7838 Inorg. Chem. 2009, 48, 7838–7852 DOI: 10.1021/ic900814b
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Prediction of the Spin Transition Temperature in FeII One-Dimensional Coordination Polymers: an Anion Based Database Marinela M. Dıˆrtu,† Aurelian Rotaru,‡,§ Damien Gillard,† Jorge Linares,‡ Epiphane Codjovi,‡ Bernard Tinant, and Yann Garcia*,† †
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Unite de Chimie des Materiaux Inorganiques et Organiques, Departement de Chimie, Universite Catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve, Belgium, ‡Groupe d’Etude de la Matiere Condensee, 45 avenue des Etats-Unis, Universite de Versailles Saint Quentin en Yvelines, 78035 Versailles Cedex, France, § Department of Solid State and Theoretical Physics, “Alexandru Ioan Cuza” University, 700506 Iasi, Romania, and Unite de Chimie Structurale et des Mecanismes Reactionnels, Departement de Chimie, Universite Catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve, Belgium Received April 27, 2009
One-dimensional (1D) coordination polymers of formula [Fe(NH2trz)3]A 3 nH2O, {A = TiF62-, n = 0.5 (1) and n = 1 (2); A = ZrF62-, n = 0.5 (3) and n = 0 (4); A = SnF62-, n = 0.5 (5) and n = 1 (6); A = TaF72-, n = 3 (7) and n = 2.5 (8); A = GeF62-, n = 1 (9) and n = 0.5 (10), NH2trz = 4-amino-1,2,4-triazole} have been :: synthesized, fully characterized, and their spin crossover behavior carefully studied by SQUID magnetometry, Mossbauer spectroscopy, and differential scanning calorimetry. These materials display an abrupt and hysteretic spin transition around 200 K on cooling, as well :: as a reversible thermochromic effect. Accurate spin transition curves were derived by 57Fe Mossbauer spectroscopy considering the corrected f factors for the high-spin and low-spin states determined employing the Debye model. The unusual hysteresis width of 3 (28 K), was attributed to a dense hydrogen bonding network involving the ZrF62counteranion and the 1D chains, an organization which is also revealed in [Cu(NH2trz)3]ZrF6 3 H2O (11). Trinuclear spin crossover compounds of formula [Fe3(NH2trz)10(H2O)2](SbF6)6 3 S {S = 1.5CH3OH (12), 0.5C2H5OH (13)} were also obtained. A structural property relationship was derived between the volume of the inserted counteranion and the transition temperature T1/2 of the 1D chains. Two linear size regimes were identified for monovalent anions (0.04 e V (nm3) e 0.09) and for divalent anions (above V g 0.11 nm3) with saturation around T1/2 = 200 K. These characteristics allowed us to derive an anion based database that is of interest for the prediction of the transition temperature of such functional switchable materials. Diffuse reflectivity measurements under hydrostatic pressure for 3,4 combined with calorimetric data allow an estimation of the electrostatic pressure between cationic chains and counteranions in the crystal lattice of these materials. The chain length distribution that ranges between 1 and 4 nm was also derived.
1. Introduction Major developments in advanced electronic technology require new switchable magnetic materials presenting a bistability behavior around room temperature. Iron(II) spin *To whom correspondence should be addressed. E-mail: yann.garcia@ uclouvain.be. :: Fax: þ32-10-472330. (1) (a) Gutlich, P.; Hauser, A.; Spiering, H. Angew. Chem. 1994, 106, 2109. :: Gutlich, P.; Hauser, A.; Spiering, H. Angew. Chem., Int. Ed. Engl. 1994, 33, :: 2024. (b) Gutlich, P.; Hauser, A.; Spiering H. In Inorganic Electronic Structure and Spectroscopy, Vol. II; A. B. Lever, P., Solomon E. I., Eds.; John Wiley & :: Sons: New York, 1999 p 575. (c) Gutlich, P.; Garcia, Y.; Goodwin, H. A. Chem. :: Soc. Rev. 2000, 29, 419. (d) Gutlich, P.; Garcia, Y.; Woike, Th. Coord. Chem. :: Rev. 2001, 219-221, 839. (e) Gutlich, P.; Garcia, Y.; Spiering, H. In Magnetism: From Molecules to Materials, Vol. IV; Miller, J. S., Drillon, M., Eds.; WileyVCH, New York, 2003; p 271. (f ) Spin Crossover in Transition Metal Com:: pounds. In Top. Curr. Chem.; Gutlich, P.; Goodwin, H. A., Eds.; Springer: Berlin-Heidelberg, 2004; Vols. 233-235.
pubs.acs.org/IC
Published on Web 07/20/2009
transition (ST) coordination compounds belong to such an appealing class of switchable materials with spin state being reversibly triggered by temperature, pressure, or electromagnetic radiation.1 In this context, the reversible thermochromic ST of one-dimensional (1D) chain compounds of formula [Fe(NH2trz)3](anion)2 3 nH2O (NH2trz = 4-amino1,2,4-triazole), that can occur around room temperature, has been thoroughly investigated,2,3 with prospective potential (2) (a) Lavrenova, L. G.; Ikorskii, V. N.; Varnek, V. A.; Oglezneva, I. M.; Larionova, S. V. Koord. Khim. 1986, 12, 207. (b) Lavrenova, L. G.; Ikorskii, V. N.; Varnek, V. A.; Oglezneva, I. M.; Larionov, S. V. Koord. Khim. 1990, 16, 654. (c) Lavrenova, L. G.; Yudina, N. G.; Ikorskii, V. N.; Varnek, V. A.; Oglezneva, I. M.; Larionov, S. V. Polyhedron 1995, 14, 1333. (d) Lavrenova, L. G.; Shakirova, O. G.; Shvedenkov, Y. G.; Ikorskii, V. N.; Varnek, V. A.; Sheludyakova, L. A.; Larionov, S. V. Koord. Khim. 1999, 25, 208. (e) Lavrenova, L. G.; Shakirova, O. G.; Ikorskii, V. N.; Varnek, V. A.; Sheludyakova, L. A.; Larionov, S. V. Koord. Khim. 2003, 29, 22.
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applications (e.g., thermal displays, memory devices, and sensors).4,5 Because these materials hardly crystallize, their structure was deduced by EXAFS at the Fe-K edge6-8 and confirmed by single crystal X-ray analyses of a few CuII analogues.7f,9-11 It shows linear chains where FeII ions are bridged by three N1,N2-1,2,4-triazoles in the low-spin (LS) state as well as in the high-spin (HS) state.7 Most of these FeII complexes exhibit an abrupt ST with hysteresis loops of 2 to 20 K wide that is accompanied by a pronounced thermochromic effect, characteristics which can suit a potential application.12 The origin of the hysteresis loop was primarily attributed to the effective propagation of short-range elastic cooperative effects through the rigid NH2trz bridges between neighboring spin changing FeII ions located at ∼ 3.5 A˚ each.7 Indeed, the use of a more flexible bridging ligand connecting the active centers, such as 1,2-bis(tetrazol-1-yl)propane, afforded a linear chain with triply bridged bis monodentate ligands linking the FeII ions at ∼7 A˚. As a result, (3) (a) Drabent, K.; Bronisz, R.; Rudolf, M. F. Conf. Proc. ICAME95 1996, 50, 7. (b) Bronisz, R.; Drabent, K.; Polomka, P.; Rudolf, M. F. Conf. Proc. ICAME95 1996, 50, 11. (c) Codjovi, E.; Sommier, L.; Kahn, O. New. J. Chem. 1996, 20, 503. (d) Van Koningsbruggen, P. J.; Garcia, Y.; Codjovi, E.; Lapouyade, R.; Kahn, O.; Fournes, L.; Rabardel, L. J. Mater. Chem. 1997, 7, 2069. (e) Toyazaki, S.; Murakami, Y.; Komatsu, T.; Kojima, N.; Yokoyama, T. Mol. Cryst. Liq. Cryst. 2000, 343, 175. (f) Murakami, Y.; Komatsu, T.; Kojima, N. Synth. Met. 1999, 103, 2157. (g) Toyazaki, S.; Nakanishi, M.; Komatsu, T.; Kojima, N.; Matsumura, D.; Yokoyama, T. Synth. Met. 2001, 121, 1794. (h) Kojima, N.; Toyazaki, S.; Itoi, M.; Ono, Y.; Aoki, W.; Kobayashi, Y.; Seto, M.; Yokoyama, T. Mol. Cryst. Liq. Cryst.::2002, 376, 567. (4) (a) Kahn, O.; Krober, J.; Jay, C. Adv. Mater. 1992, 4, 718. (b) Kahn, O.; Codjovi, E.; Garcia, Y.; Van Koningsbruggen, P. J.; Lapouyade, R.; Sommier, L. In Molecule-Based Magnetic Materials; Turnbull, M. M., Sugimoto, T., Thompson, L. K., Eds.; ACS Symposium Series, American Chemical Society: Washington, DC, 1996; Vol. 44, p 298. (c) Kahn, O.; Jay-Martinez, C. Science 1998, 279, 44. :: (5) Garcia, Y.; Ksenofontov, V.; Gutlich, P. Hyperfine Interact. 2002, 139/140, 543. (6) (a) Bausk, N. V.; Erenburg, S. B.; Lavrenova, L. G.; Mazalov, L. N. J. Struct. Chem. 1994, 35, 509. (b) Erenburg, S. B.; Bausk, N. V.; Lavrenova, L. G.; Mazalov, L. N. J. Synchr. Rad. 1999, 6, 576. (c) Erenburg, S. B.; Bausk, N. V.; Lavrenova, L. G.; Mazalov, L. N. J. Magn. Magn. Mater. 2001, 226, 1967. (7) (a) Michalowicz, A.; Moscovici, J.; Ducourant, B.; Cracco, D.; Kahn, O. Chem. Mater. 1995, 7, 1833. (b) Michalowicz, A.; Moscovici, J.; Kahn, O. J. Phys. IV 1997, 7, 633. (c) Garcia, Y.; Van Koningsbruggen, P. J.; Bravic, G.; Guionneau, P.; Chasseau, D.; Cascarano, G. L.; Moscovici, J.; Lambert, K.; Michalowicz, A.; Kahn, O. Inorg. Chem. 1997, 36, 6357. (d) Michalowicz, A.; Moscovici, J.; Garcia, Y.; Kahn, O. J. Synchrotron Radiat. 1999, 6, 231. (e) Michalowicz, A.; Moscovici, J.; Charton, J.; Sandid, F.; Benamrane, F.; Garcia, Y. J. Synchrotron Radiat. 2001, 8, 701. (f) Garcia, Y.; Moscovici, J.; Michalowicz, :: A.; Ksenofontov, V.; Levchenko, G.; Bravic, G.; Chasseau, D.; Gutlich, P. Chem.;Eur. J. 2002, 8, 4992. (8) (a) Yokoyama, T.; Murakami, Y.; Kiguchi, M.; Komatsu, T.; Kojima, N. Phys. Rev. B 1998, 58, 14238. (b) Kojima, N.; Murakami, Y.; Komatsu, T.; Yokoyama, T. Synth. Met. 1999, 103, 2154. (9) Garcia, Y.; Van Koningsbruggen, P. J.; Bravic, G.; Guionneau, P.; Chasseau, D.; Cascarano, G. L.; Moscovici, J.; Lambert, K.; Michalowicz, A.; Kahn, O. Inorg. Chem. 1997, 36, 6357. (10) Drabent, K.; Ciunik, Z. Chem. Commun. 2001, 1254. (11) Garcia, Y.; Van Koningsbruggen, P. J.; Bravic, G.; Chasseau, D.; Kahn, O. Eur. J. Inorg. Chem. 2003, 356. (12) Garcia, Y.; Niel, V.; Mu~noz, M. C.; Real, J. A. Top. Curr. Chem. 2004, 233, 229. (13) Van Koningsbruggen, P. J.; Garcia, Y.; Kahn, O.; Fournes, L.; Kooijman, H.; Spek, A. L.; Haasnoot, J. G.; Moscovici, J.; Provost, K.; :: Michalowicz, A.; Renz, F.; Gutlich, P. Inorg. Chem. 2000, 39, 1891. (14) (a) Lavrenova, L. G.; Ikorskii, V. N.; Varnek, V. A.; Oglezneva, I. M.; Larionov, S. V. J. Struct. Chem. 1993, 34, 960. (b) Shvedenkov, Y. G.; Ikorskii, V. N.; Lavrenova, L. G.; Drebushchak, V. A.; Yudina, N. G. J. Struct. Chem. 1997, 38, 578. (c) Varnek, A.; Lavrenova, L. G.; Gromikov, S. A. J. Struct. Chem. 1997, 38, 585. (d) Varnek, V. A.; Lavrenova, L. G. J. Struct. Chem. 1997, 38, 850. (e) Cantin, C.; Daubric, H.; Kliava, J.; Servant, Y.; Sommier, L.; Kahn, O. J. Phys.: Condens. Matter 1998, 10, 7057.
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this compound displays a gradual spin crossover (SCO) behavior on cooling.13 Decrease of short and long-range elastic cooperative interactions within a polymeric chain were also probed thanks to metal dilution studies of [Fe1-xMx(NH2trz)3](NO3)2 (MII = Zn, Ni, Mn, Cu),14 in which a systematic decrease in the steepness of the ST was observed. The intriguing magnetic behavior of the non diluted sample, [Fe(NH2trz)3](NO3)2, that displays a hysteresis loop of 35 K wide2a,3c was recently accounted by an extended hydrogen bonding network involving the nitrate anion as part of a three-dimensional (3D) supramolecular lattice of high connectivity involving the 1D chain.15 This example points out the role of interchain spacing that was not systematically considered in earlier studies.3 In particular, it is interesting to note that the ST of FeII 1D chain compounds bearing bulky substituents on the 4-position of the 1,2,4-triazole16-19 is much less cooperative pointing out at the importance of chain packing in the crystal lattice. It was also noted that the modification of the nature and the geometry of non-coordinated anions can affect the transition temperature, T1/2, of these materials without dramatically modifying the hysteresis loop. This feature has been observed for monovalent inorganic anions (Cl-, Br-, I-, BF4-, ClO4-)2a-2c and organic sulfonate anions (alkyl,3a,3f,3h phenyl derivatives,3c,3e,3g 2-naphthalene derivatives,3d and spiropyrane sulfonate3g) for the series [Fe(NH2trz)3](anion)2 3 nH2O. Indeed, the insertion of spherical counteranions, such as halogen anions, leads to higher T1/2 as compared with bulkier anions such as BF4and ClO4-. A relationship was proposed between the anion radii and the transition temperatures for [Fe(hyetrz)3]A2 3 nH2O (hyetrz=4-(20 -hydroxyethyl)-1,2,4-triazole ; A=Cl-, NO3-, Br-, I-, BF4-, ClO4-, PF6-),20 but little is known, however, on the role of divalent anions in promoting/ decreasing interchain interactions in such 1D switchable systems. We selected in this work novel fluorinated inorganic anions (TiF62-, ZrF62-, SnF62-, GeF62-, TaF72-) that are expected to favor the engineering of H-bonding networks.21 1D coordination polymers of formula [Fe(NH2trz)3]Anion 3 nH2O were thus synthesized, and their ST investigated by a set of relevant techniques. We also report on the crystal structure of [Cu(NH2trz)3]ZrF6 3 H2O which represents a rare example of a crystallized 1D chain complex with triple N1,N2-1,2,4-triazole bridges. A preliminary account on the ST properties of some of the FeII materials was communicated.22 (15) Garcia, Y.; Campbell, S. J.; Lord, J. S.; Boland, Y.; Ksenofontov, V.; :: Gutlich, P. J. Phys. Chem. B 2007, 111, 11111. (16) Schwarzenbacher, G.; Gangl, M. S.; Goriup, M.; Winter, M.; Grunert, M.; Renz, F.; Linert, W.; Saf, R. Monatsh. Chem. 2001, 132, 519. (17) Fujigaya, T.; Jiang, D. L.; Aida, T. J. Am. Chem. Soc. 2005, 127, 5484. (18) (a) Seredyuk, M.; Gaspar, A. B.; Ksenofontov, V.; Reiman, S.; :: Galyametdinov, Y.; Haase, W.; Rentschler, E.; Gutlich, P. Hyperfine Interact. 2006, 166, 385. (b) Seredyuk, M.; Gaspar, A. B.; Ksenofontov, V.; :: Reiman, S.; Galyametdinov, Y.; Haase, W.; Rentschler, E.; Gutlich, P. Chem. Mater. 2006, 18, 2513. :: (19) Sonar, P.; Grunert, C.; Wei, M. Y.-L.; Kusz, J.; Gutlich, P.; :: Schluter, A. D. Eur. J. Inorg. Chem. 2008, 1613. (20) Garcia, Y.; Van Koningsbruggen, P. J.; Lapouyade, R.; Rabardel, L.; Kahn, O.; Wierczorek, M.; Bronisz, R.; Ciunik, Z.; Rudolf, M. F. C. R. Acad. Sci. Paris 1998, IIc, 523. (21) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G. Angew. Chem., Int. Ed. 2008, 47, 6114. (22) Dıˆ rtu, M. M.; Garcia, Y.; Nica, M.; Rotaru, A.; Linares, J.; Varret, F. Polyhedron 2007, 26, 2259.
7840 Inorganic Chemistry, Vol. 48, No. 16, 2009
Figure 1. (a) X-ray powder diffraction patterns at 293 K for 1-10. (b) SEM imaging at 293 K for 1, 4, 5, and 8.
2. Results 2.1. Synthesis. The 1D coordination polymers were obtained as white powders by self-assembly of the corresponding FeII inorganic precursors [Fe(H2O)6]Anion, prepared in situ and in air, with an alcoholic solution of NH2trz (methanol or ethanol). These compounds were successfully characterized by CHN and TGA analyses, atomic absorption, X-ray powder diffraction (293 K), IR, :: UV-vis, and 57Fe Mossbauer spectroscopy. Thermogravimetric and elemental analyses did not reveal the presence of alcohol guest molecules but instead revealed non-coordinated water molecules, affording the following general formula [Fe(NH2trz)3]Anion 3 nH2O: {anion= TiF62-, n=0.5 (1) and n=1 (2); anion=ZrF62-, n=0.5 (3) and n=0 (4); anion=SnF62-, n=0.5 (5) and n=1 (6); anion=TaF72-, n=3 (7) and n=2.5 (8); anion=GeF62-, n=1 (9) and n=0.5 (10)}. Hemihydrate or monohydrate compounds were thus obtained, except for Zr and Ta. Inclusion of solvent used for synthesis was only observed for [Fe3(NH2trz)10(H2O)2](SbF6)6 3 S {S = 1.5CH3OH (12), 0.5C2H5OH (13)} whose trinuclear nature was con:: firmed by both elemental analysis and Mossbauer spectroscopy (vide infra). Isostructurality of the chain complexes was concluded from X-ray powder diffraction patterns that revealed the presence of principal peaks in all diffractograms (Figure 1a). Compounds 4 and 8 show the better resolved diffractograms of the series. Spherical particles of 484 nm
D^irtu et al. (4) and 1.80 μm (8) diameter are distinguished in the aggregates, as well as elongated rods of dimensions (457 108 nm) for (5) by SEM imaging. Compound 1 is, however, much less crystalline (Figure 1b). This series of materials have also essentially identical IR spectra. The bands assigned to ring torsion of NH2trz at ν=619 cm-1 and the N-N stretching band at ν = 1197 cm-1 are shifted23 upon complexation to 624 cm-1 and 1210 cm-1, respectively, for example, for [Fe(NH2trz)3]ZrF6 (4). These values confirm a coordination of the iron to the 1,2,4-triazole ring.24 Presence of non-coordinated divalent counteranions originating from the inorganic precursors is also confirmed by IR as listed in the synthesis :: section. 57Fe Mossbauer spectroscopy confirms the presence of only one FeIIN6 site, undergoing SCO behavior on cooling and the absence of oxidation product of iron :: (see Figure 5). Mossbauer parameters of these compounds (see section 2.3.2) are typical for 1D polymeric chains with NH2trz as ligand.3d These materials including trinuclear complexes, prepared as white powders, present a reversible thermochromism to pink on cooling. These colors depend on the spin state of the FeII centers. The white color is due to the location of the spin-allowed lowest energy d-d transition, 5 T2g f 5Eg, for the HS sites in the near-infrared region (∼ 11800 cm-1).2a The pink color is due to the 1A1g f 1T1g d-d transition of LS FeII sites observed at ∼19250 cm-1. 2.2. X-ray Crystal Structure of [Cu(NH2trz)3]ZrF6 3 H2O. Blue needles single crystals of [Cu(NH2trz)3]ZrF6 3 H2O (11) were successfully obtained by slow evaporation of an aqueous solution of [Cu(H2O)6]ZrF6 and NH2trz at room temperature. Attempts to crystallize other FeII and CuII complexes of the series failed. Crystallographic data at 100(1) K and structure refinement of 11 that crystallizes in the monoclinic P21/n space group are given in Table 1. Figure 2a shows a view of the 1D polymeric chain built of cationic [Cu(NH2trz)3]2þ units. The asymmetric unit consists of two CuII atoms, Cu1 and Cu2, located on inversion centers. These copper ions are linked by three bidentate bridging NH2trz ligands through N1, N2 atoms. Both copper ions are arranged in a CuN6 core of octahedral geometry within the chain. The basis of the octahedron is formed by four ligands with bond lengths ranging between 2.014(3)-2.080(3) A˚ (Table 2). Two NH2trz ligands are axially coordinated to copper (Cu1-N1 = 2.080(3), Cu2-N12 = 2.385(3) A˚) with difference in bond length indicating a distortion. The ligand bridges Cu1 and Cu2 ions almost at the same distance with Cu1-N21 = 2.029(3) A˚ and Cu2-N22 = 2.029(3) A˚. The Cu1-N11 distance is 2.014(3) A˚ which corresponds to an angle of 122.6(2)° for Cu1-N11-N12. As the distance Cu2-N12 = 2.385(3) A˚ increases, the (Cu2-N12-N11) angle widens to 125.5(2)°. In this case, only a torsion angle (Cu1-N11-N12-Cu2)=-12.8(3)° maintains this geometry. The coordination mode of N1, N2 of NH2trz presents quite a high degree of asymmetry compared to the Cu-N-N bridge angles, which are (23) Haasnoot, J. G.; Vos, G.; Groeneveld, W. L. Z. Naturforsch. B 1977, 32, 421. (24) Sinditskii, V. P.; Sokol, V. I.; Fogel’zang, A. E.; Dutov, M. D.; Serushkin, V. V.; Porai-Koshits, M. A.; Svetlov, B. S. Russ. J. Inorg. Chem. 1987, 32, 1586.
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Table 1. Crystallographic Data and Structure Refinement for [Cu(NH2trz)3] ZrF6 3 H2O (11) at 100(1) Ka empirical formula C6H14OCuN12ZrF6 T [K] 100(1) M [g/mol] 539.05 crystal system monoclinic space group P21/n (No. 14) a [A˚] 10.997(4) b [A˚] 7.771(3) c [A˚] 19.421(8) β [deg] 91.39(2) 1659.2(1) V [A˚3] Z 4 2.158 D [g.cm-3] crystal size [mm] 0.40 0.10 0.06 F(000) 1060 reflections collected 15701 independent reflections 3352 (Rint=0.051) observed reflections [I > 2σ(I)] 3166 completeness to θ=26.4 98.5% no. parameters 291 2 1.172 goodness of fit on F R1, wR2 [I > 2σ(I)] 0.0382, 0.1061 0.86 and -0.88 largest difference peak and hole [e A˚-3] P P P a R= ||Fo| - |Fc||/ |Fo| for observed reflections, wR=[ w(Fo2 2 2 2 2 P 2 1/2 2 Fc ) / wFo ] , w=1/(σ (Fo ) þ 0.025F ), F=(2Fo þ Fc)/3.
127.2(3)° for Cu1-N1-N2 and 122.1(3)° for Cu2-N2N1. The Cu1-N1-N2-Cu2 torsion angle is þ18.5(3)°. In fact, the connection of CuII ions, whose octahedra are distorted, should involve a deviation from the b axis which is clearly seen on Figure 3a. The Cu octahedra are oriented in an ababa fashion (Figure 2b) as observed for [Cu(NH2trz)3](BF4)2 3 H2O10 and two other 1D CuII chain complexes.7f,11 Other arrangements were found for [Cu(NH2trz)3]SiF6 3 8/3H2O (abcabc)23 and [Cu(hyetrz)3](ClO4)2 3 3H2O (abcbab).9 The Cu 3 3 3 Cu intrachain distance of 3.8850(3) A˚ is shorter than the Cu 3 3 3 Cu distance found for [Cu(NH2trz)3]Ax 3 nH2O, (A = BF4-, (x = 2, n = 1); SiF62(x=1, n=8/3)),10 with 3.922 A˚ and 3.904 A˚, respectively (Table 3). In [Cu(hyetrz)3](CF3SO3)2 3 2H2O,11 there exist three types of CuII ions, with Cu1 3 3 3 Cu2=3.8842(4) A˚ and Cu2 3 3 3 Cu3=3.9354(4) A˚, which reflects a difference between the coordination geometry of two pairs of triple N1-N2-1,2,4-triazole bridges. A similar situation is found for [Cu(hyetrz)3](ClO4)2 3 3H2O with two types of distances at 3.853(2) A˚ for Cu1 3 3 3 Cu2 and 3.829(2) A˚ for Cu2 3 3 3 Cu3. These distances are a little shorter than the ones observed in 11, which gives a very slight zigzag arrangement to the chain. This can also be seen by the value of the angle between the vectors of CuII pairs ions, (Cu1, Cu2) and (Cu2, Cu3) which is 175°. For [Cu(hyptrz)3](4-chloro-3-nitrophenylsulfonate)2 3 2H2O (hyptrz=4-(30 -hydroxypropyl)-1,2,4-triazole),7f the Cu1 3 ˚ 3 3 Cu2 distance increases up to 3.962 A. Non-coordinated species are also found in the crystal packing (Figure 3a). A hexafluorozirconate anion is connected to the amino group of the triazole through hydrogen bonding. In addition, the fluorine atoms allow interchain interactions though the connection to nitrogen atoms belonging to two different chains. The involvement of the counteranion in the H-bonding network is probed (25) Marchivie, M.; Guionneau, P.; Letard, J. F.; Chasseau, D. Acta Crystallogr. 2005, B61, 25.
Figure 2. (a) Drawing and atomic labeling system showing the 1D chain of [Cu(NH2trz)3]ZrF6 3 H2O along the a-axis. Non-coordinated counteranions and water molecules have been omitted for clarity. (b) Orientation of CuN6 octahedra in a [Cu(NH2trz)3]ZrF6 3 H2O chain.
by its distortion parameter Σ=22.05(5)° that was determined following ref 25. Indeed, there are two intermolecular interactions between fluoride and the noncoordinated water molecule, (O1-H-F2 and F4), but both fluorine F2 and F4 are linked to N6 and N16, respectively. There is one hydrogen bond between the water molecule and the amino group of the triazole at 2.836 A˚, O1 3 3 3 N6 (Table 2b). Water molecules also connect two metallic sites by C-H 3 3 3 O interactions through the triazole rings (Figure 3b). It is found at 2.12 A˚ (C5-H5 3 3 3 O1) and at 2.20 A˚ (C3-H3 3 3 3 O1). Thus, these interactions set up a dense hydrogen bonding network. 2.3. Thermal Spin-Crossover Properties. 2.3.1. SQUID Magnetometry. Magnetic susceptibility data for (1, 2, 9, 10) were recorded over the temperature range 70-300 K range, and over 4-300 K for 3-8. The magnetic data of all compounds were converted to the HS molar fraction γHS(T) by means of eq (a) and are displayed on Figure 4: γHS ¼
χM T - χM LS ðTÞ χM HS ðTÞ - χM LS ðTÞ
ðaÞ
χΜ LS(T)=184.10-6 cm3 mol-1,26 and χΜHS(T) is the paramagnetic susceptibility determined by fitting the susceptibility data in the HS region with the Curie law. On cooling, compounds 1-10 reveal an abrupt hysteretic ST. At room temperature, 1-4 are fully HS. γHS first decreases slightly to ∼235 K, and more abruptly down to ∼100 K reaching ∼0.17 for 1 and 0.22 for 2, indicating an incomplete ST. The transition temperatures on slow cooling and warming are T1/2V=194 K and T1/2v= 200 K for 1, and T1/2V = 189 K and T1/2v = 196 K for 2, (26) Carlin, K. D.; van Duynevedt, A. J. Magnetic properties of transition metal compounds; Springer-Verlag: New York, 1977.
D^irtu et al.
7842 Inorganic Chemistry, Vol. 48, No. 16, 2009 Table 2. (a) Selected Bond Distances (A˚) and (b) Inter-Atomic Distances (up to 3.2 A˚) and Angles (deg) for Hydrogen Bonds Interactions in [Cu(NH2trz)3]ZrF6 3 H2O (11) Cu1 3 3 3 Cu2 bond lengths Cu1-N1 Cu1-N21 Cu2-N2 Cu2-N12 Cu2-N22 Cu1-N11
D-H
N11-N12 N11-C15 N12-C13 N14-C13 N14-N16 N14-C15 N21-N22 N21-C25 N22-C23 N24-N26 N24-C25 C23-N24
3.8850(3) 2.299(3) 2.080(3) 2.023(3) 2.385(3) 2.029(3) 2.014(3)
D-H H 3 3 3 A
