) cm1, g = 2.155(3) and R = 1.9 104. This ferromagnetic interaction lies in the range of those observed in previous magneto-structural studies of 609



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Table 8. Selected Magneto-Structural Data for Some Carboxylate-(R-Malonate) Bridged Copper(II) Complexes compounda

carboxylate pathway

Cu(O)ap

τb Cu1/Cu2

J (cm1)c

ref

[Cu(H2O)4][Cu(mal)2(H2O)2]

equatorial-apical

2.383

Oct/0.05

+1.8

5a

[Cu(H2O)4]2[Cu(mal)2(H2O)]2+

equatorial-apical

2.381

Oct/0.12

+1.2

5a

{[Cu(H2O)3][Cu(mal)2(H2O)]}n

equatorial-apical

2.185

0.24/0.28

+1.9

5a

[Cu(Im)2(mal)]n

equatorial-apical

2.394

0.02

+1.6

5i

[Cu(2-MeIm)2(mal)]n

equatorial-apical

2.270

0.18

+0.4

5i

{(H2bpe)[Cu(mal)2]}n 3 4nH2O

equatorial-apical

2.611

Oct

+0.049

6

[Cu(2,20 -bpym)Phmal]n

equatorial-apical

2.262

0.08

+0.10

35a

[Cu(phen)(Phmal)]n 3 3nH2O [Cu(L1)mal]2

equatorial-apical equatorial-apical

2.314 2.336

0.10 0.02

+0.31 +1.49

35a 35b

[Cu(phen)(Memal)]n 3 nMeOH

equatorial-apical

2.296

0.05

+0.24

35c

[Cu(bpy)(Memal)]n

equatorial-apical

2.358

0.13

+0.09

35c

{[Na(H2O)]2[Cu(mal)2]}n

equatorial-apical

2.601

Oct

+0.90

5d

{[K(H2O)1.5]2[Cu(mal)2]}n

equatorial-apical

2.689

Oct

+0.77

5d

{[Rb(H2O)]2[Cu(mal)2]}n

equatorial-apical

2.589

0.14

+0.82

5d

{(MeNH3)2[Cu(mal)2]}n

equatorial-apical

2.562

Oct

+0.75

5e

{(ampyH)2[Cu(mal)2]}n

ecuatorial-apical

2.762

Oct

+0.17

35d

a

Abbreviations: H2mal = malonic acid, Im = Imidazole, 2-MeIm = 2-Methylimidazole, bpe =1,2-bis(4-pyridyl)ethylene, H2Phmal = phenylmalonic acid, 2,20 -bpym =2,20 -bipyrimidine, phen =1,10-phenanthroline, L1 = 2-methylamino-5-(pyridin-2-yl)-1,3,4-oxadizole, H2Memal = methylmalonic acid, bpy =2,20 -bipyridine, ampyH = 4-aminopyridine. b The τ parameter16 defined as 0 for square pyramidal and 1 for trigonal bipyramid environment. Oct stands for octahedral. c Values of the magnetic coupling constant (J).

coordination polyhedron. A refinement of the crystal structure without the restrain of the reflection plane where Cu(2) lays was carried out in order to test if O(3) and O(3e) systematically present the same bond distance to Cu(2). This refinement on the noncentrosymmetric P21 space group gives two different bond distances for the new O(3A) and O(3B) atoms, one shorter [2.109(7) Å] than the other [2.202(6) Å], supporting a scheme where the carboxylate bridge alternatively exhibits the equatorial-equatorial and apical-equatorial linking pathways. The appropriate Hamiltonian to model the magnetic behavior of 4 is given by the following equation: H^ ¼ J1

∑i ½

S^2i 3 S^2iþ1 þ α S^2i 3 S^2i1

Cu(2) due to the highly distorted copper environment. The dihedral angle between the copper(II) ions is nearly orthogonal [87.6(2)], supporting the assignation of the strong ferromagnetic coupling to the equatorial-equatorial bridge. In the case of the equatorial-apical carboxylate bridge, a weaker interaction is expected due to the out-of-plane magnetic pathway.34 The strong distortion (τ = 0.56) of the Cu(2) environment in 4, accounts for the occurrence of an important mixture of the dx2y2 magnetic orbital with the dz2 located mainly in the axial direction defined by Cu(2)O(3) (in the direction of the longer MO bond of the noncentrosymmetric refinement). The most likely poor net overlap between the magnetic orbitals of the adjacent copper atoms through this pathway would provide a small antiferromagnetic coupling, as the one obtained by this fit. The values of the two exchange interactions could be compared with those observed for other malonate-containing copper(II) complexes (see references of Table 8). As seen in Table 8, the values of the exchange interaction through the anti-syn equatorialequatorial pathway is within the range observed for this type of bridge in malonate complexes. In the case of the equatorial-apical exchange pathway, 4 provides the first case of the occurrence of an antiferromagnetic interaction in a malonate-containing copper(II) complex, this fact being most likely due to the high distorted environment of the Cu(2) atom. [Co2(mal)2(dpo)(H2O)6] 3 2H2O (5). The magnetic properties of 5 under the form of χMT versus T plot [χM is the magnetic susceptibility per two Co(II) ions] are shown in Figure 13. χMT at 250 K is equal to 6.02 cm3 mol1 K (μeff per CoII of 4.90 μB), a value which is greater than the expected one for the spin-only case (μeff = 3.87 μB with SCo = 3/2 and gCo = 2.0). This feature indicates that the distortion of the octahedral symmetry of Co(II) in 5 is not so large as to induce the total quenching of the 4T1 g ground state. Upon cooling, χMT continuously decreases to reach a value of 3.73 cm3 mol1 K at 2.0 K. No maximum is observed in the magnetic susceptibility in the temperature range explored. The decrease of χMT can be due to the progressive

ð6Þ

where α is the alternation parameter α = J2/|J1|, J1 being the antiferromagnetic interaction. As indicated above, the shape of the χMT versus T plot is indicative of the occurrence of a dominant ferromagnetic interaction. Consequently, the value of the alternation parameter α must be higher than 1. The previously reported numerical extrapolated expression for alternated chains32 allowed us to successfully match the magnetic data. The best-fit parameters are J1 = 1.48(1) cm1, J2 = α|J1| = +10.4(1) cm1, g = 2.151(3), θ = 0.984(1) K and R = 8.3 106 (θ is a CurieWeiss term accounting for the interchain magnetic interactions). The calculated curve matches very well the magnetic data in the whole temperature range investigated. The Hatfield numerical model33 to take into account the possibility that both intrachain magnetic coupling constants (J1 and J2) were ferromagnetic was also tested, but the negative value of the α parameter in the refinement is enough evidence for such interactions to be alternatively ferro- and antiferromagnetic. The magnetic orbital at each copper atom in 4 is of the dx2y2 type with possibly some mixture of the dz2 character (x and y roughly defined by the short equatorial bonds). It deserves to be noted that this mixture will be quite important in the case of 610



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depopulation of the high-energy Kramers doublets (spinorbit coupling effects), as expected for six-coordinated high-spin cobalt(II) complexes. This feature can mask the presence of weak magnetic interactions in this type of complex. In this respect, the fact that the value of χMT at the minimum for 5 [ca. 1.86 cm3 mol1 K per Co(II) ion at 2.0 K] is slightly above the calculated for a magnetically isolated cobalt(II) ion (1.73 cm3 mol1 K for a Seff = 1/2 with g ≈ 4.3)36 supports the presence of a weak ferromagnetic interaction between the Co(II) ions. In the light of the structure of 5, it is clear that the significant exchange pathway is the anti-syn carboxylate bridge between the cobalt(II) ions separated by only 5.2565(13) Å. Consequently, from a magnetic point of view, the magnetic behavior of 5 would correspond to magnetically isolated dinuclear cobalt(II) units. In general, six-coordinated Co(II) ions present an important first-order orbital momentum and the spin Hamiltonian is insufficient to treat the magnetic properties of their complexes. It must be supplemented by consideration of orbitally dependent exchange interactions as well as spinorbit coupling effects.37 Recently, we have shown that the magnetic properties of six-coordinated Co(II) in homodinuclear species can be perfectly described by using the Hamiltonian of eq 7.38 2

2

Figure 13. Thermal dependence of χMT product for compound 5: (O) experimental data, () best-fit curve (see text).

αi λi Lî Sî þ ∑ Δi ½ L^zi 2=3 ∑ i¼1 i¼1

^ ¼ J S^ S^ H 1 2 þ βH

2

∑ ð αi Lî þ ge Sî Þ i¼1

2

ð7Þ

The meaning of its different terms is as follows: the first term accounts for the magnetic interaction between the local spin quartets [S = 3/2 for each cobalt(II) ion]; the second one concerns the spinorbit coupling of the 4T1g ground term in octahedral symmetry where λ is the spinorbit coupling parameter and α is an orbital reduction factor defined as α = Ak (the value of A cover the range 11.5 for strong and weak crystal-field limits, respectively, and k takes into account the covalence effects). In the frame of T1 and P terms isomorphism,37 L(T1g) = AL(P), we can ^ 3 ^S term as an isotropic Hamiltonian use L = 1 and to treat the αλL describing the interaction between two angular moments L = 1 and S = 3/2, being αλ the coupling parameter. The third term is related to the axial distortion, the triplet orbital ground state 4T1g splits into a singlet 4A2 and a doublet 4E levels with an energy gap of Δ; finally, the last term is the Zeeman interaction. No analytical expression for the magnetic susceptibility (which would depends on J, α, λ, and Δ) can be derived. Numerical matrix diagonalization techniques39 allowed us to determine the values of these parameters for 5. The best-fit parameters are as follows: J = +0.02 cm1, λ = 155 cm1, α = 1.18, Δ = 550 cm1 and R = 2.1 105. The calculated curve matches well the experimental data in the temperature range 2.0250 K (see solid line in Figure 13). The value of the exchange coupling obtained by fit shows that the anti-syn carboxylate bridge linking cobalt(II) ions is able to mediate weak but significant magnetic interactions, in agreement with previous reports for this type of system.40 [Co(mal)(phen)(H2O)]n 3 2nH2O (6). The magnetic properties of 6 under the form of χMT versus T plot [χM is the magnetic susceptibility per one Co(II) ion] are shown in Figure 14. χMT at room temperature is equal to 3.03 cm3 mol1 K (μeff per CoII of 4.92 μB), a value which is greater than the expected one for the spin-only case (μeff = 3.87 μB with SCo = 3/2 and gCo = 2.0). Upon cooling, χMT first decreases to a minimum value of 2.08 cm3 mol1 K at T ca. 3.5 K and below this temperature, χMT

Figure 14. Thermal dependence of χMT product for compound 6: (O) experimental data, () best-fit curve (see text).

increases to reach a value to 2.22 cm3 mol1 K at 1.9 K. This behavior is due to the depopulation of the higher energy Kramers doublets together with the presence of a weak ferromagnetic interaction. The fact that the value of χMT at the minimum for 6 [2.08 cm3 mol1 K per Co(II) ion at 3.5 K] is somewhat above the calculated for a magnetically isolated cobalt(II) ion (1.73 cm3 mol1 K for a Seff = 1/2 with g ≈ 4.3)36 supports the presence of a weak ferromagnetic interaction between the Co(II) ions. Looking at the chain structure of 6, the interaction through anti-syn carboxylate would be the main exchange pathway. Therefore, the magnetic behavior of 6 would correspond to a uniform chain of carboxylate-bridged cobalt(II) ions which are further held together by means of hydrogen bonds involving solvent molecules. The full Hamiltonian to account for the magnetic behavior of 6 is given by eq 8 ^ H¼

∑nn J Sî S^j ∑nn þ βH

αi λi Lî S^ þ

∑nn Δi ½ L^zi 2=3

∑nn ð αi Lî þ ge Sî Þ

2

ð8Þ

where ∑nn runs over all pairs of nearest-neighbor spins i and j within the chain. In order to determine the intrachain magnetic interaction in 6, we have used an approach that some of us reported recently.41 611



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This approach allows the analysis of the magnetic data of highspin cobalt(II) compounds in the whole temperature range in the limit of the weak magnetic coupling as compared to the spin orbit coupling, |J/λ| < 0.1. The cobalt(II) ions in axial symmetry are treated therein as effective spin doublets (Seff = 1/2) which are related with the real spins (S = 3/2) by Seff = (3/5)S. For that, the value of g0 Lande factor of the ground Kramers doublets is replaced by the G(T,J) function which takes into account the magnetic behavior of the magnetically isolated cobalt(II) ions as well as the influence of the magnetic interactions between the ground Kramers doublets of different Co(II) centers on the g0 value. So, this G(T,J) is an effective g factor depending on the temperature, J (magnetic coupling), λ (spinorbit coupling), α (orbital reduction), and Δ (energy gap between the singlet 4A2 and doublet 4E levels issued from the splitting of the orbital triplet 4T1 g ground state under an axial distortion). From a magnetic point of view, complex 6 can be viewed as a uniform chain of ferromagnetically interacting spin doublets. In this sense and following the above approach (compound 3), the magnetic data of 6 in the whole temperature range can be treated as those of a uniform chain of interacting spin doublets through the numerical expression from Baker-Rushbrooke [eq 9]30 where the g factor has been replaced by the G(T,J) function. NGðT, JÞ2 β2 N 2=3 ð9Þ χM ¼ D kT

complexes where the ferromagnetic interactions are more frequent than in general compounds.5mo,34 Malonate is a strong complexing agent due to its bidentate coordination, usually filling equatorial or basal positions with short MO distances. This chelation is often accompanied in its polynuclear complexes by a unidentate coordination mode as weaker interactions and longer M0 O distances. The metal ion that is chelated usually remains in the same plane of the carboxylate groups with small deviations; on the other hand the unidentate coordinated metal can deviate considerably from the carboxylate plane, notably reducing the overlap between the magnetic orbitals of the paramagnetic centers. This minimizes the antiferromagnetic contribution and the magnetic coupling becomes ferromagnetic. Another feature of the malonate is the fact that when these latter M0 O distances are long enough, this oxygen becomes axial or apical. Then, as a consequence of the accidental orthogonality between the interaction magnetic orbitals, the interaction is ferromagnetic, as exemplified by many malonate-containing copper(II) complexes.34 Here we complete this study by investigating Cu(II) and Co(II) derivatives having N- and NO-donors as coligands (dpo, dpp, bpe, dien, and phen). The terminal coligands will always block the available coordination sites of the metal ions causing a decrease of the possibility to form higher-dimensional structures. Magnetically, they are normally adverse to the purpose of achieving high-Tc magnets. However, they make the design of low-dimensional magnetic materials easier. The bridging coligands are very important in our study. Considering their ability to transfer magnetic interactions, they can be divided into magnetically active and inactive. Several coligands, such as dpo and dpp, can not only influence the structures of the complexes but also directly modify the magnetic properties. However, magnetically inactive bridges, which are actually the majority of cases, are usually long ditopic organic compounds. Their roles lay mainly in the structural modulation, and they can subtly adjust the magnetic properties of the materials by modifying the weaker magnetic interaction, such as interchain or interlayer exchange pathways. Furthermore, the bridging coligands can be either rigid or flexible. The prediction of the resulting structures is sometimes possible for the rigid ones, although it is very difficult in most of the cases. On the contrary, the conformational flexibility of the flexible coligands (such as bpe) adds more freedom and it may induce a variety of structures, such as the formation of supramolecular isomers. In summary, we show here how the reactions of copper(II) with malonate and several coligands afforded four novel malonate-containing copper(II) coordination polymers. The structural diversity of these materials is reflected by the variety of coordination polyhedra around the copper(II) sites: square pyramidal (1 and 3), trigonal bipyramidal (4), and elongated octahedral (2 and 4). The cobalt(II) ion in compounds 5 and 6 present an octahedral environment. The malonate ligand in this family acts as either as a blocking (1 and 5) or bridging ligand (26). The rodlike molecules dpo (1 and 5) and bpe (3) exhibit the bis-monodentate (1 and 3) and monodentate (5) coordination modes, whereas dpp (2), dien (4), and phen (6) act as bis-bidentate (2), tridentate (4), and bidentate (6) ligands. Several differences deserve to be pointed out with respect to the previously reported compounds. First, the coordination of the malonate and the auxiliary ligand to the metal(II) ions [Cu(II) (14) and Co(II) (5 and 6)] leads to neutral 1D compounds (1, 2, and 46). An important singular feature is that

where, N ¼ 1:0 þ 5:7979916y þ 16:902653y2 þ 29:376885y3 þ 29:832959y4 þ 14:036918y5 D ¼ 1:0 þ 2:79799y þ 7:0086780y2 þ 8:653844y3 þ 4:5743114y5

and, y ¼ ð25=18ÞJ=kT A very good fit (solid line in Figure 14) is obtained for the magnetic data of 6 in the whole temperature range through eq 9 with the following set of best-fit parameters: J = +0.29 cm1, λ = 133 cm1, α = 1.23 and Δ = 440 cm1 with R = 7.1 105. The value of the exchange coupling shows that the magnetic interaction between the cobalt(II) ions through the anti-syn carboxylate bridge has a weak ferromagnetic character, as in 5. The correct use of this approach is justified in both cobalt compounds by the low value of the of the |J/λ| quotients, the values of the λ, α, and Δ parameters obtained for both 5 and 6 are within the range of those observed in other six-coordinated highspin cobalt(II) complexes.42

’ CONCLUSIONS This work was undertaken with the aim of investigating new malonate-based metalorganic frameworks containing either terminal (endo) or bridging (exo) ligands. As mentioned in the Introduction, we have already reported several studies, where the synthesis, crystal structures, and magnetic properties of malonate-containing compounds were described. As a result of these studies, the bis(bidentate) coordination mode which is dominant in the oxalate complexes, becomes sterically forbidden for the malonate. The bidentate + monodentate and the bidentate + bis(monodentate) coordination modes dominate in the chemistry of this last ligand. This feature dramatically affects the structure and properties of the malonate complexes, a family of 612



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the zigzag chains in 1 are pair-wised through a double CH 3 3 3 O synthon involving dpo atoms and parallel displaced ππ interactions between dpo molecules forming small nanotubes of 6.6 3.5 Å2 by interlinking of the double chains. Second, all of the compounds display low dimensional structures. Third, from a magnetic point of view, all of the compounds display weak interactions, caused mainly by the conformation of the carboxylate bridges (3, 46) or by the exchange coupling through hydrogen bonds (1), double oxo(carboxylate) (2), or the extended bridging ligands (pyrazine-dpp in 2). The value of the exchange interactions through the anti-syn equatorial-equatorial pathway in 4 could be compared with those observed for other malonate-containing copper(II) complexes; however, regarding the equatorial-apical exchange pathway, compound 4 provides the first case of the occurrence of an antiferromagnetic interaction in a malonate-containing copper(II) complex, this fact being due to the highly distorted environment of the Cu(2) atom.

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’ ASSOCIATED CONTENT

bS

Supporting Information. Crystallographic details and X-ray crystallographic data for 16 in CIF format. Figures with details of the weak interactions and the crystal packing of 16 (Figures S1S9). This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Present Addresses ^

Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, C/Pedro Cerbuna 12, E-50009, Zaragoza, Spain and Institut Laue-Langevin, Grenoble, 6 rue Jules Horowitz, B.P. 156, 38042 Grenoble Cedex 9, France.

’ ACKNOWLEDGMENT Financial support from the Ministerio Espa~ nol de Ciencia e Innovacion (MICIIN) through projects MAT2010-16891, DPI2010-21103-C04-03, and CTQ2010-15364 and “Factoría de Crystalizacion” (Consolider-Ingenio2010, CSD2006-00015), from the Agencia Canaria de Investigacion, Innovacion y Sociedad de la Informacion (ACIISI) through project PIL2070901 and structuring projects NANOMAC and FONDECYT 1080262 are gratefully acknowledged. J.P. also thanks the NANOMAC project for a postdoctoral contract. ’ REFERENCES (1) (a) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460. (b) Robson, R. Dalton Trans. 2000, 21, 3735. (c) O’Keeffe, M.; Eddaoudi, M.; Li, H.; Reineke, T.; Yaghi, O. M. J. Solid State Chem. 2000, 152, 3. (d) Long, J.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1203. (entire issue). (e) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629. (2) (a) Hosseini, M. W. Coord. Chem. Rev. 2003, 240, 157. (b) Hosseini, M. W. Acc. Chem. Res. 2005, 38, 313. (c) Lehn, J.-M. Supramolecular Chemistry: Concepts and Perspectives; VCH: Weinheim, 1995. (3) (a) Robin, A. Y.; Fromm, K. M. Coord. Chem. Rev. 2006, 250, 2127. (b) Roesky, H. W.; Andruh, M. Coord. Chem. Rev. 2003, 236, 91. 613



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Novel Malonate-Containing Coordination Compounds with Ligands

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