摘要:

Spin-crossover behaviour of the coordination polymer Fe" (C5H,N),Ni" (CN), Takafumi Kitazawa,"" Yuji Gomi," Masashi Takahashi," Masuo Takeda," Miki Enomoto,b Akira Miyazakib and Toshiaki Enokib "Departmentof Chemistry, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274, Japan bDepartment of Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152, Japan The iron@) spin state of Fe(C5H5N),Ni(CN), changes from paramagnetic to diamagnetic when the temperature is lowered, while that of Fe(NH,),Ni(CN),*2C6H6 does not. Although Gonsiderable progress has been made in the family of mineralomimetic multi-dimensional structures using cad- mium cyanide and polycyanopolycadmate the Hofmann-type inclusion compounds and related compounds have been known for almost 100 Recently, theoretical studies on the host-guest interactions in the Hofmann-type inclusion compounds have been reported.'-'' The Hofmann- type clathrate compounds M"(NH,),M'"(CN), -2G (M = Mn, Fe, Co, Ni, Cu, Zn or Cd; M'=Ni, Pd or Pt) consist of two- dimensional (2D) extended metal cyanide host sheets and aromatic guest molecules (G) between the sheets.The 2D sheet is constructed by the alternate linkage between square-planar M'" and the octahedral M" through the cyano bridges. MI1 is octahedrally coordinated by four terminal N atoms of the cyano groups and two N atoms of two NH, ligands in a trans configuration. Each sheet has NH, ligands protruding up and down at each octahedral M" atom. The Hofmann pyridine com- plexes M(C,H,N),M'(CN), are obtained by replacing the NH:, in the sheet M( NH,),M'(CN), with pyridine, C5H5N.11-'3 The large pyridine ligand is responsible for the lack of room for a guest.Some of these compounds would be considered as 2D networks potentially containing interesting cooperative effects. The magnetic susceptibilities of Ni( NH,),Ni(CN), 2C& and Ni(C,H,N),Ni(CN), indicate that the square-planar Ni2+ ion is in the diamagnetic state and the octahedral Ni2+ ion is in the paramagnetic state.', Ni(NH,),Ni(CN), *2C&&, is an anti- Fig. 1 Crystal structures of (a) Fe(C,H,N),Ni(CN),, 1, showing the unit cell, and (b)Fe(NH,),Ni(CN), '2C6H6, 2, showing the unit cell. Benzene molecules are disordered. ferromagnet which has a transition point at TN=2.39 K with a typical Ising spin system.', Recently, thermal and optical switching of iron@) complexes has been de~eloped.'~.'~ The first iron@) complex with a temperature-dependent spin transition, [ Fe"( NCS),( phen),] (phen= 1,lO-phenanthroline) was discovered more than thirty years ago." Its paramagnetic state at higher temperatures is converted to a diamagnetic state at low temperatures.The spin-crossover iron@) compounds are [ FeNJ complexes; the iron@) atom is coordinated by six N atoms.', We were there- fore interested in the 2D coordination polymer compounds based on iron(I1) tetracyanonickelate(u), [Ni(CN),Fe],19 con-taining [FeN,] moieties. We report here the 37Fe Mossbauer spectra and X-ray crystal structures for the Hofmann-type pyridine complex Fe(C5H,N),Ni(CN),, 1 and the Hofmann- type clathrate Fe(NH,),Ni(CN), -2C6H6,2.Since only the unit cell dimensions of lI3 and 2,' have been determined from X-ray powder diffraction data, we carried out single crystal X-ray determinations at room temperature (298 K) for 1 and 2 in order to obtain further structural information. Yellow single crystals of 1 and 2 were prepared by a method similar to that for Fe(H,0)2Ni(CN),-2C4H802,3.19 The X-ray crystal structuret of 1 [Fig. l(a)] is similar to that of Cd(C5H5N),Ni(CN),.12 The complex layers consist of a square-meshed network of the square-planar Ni" and the six-coordinate Fe" atoms alternately linked by the bridging cyano ligands.The six-coordination of iron@) is accomplished by four terminal N atoms from the cyano groups and two N atoms from the pyridine ligands in a trans configur- ation. The distances of Fe-Njpyridine) and Fe-N(cyanide) were 2.208( 7) and 2.155(5) A, respectively. The distance between layers is ca. 7.76 A (half of cell dimension a). The neighbouring layers are shifted by a symmetry operation of the base-centred space group C2/m. The shift is associated with the large size of the pyridine ligand because an eclipsed layer stacking pattern would make a large void space. The X-ray structure$ of 2 [Fig. l(b)] shows that the host framework tCrystal data for Fe(C,H,N),Ni(CN),, 1: M = 376.F2; monoclinic, C2/m (no. 12),a= 15.526(3), b=7.392(2), c=7.067(2) A, p= 101.26(2), V=795.5(6) A3, 2=2, D,= 1.56(2), D,= 1.57 g cmP3, p(Mo-Ka)= 21.04 cm-', Rigaku AFC5S diffractometer.The unit cell dimensions are different from those in ref. 13. 1021 Reflections observed, 653 used; 63 parameters refined; R = 0.041, R, = 0.042, goodness of fit (gof ) = 2.31. The structure was solved using the TEXSAN software package. All the non-hydrogen atoms were refined anisotropically. Hydrogen atoms were not inserted in the refinement. $Crystal data for Fe(NH,),Ni(CN), '2C6H6, F: M=408.91; tebragonal, P4/mmm (no. 123), a=7.353(2), c=8.316(2) A, U=449.6(2)A3, Z=1, D,= 1.48(2), D,= 1.51 g cmP3, p(Mo-Km)= 18.68 cm-', Rigaku AFCSS diffractometer. 642 Reflections observed, 283 used; 29 param-eters refined; R = 0.051, R, = 0.064, gof = 5.90.The structure was solved using the TEXSAN software package. All the non-hydrogen atoms were refined anisotropically. Hydrogen atoms were not inserted in the refinement. The host lattice is isostructural with other Hofmann-type clathrates; however, the benzene molecules are disordered, taking two alternative orientations. Atomic coordinates, bond lengths and angles, and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre. See Information for Authors, Issue No. 1. J. Muter. Chem., 1996, 6(1), 119-121 119 0.00.)3.0 [ -2.5 --z g 2.0 -> 1.5 -2 1.0 -OS 0.0 01*. ..... ...0 I00 I 0 50 100 150 200 250 300 TIK Fig. 3 Temperature dependence of the magnetic susceptibility for Fe(C,H,N),Ni(CN), 1 tation of the benzene rings is disordered about the mirror plane normal to the ab plane.Mossbauer spectra of 1 show that the spin state of the iron@) atom changes from high spin with a (t2,)4(e,)2 electron configuration (IS= 1.06 mm s-l, QS=0.86 mm s-' at room temperature) to low spin with a (t2J6 electron configuration (IS =0.47 mm s-', QS =0 at 78 K) when the temperature is lowered. Temperature-dependent Mossbauer measurements indicate that the spin-crossover behaviour occurs between 210 and 170 K (Fig. 2). Since the energies of the two possible states are very similar at these temperatures, both forms are capable of coexistence. The minor component is probably due to Fe3+ produced by air oxidation during the synthesis or powdering process before the Mossbauer measurement.Magnetic suscep- tibility data for a polycrystalline sample of 1 were recorded at 0.1 T with a SQUID magnetometer. The temperature-depen- dent magnetic susceptibility for 1 also shows spin-crossover behaviour with hysteresis (Fig. 3). The paramagnetic behaviour +96 did not disappear because the sample contains Fe3 species. The result of the magnetic susceptibility agrees with the minor component of the Mossbauer spectra. The Mossbauer spectra 92 at 298 and 78 K for 2 indicate that the iron@) atom is in a 100 high-spin state (IS= 1.10mm s-l, QS=O.89 mm s-' at 298 K; IS =1.22 mm s-l, QS =1.47 mm s-l at 78 K). Although both 96 1 and 2 are [FeNs] complexes, the behaviour of the spin state of 1 is different from that of 2.The differences of spin behaviour 92 between 1 and 2 are related to the ligands C5H5N and NH,. The pyridine ligand is associated with a temperature-dependent 100 spin transition in 1. The spectra at 298 and 78 K for Fe(H20)2Ni(CN), *2C4Hs02, 3 indicate that the iron@) of the [FeN402] complex is also in a high-spin state.lg The pyridine n-electrons may play a key role in the spin crossover. 9G192 References -2velocity0/ rnrn S44 1 T. Kitazawa, S. Nishikiori and T. Iwamoto, J. Chem. SOC., Dalton Trans., 1994,3695. 2 T. Kitazawa, T. Kikuyama, M. Takahashi and M. Takeda, Fig. 2 57Fe Mossbauer spectra for Fe(C,H5N)2Ni(CN)4 1 at various J. Chem. SOC., Dalton Trans., 1994,2993 temperatures 3 T.Iwamoto, T. Kitazawa, S. Nishikiori and R. Kuroda, Chemical Physics of Intercalation 11, Nato AS1 Series B, Physics, ed. P. Bernier, J. E. Fischer, R. Roth and S. A. Solin, Plenum, New is isostructural to that of the other Hofmann-type ~lathrates.~,~ York, 1993, vol. 305, p. 325. The octahedral iron@) atom is coordinated by four terminal 4 T. Iwamoto, Inclusion Compounds, ed. J. L. Atwood, 1.E. D. Davies N atoms of cyano groups and two NH, ligands. Each sheet of and D. D. MacNicol, Academic Press, London, 1984, vol. 1, p. 29. [Ni(CN),Fe], has NH3 ligands protruding up and down at 5 K. A. Hofmann and F. Z. Ktispert, 2. Anorg. Chem, 1897,15,204. each iron@) atom in the network. The Fe-N(NH3) and 6 J. H. Rayer and H. M. Powell, J.Chem. SOC., 1952,319. Fe-N(cyanide) distances are 2.20( 1) and 2.;83(8) A, respect- 7 S. Nishikiori, T. Kitazawa, R. Kuroda and T. Iwamoto, J.Inclusion Phenom., 1989,7,369.ively. The distance between layers is 8.316 A (cell dimension 8 E. Ruiz, S. Alvarez, R. Hoffmann and J. Bernstein, J. Am Chem. c). The neighbouring layers are arranged in an eclipsed stacking SOC.,1994, 116,8207. pattern. The benzene molecules are trapped between the sheets 9 E. Ruiz, J. J. Novoa and S. Alvarez, J.Phys. Chem., 1995,99,2296. with their aromatic planes vertical to the sheets. The orien- 10 E. Ruiz and S. Alvarez, Inorg. Chem., 1995,34, 3260. 120 J. Muter. Chern., 1996, 6(1), 119-121 11 12 13 14 15 S. Akyiiz, A. B. Dempster, R. L. Morehouse and S. Suzuki, J. Mol. Struct., 1973, 17, 105. D. Ulkii, 2.Kristallogr., 1975,142,271. R. L. Morehouse, K. Aytac and D. Ulkii, 2. Kristallogr., 1977, 145, 157. M. Kondo and M. Kubo, J. Phys. Chem., 1957,61,1948. H. Kitaguchi, S. Nagata and T. Watanabe, J. Phys. SOC.Jpn., 1975, 38,998. 17 18 19 20 0.Kahn, J. Krbiier and C. Jay, Adu. Muter., 1992,4,718. W. A. Baker and H. M. Bobonich, Inorg. Chem., 1964,3,1184. T. Kitazawa, M. Fukunaga, M. Takahashi and M. Takeda, Mol. Cryst. Liq. Cryst., 1994,244, 331. T. Iwamoto, N. Nakano, M. Morita, T. Miyosi, T. Miyamoto and Y. Sasaki, Inorg. Chim. Acta, 1968,2, 313. 16 P. Gutlich, A. Hauser and H. Spiering, Angew. Chem., Int. Ed. Engl., 1994,33,2024. Communication 5/05501F; Received 18th August, 1995 J. Muter. Chem., 1996,6( l), 119-121 121

ISSN:0959-9428    

DOI:10.1039/JM9960600119

出版商:RSC    

年代:1996

数据来源: RSC