Guest Driven Structural Correlations in DPDS [Di(4-pyridyl)disulfide]-Based Coordination PolymersNoelia De la Pinta,†,‡ Luz Fidalgo,§ Gotzon Madariaga,‡ Luis Lezama,† and Roberto Cortes*,†
†Departamento de Química Inorganica and ‡Departamento de Física de la Materia Condensada, Fac. de Ciencia y Tecnología,Universidad del País Vasco UPV/EHU, Apartado 644, 48080 Bilbao, Spain§Departamento de Química Inorganica, Fac. de Farmacia, Universidad del País Vasco UPV/EHU, Apartado 450, 01080Vitoria-Gasteiz, Spain
*S Supporting Information
ABSTRACT: Three novel coordination polymers have been obtained bythe reaction of M(NO3)2·6H2O (M = MnII and CoII) or FeCl2·4H2O withKNCS and DPDS [d i(4 -pyr idy l)d i su lfide] l igand , [Mn-(NCS)2(DPDS)2]2·DPDS·H2O (1), [Fe(NCS)2(DPDS)2]·3H2O (2),and [Co(NCS)2(DPDS)2]·2H2O (3). The three complexes exhibit infinitelinear chain structures, where the metal ions are connected by doubleN,N′-DPDS bridges, that are further connected through hydrogenbonding to give pseudo-3D structures which contain channels wheresolvent and/or free DPDS molecules are located. The number and type ofthese guest molecules will have a determining influence in the final crystalsystem and space groups adopted for every compound obtained, whichwill be analyzed. H-bonding promotes interpenetrated 3D networks in 1−3. Characterization by IR, UV−vis, X-ray diffraction, ESR spectroscopy, and magnetic measurements is developed. Slightantiferromagnetic interactions are observed, essentially in the Fe(II) and Co(II) compounds, that are associated with the doubleDPDS bridges.
■ INTRODUCTION
The quick development in the very recent years of the researchon the formerly known 4,4′-dipyridine type of ligands is relatedto their use in very important present fields of investigation,such as metal organic frameworks (MOFs),1 coordinationpolymers (CPs),2 spin crossover (SCO) systems,3 and others.These ligands are well-known to be excellent different-sizespacers in order to connect chains or sheets, increasing theirdimensionality, increasing the structural flexibility, andgenerating voids of a quadrangular type. The 4,4′-relativeposition of the N donor atoms provides the extension of thesepolymers, with the rigidity being a limiting factor for a self-assembly strategy. The design and synthesis of coordinationpolymers are of great interest for crystal engineering. Thestructural motifs in the CPs range from zero to three-dimensional, and their infinite network topologies areinteresting for the development of host−guest functionalmaterials such as multiferroics,4 since many of these types ofcompounds present some kind of magnetic ordering. Inparticular, porous MOFs are increasingly being studied forpotential storage of different kinds of molecules.5 Structuresand, therefore, the properties of these materials may becontrolled by choosing appropriate bridging ligands and metalions.Among this kind of ligands, one of the less studied groups is
that where the extreme pyridine rings are connected throughsulfur atoms. In particular, the di(4-pyridyl)disulfide (DPDS)
ligand6 has an intermediate rigidity associated with the S−Sbond, allowing a characteristic twisted shape and giving rise, incombination with the geometry of the metal ion, to a structuraldiversity of coordination polymers. This ligand also possessestwo enantiomer forms (M and P) and even has potentialbiological applications in their broken conformations.7
Furthermore, the DPDS ligand is known to transform in theDPS (di(4-pyridyl)sulfide) one and others under solvothermalconditions at temperatures higher than 100 °C via in situdisulfide cleavage reactions.1b,8
On the other hand, the molecule chosen to reachelectroneutrality in this case has been the thiocyanate (NCS)pseudohalide.9 The ability of this anion to act as terminal orbridging ligand opens a wide range of possibilities to givedifferent structural conformations in the compounds it forms.In this work, three DPDS-based compounds are presented,
[M n (NCS ) 2 (DPDS ) 2 ] 2 ·DPDS ·H 2O ( 1 ) , [ F e -(NCS)2(DPDS)2]·3H2O (2), and [Co(NCS)2(DPDS)2]·2H2O(3). Although they are one-dimensional polymers, apseudosupra dimensional structure is achieved through hydro-gen bonding. The resulting network of channels accommodatesdifferent amounts and types of disordered guest molecules,which determine the final crystal system and space group.
Received: July 19, 2012Revised: August 23, 2012Published: August 28, 2012
Characterization by different spectroscopies (IR, UV−vis,ESR), X-ray single-crystal structures, and magnetic measure-ments is also provided.
■ EXPERIMENTAL SECTIONMaterials. All solvents and starting materials for synthesis were
purchased commercially and were used as received. Metal(II) nitratehydrates (Aldrich), di(4-pyridyl)disulfide (Aldrich), and potassiumthiocyanate were used without further purification.Synthesis of [Mn(NCS)2(DPDS)2]2·DPDS·H2O (1). This com-
pound was obtained by mixing of KNCS (0.048 g, 0.5 mmol) andMn(NO3)2·6H2O (0.072 g, 0.25 mmol) in an aqueous solution (20mL). After stirring (about 30 min), a methanol solution (20 mL) ofdi(4-pyridyl)disulfide (DPDS) (0.055 g, 0.25 mmol) was added. Theresulting solution was filtered off the precipitate and was left to standat room temperature. Several days later, yellow prismatic X-ray qualitycrystals were obtained. Anal. Calcd for Mn2C54H40N14S14O: C 44.43,H 2.76, N 13.43, S 30.75; found C 43.86, H 2.64, N 13.74, S 31.45.Synthesis of [Fe(NCS)2(DPDS)2]·3H2O (2). This compound was
synthesized by slow diffusion of a water solution (10 mL) containingKNCS (0.097 g, 1 mmol) and FeCl2·4H2O (0.050 g, 0.25 mmol) witha methanol solution (10 mL) of DPDS (0.055 g, 0.25 mmol) in a tubeglass vessel. After a few days, yellow-orange prisms were isolated assingle crystals suitable for X-ray diffraction. Anal. Calcd forFeC22H22N6O3S6: C 39.63, H 3.33, N 12.60, S 28.86; found C40.87, H 3.20, N 12.41, S 29.06.Synthesis of [Co(NCS)2(DPDS)2]·2H2O (3). This compound was
synthesized by the same method as that for 2, but usingCo(NO3)2·6H2O (0.073 g, 0.25 mmol). Red prismatic crystalsappeared several weeks later. Anal. Calcd for CoC22H20N6O2S6: C40.54, H 3.09, N 12.89, S 29.52; found C 40.16, H 2.92, N 12.75, S29.19. Thermoanalytical data for 1−3 are shown in Table S1 of theSupporting Information.General Methods. Microanalyses were performed with a LECO
CHNS-932 analyzer. Infrared spectroscopy was performed on aMATTSON FTIR 1000 spectrophotometer as KBr pellets in the 400−4000 cm−1 region. Diffuse reflectance spectra were registered at roomtemperature on a CARY 2415 spectrometer in the range 5000−45000cm−1. ESR spectroscopy was performed on powdered samples at theX-band frequency, with a BRUKER ESR 300 spectrometer equippedwith a standard OXFORD low-temperature device, which wascalibrated by the NMR probe for the magnetic field. The frequencywas measured with a Hewlett-Packard 5352B microwave frequencycomputer. The magnetic susceptibility measurements of polycrystallinesamples of the complexes were carried out in the temperature range4.2−300 K at a value of the magnetic field of 1000 G, using a QuantumDesign SQUID magnetometer, equipped with a helium continuous-flow cryostat. The complex (NH4)2Mn(SO4)2.6H2O was used as asusceptibility standard. The experimental susceptibilities werecorrected for the diamagnetism of the constituent atoms (Pascaltables).10
Crystal Structure Determination. Single-crystal X-ray measure-ments for compounds 1 and 2 were taken, at room temperature, on anOxford Diffraction Xcalibur 2 diffractometer (graphite-monochro-mated Mo Kα radiation, λ = 0.71073 Å) fitted with a Sapphire CCDdetector. Data frames were processed (unit cell determination,intensity data integration) using the CrysAlis11 software package. Inthe case of compound 3, single-crystal X-ray measurements were alsotaken at room temperature on a STOE IPDS I (Imaging PlateDiffraction System) diffractometer with graphite monochromated MoKα radiation. Intensity data were collected in the θ ranges 2.93−25.06°(1), 3.34−25.00° (2), and 2.58−26.00° (3). An analysis of thediffraction pattern of compound 2 (see Figure 1) showed the existenceof twinning. All the reflections can be explained in terms of twodomains of almost equal volume, related by a 2-fold axis along c*.The structures were solved by direct methods using the program
SIR9712 and refined by a full-matrix least-squares procedure on F2
using SHELXS97.13 In Table 1, crystallographic data and processingparameters for compounds 1−3 are listed.
■ RESULTS AND DISCUSSIONCrystal Structures Refinement and Results. A glance at
the cell parameters and symmetry of the compounds indicatesthat the structure of compound 2 is slightly distorted withrespect to that of compound 3, whereas compound 1 suffersmore drastic changes and apparently it is totally uncorrelatedwith compounds 2 and 3. The positions of the metal ions andthe covalent backbone can be found straightforwardly. Thelattices of compounds 2 and 3, being essentially identical, areclosely related (see Figure 2) to that of compound 1.Moreover the space groups follow the group−subgroup
chain:
> > −
⎛
⎝⎜⎜
⎞
⎠⎟⎟
⎛
⎝
⎜⎜⎜⎜
⎞
⎠
⎟⎟⎟⎟Ccc Cc P2
1 0 00 1 00 0 1
2
12 0 1
2
12 0 1
20 2 0
1
The transformation matrices relate the monoclinic directbases to that of the orthorhombic one in the form am,i = ao,jMji:i, j = 1, 2, 3. In the case of compound 1, notice that the latticeparameters derived from the transformation matrix are a′m ≈12.28 Å, b′m ≈ 21.82 Å, c′m ≈ 12.28 Å, and β′ ≈ 110.8°, whichare of the order of the values found experimentally.At the most basic level of the structure, the metal atoms are
located on two interpenetrated networks that from now on willbe labeled as blue and as orange, given the colors used in Figure3. Whereas compounds 2 and 3 show an essentially identicalmetal distribution, in compound 1 at least one of the networksappears to be very distorted.The edge length of each network is determined by the tilt of
the molecules that coordinate the metal ions (see Figure 3). Inthe case of compound 2, the edge lengths are 8.741(4) Å [and9.037(4) Å owing to the small monoclinic distortion] for theblue lattice and 11.540(4) [11.530(4) Å] for the orange one.For compound 3 the corresponding lengths are 8.853(4) Å and11.487(4) Å, respectively. Compound 1 is a bit more difficult todescribe. The orange lattice defines alternatively identical sheetsof Mn1 and Mn2 atoms with edges of 10.8883(16) Å and11.3297(11) Å similar to that of compounds 2 and 3. However,the blue lattice is a very distorted honeycomb distribution of
Figure 1. Reconstruction of the (h0l) reciprocal plane of compound 2showing the twinning present in the sample. The twin law is a 2-foldrotation around c*.
Mn1 and Mn2 atoms (Figure 3a and 4b) whose edges havelengths of 7.2257(14) Å, 8.9437(15) Å, and 9.6014(12) Å. A
common structural feature for the three compounds is theexistence of channels along the c axis (see Figure 4).An analysis of the residual electron density within the
channels (Figure 5) indicates the origin of the differentstructural distortions and the corresponding symmetrydecrease.The guest molecules used to model the different residual
electron density are DPDS and H2O, in the case of compound1, and water in different proportions for the Fe (2) and Co (3)compounds. Water molecules are distributed in zigzag chainswith two equally probable dispositions, whereas the DPDSguest molecules appear in the two possible enantiomerconfigurations (M and P), in agreement with the usual achiraldistribution of DPDS.6c In compounds 2 and 3, the set oflattice planes belonging to the orange network, which areparallel to the (b,c) plane, define the average positions of theDPDS ligands, whereas the lattice planes parallel to the (a,c)
Table 1. Crystallographic Collection and Refinement Parameters for Compounds 1−3
plane (blue network) contain the average positions of the NCSmolecules. In compound 1 the average positions of all theDPDS molecules lie on planes that are parallel to (a,c) andbelong to (or are parallel to those of) the orange network. The(a,b) planes of the blue network contain the average positionsof the NCS ligands, but owing to the peculiar geometry of thenetwork, they are distributed following a zigzag arrangement(Figure 4a). Table 2 shows the minimum and maximumdistances and details of their octahedral coordination environ-ment for every compound 1−3.The structure of compound 1 contains two crystallo-
graphically independent metal centers, Mn1 and Mn2. At ahigher level of complexity, it can be described as consisting ofchains (Figure 6) extending along the [1 0 0] direction, wherethe Mn(II) ions are double linked through N,N′-coordinatedDPDS ligands (dihedral angles, C134−S13−S14−C141 =87.6(3)° and C121−S12−S11−C111 = 87.2(3)° for Mn1;C211−S21−S24−C241 = 87.1(3)° and C221−S22−S23−
C231 = 86.5(3)° for Mn2); the Mn···Mn intrachain distancefor both units has the same value (10.88 Å for one of the edgesof the orange network). The octahedral coordination of thesecations is completed by two thiocyanate groups in the axialpositions, which exhibit a quasi linear conformation (N15−C151−S151 = 178.4(6)° and N16−C161−S161 = 179.4(8)°for Mn1; N25−C251−C251 = 179.0(6)° and N26−C261−S261 = 178.1(8)° for Mn2).These chains are interconnected by intermolecular H-bonds
[the most important being C235···S151 = 3.604(6) Å, whereC235−H235 = 0.930(7) Å, H235···S151 = 3.161(2) Å, and
Figure 4. (a) Projection along the c axis of the two interpenetrated networks for compound 3 (almost identical to that of compound 2) showing thedistribution of organic ligands. (b) Same for compound 1, indicating the labels of each atomic site. In both cases the structures exhibit continuouschannels along c.
Figure 5. Difference Fourier maps along the c axis for the following:(a) compound 1 x-range [0, 0.5], y-range [0.13, 0.26], electron densitylevels at 0.35 e/Å3, 0.60 e/Å3, and 1 e/Å3; (b) compound 2 x-range[0.4, 0.6], y-range [0.4, 0.6], electron density levels at 0.43 e/Å3, 0.60e/Å3, and 0.8 e/Å3; (c) compound 3 x-range [0.4, 0.6], y-range [0.4,0.6], electron density levels at 0.23 e/Å3, 0.50 e/Å3, and 0.75 e/Å3.The atomic model is also shown. Water hydrogens could not bedetermined for compound 2.
Table 2. Details of the Coordination Environment forCompounds 1, 2, and 3a
Mn (1)
Mn1 Mn2 Fe (2) Co (3)
mindistance
N15 =2.148(6)
N26 =2.139(7)
N6 =2.005(12)
N12 =2.058(3)
max.distance
N14 =2.328(5)
N24 =2.324(5)
N2 =2.250(11)
N3 =2.198(4)
Lav (Å) 2.2643 2.2582 2.1439 2.1691volume(Å3)
15.4484 15.3201 13.0877 13.5359
D 0.03245 0.03322 0.02685 0.03720λ 1.0025 1.0027 1.0035 1.0053σ2 (deg2) 0.3209 0.6186 6.4267 6.9550aLav = average bond length; D14 = distortion index (bond length) D =(1/n)∑i=1
n |li − lav|/lav, where l0 = center to vertex distance of a regularpolyhedron of the same volume; λ15 = quadratic elongation, ⟨λ⟩ = (1/n)∑i=1
n (li)/(l0)2, where li = distance from the central atom to the ith
C235−H235−S151 = 111.3(4)°], giving rise to the formationof layers Mn1−Mn2 along the xy planes (Figure 7a). Thedisposition of these layers, that are linked by intermolecular H-bonds too (Table 3), produces channels (size 11.371 Å ×10.888 Å) where the lattice molecules (DPDS and H2O) arelocated (Figures 4b and 7b).
As can be seen in Figure 8, the guest groups are disposedalong the [0 0 1] direction between the layers, which arearranged in the yz plane. In this case, the torsion angles ofDPDS guests are C11−S1−S2-C21 = 108(1)° and C31−S3−S4-C41 = 107(2)°. The resulting arrangement provides a filling
of the space based on a great number of intermolecular H-bonds (see table 4). The disordered description of guestmolecules through their two possible enantiomer configura-tions makes the structure achiral. The lack of chirality is acommon feature of all DPDS-containing compounds reportedup to now.6c
The covalent architectures of compounds of FeII (2) andCoII (3) are almost iso-structural, and therefore, they will bedescribed together.These structures consist of chains extending along the [0 0
1] direction (Figure 9), where the metal ions are connected bydouble N,N′-coordinated DPDS bridging ligands, which site inthe equatorial plane. The octahedral coordination sphere ofthese ions is completed by two terminal N-bonded disorderedthiocyanate groups (in axial positions), with their averageconformation being quasi linear (Figure 9).Due to the slightly different C−S−S−C torsion angles
[C21−S2−S1−C11 = 91.8(6)° and C41−S4−S3−C31 =91.4(7)° for compound 2; C5−S1−S6−C6 = 91.32(19)° forcompound 3], the intermetallic distance through DPDS-bridgesslightly modifies from 10.927 Å to 10.911 Å for compounds 2and 3, respectively.The most important H-bonds responsible for connecting M-
(DPDS)2-M chains [M = Fe (2) or Co (3)], located in the xzand yz planes, are listed in Table 5. Whereas Figure 10 showsthe packing of these chains in the plane xy, which leads to theformation of corrugated layers extending in the [1 0 0] and [0 10] directions. In the same way, the disposition of these layers,also linked by H-bonds, originates channels along c (11.530 Å× 8.741 Å for compound 2 and 11.487 Å × 8.854 Å forcompound 3) in which water guest molecules connected by Hbonds are located (see Figures 10 and 11).In both compounds, the water guest molecules stack along
the [0 0 1] direction (Figure 11), the same as that for extendingof the chains.
Infrared Spectra. A summary of the most important IRbands corresponding to compounds 1−3, together with theirtentative assignment, is given in Table 6. On the other hand,the frequencies of the IR bands related to the DPDS ligand inthe compounds are slightly higher than their positions in thefree ligand, showing that the pyridyl rings behave similarly inthe complexes. The frequency values and the non split observedin the νas(C−N)NCS band for compounds 2 and 3, agree well
Figure 7. (a) Packing of the chains on the xy plane to give layers Mn(2)−Mn(1); (b) sites of the guest molecules in the channels between the layers.The H-bonds and hydrogen atoms are omitted for clarity.
Table 3. Selected Most Important Intermolecular H-Bondsbetween the Layers (Maximum = Sum of vdW Radii + 0.5 Å)for Compound 1
with equivalent N-terminal dispositions for this ligand. Thesplit of this band observed in 1 is associated to the existence ofnonequivalent terminal NCS groups in this compound. Thecorresponding spectra have been grouped and can be observedin Figure S2 of the Supporting Information.UV−Vis Spectroscopy. The diffuse reflectance spectra for
compounds 2 and 3 can be observed in Figure 12, and theresults have been listed in Table 7. The spectra have beeninterpreted following Tanabe-Sugano diagrams.17 Results are ingood agreement with the values found in the literature for eachion in their respective coordination environment.18
The diffuse reflectance spectrum for the FeII compound (2)exhibits a single allowed transition (5T2g to
5Eg), split due to theJahn−Teller effect (5Eg is split into
5A1 +5B1), in agreement
with high-spin slightly distorted octahedral FeII. At highwavenumbers, the spectrum shows a charge-transfer bandoverlapping with the triplet states. The values of Dq and the8/3dσ are 916 cm−1 and 1700 cm−1, respectively.The diffuse reflectance spectrum for the CoII compound (3)
exhibits three spin-allowed transitions from the ground state4T1g to the excited states 4T2g,
4A2g, and4T1g, respectively, as
corresponds to high-spin octahedral CoII. At 35000 cm−1, the
spectrum shows a band associated with a charge transfer. Thevalues calculated from these transitions are Dq = 880 cm−1 andB = 673 cm−1. The value of B is indicative of 69.3% ofcovalence of the Co−N bonds in this compound.
ESR Spectroscopy. ESR measurements were carried out atseveral temperatures in the range 4.2−300 K. For compound 1,the thermal variation of the ESR spectra (Figure S3 of theSupporting Information (SI)) shows apparently isotropicsignals at g = 2, being very wide [more than 600 G “peak-to-peak” (ΔHpp) at room temperature] and with almostimperceptible shoulders to both sides of the main signal. Amuch weaker half-field signal (spin forbidden ΔMs = 2transition) can also be observed. On the other hand, theintensity of the mean signal strongly increases upon cooling,but its line-width remains practically constant. Besides, slightmodifications of the form of this signal are also observed(Figure S3).The ESR spectrum at 4.2 K (Figure 13) can be described as
that corresponding to an isotropic g tensor. After consideringdifferent effects (hyperfine interaction, ZFS, g anisotropy, anddipolar interactions), the best fit for the signal was obtained bytaking into account both the effect of hyperfine interaction andthe zero field splitting (ZFS) associated with the S = 5/2 spinstate. Under this hypothesis, the simulation shown in Figure 13was obtained with the following values: g = 1.995, ΔHpp = 260G, A = 85 G, D = 150 G, and E = 40 G, showing an excellentagreement between the experimental and calculated spectra,with the half-field signal (forbidden) not being considered.These values are similar to that found for Mn(II) ions in anoctahedral environment having a small distortion.19
Due to observation of both effects, hyperfine coupling andZFS, the magnetic interactions can be predicted to be extremelyweak, but not negligible, due to the Lorentzian lines observed.In the case of compound 3, the ESR spectra at low
temperatures show very wide signals, and above 125 K, the ESRsignal is not yet detected. By decreasing from this temperature,the spectrum shows an isotropic appearance down to 20 K,where an axial component appears. As can be observed in
Table 4. Selected Most Important Intermolecular H-Bonds between the Layers and the Guest Molecules (Maximum = Sum ofvdW Radii + 0.5 Å) for Compound 1
DPDS(1) guest (50%) with the layers DPDS(2) (50%) with the layersC14···H14 C14···S261 H14···S261 C14−H14···S261 C43···H43 C43···S161 H43···S161 C43−H43···S1610.94(3) 3.67(2) 3.250(4) 110(2) 0.93(4) 3.47(3) 2.796(4) 130(3)
H2O(1) with the DPDS (1) guests (50%) H2O(2) with the DPDS (2)(50%)C23···H23 C23···O1W H23···O1W C23−H23···O1W N4···O2W0.92(3) 1.98(5) 1.39(4) 116(2) 2.49(6)
N2···O1W2.43(3)
H2O(1) with the layersC143···H143 C143··O1W H143···O1W C143−H143···O1W0.930(6) 3.66(2) 2.94(2) 134.6(7)
Figure 14, the signal at 4.2 K shows a g-tensor with an axialsymmetry, common in Co(II) ions with S = 1/2. Despite theline-width at this temperature, the g∥ and g⊥ acquire the values6.80 and 3.05, respectively.Magnetic Measurements. Magnetic susceptibility meas-
urements were performed on powdered samples in the 300−4.2K temperature range for all compounds. Thermal variations ofχm for 1−3 are shown in Figures S4, S5, and S6 of the SI.As can be observed in Figure 15, the variation of χm
−1 is welldescribed by the Curie−Weiss law within the whole temper-ature range, with values of Cm = 4.24 cm3·K·mol−1 and θ = 0.24
K. The value of the χmT product for compound 1 remainspractically constant (4.02 cm3·K·mol−1 at RT) in all thetemperature range, with a minor decrease at low temperature.So, in good agreement with the ESR spectroscopy results, thiscompound should show very weak magnetic interactions due tothe zero field splitting and the hyperfine coupling.The value of χm for compound 2 increases upon cooling from
10.9 × 10−3 cm3·mol−1 at room temperature, being exponentialat the low temperature (Figure S5 of the SI). As can beobserved in Figure 16, the variation of χm
−1 is well described bythe Curie−Weiss law within the whole temperature range, with
Table 5. Selected Most Important Intermolecular H-Bonds between the Chains (Maximum = Sum of vdW Radii +0.5 Å) forCompounds 2 and 3
Fe compd (2) chain with the molecules of waterC13···H13 C13···S1 H13···S1 C13−H13···S1 O5···S6′0.93(1) 3.54(1) 3.097(4) 111.3(9) 3.21(4)
C35···H135 C35···S3 H35···S3 C35−H35···S30.93(2) 3.68(1) 3.361(4) 103(1) between the molecules of water
values of Cm = 3.25 cm3·K·mol−1 and θ = −1.40 K. In the sameway, the product χmT is practically constant (3.23 cm3·K·mol−1
at RT) down to 50 K, rapidly decreasing upon further cooling.The thermal behavior described for χmT, together with the
negative sign of the Weiss constant, is indicative of slightantiferromagnetic coupling between the metallic centers.Equation 1 is the theoretical approach for the magnetic
behavior of this compound. In this expression, χm is a functionof the J parameter due to the exchange coupling along aninfinitive spin20 linear chain scaled to S = 2 and based upon thespin Hamiltonian H = −2J∑SiSi+1.
χβ
= −+
⎜ ⎟⎛⎝
⎞⎠
N gKT
uu
63
11m
2 2
(1)
Where
= − =uTT
TT
TJ
Kcoth ; 12
0 00
According to eq 1, the best fitting parameters are g = 2.08and J = −0.18 K, where the value of g is a usual one foroctahedral Fe(II) ions.21
Figure 11. View of the channels in the xy and yz planes, includingwater guest molecules, for 2 and 3.
Table 6. IR Bands (cm−1) and Assignments for Compounds 1−3 and Free DPDS Ligand
The value of χm for compound 3 (Figure S6 of the SI)increases upon cooling from a value of 10.48 × 10−3 cm3·mol−1
at room temperature, being exponential at low temperature.Figure 17 shows the thermal variation of the χm
−1 and χmTmagnitudes for this compound. As can be observed, the Curie−Weiss law is obeyed down to 25 K with the values of Cm = 3.15cm3·K·mol−1 and θ = −18 K.
The values of χmT for 3 are observed to decrease uponcooling, from 2.95 cm3·K·mol−1 at room temperature to 1.84cm3·K·mol−1 at 5 K.The thermal behavior of χm
−1 and χmT could be interpretedas caused by antiferromagnetic interactions between the Co(II)centers. However, the strong decrease of μeff should be mainlyattributed in this case to the spin−orbit coupling effectcharacteristic of CoII ions. Unfortunately, this effect does notallow calculation of the magnetic exchange coupling constant(J) associated with this compound.
■ CONCLUSIONSThe mean structural motif in compounds 1−3 consists of -M-(DPDS)2-M- linear chains, which group through hydrogenbonding to give interpenetrated 3D highly flexible networks.The resulting network of channels in compounds 1−3
Figure 14. Thermal variation of the experimental X-band powder ESRspectra for 3.
Figure 15. Thermal evolution of χmT (circles) and χm−1 (triangles) for
1 and the corresponding Curie−Weiss line (green), which representsthe best fit obtained.
Figure 16. Thermal variation of χmT (circles), χm−1 (triangles), and the
Curie−Weiss law for 2. The solid lines (green) represent the best fitsobtained.
Figure 17. Thermal evolution of χmT (circles) and χm−1 (triangles) for
compound 3 and the corresponding Curie−Weiss law. The solid line(green) represents the best fit obtained.
accommodates different amounts and types of disordered guestmolecules. In the case of [Co(NCS)2(DPDS)2]·2H2O (3) and[Fe(NCS)2(DPDS)2]·3H2O (2), the addition of an extramolecule of water reduces the symmetry from Ccc2 to Cc,respectively. The inclusion of the DPDS guest (in its twoenantiomer forms M and P) in 1 provokes more drasticchanges, lowering the symmetry to P21. However, thissymmetry reduction follows an interesting group−subgroupchain Ccc2 > Cc > P21, which establishes a clear structuralcorrelation for further materials design.The thermal variation of the χm
−1 and χmT for the threecompounds indicates very weak interactions in the manganesecompound (1), while slight antiferromagnetic interactions areobserved for the iron compound (2) and the cobalt compound(3), in this latter case associated with the spin orbit coupling.
■ ASSOCIATED CONTENT*S Supporting InformationFigures depicting some views of the structures (S1), IR spectra(S2), ESR spectra (S3), magnetic susceptibility (S4−S6), andthermoanalytical data (Table S1), as well as global X-raycrystallographic files, in CIF and check-cif formats. Thismaterial is available free of charge via the Internet at http://pubs.acs.org.
■ ACKNOWLEDGMENTSThis work was supported by the Universidad del Pais VascoUPV/EHU (EHU2010/14), the Basque Government SPRI-SAIOTEK (Project S-PE11UN040), and the Basque Govern-ment (Project IT-282-07). N.D.l.P. thanks UPV/EHU forfinancial support from “Convocatoria para la concesion deayudas de especializacion para investigadores doctores en laUPV/EHU (2008)”.
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