Coordination Networks with Dicarboxylate and ... - ACS Publications

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Six Flexible and Rigid Co(II) Coordination Networks with Dicarboxylate and Nicotinamide-Like Ligands: Impact of Noncovalent Interactions in Retention of Dimethylformamide Solvent Diana Chisca,† Lilia Croitor,† Eduard B. Coropceanu,‡,§ Oleg Petuhov,‡ Galina F. Volodina,† Svetlana G. Baca,† Karl Kram ̈ er,∥ Jürg Hauser,∥ Silvio Decurtins,∥ Shi-Xia Liu,∥ and Marina S. Fonari*,† †

Institute of Applied Physics Academy of Sciences of R. Moldova, Academy str., 5 MD2028, Chisinau, Moldova Institute of Chemistry Academy of Sciences of R. Moldova, Academy str., 3 MD2028, Chisinau, Moldova § Tiraspol State University, Iablocikin str., 5 MD2069, Chisinau, Moldova ∥ Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland ‡

S Supporting Information *

ABSTRACT: Six mixed-ligand Co(II) coordination polymers, {[Co(adi)(iso-nia)2]·dmf}n (1), [Co(adi)(iso-nia)2]n (2), {[Co2(suc)(ac)2(iso-nia)4][Co2(suc)(sucH)2(iso-nia)4]·2dmf}n (3), [Co(adi)(nia)2]n (4), {[Co(bdc)(nia)2]·dmf}n (5), and {[Co(mal)(S-nia)(H2O)]·dmf}n (6), were synthesized and characterized by single crystal X-ray analysis. They are based on four dicarboxylic acids, namely, malonic (H2mal), succinic (H2suc), adipic (H2adi), and 1,4-benzenedicarboxylic (H2bdc) acids, as well as three nicotinamide-like ligands, isonicotinamide (iso-nia), nicotinamide (nia) and thionicotinamide (S-nia). Compounds 1, 2, and 3 represent one-dimensional coordination polymers, whereas 4, 5, and 6 exhibit two-dimensional structures. The coordination arrays in 1−5 are built from the similar [Co2(COO)2] binuclear clusters, while framework 6 is based on mononuclear metal nodes. All crystal lattices are supported by hydrogen bonding with nicotinamide-like ligands acting as pillars or dangling terminal ligands. Four crystal lattices 1, 3, 5, and 6 host dmf solvent via NH···O hydrogen bonding and π−π stacking interactions with the coordination networks. Details of the reversible dmf release−uptake by 1 and 2, and contribution of hydrogen bonding in stabilization of the solvent-free structures 2 and 4 are discussed. All new solids were characterized by IR spectroscopy and thermogravimetric analysis, while magnetic measurements are reported for compounds 1, 5, and 6. The magnetic data show the typical behavior of Co(II) ions originating from pronounced zero-field splitting within the ground state with contributing effects from weak antiferromagnetic exchange interactions.

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INTRODUCTION Since metal−organic framework (MOF) strategies were launched in the 1990s, interest in the adsorption properties of these crystalline solids has been continuously growing.1−7 Among MOFs (M = Zn, Cu, Fe, Zr, etc.),8−14 Co-based MOFs are distinct due to their notable adsorption capacities to N2, H2, CO2, hydrocarbons, and different solvents.15−32 As a matter of fact, the scientific interest in the investigation of Co(II) coordination networks33−35 stems on one hand from their remarkable adsorptive,15−32 catalytic,36 and magnetic properties,37−46 and on another hand from their unique solvatochromic and vaporchromic behavior that makes these materials attractive targets for sensing.47,48 In light of the increased © 2016 American Chemical Society

attention on environmental problems, specifically connected with the increased CO2 content in the atmosphere, the physisorption of CO2 by coordination networks, and the factors facilitating its uptake and consecutive release are also in the focus of those scientists working in the field of coordination polymers. In this regard, coordination polymers decorated by amino- and amido-groups proved their values.49−53 Not only rigid three-dimensional (3D) MOFs but also flexible ones and lower dimensional (two-dimensional (2D) and one-dimensional Received: August 18, 2016 Revised: October 18, 2016 Published: October 26, 2016 7011

DOI: 10.1021/acs.cgd.6b01226 Cryst. Growth Des. 2016, 16, 7011−7024

Crystal Growth & Design

Article

with pyridine-n-oxime ligands (which in some sense can be considered as positional analogues of nicotinamide ligands used herein),72 we present herein the synthesis and single-crystal structures for six coordination polymers, one-dimensional (1D) arrays {[Co(adi)(iso-nia)2]·dmf}n (1), [Co(adi)(iso-nia)2]n (2), {[Co2(suc)(ac)2(iso-nia)4][Co2(suc)(sucH)2(iso-nia)4]· 2dmf}n (3), and 2D sheets [Co(adi)(nia)2]n (4), {[Co(bdc)(nia)2]·dmf}n (5), and {[Co(mal)(S-nia)(H2O)]·dmf}n (6) (see Scheme 1 for abbreviations). Thereby, the successful strategy for the design of coordination polymers based on the building block approach is applied.73 In addition, the limits of thermal stabilities of 1−6 were probed by thermogravimetry. Desorptive-adsorptive experiments reveal a reversible transformation for the 1D coordination polymers in the order 1 > 2 > 1s, while 5 shows a tough steadiness to dmf removal under the same desorption conditions. The results of magnetic measurements are reported for 1, 5, and 6.

(1D)) coordination polymers demonstrate their efficiency in gas adsorption, also with preferential CO2 capture. Experimental results demonstrated that layered MOFs can have remarkable thermal stability and moisture resistance, which are particularly advantageous for practical CO2 capture. Having a rather moderate size of surface area, they can nevertheless show high CO2 adsorption capacity, comparable to that of previously reported MOFs with much higher surface areas. It has been shown that acidic carbonyl functionalities in addition to amino groups are also favorable to bind CO2 molecules. The adsorption sites generated from polar functionalities are key factors leading to high CO2 uptake.54−61 As a further aspect, the ligand-based hydrogen-bond functionality, acting as “supramolecular glue”, enhances the crystal structure stability and affords some flexibility for the accommodation of guests within or in between the coordination layers.50−53 It is also possible to introduce flexibility into the linkers themselves, and aliphatic dicarboxylic acids are very popular spacers in this regard. Within the family of carboxylate networks, many Co(II)-based coordination polymers exhibit mixed-ligand systems as well, for instance, with ditopic ligands that combine both carboxylic and pyridine functions in one molecule. Nicotinic acid and its derivatives, for example, are often used,9−48,62−65 and both types of ligands are relevant in this study (Scheme 1). Nicotinamide (nia) is a form of niacin (vitamin B3), an important respiratory stimulant, and its complexation appears to be a useful approach to increase the solubility of physiologically relevant systems. One of the commercially available analogues of nicotinamide is thionicotinamide (S-nia), where the amide oxygen of nicotinamide is substituted by sulfur (Scheme 1). The retrieval of Cambridge Structure Database (CSD)66 reveals examples of polymeric structures where the nia and iso-nia ligands coordinate to metal ions such as Pb(II), Cu(II), Sr(II), Ag(I), and Mn(II) in a bidentate mode through pyridine nitrogen and carbonyl oxygen atoms. However, the particular search for the same ligands combined with Co(II) resulted in only four coordination polymers,67−71 with nia and iso-nia ligands working as terminal ligands and acting in a monodentate mode exclusively via the pyridine nitrogen atom. For the S-nia ligand, only two 2D coordination polymers were recently reported, {[Co2(μ2-H2O)(bdc)2(S-nia)2(H2O)(dmf)]· dmf·2H2O}n and [Co(bdc)(S-nia)]n. They represent the starting and end systems of transformation from the solvated form to the solvent-free one that occurs as a reversible crystalto-crystal transformation by the reconstruction of the 2D coordination network together with a visible color change.34 In this context and based on our previous successful strategy in combining dicarboxylic acids of different lengths and flexibilities

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EXPERIMENTAL SECTION

Materials and Methods. All reagents and solvents were obtained from commercial sources and used without further purification. Elemental analyses were performed on an Elementar Analysensysteme GmbH Vario El III elemental analyzer. The IR spectra were obtained in Nujol on a FT IR Spectrum-100 PerkinElmer spectrometer in the range of 400−4000 cm−1. Thermal Analysis. Thermal behaviors of the complexes have been studied by thermogravimetric (TG), derivative weight loss (DTG), and differential thermal analyses (DTA) in a dynamic air atmosphere. Thermal analysis was performed on a Derivatograph Q-1500 system. Each sample (about 20 mg) was placed in a platinum crucible and was heated under an air flow rate of 100 mL/min and a heating rate of 10 °C/min from 20 to 1050 °C. TG, DTG, and DTA curves were simultaneously registered. Gas Adsorption Characterization. Adsorption parameters of the samples were obtained from nitrogen adsorption isotherms at 77 K. The adsorption isotherms were measured using Autosorb-1-MP (Quantachrome), with prior degassing at 110 °C for 12 h. The specific surface area (SBET) was calculated using the Brunauer−Emmett−Teller (BET) equation. The total pore volume (Vt) was calculated by converting the amount of N2 gas adsorbed at a relative pressure of 0.99 to equivalent liquid volume of the adsorbate (N2). Magnetic Measurements. Magnetic susceptibility measurements were made on a Quantum Design MPMS SQUID-XL magnetometer under an applied magnetic field of 103 Oe between 300 and 1.9 K. Magnetization measurements were conducted at 1.9 K up to a magnetic field of 50 kOe. The samples were prepared in a gelatin capsule. Diamagnetic corrections were made for the samples using the approximation −0.45 × molecular weight × 10−6 cm3 mol−1, and the sample holder was corrected for by measuring directly the susceptibility of the empty capsule.

Scheme 1. Schematic Presentation of Ligands Used in This Study with the Abbreviations

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Article

X-ray Powder Diffraction. The data were collected with a DRON-UM X-ray powder diffractometer equipped with a Fe−Kα radiation (λ = 1.93604 Å) source. The diffractometer was operated at 30 kV and 30 mA. The data were collected over an angle range of 5−50° at a scanning speed of 5° per minute. Synthesis of {[Co(adi)(iso-nia)2]·dmf}n (1). Co(ac)2·4H2O (0.025 g, 0.1 mmol), H2adi (0.015 g, 0.1 mmol), and iso-nia (0.024 g, 0.2 mmol) were dissolved upon heating in a mixture (12 mL) of CH3OH/dmf/ H2O (6:3:3) and stirred to form a pink solution. Then, three drops of 0.01 mol·L−1 NaOH solution were added. The reaction mixture was stirred for ∼5 min, filtered off and then cooled to room temperature to obtain orange-red crystals in 62% yield (based on Co). Anal. Calcd for C21H27CoN5O7: C, 48.42; H, 5.18; N, 13.45. Found: C, 48.39 ; H, 5.1; N, 13.41. IR (cm−1): 3300(w), 3167(m), 2966(w), 2861(w), 1702(s), 1596(s), 1554(s), 1392(m), 1332(w), 1316(w), 1299(w), 1230(m), 1017(s), 856(s), 808(m), 791(m), 762(m). Compound [Co(adi)(iso-nia)2]n (2) Was Obtained by dmf Evacuation from 1. Synthesis of {[Co2(suc)(ac)2(iso-nia)4][Co2(suc)(sucH)2(iso-nia)4]·2dmf}n (3). To a hot solution of Co(ac)2·4H2O (0.025 g, 0.1 mmol) and iso-nia (0.024 g, 0.2 mmol) in 14 mL CH3OH/dmf/H2O (6:1:3), H2suc (0.011 g, 0.1 mmol) dissolved in 4 mL of H2O was added. The reaction mixture was heated in an open container for 5 min at 150 °C. To the obtained precipitate, 1 drop of nitric acid was added. Pink crystals precipitated upon cooling were filtered, washed with CH3OH/dmf (2:1), and dried in air. Yield: 45% (based on Co). Anal. Calcd for C37H43Co2N9O15: C, 45.69; H, 4.42; N, 12.96. Found: C, 45.51; H, 4.38; N, 12.84. IR (cm−1): 3304(m), 3168(m), 2989(w), 2973(w), 1701(s), 1599(s), 1556(s), 1394(s), 1227(s), 1149(m), 1066(s), 1060(w), 1018(m), 859(s), 763(m), 681(s), 660(w). Synthesis of [Co(adi)(nia)2]n (4). To a hot solution of Co(ac)2· 4H2O (0.025 g, 0.1 mmol) and nia (0.024 g, 0.2 mmol) dissolved in 10 mL of CH3OH/dmf (2:1), H2adi (0.015 g, 0.1 mmol) dissolved in 4 mL of H2O was added. The reaction mixture was heated for 10 min. Pink crystals precipitated upon cooling were filtered, washed with CH3OH/dmf (2:1), and dried in air. Yield: 45% (based on Co). Anal. Calcd for C18H20CoN4O6: C, 48.28; H, 4.47; N, 12.51. Found: C, 48.32; H, 4.38; N, 12.45. IR (cm−1): 3365 (w), 3177 (m), 2988 (w), 2972 (w), 1702 (s), 1599 (s), 1548 (s), 1439 (m), 1384 (s), 1314 (w), 1256 (m), 1203 (m), 1074 (w), 1066 (w), 1053 (s), 892 (m), 792 (w), 775 (m), 694 (m). Synthesis of {[Co(bdc)(nia)2]·dmf}n (5). Co(ac)2·4H2O (0.025 g, 0.1 mmol) and nia (0.024 g, 0.2 mmol) were dissolved in a mixture (12 mL) CH3OH/dmf/H2O (6:3:3) upon heating and stirred to form a pink solution. Then, H2bdc (0.016 g, 1 mmol) was added and the mixture was stirred for 30 min. The resulting solution was allowed for crystallization (∼26 days) at room temperature. The crystals were filtered, washed with cold methanol and dmf, and air-dried. Yield: 39% (based on Co). Anal. Calcd for C23H23CoN5O7: C, 51.07; H, 4.25; N, 12.95. Found: C, 51.01; H, 4.19; N, 12.83. IR (cm−1): 3358(w), 3179(m), 1664 (s), 1618 (m), 1599 (m), 1541 (m), 1500 (w), 1375 (s), 1303 (w), 1203 (m), 1151(w), 796 (m), 747 (m), 697 (s), 658 (m). Synthesis of {[Co(mal)(S-nia)(H2O)]·dmf}n (6). CoCl2·6H2O (0.024 g, 0.1 mmol), S-nia (0.028 g, 0.2 mmol) and H2mal (0.01 g, 0.1 mmol) were dissolved in mixture (8 mL) of methanol and dmf (5:3). The reaction mixture was stirred in the ultrasonic bath at 60 °C for ∼50 min, filtered off and then cooled to 5 °C temperature giving orange crystals. Yield: 52% (based on Co). Anal. Calcd for C12H17CoN3O6S: C, 36.89; H, 4.35; N, 10.76. Found: C, 36.77; H, 4.37; N, 10.73. IR (cm−1): 3141(m), 2925(v.w.), 1674(m), 1628(m), 1560(s), 1475(w), 1446(m), 1301(m), 1350(m), 1253(w), 1188(m), 1095(m), 1051(m), 1030(w), 862(w), 739(m), 697(w), 658(m), 587(w). Crystallographic Studies. Diffraction measurements for 1−6 (Figure 1S) were carried out on an Xcalibur E diffractometer equipped with a CCD area detector and a graphite monochromator utilizing MoKα radiation (λ = 0.71073 Å) at room temperature. Final unit cell dimensions were obtained and refined on an entire data set. The calculations to solve the structures and to refine the model proposed were carried out with the programs SHELXS97 and SHELXL2014.74

Hydrogen atoms attached to carbon atoms were positioned geometrically and treated as riding atoms using SHELXL default parameters with Uiso(H) = 1.2Ueq(C), the O-bounded H atoms were found from differential Fourier maps at intermediate stages of the refinement and their positions were constrained using the AFIX 83 instruction in SHELXL for hydroxyl groups. The N-bound H atoms in amino-groups were found from differential Fourier maps, and their positions were restrained using the DFIX instruction (N−H = 0.86 Å). These hydrogen atoms were refined with isotropic displacement parameter Uiso(H) = 1.5Ueq(N). In 3, one of the O atoms in the carboxylic group and dmf molecules are disordered over two positions with partial occupancies of 0.739(13)/0.261(13) and 0.56(2)/0.44(2), each. In 6, the S-nia and dmf molecules are disordered over two positions in a synchronized order with almost equal partial occupancies of 0.517(8) and 0.483(8). Additionally, the low temperature X-ray experiments were carried out for 1, 5, and 6 on an Oxford Diffraction SuperNova area-detector diffractometer using mirror optics monochromated Mo Kα radiation to get accurate data for the occupancy factors for the disordered fragments and the accommodated dmf molecules. The X-ray data and the details of the refinement for 1−6 are summarized in Table 1, H-bonding parameters are given in Table 2, and selected geometric parameters are summarized in Table S1. The figures were produced using Mercury.75 The solvent accessible voids (SAVs) were calculated using PLATON.76

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RESULTS AND DISCUSSION Synthesis and IR Characterization. Except for 6 which has been obtained using CoCl2·6H2O as a starting salt, all other compounds were prepared similarly by mixing Co(ac)2·4H2O, dicarboxylic acid, and nicotinamide-like ligands in a 1:1:2 ratio in the CH3OH/dmf/H2O solution. The IR spectra of the complexes exhibit very strong and broad bands due to asymmetric stretching vibrations of carboxylic groups (υasCOO) at 1554 cm−1 (1), 1556 cm−1 (3), 1548 cm−1 (4), 1578 (5), and 1562 cm−1 (6), and the symmetric ones (υsCOO) at 1392 (1), 1394 (3), 1440, 1416, 1384 cm−1 (4), 1383 cm−1 (5), and 1449, 1406, 1384 cm−1 (6). The presence of aromatic rings in the complexes is documented by IR absorptions at 1596 cm−1 (1), 1599 cm−1 (3, 4), 1618, 1500 cm−1 (5), and 1628 cm−1 (6). The bands at 1299, 1230 cm−1 (1), 1227, 1149 cm−1 (3), 1314, 1203 cm−1 (4), 1303, 1203, 1151 cm−1 (5), and 1301, 1253, 1188 cm−1 (6) belong to the υ(C−N) vibration of the pyridine rings. The presence of NH2 groups is shown by absorptions at 3300, 3167 cm−1 (1), 3304, 3168 cm−1 (3), 3365, 3177 cm−1 (4), 3358, 3179 cm−1 (5), and 3141 cm−1 (6). The band for the υ(CS) group in 6 was observed at 1195 cm−1. In all spectra, the C−H deformation modes are present at 791, 796, 763, 792, 739, 697, 681, 658 cm−1. Structural Description. Photographs of the crystals 1−6 are shown in Figure 1S. To obtain accurate values of the dmf occupancy in coordination networks, the structure determinations for three samples, 1, 5, and 6 were carried out under ambient conditions (293 K) and at low temperature (100 K). For consistency, the comparison of the crystal unit cell parameters and the values of the solvent-accessible voids (SAVs) in all structures are given at room temperature. One-Dimensional Coordination Polymers. Three 1D coordination polymers 1−3 were obtained using the H2adi and H2suc acids as the linkers and iso-nia ligand as the terminal pillar (Scheme 1). Compounds 1 and 3 are solvates77 with the dmf inclusion in the crystal lattices, while compound 2 is a solvent-free apohost obtained from 1 by the delicate evacuation of the solvent. Compound 1 with the composition {[Co(adi)(iso-nia)2]·dmf}n crystallizes in the centrosymmetric triclinic space group P1̅. 7013


72.069(5)

82.341(4)

80.616(4)

1156.79(9)

2

1.494

0.794

542

8101/4539 23459/4653 6367/4037 4907/3217 12760/7862 6611/3550 7034/2992 52974/4676 2499 3072 [R(int) = 0.0262] [R(int) = 0.0306] [R(int) = 0.1158] [R(int) = 0.0735] [R(int) = 0.0374] [R(int) = 0.0621] [R(int) = 0.0338] [R(int) = 0.0343] [R(int) = 0.0246] [R(int) = 0.0305]

4539/6/325

1.076

α/deg

β/deg

γ/deg

V/Å3

Z

Dcalcd Mg/m3

μ/mm−1

F(000)

reflns collected/ unique

data/restraints/ parameters

7014

GOF

0.0318, 0.0746

R indices (all data) R1, wR2

0.0556, 0.1158

0.0284, 0.0729

0.0440, 0.1060 R indices [I > 2σ(I)], R1, wR2

1.052

4653/0/325

542

0.809

1.523

2

1135.04(6)

79.883(2)

82.357(2)

72.247(2)

14.6162(4)

0.2939; 0.4881

0.1893; 0.4355

1.172

4037/0/307

542

0.792

1.490

2

1160.2(7)

80.79(3)

82.32(3)

72.33(3)

14.706(5)

0.2285, 0.2254

0.0959, 0.1675

0.934

3217/6/274

462

0.979

1.615

2

919.6(4)

99.840(15)

91.257(16)

100.79(2)

10.913(3)

9.613(2)

9.0713(14)

11.1597(4)

0.1181, 0.2276

0.0817, 0.2038

1.017

7862/91/648

1004

0.836

1.477

2

2185.3(2)

92.022(4)

104.329(4)

95.893(5)

15.8473(9)

12.8466(8)

11.2701(8)

0.1407, 0.0896

0.0638, 0.0694

0.934

3550/0/274

924

0.938

1.547

4

1920.2(2)

90

99.795(7)

90

11.9218(11)

14.5025(8)

18.0026(2)

0.0371, 0.0811

0.0315, 0.0765

1.000

2992/1/344

4464

0.801

1.557

16

9219.0(2)

90

90

90

28.4456(6)

18.0026(2)

0.0201, 0.0492

0.0192, 0.0485

1.042

4676/1/344

4464

0.808

1.572

16

9133.05(12)

90

90

90

28.3053(2)

17.9628(1)

17.9628(1)

0.0545, 0.0930

0.0419, 0.0859

1.078

2499/16/240

804

1.191

1.562

4

1660.01(16)

90

90

90

7.3820(4)

7.0769(4)

31.7756(18)

Pna21

0.0344, 0.0682

0.0297, 0.0659

1.042

3072/32/276

804

1.201

1.574

4

1647.02(7)

90

90

90

7.34471(14)

7.08646(18)

31.6443(9)

Pna21

orthorhombic

390.27

173

14.6846(7)

9.311(3)

9.046(3)

I41cd

orthorhombic

390.27

295

c/Å

9.2574(3)

8.9794(2)

I41cd

tetragonal

540.39

173

9.2949(5)

P21/n

tetragonal

540.39

295

9.0642(3)

P1̅

monoclinic

447.31

295

b/Å

P1̅

triclinic

971.66

295

a/Å

P1̅

triclinic

447.31

295

P1̅

triclinic

520.41

295

P1̅

520.41

space group

6_LT C12H17CoN3 O6S

triclinic

6_RT C12H17CoN3O6S

triclinic

5_LT C23H23CoN5O7

crystal system

5_RT C23H23CoN5O7

173

4 C18H20CoN4O6

520.41

3 C37H43Co2N9O15

295

2 C18H20CoN4O6

fw (g mol−1)

1s C21H27CoN5O7

T, K

1_LT

C21H27Co N5O7

empirical formula C21H27Co N5O7

1_RT

Table 1. Crystal Data and Structure Refinement for 1−6

Crystal Growth & Design Article



Article

Table 2. Selected Hydrogen Bonds for 1−6 D−H···A

d(D−H), Å

d(H···A), Å

N(4)−H(3N)···O(4) N(4)−H(4N)···O(7) N(2)−H(2N)···O(7) N(2)−H(1N)···O(6)

0.84(2) 0.83(2) 0.80(3) 0.84(2)

2.02(2) 2.20(2) 2.20(2) 2.03(2)


0.87(2) 0.86(2) 0.85(2) 0.86(2)

2.04(4) 2.46(5) 2.24(5) 2.23(3)

N(8)−H(8N)···O(2) N(8)−H(7N)···O(13) N(6)−H(6N)···O(14) N(6)−H(5N)···O(1) N(4)−H(4N)···O(9) N(4)−H(3N)···O(7) N(2)−H(2N)···O(8) N(2)−H(1N)···O(10) O(5)−H(5)···O(8)

0.86(2) 0.85(2) 0.85(2) 0.84(2) 0.86(2) 0.85(2) 0.86(2) 0.85(2) 0.82

2.03(3) 2.10(2) 2.12(3) 2.16(3) 2.15(4) 2.02(2) 2.09(3) 2.16(3) 2.34


0.85(4) 1.02(5) 0.90(5) 0.95(5)

2.30(5) 2.18(5) 1.93(5) 2.02(5)


0.84(3) 0.90(3) 0.87(3) 0.85(3)

2.35(3) 2.09(3) 2.14(3) 2.01(3)

O(5)−H(2O5)···O(2) O(5)−H(2O5)···O(4) O(5)−H(1O5)···O(3) N(2)−H(2C)···O(1P) N(2A)−H(2A1)···O(1S)

0.87(2) 0.87(2) 0.85(2) 0.86 0.86

2.56(5) 1.81(3) 1.95(4) 2.06 2.02

d(D···A), Å 1_LT 2.855(2) 3.016(2) 2.932(2) 2.860(2) 2 2.880(11) 3.242(12) 2.997(11) 3.072(10) 3 2.876(6) 2.940(7) 2.953(7) 2.972(7) 2.976(7) 2.868(7) 2.925(7) 2.992(7) 2.900(12) 4 3.113(5) 3.183(6) 2.825(5) 2.935(6) 5_LT 3.144(3) 2.991(3) 2.978(3) 2.852(3) 6_LT 3.063(10) 2.672(13) 2.692(12) 2.82(2) 2.82(3)

∠DHA, °

symmetry operation for acceptor

170(2) 166(2) 150(2) 166(2)

2−x, 2−y, 1−z x+1, y+1, z x, y, z+1 x−1, y−1, z+1

162(9) 151(8) 148(9) 164(7)

x+1, y−1, z−1 1−x, 2−y, 1−z 1−x, 1−y, −z 2−x, 2−y, −z

170(7) 174(8) 165(8) 161(7) 159(8) 173(8) 164(7) 165(8) 126.2

1−x, 1−y, 1−z x−1, y, z−1 x+1, y, z+1 1−x, 1−y, 2−z 1−x, 1−y, 2−z x+1, y, z+1 x−1, y, z−1 1−x, 1−y, 1−z 1−x, 2−y, 2−z

160(5) 170(4) 174(5) 161(4)

x, y−1, z −x−1/2, y−1/2, 3/2−z x, y+1, z 1/2−x, y+1/2, 3/2−z

158(3) 173(3) 163(3) 171(3)

3/2−y, x+0, z−1/4 1−y, x−1/2, z+1/4 x, 1−y, z+1/2 y+0, x+1/2, z−1/4

118(4) 173(7) 145(5) 146.9 154.8

x, y, z 1/2−x, y−1/2, z−1/2 1/2−x, y−1/2, z+1/2 −x, 1−y, z+1/2 −x, 1−y, z−1/2

this network is the stoichiometric inclusion and exact location of dmf molecules in the crystal structure, since due to the participation of each dmf molecule in two NH···O hydrogen bonds (Table 2), it fixes tightly and precisely in the crystal lattice (Figure 1c). In the “Napoleon cake-like” structure, the more rigid hybrid “coordination − H-bonded’ sheets are covered by the dmf “soft blankets” (Figure 1d). Following the previously reported desorption conditions for a smooth removal of dmf from the coordination networks,34,35 the complete loss of dmf from 1 could be achieved which was accompanied by a single-crystal-to-single-crystal (SC−SC) transformation of 1 to the solvent-free apohost 2 with the composition [Co(adi)(iso-nia)2]n. Figure 2 displays the experimental and simulated75 powder X-ray diffraction (PXRD) patterns for 1 and 2, both showing the crystallinity of the compounds, indicate in practically full conversion of the solvated form 1 into the desolvated form 2 in bulk. The peak at 2θ = 8.027° (h, k, l = 0, 0, 1) marked by “o” (“origin”) at Figure 2b (black plot) corresponds to the impurity of the compound 1 in the bulk of the compound 2. Despite some deterioration of the crystal quality caused by the thermal stress, the new solid 2 retains its crystallinity that allowed determining the crystal structure by single crystal X-ray diffraction. The comparison of the RT unit cell parameters

The asymmetric unit comprises one Co(II) atom, one adipate anion, two iso-nia ligands, and one dmf solvate molecule (Figure 1a). The Co(II) coordination core is a distorted octahedron with a N2O4-set of donor atoms from three adipate residues in the equatorial plane and two iso-nia ligands in axial positions. The Co−O distances are in the range of 2.0163(12)−2.2102(12) Å, and Co−N distances adopt the values of 2.1518(13) and 2.1648(13) Å. Two iso-nia ligands upraise virtually perpendicular to the metal-carboxylate coordination plane, being situated nearly in parallel planes as the dihedral angle of 11.7° between their pyridine rings indicates. Through two carboxylic groups that act in a bidentate bridging mode, two Co(II) atoms are linked into a centrosymmetric binuclear unit [Co2(COO)2] with a Co···Co separation of 4.0332(3) Å. The structure extension in double polymeric tapes occurs via the second carboxylic group of the adipate ligand that provides the next short separation of 6.6466(4) Å between two Co(II) atoms (Figure 1b). The bridging mode of the adi binding results in the alternation of 8- and 20-membered metallocycles along the coordination tape. These tapes are further associated in the H-bonded 2D layer achieved through the NH···O hydrogen bonds (Figure 1b, Table 2) and situated parallel to the (101) coordination plane. The notable feature of 7015



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Figure 1. (a) View of the [Co2(COO)2] binuclear unit in 1 with the partial atom numbering scheme. C-bound H atoms are omitted for clarity. (b) Coordination tapes combined in the H-bonded layer via hydrogen bonds. (c) Mode of association of dmf molecules in the crystal lattice via two NH···O hydrogen bonds. (d) Crystal packing in 1 with the dmf inclusion in the crystal lattice, the latter one is shown in space-filling mode.

Figure 2. Experimental (black, down) and simulated (blue, up) by the MERCURY software PXRD patterns for 1 (a) and 2 (b).

being rather close to 1 (Figure 3, Table S1). It retains the [Co2(COO)2] binuclear core along with the double-tape architecture of the coordination array (Figure 3a,b). The increased Co···Co separations along the coordination tape up to 4.136(2) and 7.141(3) Å were registered, along with the more perfect alignment of the two iso-nia molecules, indicated by the dihedral angle of 7.6° between the pyridines of the iso-nia ligands.

for 1 and 2 (Table 1) reveals that crystal 2 retains the triclinic unit cell with the slight elongation of two (a and b) and contraction of one (c) unit cell parameters. The total contraction of the unit cell volume comprises 237.2 Å3 or 20.5% of the unit cell volume that stands very close to the calculated value of SAVs in 1 (210.7 Å3 or 18.2%). The crystal structure of 2 reveals a 1D coordination array with geometric characteristics 7016



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Figure 3. (a) View of the [Co2(COO)2] binuclear unit in 2 with partial atom numbering scheme. (b) Coordination tapes combined in the H-bonded layer via hydrogen bonds. (c) Mode of association of the iso-nia molecules in the crystal lattice via NH···O hydrogen bonds. (d) The fragment of dense crystal packing in 2 supported by hydrogen bonding. C-bound H atoms are omitted for clarity.

caused by the solvation stress (see Table 1 for crystallographic data). Surprisingly, the dmf molecules reoccupy in 1s virtually the same sites as in 1 through their participation in the hydrogen bonding system. Compound 3 with the composition {[Co2(suc)(ac)2(isonia)4][Co2(suc)(sucH)2(iso-nia)4]·2dmf}n crystallizes in the centrosymmetric triclinic space group P1̅. The asymmetric unit comprises two types of neutral 1D tapes, [Co2(suc)(ac)2(iso-nia)4]n and [Co2(suc)(sucH)2(iso-nia)4]n, where again in both cases the binuclear [Co2(COO)2] moieties act as nodes, while the suc residues are the linkers in between. Similar to 1 and 2, the Co(II) coordination cores of the two nonequivalent Co(II) atoms are distorted octahedral with the

As it is evident from Figure 3c, in 2, the space of dmf molecules evacuated from 1 is occupied by the iso-nia ligands from the next closest layer, thus resulting in a denser crystal packing with a lack of voids in this structure. The removal of dmf results in the partial redistribution of the hydrogen bonding and in the self-association of the neighboring 1D tapes via two NH···O hydrogen bonds (Table 2), that in turn, results in a tighter bonding of the neighboring coordination tapes. The soaking of 2 in dmf for 24 h demonstrates the reversible transformation of the system, since the solvated compound 2 reveals the unit cell parameters of 1 (furthermore addressed as 1s), as confirmed unambiguously by repeated X-ray experiments, despite the further deterioration of the crystal quality 7017



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Figure 4. (a, b) View of the [Co2(COO)2] binuclear units in 3 with partial atom numbering scheme. (c, d) Fragments of coordination tapes in 3 combined in the H-bonded layers via the centrosymmetric R22(8) amide homosynthons; both positions for the disordered ac anion are shown in Figure 4d. (e) View of the H-bonded 3D homomeric grid built of the “Hsuc-suc” coordination tapes. (f) Mode of enclathration of dmf in the crystal lattice in 3. The 3D and 2D interconnected H-bonded networks are shown in red and green, and dmf molecules are shown in space-filling mode. C-bound H atoms are omitted for clarity.

N2O4-sets of donor atoms originating from three carboxylic groups in the equatorial planes, and two pyridine nitrogen atoms from two iso-nia ligands in the axial positions. The Co−O and Co−N distances are typical, being in the range of 2.012(4)− 2.257(4) Å and 2.144(4)−2.173(4) Å, respectively. The terminal Hsuc ligands and ac anions, that make the difference between these two tapes, fulfill similar structural functions while acting as bidentate bridging ligands and affording similar centrosymmetric

[Co2(COO)2] binuclear units (Figure 4a,b). The Co···Co separations in these two tapes alternate with values of 4.046(1) and 8.896(1) Å for Co(1), and 4.075(1) and 8.805(1) Å for Co(2), respectively (Figure 4c,d). The iso-nia pillars are in convex and concave shapes in these two tapes with twisted angles between the mean planes of the pyridine rings of the iso-nia ligands being 9.7° in the Hsuc-suc tape [with Co(1)], against 41.4° in the suc-ac tape [with Co(2)]. The latter 7018



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the mean plane of the coordination layer. This arrangement is supported by the NH···O hydrogen bonds through the double R22(8) amide synthons and single NH···O hydrogen bonds, all acting within the layers’ planes (Figure 5b, Table 2). The stacking of the layers along the [100] axis is supported by single NH···O hydrogen bonds (Figure 5c) and impedes the solvent accommodation in this crystal lattice. Compound 5 with the composition {[Co(bdc)(nia)2]·dmf}n crystallizes in the non-centrosymmetric tetragonal space group I41cd. The asymmetric unit comprises one Co(II) atom, one bdc anion, two nia ligands, and one dmf molecule (Figure 6a). Contrary to the centrosymmetric clusters in 1−4, herein the [Co2(COO)2] binuclear unit resides on a 2-fold rotation axis, although it does not influence significantly the cluster’s geometry. The cobalt atom shows a N2O4-distorted octahedral geometry, comprising four oxygen atoms from three bdc ligands in the equatorial plane, the Co−O distances being in the range of 2.002(2)−2.330(3) Å, and two nitrogen atoms from two nia ligands in the axial positions, the Co−N distances being 2.162(4) Å and 2.195(4) Å (Table S1). The bdc linker shows two bridging styles, namely, syn,syn-bidentate-bridging within the cluster and bis-monodentate between the clusters. Similar to 4, each Co(II) atom coordinates three bdc residues, and each bdc residue bridges three Co(II) atoms. The Co···Co separations are 4.172 Å in the cluster and 10.743 or 10.899 Å across the bdc ligand. The bdc residues lie in the layer’s mean plane, while two nia ligands upraise in a parallel manner perpendicular to the same plane; the interplanar angle between the pyridine rings of two nia molecules is 5.3°. Considering the binuclear unit as a single coordination node in the coordination layer, the 2D coordination network exhibits a (4,3) topology, being extended parallel to the ab crystallographic plane and forming square meshes with the dimensions 12.73 × 12.73 Å2, calculated as the separations between the centroids of the binuclear units (Figure 6b). The nia pillars give premise to the formation of a polythreading network.55,63,78,79 In fact, double pillars of one layer are inserted into these large grids of two adjacent layers up and down. Therefore, each grid is penetrated by a pair of nia entities from opposite directions. As a consequence, three adjacent 2D arrays are entangled into uncommon

increase is the sequence of the steric hindrance due to the bulky anionic ac bridge in the [Co2(COO)2] cluster. Each type of tape is linked in similar H-bonded layers via the same R22(8) NH(NH2)···O(OC) homomeric centrosymmetric amide synthon built of alternating narrow and wide rectangular cages with the same Co···Co separation of 16.975 Å across both synthons (Figure 4c,d). The “Hsuc-suc” layers participate through the Hsuc pillars in the OH(Hsuc)···O(iso-nia) hydrogen bonds forming the 3D H-bonded homomeric network (Figure 4e). The “suc-ac” sheets are interwoven in the voids of this 3D grid via NH···O hydrogen bonds (Table 2). Because of this interpenetration, the disordered dmf molecules appear to be accommodated in closed cages, and the disorder model with the shift of two in-plane positions for dmf molecules correlates perfectly well with the disorder of carboxylic groups in the acetate anions with whom the solvent synchronizes (Figure 4f). Two-Dimensional Coordination Polymers. The three 2D coordination polymers 4−6 were obtained using the flexible H2adi and rigid H2bdc acids as linkers, and nia and S-nia ligands as terminal pillars (Scheme 1). Compound 4 is the solvent-free network, while compounds 5 and 6 are solvates with the dmf inclusion in the crystal lattices. Compound 4 with the composition [Co(adi)(nia)2]n, crystallizes in the centrosymmetric monoclinic space group P21/n. The asymmetric unit comprises one Co(II) atom, one adi anion, and two nia ligands. The distorted octahedral N2O4-coordination core is formed by three adi residues and two nia ligands. The Co−O distances are in the range of 2.002(3)−2.377(3) Å, and Co−N distances are 2.142(4) and 2.147(4) Å (Table 1S). Similar to 1−3, two crystallographically equivalent Co(II) atoms form the [Co2(COO)2] binuclear centrosymmetric unit via two bidentate bridging carboxylato groups (Figure 5a). The adi linker shows two bridging styles, namely syn,syn-bidentate-bridging within the unit and bis-monodentate between them. The Co···Co separations are 4.025 Å in the cluster and 8.873 Å across the adi ligand. The adi linker adjusts a bent conformation with the carboxylic groups, twisted by a dihedral angle of 76.8°. Two nia ligands remain virtually parallel with the dihedral angle between the pyridine rings of 7.6°. The specific feature of this 2D network is an arrangement of nia molecules virtually parallel to

Figure 5. (a) View of the [Co2(COO)2] binuclear unit in 4 with partial atom numbering scheme. (b) The coordination layer in 4 supported by NH···O hydrogen bonds through the R22(8) amide synthons and single NH···O hydrogen bonds that act in the layers’ plane (top view). (c) Packing of layers with interplay of NH···O hydrogen bonds; view along the b axis. 7019



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Figure 6. (a) View of the [Co2(COO)2] binuclear unit in 5 with partial atom numbering scheme. (b) Fragment of the coordination layer; view along the c axis. (c) Fragment of crystal packing showing the interpenetration of the four double-pillared layers reinforced by NH···O hydrogen bonds.

3D polythreaded architecture (2D → 3D, Figure 6c). The crystal packing is reinforced via NH···O hydrogen bonds with participation of all NH2-donors (Table 2). These hydrogen bonds combine the staggered layers in the 3D network, nevertheless providing an opportunity for the dmf inclusion in the crystal lattice. Again, the stoichiometric inclusions and the lack of disorder for the enclathrated dmf molecules witness in favor of the solvent’s tight accommodation in the crystal lattice. This is enforced exclusively by stacking interactions between the π-electronic systems of dmf and bdc entities oriented in a parallel mode, since dmf is situated exactly in the middle between two parallel bdc residues, at the same distance of 3.7 Å from the two closest bdc walls. At the same time, they also participate in the CH···π interactions with the nia pillars to whom the dmf solvent molecules are oriented in the T-shape mode, CH(dmf)···Cg(nia) = 2.63 Å (Figure 6d). It might be emphasized that the similar [Co2(COO)2] secondary building unit (SBU) has been documented in the coordination polymers catena-(bis(μ3 -terephthalatoO,O′,O″,O‴)-dipyridyl-cobalt) dimethylformamide pyridine solvate80 and catena-[(μ3-terephthalato)-(μ2-pyrazine)-cobalt(II)].81

In a similar way, each Co(II) center is surrounded by four carboxylate oxygen atoms from three bdc ligands and two nitrogen atoms from two axial ligands, giving a distorted octahedral geometry. In the first one, the axial positions are occupied by pyridine ligands, while in the second one the sheets are linked with each other via axial pyrazine ligands, forming a 3D network. Compound 6 with the composition {[Co(mal)(S-nia)(H2O)]·dmf}n is the third known coordination compound so far with the S-nia ligand coordinated to the metal. In the S-nia pillar arrangement it is similar to the reported ones34 and represents the 2D coordination polymer with the terminal S-nia ligands coordinated to Co(II) in a monodentate mode via pyridine nitrogen atoms (Figure 7a). Compound 6 is also characterized by the maximal ligands’ diversity among 1−6 because of water coordination to the Co(II) center. It crystallizes in the non-centrosymmetric Pna21 space group. The asymmetric unit includes one Co(II) atom, one malonate anion, one S-nia and one water ligand, along with one dmf solvent, all occupying general positions. It is the only compound in this series with the single Co(II) atom as a metal building block (Figure 7a). The octahedral NO5 Co(II) 7020



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Figure 7. (a) View of the Co(II) coordination core in 6 with partial atom numbering scheme. (b) Fragment of the coordination layer, viewed along the a axis. C-bound H atoms are omitted for clarity. (c) The dmf encapsulation in the crystal lattice in 6. The second positions for the disordered S-nia and dmf molecules are shown by dots.

coordination core comprises one S-nia ligand and one water molecule which occupy two axial positions in the Co(II) coordination polyhedron (Co−N = 2.194(12), Co−O(5) = 2.159(2) Å) and three mal anions that act in bis-bidentate bridging modes, each anion linking three metal cations in the carboxylate-equatorial plane, Co−O distances being in the range of 2.059(7)−2.097(6) Å, thus generating the 2D coordination network with the (3,3) topology. The rhomboidal meshes in the coordination network are partly closed by two OH···O hydrogen bonds from the coordinated water molecules (Figure 7b, Table 2). The coordination network topology and architecture are identical with those ones recently reported by some of us for the pair of 2D coordination polymers [Zn(mal)(4-pyao)(H2O)]n and [Cd(mal)(4-pyao)(H2O)]n with the pyridine-4-aldoxime pillars.72 The network 6 differs by the dmf inclusion in the crystal lattice between the coordination layers, compared with the solvent-free above-mentioned structures, where the coordination layers are interconnected due to the hydrogen bonds between the terminal oxime groups. Those hydrogen bonds between the neighboring layers prevent the solvent inclusion in the interlayer space. In contrast, in 6 we observe the dmf inclusion into the interlayer space, fixed through the single NH···O hydrogen bond with S-nia. The mode of synchronized disorder of S-nia ligands (two S-nia images form a dihedral angle of 22.6° between the pyridine rings) and accommodated dmf molecules indicate the dynamic nature of this structure, most probably originating from the substitution of carbonyl oxygen by the bigger S atom in S-nia; the weaker H-acceptor properties result in a weaker dmf retention in the crystal lattice through one NH···O(dmf) hydrogen bond (Table 2), accompanied by the solvent’s mobility as well (Figure 7c). In conclusion, four compounds 1, 3, 5, and 6 host dmf molecules in the crystal lattices. In 1 and 6, the dmf molecules

Figure 8. Thermal variation of χmT for 1, 5, and 6.

are incorporated into the interlayer space, while in 3 and 5 they are trapped in the cages of the 3D H-bonded networks. For 1, 3, and 6, H-bonds of NH···O(dmf) type contribute to the retention of the solvent, whereby only stacking interactions act in 5, because all hydrogen bonds act within the 3D grid (Figure 7c). Using the Mercury facilities, we have tested the potential solvent accessible voids in all actual structures, and in 1, 3, 5, and 6 after the hypothetical evacuation of dmf. Surprisingly, the actual crystal networks 3 and 4 reveal negligible SAVs, 15 Å3 (0.7% of the unit cell volume) and 59.76 Å3 (3.1%), correspondingly, while for the hypothetical solvent-free networks these values constitute 210.7 Å3 (18.2%) for 1, 236.9 Å3 (10.8%) for 3, 1330.5 Å3 (14.4%) for 5, and 148.5 Å3 (8.9%) for 6. Figure 2S shows the fragments of crystal lattices with distribution of SAVs in the structures. Thermal Properties. The DTA, DTG, and TG curves are illustrated in Figure 3S. The TG experiments were carried out to study the thermal stabilities of coordination networks 1, 3, 4, 5, and 6. We followed our previously applied protocols for the smooth evacuation of solvents from crystalline solids to minimize destructive stress of the coordination grids.34,35 After the SC−SC transformation of solvate 1 to the solvent free 7021



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compounds, only one type of pores being in the narrow field is present, indicating the homogeneous structure of the substances. Magnetic Properties. The magnetic properties of the 1D coordination polymer 1 and the 2D coordination networks 5 and 6 have been investigated (Figure 8). The χmT(T) plot of a polycrystalline sample of 1 exhibits a value of 3.19 cm3 K mol−1 at 295 K which decreases only slightly with lowering the temperature to around 70 K; at lower temperatures a pronounced decrease of χmT is observed leading to a value of 0.9 cm3 K mol−1 at 1.9 K. The high temperature value is much higher than a spin-only value of 1.88 cm3 K mol−1 (S = 3/2 and g = 2) due to the orbital contribution of Co(II) from its 4T1g ground state (in Oh symmetry). First, the shape of the curve is typical for a Co(II) center, and it mainly demonstrates a zerofield splitting (ZFS) pattern due to the combined action of spin−orbit coupling and ligand field distortion.82 Second, on the basis of the occurrence of the binuclear units [Co2(COO)2], the experimental χmT data comprise as well a possible weak antiferromagnetic exchange interaction within these moieties, and importantly both effects in combination lead to the energy splitting of the ground state. Clearly, this behavior is also reflected in the plot of the inverse magnetic susceptibility vs temperature (Figure 5S). The high temperature part (245−295 K) is linear, and by extrapolation to low temperature, a θ value (Weiss constant) of −15.8 K results. Again, this value estimates the size of the energy splitting of the ground-state; its physical origin lies in the ZFS and a possible weak antiferromagnetic exchange interaction; however, an elucidation of the individual contributions lies not within the scope of the present study. The χmT(T) plot of a polycrystalline sample of 5 exhibits a value of 2.97 cm3 K mol−1 at 300 K, which decreases steadily with lowering the temperature to around 100 K; at lower temperatures a pronounced decrease is observed leading to a value of 0.35 cm3 K mol−1 at 1.9 K. A Curie−Weiss fit of χm−1(T) for 5 (Figure 6S) reveals a θ value of −33 K. The χmT(T) plot of a polycrystalline sample of 6 exhibits a value of 3.38 cm3 K mol−1 at 300 K, which decreases steadily with lowering temperature and is more pronounced below 20 K leading to 1.3 cm3 K mol−1 at 1.9 K. A Curie−Weiss fit of χm−1(T) for 6 (Figure 7S) reveals a θ value of −24.2 K. The magnetization data M(H) at 1.9 K for 1, 5, and 6 (Figures 8S−10S) reflect paramagnetic behavior with saturation values at 50 kOe of 2.66 Nβ, 2.30 Nβ, and 2.31 Nβ, respectively. These values lie in the expected range of 2−3 Nβ for Co(II).83 The overall magnetic behavior of these three compounds is similar, and the differences lie in slight variations of their coordination spheres and of the magnitudes of the weak magnetic exchange couplings.84

crystal 2 with the preservation of the coordination tapes and Hbonded layer, the thermic degradation of 2 occurs in several steps in the temperature interval 180−430 °C. Starting from 180 °C, the decarboxylation of adi occurs with a mass loss of 16.4% (16.9% calcd). From 350 °C on, oxidative degradation of nia occurs, accompanied by two exothermic effects. Complete degradation results in Co2O3 as a final product. Thermal analysis of compound 3 was performed after solvent evacuation. After the degassation stage, before adsorption analysis, the compound did not contain dmf solvent registered in the initial solid 3. Starting from 200 °C the first degradation stage is observed that corresponds to the degradation of suc anion and is accompanied by the 27.7% weight loss (27.7% calcd), the process occurs in the temperature range 200−268 °C and is accompanied by the endothermic effect with maximum at 260 °C. Further heating results in decomposition of the iso-nia ligands, accompanied by two strong exothermic effects at 352 and 386 °C. The final mass loss constituted 80.2% (80.2% calcd), and the residue corresponds to the Co(III) oxide. Compound 4 is thermally stable up to 165 °C when it begins to decompose, which most probably happens due to the decarboxylation of adipic ligand, a process is accompanied by a weak endothermic effect. With a temperature increase, the beginning of the oxidative degradation of organic residue occurs, and the process is highly exothermic, which eventually leads to a total mass loss of 80.71%. The final residue corresponds to the Co(III) oxide (18.57% calcd.). Compound 5 is thermally stable up to 195 °C when the first stage of decomposition is observed at the TG curve which is due to the decomposition of the nia ligand, the process most likely resulting in the formation of formamide and its volatilization. The process leads to the destruction of the crystal lattice and volatilization of dmf molecules which remain in the crystal structure until this temperature. The combined weight loss for both processes is 21.74% (21.83% calcd.). Further heating leads to oxidative degradation of carboxylic framework with the formation of Co(III) oxide. The mass of the residue constitutes 15.35% (15.37% calcd). Interestingly, for this compound the repeated heating in a vacuum under conditions similar to those used for transformation 1 → 2 did not allow evacuation of dmf from the crystal lattice, indicative of the occurrence of a trapping phenomenon determined by the size of the pore windows. Compound 6 with the weakest binding of dmf in the crystal lattice is stable until 115 °C and starts to lose dmf in the interval 115−175 °C. The weight loss constitutes 21.4% (19.6% calcd) and is accompanied by an endothermic effect. At higher temperatures, mal and S-nia ligands get decomposed. As a result of thermal degradation of all compounds, Co(III) oxide is formed, which after 600 °C interacts with dioxygen from air with the formation of Co3O4, the latter one decomposes at 960 °C into Co2O3. Adsorption. The N2 sorption isotherms were recorded for 1, 3, 4, 5, 6 (Figure 4S). All compounds hardly adsorb N2 at 77 K, which leads to small BET surface areas in the range of 9−58 m2 g−1 (Table 2S). The isotherms for 1, 3, and 4 are of type V, while for 5 and 6 they are of type IV in IUPAC classification. All isotherms have a wide hysteresis until rather low pressures. This can be explained by the mechanical deformation of the skeleton of the compounds during adsorption and formation of traps for nitrogen molecules, which hindered their removal. The pore volume distribution by radius indicates the presence of mesopores for all compounds (Table 2S), and the volume of these pores is also relatively small. For all

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CONCLUSIONS Six new Co(II) coordination networks {[Co(adi)(iso-nia)2]·dmf}n (1), [Co(adi)(iso-nia)2]n (2), {[Co2(suc)(ac)2(iso-nia)4][Co2(suc)(sucH)2(iso-nia)4]·2dmf}n (3), [Co(adi)(nia)2]n (4), {[Co(bdc)(nia)2]·dmf}n (5), and {[Co(mal)(S-nia)(H2O)]·dmf}n (6), which include three 1D (1−3) and three 2D coordination polymers (4−6), were obtained from the dicarboxylic acid−nicotinamide-like ligand blends. In five of them (1−5) the binuclear clusters [Co2(COO)2] act as secondary building blocks with nicotinamide ligands acting as double pillars, and only 6 with the thionicotinamide ligand is built on the single-metal building block. All the networks are reinforced by hydrogen bonds with participation of amide-functional groups 7022



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that provide dmf retention in the crystal lattices and different polythreading patterns affording the association of 1D and 2D coordination arrays in the 2D and 3D H-bonded networks, 1D → 2D in 1, {1D → 2D → 3D + 1D → 2D} → 3D in 3, 2D → 3D in 5. The hydrogen-bonding system affords the stability of the 1D coordination polymer 1, balancing the thermal stress accompanied by the solvent evacuation and SC−SC transformation to the solvent free form 2, with the consecutive return to the solvated form 1s after soaking in dmf. On the other hand, the hydrogen bonding system in 5 impedes the evacuation of the same solvent entrapped in the closed cages. The identification of the binding sites responsible for the retention of the dmf molecules reveals the potential of these networks for adsorption studies of polar liquids and gases. The magnetic data for the selected compounds 1, 5, and 6 reveal the typical behavior of Co(II) ions with the signature of ZFS combined with weak contributions from antiferromagnetic exchange interactions.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b01226. Additional figures, selected bond distances and angles, the DTA, DTG, and TG curves for 1, 3−6; the N2 sorption isotherms for 1, 3−6; inverse magnetic susceptibility vs temperature plots and magnetization data M(H) for 1, 5, 6 (PDF) Accession Codes

CCDC 1499565−1499573 and 1511405 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: + 373 22 738154; fax: + 373 22 725887; e-mail: fonari. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge the financial support from the project SCOPES (IZ73Z0_152404/1). The authors from Moldova are indebted to Project CSSDT 15.817.02.06F for support.

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REFERENCES

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Coordination Networks with Dicarboxylate and ... - ACS Publications

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