Ferromagnetic End-to-End Azides and Tetrahedral Cobalt: Unusual

ARTICLE pubs.acs.org/crystal

Ferromagnetic End-to-End Azides and Tetrahedral Cobalt: Unusual Findings in the M-BPA-Pseudohalide2 System Noelia De la Pinta,† M. Luz Fidalgo,‡ Luis Lezama,† Gotzon Madariaga,# Lorena Callejo,§ and Roberto Cort
es*,† †

Departamento de Química Inorg
anica and #Departamento de Física de la Materia Condensada, Facultad de Ciencia y Tecnología, UPV/EHU, Aptdo. 644, 48080 Bilbao, Spain ‡ Departamento de Química Inorg
anica, Facultad de Farmacia, UPV/EHU, Aptdo. 450, 01080 Vitoria-Gasteiz, Spain § Unidad de Siderurgia, Fundaci
on Tecnalia, C/Geldo, Ed. 700, Derio 48160, Spain

bS Supporting Information ABSTRACT:

Two novel unusual compounds [Co(NCO)2(bpa)] (1) and [Cu(N3)2(bpa)] (2) with cyanate and azide pseudohalides are shown in this work. These compounds have been characterized by X-ray diffraction measurements, Fourier transform-infrared (FT-IR) and UV-visible spectroscopies, thermogravimetric studies, electron spin resonance (ESR) spectroscopy, and magnetic measurements. Compound 1 shows a one-dimensional (1D) structure with the cobalt atoms bridged by bpa ligands and with the metal atoms showing an unusual tetrahedral coordination sphere. Compound 2 shows a two-dimensional (2D) structure, where the copper(II) ions are bridged by double 1,3-azido ligands to form chains that are joined through single bpa bridges to give the global 2D structure. Magnetic measurements show predominance of spin-orbit coupling for the cobalt compound (1), while ferromagnetic interactions, unusual for the 1,3-azido bridging, are observed in compound 2. This compound represents the first example of copper-double (μ1,3-azido)-bridged chain exhibiting ferromagnetic interactions through this kind of bridging.

’ INTRODUCTION The design and synthesis of molecular-based magnetic materials with ferromagnetic coupling continue to be a challenge in magnetochemistry.1 Azide and cyanate pseudohalides have focused the attention in this field due to their ability as magnetic, even ferromagnetic, exchange couplers. As we know, azide as a short bridging ligand that can provide rich coordination modes and efficient pathways of magnetic exchange, and hence can affect the spin ground state of a molecule, has been widely used in magnetochemistry.2 This ion can act as a bridging ligand either in the end-to-end (μ-1,3-N3) or in the end-on (μ-1,1-N3) mode to give polynuclear complexes from dinuclear to three-dimensional (3D) systems. It is the general norm that the μ-1,3-coordination mode gives rise to antiferromagnetism, while μ-1,1-coordination results in ferromagnetic3 interactions between the metal centers. From the large number of complexes with azido ligands magnetically r 2011 American Chemical Society

characterized in the last decades,2,4 examples exhibiting ferromagnetic coupling for the end-to-end type of bridging are really scarce.5 The characterized compounds with the cyanate ligand are very scarce in comparison with those of the azide ligand.6 This ion shows a lower versatility and clearly prefers the end-on N-cyanate bridging mode, which has been shown to give ferromagnetic type interactions. It is therefore interesting to obtain more examples concerning this bridging ligand. On the other hand, the 4-40 -type bpa ligand has been chosen because of its recognized ability to interconnect metal ions and increase the dimensionality of the systems where it participates.7

Received: November 18, 2010 Published: February 22, 2011 1310

dx.doi.org/10.1021/cg1015324 | Cryst. Growth Des. 2011, 11, 1310–1317

Crystal Growth & Design In this work, we report two novel and unusual compounds, [Co(NCO)2(bpa)] (1) and [Cu(N3)2(bpa)] (2). The first one is one-dimensional and shows a tetrahedral coordination polyhedron for the cobalt(II) ion. The second one is two-dimensional and shows chains of copper ions with double end-to-end azido bridges that are further connected by single bpa bridges. Magnetic measurements indicate that the exchange coupling between the copper ions through double end-to-end azido bridges unusually is ferromagnetic. Both unusual compounds were obtained in our thorough study of the family M/(pseudohalide)2/bpa.

ARTICLE

Table 1. Crystallographic Collection and Refinement Parameters for Compounds 1 and 2

’ EXPERIMENTAL SECTION

[Co(NCO)2(bpa)] (1)

[Cu(N3)2(bpa)] (2)

formula

CoC14H12N4O2

CuC12H12N8

Mr cryst syst

327.21 monoclinic

324.78 monoclinic

space group

C2/c

P21/n

a [Å]

16.394(6)

9.993(8)

b [Å]

4.8590(15)

13.395(9)

c [Å]

18.591(7)

10.502(6) 106.04(6)

β [deg]

98.34(5)

Materials. All solvents and starting materials for synthesis were

V [Å3]

1465.3(9)

1351.0(8)

purchased commercially and were used as received. Metal(II) nitrate hydrates (Aldrich), 1,2-bispyridylethane (Lancaster), and potassium cyanate and sodium azidure (Aldrich) were used without further purification. Caution! Azide metal complexes are potentially explosive. In fact, the Cu(N3)2 is explosive. Only a small amount of material should be prepared, and it should be handled with caution. Synthesis of [Co(NCO)2(bpa)]n (1). This compound was synthesized by mixing an aqueous solution (10 mL) of KNCO (41 mg, 0.5 mmol) with an aqueous solution (20 mL) of Co(NO3)2 3 6H2O (73 mg, 0.25 mmol). After a 30 min stirring, a warm methanolic solution (20 mL) of 1,2-bis(4-pyridyl)ethane (bpa) (46 mg, 0.25 mmol) was added. The resulting solution was filtered off the precipitate and was left to stand at room temperature. Several days later, prismatic, blue, X-ray quality single crystal were obtained. The crystals were filtered off, washed with ether, and dried in air. Yield was 42.3%. Anal. Calcd for CoC14H12N4O2: C 51.39, H 3.70, N 17.12; found C 50.43, H 3.58, N 17.02. Synthesis of [Cu(N3)2(bpa)]n (2). Synthesis of 2 was carried out in a U-shaped tube. At the bottom of the tube is placed a silica gel (pH = 6.0). The right compartment is filled with an aqueous solution of NaN3 (0.5 mmol/20 mL H2O) and into the other branch is placed the other solution [0.25 mmol of Cu(NO3)2 3 2.5H2O/20 mL of H2O mixed with 0.25 mmol of bpa/20 mL of CH3OH)]. Blue-green prismatic crystals appeared after several weeks. The crystals were collected, washed with ether, and dried in air. Yield was 62.2%. Anal. Calcd for CuC12H12N8: C 43.44, H 3.65; N 33.77; found C 42.02, H 3.51; N 32.33. General Methods. Microanalyses were performed with a LECO CHNS-932 analyzer. Infrared spectroscopy was performed on a MATTSON FTIR 1000 spectrophotometer as KBr pellets in the 4004000 cm-1 region. Thermal analyses were obtained using a TAInstruments SDT-2960 DSC-TGA unit at a heating rate of 5
C under an argon atmosphere. Diffuse reflectance spectra were registered at room temperature on a CARY 2415 spectrometer in the range of 500045000 cm-1. Electron spin resonance (ESR) spectroscopy was performed on powdered samples at the X-band frequency, with a Bruker ESR 300 spectrometer equipped with a standard OXFORD lowtemperature device, which was calibrated by the NMR probe for the magnetic field. The frequency was measured with a Hewlett-Packard 5352B microwave frequency computer. The magnetic susceptibilities and the magnetization of polycrystalline samples of the complexes were carried out in the temperature range 4.2-300 K at a value of the magnetic field of 1000 G, using a Quantum Design Squid susceptometer, equipped with a helium continuous-flow cryostat. The experimental susceptibilities were corrected for the diamagnetism of the constituent atoms (Pascal tables).8 Crystal Structure Determination. A single crystal of compound 1 was glued to a thin glass fiber and collected, at room temperature, on an STOE IPDS I (Imaging Plate Diffraction System) diffractometer with graphite-monochromated Mo-KR radiation (λ = 0.71070 Å). Intensity

Z F(000)

4 668

4 648

Fcaled[g cm-3]

1.483

1.597

μ(Mo KR)/mm-1

1.180

1.622

scan type

ω-2θ

ω-2θ

range [deg]

2.21-25.99

2.53-29.97

reflns colled

5234

3564

indep reflns

1397

1819

parameters R1 (F0)a

96 0.0357

190 0.0397

wR2(F02)b

0.0669

0.1138

GOF

0.804

1.004

R1(F0) = [(∑||F0| - |Fc||)/(∑|F0|)]. = [∑[w(F02 - Fc2)2]/ 2 2 2 1/2 ∑[w(F0 ) ]] , where w = 1/[σ (|F0|) þ (0.03P)2], with P = (Fo2 þ 2Fc2)/3. a

b

wR2(F02)

data were collected in the θ range 2.21-25.99
for this compound. In the case of compound 2, a single crystal was glued to a thin glass fiber with epoxi resin and collected, at room temperature, on an Enraf-Nonius CAD-4 automatic four-circle diffractometer with graphite-monochromated Mo-KR radiation, operating in ω/2θ scanning mode using suitable crystals for data collection. In this case, accurate lattice parameters were determined from least-squares refinement of 25 wellcentered reflections. Intensity data were collected in the θ range 2.5329.97
for the compound 2. Corrections for Lorentz and polarization factors were applied to the intensity values. The structures were solved by direct methods using the program SIR979 and refined by a full-matrix least-squares procedure on F2 using SHELXS97.10 Non-hydrogen atomic scattering factors were taken from International Tables of X-ray Crystallography.11 In Table 1 crystallographic data and processing parameters for compounds 1 and 2 are shown. Given the very different symmetries found in the otherwise isomorphic structures, [Mn(N3)2 (bpa)] (Hong et al. 1999;12 Cortes et al. 2000)7e and [Fe(N3)2(bpa)] (Konar et al., 2003),13 particular attention was paid to the space group assignment for compound 2. It should be noticed that the transformation a0 = -a - b, b0 = -a þ b, c0 = c of the cell parameters chosen in ref 12 allows the recovery of the metrics (a0 = 9.996 Å, b0 = 13.893 Å, c0 = 10.501 Å, R0 = 89.95
, β0 = 103.11
, γ0 = 89.99
) used in ref 13 and in this work, indicating perhaps a possible underestimation of the true monoclinic symmetry in 12. On the other hand, a preliminary refinement of 2 in the C2/c space group showed a significant disorder very similar to that reported in refs 7e and 13. However, the data set of compound 2 is clearly incompatible with a C-centered lattice (290 reflections have an intensity greater or equal than 3 times their standard uncertainty and 57 more that 12 times) and the symmetry had to be lowered to P21/n. This space group removed thoroughly the disorder that should be considered, at least in this case, as an artifact provoked by an overestimation of the true symmetry of compound 2. 1311

dx.doi.org/10.1021/cg1015324 |Cryst. Growth Des. 2011, 11, 1310–1317

Crystal Growth & Design

ARTICLE

Figure 3. ORTEP for complex 2, with atom numbering, at the 50% probability level.

Table 3. Selected Bond Lengths (Å) and Angles (
) for Compound [Cu(N3)2bpa] (2)a Figure 1. ORTEP view, with atom numbering, showing 50% probability ellipsoids of compound 1.

Table 2. Selected Bond Lengths (Å) and Angles (
) for Compound [Co(NCO)2bpa] (1)a

2.008(4)

N(8)-Cu(1)-N(7)

2.009(4)

N(1)-Cu(1)-N(6)

178.9(3) 90.7(3)

Cu(1)-N(8)

2.030(3)

N(4)-Cu(1)-N(6)

90.9(3)

Cu(1)-N(7)

2.030(3)

N(8)-Cu(1)-N(6)

87.5(3)

Cu(1)-N(6)

2.514(10)

N(7)-Cu(1)-N(6)

93.3(3)

Co(1)-N(1)

2.038(3)

C(5)-N(1)-Co(1)

121.4(3)

Co(1)-N(2)

1.931(4)

N(2)-Co(1)-N(1)

105.39(13)

2.541(10) 178.4(4)

N(1)-Cu(1)-N(3)i N(4)-Cu(1)-N(3)i

89.6(3) 88.8(3)

O(1)-C(7)

1.190(5)

N(2)i-Co(1)-N(2)

Cu(1)-N(3)i N(1)-Cu(1)-N(4)

127.1(2)

N(1)-Cu(1)-N(8)

90.27(15)

N(8)-Cu(1)-N(3)i

89.2(3)

1.135(5) 112.89(15)

C(7)-N(2)-Co(1) N(2)-C(7)-O(1)

169.9(4) 178.6(5)

N(4)-Cu(1)-N(8)

89.94(15)

N(7)-Cu(1)-N(3)i

89.9(3)

N(1)-Cu(1)-N(7)

90.46(15)

N(6)-Cu(1)-N(3)i

176.77(14)

N(2)-N(1)-Cu(1)

117.4(6)

N(2)-C(7) N(1)-Co(1)-N(1)i a

Cu(1)-N(1) Cu(1)-N(4)

Symmetry code: i = -x, y, -z þ 1/2.

N(4)-Cu(1)-N(7)

a

Figure 2. View [101] of the chains Co-bpa-Co and the packing of the chains along the direction [010].

’ RESULTS AND DISCUSSION Crystal Structures. Compound 1 consists of zigzag chains extending along the [101] direction, where the CoII ions are linked through N,N0 -coordinated anti-bpa ligands. As you can see in Figure 1, the cobalt coordination sphere is tetrahedral, also exhibiting two terminal N-bonded cyanate groups. As can be seen in Table 2, the tetrahedral coordination sphere is slightly distorted and cyanate ligands are nearly linear. The Co-Nbpa distance [2.038(3) Å] is slightly longer than the CoNNCO distance [1.931(4) Å]. The intermetallic distance through bpa-bridges is 13.36 Å. This is because py-C-C-py torsion angle for the bpa groups is 180
. On the other hand, the shortest intermetallic distance (4.86 Å) corresponds to metallic ions located on different chains along the [010] direction (Figure 2). Crystal Structure of 2. The structure of compound 2 consists of a two-dimensional (2D) arrangement where double azidebridged copper(II) chains are connected through bpa ligands. The copper(II) ions are octahedrally coordinated to four end-toend (μ-1,3)-azide ligands, two occupying axial positions [N(3) and N(6)] and the other two [N(1) and N(4)] the equatorial

89.30(15)

N(3)-N(2)-N(1)

177.1(10)

N(6)ii-N(5)-N(4)

176.9(11)

N(2)-N(3)-Cu(1)i

130.1(6)

N(5)ii-N(6)-N(4)ii

138.6(7)

N(5)-N(4)-Cu(1)

117.5(7)

Symmetry code: i = -x þ 1, -y, -z þ 1; ii = -x þ 1, -y, -z.

ones, and two anti-bpa ligands in equatorial positions. It conforms to an elongated octahedron as usually observed due to the Jahn-Teller effect of the copper(II) ion (Figure 3). This elongated octahedron shows two axial distances with the same value [Cu(1)-N(6) = Cu(1)-N(3)i = 2.514(10) Å)] and four equatorial ones [Cu(1)-N(1) = 2.008(4) Å, Cu(1)-N(4) = 2.009(4) Å, and Cu(1)-N(8) = Cu(1)-N(7) = 2.030 Å] (Table 3). The one-dimensional (1D) chains [Cu-(μ-1,3-N3)2]n extend along the [001] with a copper-copper intrachain distance of 5.4 Å. These chains are interconnected by bpa ligands, which are extended along the [010] direction (Figure 4). This clearly shows that two types of bridging ligands play an important role in constructing a higher dimensional system. The intermetallic distance through the anti-bpa ligand (torsion angle py-CC-py is 176
) is 13.4 Å. With respect to the skew propeller configurations of the coordinated pyridine moieties around metal ion, the dihedral angle formed by the two pyridyl rings of anti-bpa ligand is 79.4(4)
. Table 3 summarizes the most significant bond and angle parameters. As observed, the Cu-Nazide equatorial bond distances are shorter than that of Cu-Nbpa. On the other hand, the almost linear azide (N-N-N is 177.1(10)
and 176.9(11)
) bridges which adopt the chair conformation can be described by N(2)-N(1)-Cu = 117.4(6)
, N(5)-N(4)-Cu = 117.5(7)
, N(2)-N(3)-Cu(1)i = 130.1(6)
, and N(5)ii-N(6)-Cu(1) = 138.6(7)
. Infrared Spectra. A summary of the most important IR bands corresponding to compounds 1 and 2, together with their tentative assignment,14 are given in Table 4 (Figure 5). On the 1312

dx.doi.org/10.1021/cg1015324 |Cryst. Growth Des. 2011, 11, 1310–1317

Crystal Growth & Design

ARTICLE

Figure 5. IR spectra of compounds 1 and 2. Figure 4. 2D sheet arrangement of compound 2.

Table 4. IR Bands (cm-1) and Assignments for Compounds 1 and 2 [Co(NCO)2bpa] (1)

[Cu(N3)2bpa] (2)

ν(C-H)bpa

3200-2800

3000-2800

ν(CdC), υ(CdN)bpa

1613

1609

ν(ArC-C)bpa δip(ArC-H)bpa

1413 1079/1029

1430 1075/1033

νop (ArC-H)bpa

938

818

νas(C-N)NCO

2222

ν(C-O)NCO

1234

νas(N3)

2040, 2050 620

540

other hand, the frequencies of the IR bands related to the bpa ligand in the compounds are very close to their positions in the free ligand showing that the pyridyl rings behave similarly in the complexes. UV-Visible Spectroscopy. The diffuse reflectance spectrum for compound 1 (Figure S1 of Supporting Information) exhibits three transitions attributed to spin-allowed transitions from 4 A2(F) to 4T2(F) (ν1 = 6600 cm-1), 4T1(F) (ν2 = 9700 cm-1), and 4T1(P) (ν3 = 17300 cm-1), corresponding to high-spin tetrahedral CoII. At 35000 cm-1, the spectrum shows a chargetransfer band. The values of Dq = 660 cm-1 and B = 480 cm-1 calculated from these transitions are common for tetrahedral Co (II) complexes.15 The value of B is indicative of a 49.4% of covalence or the Co-N bonds in compound 1. Thermal Behavior. The thermogravimetric (TG) curve (Figure S2 of Supporting Information) obtained for 1 (50600
C), under an argon atmosphere, takes place in two steps. The first one, which corresponds to a weight loss of 59.62% and takes place between 197 and 298
C, can be attributed to one molecule of bpa. The second step, which takes place between 298 and 325
C, corresponds to a weight loss of 26.38%. This step can be associated with the pyrolysis of the two cyanato groups. The final residue corresponds to a mixture of Co2O3 þ CoO (spinel).

Figure 6. Experimental and calculated ESR powder spectra for 1 at 4 K.

The potentially explosive character of azide compounds precludes the study of the thermal behavior for compound 2. ESR Spectroscopy. ESR measurements were carried out at several temperatures in the range 4-300 K. For compound 1, even if X-band isotropic spectra were recorded below 100 K, just those corresponding to temperatures lower than 30 K acquired rhombic resolution. The spectrum at 4 K (Figure 6) shows a great anisotropy and occupies a large magnetic field region. Because of the tetrahedral coordination of the Co(II) ions, it can be described in terms of an spin S = 3/2 with a large zero field splitting. The attempts to fit the spectrum, supposing that the tensors g and D are collinear and Lorentzian lines with an isotropic behavior of its width, do not lead to a good fitting on the global spectrum but really do for the position of the signals. The values g = 2.30 and g^ = 2.25 and the calculated values for the parameters for zero field splitting (D = 0.11 and E = 0.03 cm-1) are in good agreement with distorted tetrahedral cobalt(II) systems. )

δ(L)L = NCO, N3

1313

dx.doi.org/10.1021/cg1015324 |Cryst. Growth Des. 2011, 11, 1310–1317

Crystal Growth & Design

ARTICLE

Figure 9. Thermal variations of both components of the axial g tensor for compound 2.

Figure 7. X-band ESR spectra at room temperature (red line) and at 4 K (blue line). The discontinuous lines show the simulated spectra.

Figure 10. Thermal evolution of χmT and χm-1 for compound 1 and the corresponding Curie-Weiss law. The solid line represents the best fit obtained. )

As can be observed in Figure 8, below 20 K, the g component of the g tensor, clearly moves to the lower field region. On the contrary, the g^ component moves to higher field region. This phenomenon is shown in the thermal variations of both the g factors (Figure 9). Magnetic Measurements. The molar magnetic susceptibility for compound 1 exponentially increases upon cooling from 1.15  10-3 cm3 3 mol-1 at room temperature. Figure 10 shows the thermal variation of the χm-1 and χmT magnitudes. As observed, χm-1 values follow the Curie-Weiss law down to 100 K with values of Cm = 3.96 cm3 3 K 3 mol-1 and θ = -51.71 K. On the other hand, the product χmT continuously decreases upon cooling from 3.43 cm3 3 mol-1 at room temperature. The decreasing values of χmT and the negative value of θ could be indicative of antiferromagnetic interactions between metallic centers. However, considering the long pathway through bpa ligands, the strong decrease of μeff should be mainly attributed to the spin-orbit coupling effect characteristic of CoII ion. The molar magnetic susceptibility for compound 2 increases upon cooling from 1.39  10-3 cm3 3 mol-1 at room temperature. The thermal variation of the χm-1 and χmT magnitudes is shown in Figure 11. As can be seen, the χm-1 values follow the Curie-Weiss law down to 100 K with values of Cm = 0.423 cm3 3 K 3 mol-1 and θ = 4.9 K. On the other hand, the

Figure 8. Experimental X-band powder ESR spectra, at different temperatures, for compound 2.

)

)

)

)

The X-band spectrum of compound 2 shows the characteristic bands of a g tensor with an axial symmetry, common in compounds of copper(II) due to the Jahn-Teller effect. The values obtained for the g tensor are g = 2.243 and g^ = 2.053 at room temperature and g = 2.276 and g^ = 2.038 at 4 K (Figure 7). The axial symmetry of the g-tensor and the sequence of values g > g^ > 2.04 suggest a dx2-y2 ground state. Moreover, the low g value is in good agreement with the strongly elongated octahedral environment for the Cu(II) ions observed in the structural analysis.

1314

dx.doi.org/10.1021/cg1015324 |Cryst. Growth Des. 2011, 11, 1310–1317

Crystal Growth & Design

ARTICLE

thermal variation of χmT exhibits an increasing tendency with decreasing temperature that becomes strong below 50 K. The positive θ value and the overall appearance of the χmT versus T curve (Figure 11) are indicative of ferromagnetic interactions between the Cu(II) centers. This behavior can be fitted satisfactorily to the empirical function introduced by Hall to represent the numerical calculations performed by Baker et al.16 proposing the expression given in eq 1 for ferromagnetic S = 1/2 chains, being based upon the spin Hamiltonian: H = -2J ∑ Si Siþ1. " #2=3 Ng 2 β2 1 þ Ax þ Bx2 þ Cx3 þ Dx4 þ Ex5 χm ¼ ð1Þ kT 1 þ A0 x þ B0 x2 þ C0 x3 þ D0 x4

approximation. The final expression of the magnetic susceptibility is given in eq 2. χm ðMFÞ ¼ χm =½1 - ð2zJ 0 =Ng 2 β2 Þχm 

ð2Þ

According to it, the best fitting parameters for compound 2 have been determined to be g = 2.12, J/k = þ1.8 K, and zJ0 /k = -0.5 K. As can be observed, the g value is in good agreement with the results of ESR measurements. Magnetostructural Correlations. The presence of ferromagnetic interactions associated with double end-to-end azido bridging in the scarce number of known copper(II)-systems has been attributed to the asymmetry and large torsion angles involving this bridging. Both of these facts may minimize the antiferromagnetic coupling.17,18 Maximum antiferromagnetic interactions are expected for a M-N-N angle close to 110
,19 decreasing rapidly when increasing this angle. In fact, accidental orthogonality, with a resulting ferromagnetic interaction, may be found for large angles or for torsion angles Δ (Cu-N3-Cu) close to 45
.19 In Table 5, we have summarized the J coupling constants for the asymmetrical double-bridged μ1,3-azido copper known compounds, together with the structural parameters: R (axial Cu-Nazide distance), R (Cu-Nazide-Nazide angles), and Δ (torsion CuN3-Cu angle for azido bridging). All the compounds show double-azido dinuclear entities, except compound 2 of this work showing double-azido chains. As can be observed, all compounds have large R, large torsion angles (Δ), and large bridging angles (R) deviating from 110
as predicted to be ferromagnetic. At a first sight, for extremely large R values (2.5-3.0 Å), the magnitude of the coupling constant is observed to fall (first and last compounds in Table 5) which may be associated with the lower capability to interact with such distances. For similar R values, increasing of Δ, next to the value of 45
, seems to increase the ferromagnetism. The exception of the bben compound may be associated with a larger R value. Definitively, a cooperative effect of all these parameters seems to be responsible for the magnitude of the ferromagnetic interactions in this kind of bridging.

where x = 2J/KT, N is Avogadro’s number, κ is the Botzmann constant, β is the Bohr magneton, g is the Land
e factor, A = 5.7979916, B = 16.902653, C = 29.376885, D = 29.832959, E = 14.036918, A0 = 2.7979916, B0 = 7.0086780, C0 = 8.6538644, D0 = 4.5742114. Considering the second pathway, it has also been included as a possible interchain interaction treated in the molecular field

Figure 11. Thermal evolution of χmT and χm-1 for compound 2 and the corresponding Curie-Weiss law. The solid line represents the best fit obtained.

Scheme 1. (a) Symmetric and (b) Asymmetric End-to-End Copper-Azide Coordination Modes

’ CONCLUSIONS The chemical reactions of cobalt and copper ions with cyanate and azido pseudohalides and the bpa ligand (in 1/2/1 proportion) have led to the obtaining of two unusual compounds, [Co(NCO)2(bpa)] (1) and [Cu(N3)2(bpa)] (2). Compound 1 has a chain structure with single bpa bridges where the

Table 5. Selected Magnetostructural Data for Known Asymmetric, Double-Bridged Bis(μ1,3)-azido Ferromagnetic Copper(II) Complexes compounda

R (Å)

R (deg)

Δ (deg)

J (cm-1)b

[Cu2(L2)2(μ-1,3-N3)2(ClO4)2] [Cu2(μ1,3-N3)2(Et3dien)2](ClO4)2

2.95 2.38

123.0, 135.2 123.8, 137.8

38.1 35.8

þ2.4 þ9.0

20 21

[Cu2L12(μ1,3-N3)2]

2.39

118.2, 129.6

46.04

þ13.6

22

[Cu2L32(μ1,3-N3)2]

2.36

117.8, 131.8

47.4

þ16.0

17

[Cu(bben)2(μ1,3-N3)2(N3)2]

2.37

113.5, 142.6

37.4

þ16.8

18

[Cu(bpa)(μ1,3-N3)2]n (2)c

2.51

117.4, 130.1

61.9

þ2.5

117.5, 138.6

46.8

ref

this work

a

Ligands: Et3dien = 1,4,7-triethyldiethylenetriamine; L1 = (E)-4-(dimethylamine)ethylimine)-1,1,1-trifluoropentan-2-one); L3 = 1,1,1-trifluoro7-(dimethylamine)-4-methyl-5-aza-3-hepten-2-onato); bben = 1,2-bis(benzylamino)ethane. b Magnetic coupling: H = -JS1S2 (compound 2 has been scaled). c Azido chain. 1315

dx.doi.org/10.1021/cg1015324 |Cryst. Growth Des. 2011, 11, 1310–1317

Crystal Growth & Design cobalt ions have an unusual tetrahedral coordination polyhedron. The tetrahedral disposition of the Co(II) ion is related with the 3d7 electronic configuration of this ion. The cyanate ligands coordinate as terminal ones probably due to the lower coordination tendency of the cyanate oxygen atom. The magnetic interactions show in this complex the predominance of the spin-orbit coupling, as expected for the low magnetic coupling through bpa bridges. Compound 2 is two-dimensional, with chains of copper(II) ions bridged by double end-to-end azido ligands that are further connected by single bpa bridges. An increasing separation of the two g components in the axial tensor is observed, at temperatures below 20 K, in the ESR measurements. This phenomenon can be due to modifications of the exchange coupling or to subtle structural modifications at very low temperatures. With respect to the magnetic interactions observed for compound 2, it must be noted that unusually for the expected for the 1,3-azido bridges (which promote antiferromagnetic interactions) ferromagnetic interactions are observed in this case. This fact may be explained by the large axial CuNazide distances, caused by the Jahn-Teller effect of the copper(II) ion, which give rise to an asymmetric bridging mode for the azides, and by the large torsion angle associated with this bridging. Although the magnetic interactions through end-toend (EE) azido bridging mode seem to be exhaustively characterized, the quite recent experimental discovery of asymmetric EE systems showing ferromagnetic behavior open new perspectives, and more compounds of this type should be characterized to understand magnetostructural relationships.

’ ASSOCIATED CONTENT

bS

Supporting Information. Crystallographic information in the form of CIF files, UV-visible and thermal behavior figures. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Fax: þ34-4-6013500.

’ ACKNOWLEDGMENT This work was supported by the Universidad del País Vasco (UPV/EHU) (UPV 00169.125-EHU2010/14), the Ministerio de Ciencia y Tecnología (MCYT) (CTQ2005-05778-PPQ), and the Basque Government (project IT-282-07). N. de la P. thanks UPV/ EHU for financial support from “Convocatoria para la concesi
on de ayudas de especializaci
on para investigadores doctores en la UPV/ EHU (2008)”. ’ REFERENCES (1) Kahn, O. Molecular Magnetism; VCH: New York, 1993. (2) (a) Pierpont, C. G.; Hendrickson, D. N.; Duggan, D. M.; Wagner, F.; Barefield, E. K. Inorg. Chem. 1975, 14, 604–610. (b) Commarmond, J.; Plumer
e, P.; Lehn, J. M.; Agnus, Y.; Louis, R.; Weiss, R.; Kahn, O.; Morgenstern-Badarau, I. J. Am. Chem. Soc. 1982, 104, 6330–6340. (c) Thompson, L. K.; Tandon, S. S. Comments Inorg. Chem. 1996, 18, 125–144.(d) Cort
es, R.; Lezama, L.; Mautner, F. A.; Rojo, T. Molecule Based Magnetic Materials; American Chemical Society, Washington, DC, 1996; Chapter 12, pp 187-200; (e) Ribas, J.; Monfort, M.; Vicente, R.; Escuer, A.; Cort
es, R.; Lezama, L; Rojo, T. Coord. Chem. Rev. 1999, 193-195, 1027–1068 and references therein.

ARTICLE

(f) Escuer, A.; Aromí, G. R. Eur. J. Inorg. Chem. 2006, 4721–4736 and references therein. (3) (a) Aebersold, M. A.; Gillon, B.; Plantevin, O.; Pardi, L.; Kahn, € O.; Bergerat, P.; von Seggern, I.; Tuczek, F.; Ohrstr€ om, L.; Grand, A.; Leli
evre-Berna, E. J. Am. Chem. Soc. 1998, 120, 5238–5245. (b) Ruiz, E.; Cano, J.; Alvarez, S.; Alemany, P. J. Am. Chem. Soc. 1998, 120, 11122– 11129. (4) (a) Abu-Youssef, M. A. M; Drillon, M.; Escuer, A.; Goher, M. A. S.; Mautner, F.; Vicente, R. Inorg. Chem. 2000, 39, 5022–5027. (b) Monfort, M.; Resino, I.; Ribas, J.; Stoeckli-Evans, H. Angew. Chem., Int. Ed. 2000, 39, 191–193. (c) Serna, Z.; Lezama, L.; Urtiaga, M. K.; Arriortua, M. I.; Barandika, M. G.; Cortes, R.; Rojo, T. Angew. Chem., Int. Ed. 2000, 39, 344–347. (d) Papaefstathiou, G. S.; Escuer, A.; Vicente, R.; Font-Bardia, M.; Solans, X.; Perlepes, S. P. Chem. Commun. 2001, 39, 2414–2415. (e) Demeshko, S.; Leibeling, G.; Maringgele, W.; Meyder, F.; Mennerich, C.; Klauss, H.-H.; Pritzkow, H. Inorg. Chem. 2005, 44, 519–528. (f) Sarkar, S.; Datta, A.; Mondal, A.; Chopra, D.; Ribas, J.; Rajak, K. K.; Sairam, S. M.; Pati, S. K. J. Phys. Chem. B 2006, 110, 12–15. (g) Mandal, D.; Bertolasi, V.; Ribas-Ari~ no, J.; Aromí, G.; Ray, D. Inorg. Chem. 2008, 47, 3465–3467. (h) Zhao, J.-P.; Hu, B.-W.; Sa~ nudo, E. C.; Yang, Q.; Zeng, Y.-F.; Bu, X.-H. Inorg. Chem. 2009, 48, 2482–2489. (i) Yoon, J. H.; Ryu, D. W.; Kim, H. C.; Yoon, S. W.; Suh, B. J.; Hong, C. S. Chem.—Eur. J. 2009, 15, 3661. (j) Stamatatos, T. C.; Abboud, K. A.; Wernsdorfer, W.; Christou, G. Inorg. Chem. 2009, 48, 807–809. (k) Zeng, M.-H.; Zhou, Y.-L.; Zhang, W.-X.; Du, M.; Sun, H.-L. Cryst. Growth Des. 2010, 10, 20–24. (l) Hu, B.-W.; Zhao, J.-P.; Tao, J.; Sun, X.-J.; Yang, Q.; Zhang, X.-F.; Bu, X.-H Cryst. Growth Des. 2010, 10, 2829–2831. (5) Li, L.; Liao, D.; Jiang, Z.; Yan, S. Inorg. Chem. 2002, 41, 1019– 1021. (6) (a) Bursmeister, J. L. Coord. Chem. Rev. 1968, 3, 225–245. (b) Norbury, A. H. Adv. Inorg. Chem. Radiochem. 1975, 17, 232–236. (c) Kohout, J.; Havastijova, M.; Gazo, J. Coord. Chem. Rev. 1987, 27, 141–172. (d) Arriortua, M. I.; Cort
es, R.; Mesa, J. L.; Lezama, L.; Rojo, T.; Villeneuve, G. Transition Met. Chem. 1988, 13, 371–375. (e) Boudalis, A. K.; Clemente-Juan, J.-M.; Dahan, F.; Tuchagues, J. P. Inorg. Chem. 2004, 43, 1574–1586. (f) Dey, S. K.; Mondal, N.; Salah El Fallah, M.; Vicente, R.; Escuer, A.; Solans, X.; Font-Bardía, M.; Matsushita, T.; Gramlich, V.; Mitra, S. Inorg. Chem. 2004, 43, 2427– 2434. (g) Habib, M.; Karmakar, T. K.; Aromí, G.; Ribas-Ari~ no, J.; Fun, H.-K.; Chantrapromma, S.; Chandra, S. K. Inorg. Chem. 2008, 47, 4109– 4117. (h) Feng, P. L.; Stephenson, C. J.; Amjad, A.; Ogawa, G.; del Barco, E.; Hendrickson, D. N. Inorg. Chem. 2010, 49, 1304–1306. (7) (a) Hennigar, T. L.; MacQuarrie, D. C.; Losier, P.; Rogers, R. D.; Zaworotko, M. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 972–74. (b) Power, K. N.; Hennigar, T. L.; Zaworotko, M. J. Chem. Commun. 1998, 595–597. (c) Hong, C. S.; Son, S.-K.; Lee, Y. S.; Jun, M.-J.; Do, Y. Inorg. Chem. 1999, 38, 5602. (d) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Rizzato, S. Chem. Commun. 2000, 1319. (e) Hernandez, M. L.; Barandika, G.; Urtiaga, M. K.; Cort
es, R.; Lezama, L.; Arriortua, M. I. J. Chem. Soc., Dalton Trans. 2000, 79–84. (f) Hernandez, M. L.; Urtiaga, M. K.; Barandika, G.; Cort
es, R.; Lezama, L.; De la Pinta, N.; Arriortua, M. I.; Rojo, T. J. Chem. Soc., Dalton Trans. 2001, 3010–3014. (g) Carranza, J.; Brennan, C.; Sletten, J.; Lloret, F.; Julve, M. J. Chem. Soc., Dalton Trans. 2002, 3164–3170. (h) Jude, H.; Krause Bauer, J. A.; Connig, W. B. Inorg. Chem. 2005, 44, 1211–1220. (i) Lima, P. P.; Almeida Paz, F. A.; Ferreira, R. A. S.; Berm
udez, V. Z.; Carlos, L. D. Chem. Mater. 2009, 21, 5099–5111. (j) Ma, L.-F.; Liu, B.; Wang, L.-Y.; Li., C.-P.; Du, M. Dalton Trans. 2010, 39, 2301–2308. (8) Earnshaw, A. Introduction to Magnetochemistry; Academic Press: London, 1968. (9) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115–119. (10) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122. (11) Cromer, D. T.; Waber, J. T. International Tables for X-Ray Crystallography; Kynoch Press: Birmingham; Vol. IV. (12) Hong, C.-S.; Son, S.-K.; Lee, Y.-S.; Jun, M.-J.; Do, Y. Inorg. Chem. 1999, 38, 5602–5610. 1316

dx.doi.org/10.1021/cg1015324 |Cryst. Growth Des. 2011, 11, 1310–1317

Crystal Growth & Design

ARTICLE

(13) Konar, S.; Zangrando, E.; Drew, M. G. B.; Ribas, J.; Chaudhuri, N. R. Inorg. Chem. 2003, 42, 5966–5973. (14) (a) Nakamoto, K. In Infrared Spectra of Inorganic Compounds and Coordination Compounds; Wiley: New York, 1997; (b) Pretsch, E.; Clerc, T.; Seibl, J.; Simon, W. In Tablas para la elucidaci
on estructural de compuestos org
anicos por m
etodos espectrosc
opicos; Springer: Barcelona, 1980. (15) (a) Lever, A. B. P. In Inorganic Electronic Spectroscopy; Elsevier: London, 1984; (b) Tanabe, Y.; Sugano, S. J. Phys. Soc. Jpn. 1954, 9, 753. (16) Baker, G. A.; Rushbrook, G. S.; Gilbert, H. E. Phys. Rev. Lett. 1964, 135, 1272–1277. (17) Aronica, C.; Jeanneau, E.; El Moll, H.; Luneau, D.; Gillon, B.; Goujon, A.; Cousson, A.; Carvajal, M. A.; Robert, V. Chem.—Eur. J. 2007, 13, 3666–3674. (18) Xie, Y.; Liu, Y. Q.; Jiang, H.; Du, C.; Xu, X.; Yu, M; Zhu, Y. New. J. Chem. 2002, 26, 176–179. (19) Escuer, A.; Vicente, R.; Ribas, J.; Solans, X.; Font-Bardia, M.; El Fallah, M. S. Inorg. Chem. 1993, 32, 3727–3732. (20) Mukherjee, P. S.; Dalai, S.; Mostafa, G.; Lu, T.-H.; Rentschler, E.; Chaudhuri, R. New. J. Chem. 2001, 25, 1203–1207. (21) Escuer, A.; Font-Bardía, M.; Massoud, S. S.; Mautner, F. A.; Pe~nalba, E.; Solans, X.; Vicente, R. New. J. Chem. 2004, 28, 681–686. (22) Shit, S.; Talukder, P.; Chakraborty, J.; Pilet, G.; El Fallah, M. S.; Ribas, J.; Mitra, S. Polyhedron 2007, 26, 1357–1363.

1317

dx.doi.org/10.1021/cg1015324 |Cryst. Growth Des. 2011, 11, 1310–1317