ChemInform Abstract: Preparation and Crystal Structure of Cs4Se16.

161

A family of spin-crossover (SC) complexes, [Fe(II)H(3)L(Me)]Cl.X (X(-) = PF(6) (-), AsF(6) (-), SbF(6) (-), CF(3)SO(3) (-)), 1-4, has been synthesized, in which H(3)L(Me) denotes the hexadentate N(6) tripod-like ligand tris[2-{[(2-methylimidazol-4-yl)methylidene]amino}ethyl]amine, containing three imidazole groups, with a view to establishing the effect of the counter anion on the SC behavior. These complexes have been found to crystallize in the same monoclinic crystal system with similar cell dimensions. The general crystal structure consists of a two-dimensional (2D) extended network constructed by NH...Cl- hydrogen bonds between Cl- and the imidazole NH groups of three neighboring [Fe(II)H(3)L(Me)]2+ ions, while the anion X exists as an isolated counter anion and occupies the space between the 2D sheets. Magnetic susceptibilities and Mössbauer spectra have revealed a variety of SC behaviors depending on the counter anion, including a one-step HS<==>(HS + LS)/2 (1, X = PF(6) (-)), a two-step HS<==>(HS + LS)/2<==>LS with a slow thermal relaxation (2, X = AsF(6) (-)), a gradual one-step HS<==>LS (3, X = SbF(6) (-)), and a steep one-step HS<==>LS with hysteresis (4, X = CF(3)SO(3) (-)). The complexes assume the space group P2(1)/n in the HS state, P2(1) in the HS + LS state, and P2(1)/n in the LS state. The Fe-N bond lengths and the N-Fe-N bond angles are indicative of the HS, HS + LS, and LS states. The molecular volumes, V, of the counter anions have been evaluated by quantum-chemical calculations as follows: 53.4 A(3) (BF(4) (-)), 54.4 A(3) (ClO(4) (-)), 73.0 A(3) (PF(6) (-)), 78.5 A(3) (AsF(6) (-)), 88.7 A(3) (SbF(6) (-)), and 86.9 A(3) (CF(3)SO(3) (-)). The size and shape of the counter anion affects the flexible 2D network structure constructed by the hydrogen bonds, leading to modifications of the SC behavior. These estimated relative sizes of the counter anions correlate well with the observed SC behaviors.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

A Variety of Spin‐Crossover Behaviors Depending on the Counter Anion: Two‐Dimensional Complexes Constructed by NH⋅⋅⋅Cl⁻ Hydrogen Bonds, [Fe^IIH₃L^Me]Cl⋅X (X = PF₆⁻, AsF₆⁻, SbF₆⁻, CF₃SO₃⁻; H₃L^Me = Tris[2‐{[(2‐methylimidazol‐4‐yl)methylidene]amino}ethyl]amine)

Yamada

Hagiwara

Torigoe

et al. 2006

161

“…The absorption correction coefficients were 1.226 (1) and 1.657 mm À1 (2). The structures were solved by direct methods using SHELXS-97 [45] and refined againsy F 2 by a full-matrix least-squares method using SHELXL-97 [46] with anisotropic displacement parameters for all non-hydrogen atoms. Scattering factors were taken from the literature.…”

Section: Methodsmentioning

confidence: 99%

A Family of Enneanuclear Iron(II) Single‐Molecule Magnets

Boudalis¹,

Sanakis²,

Clemente‐Juan³

et al. 2008

108

Complexes [Fe9(X)2-(O2CMe)8{(2-py)2CO2}4] (X(-)=OH(-) (1), N3(-) (2), and NCO(-) (3)) have been prepared by a route previously employed for the synthesis of analogous Co(9) and Ni(9) complexes, involving hydroxide substitution by pseudohalides (N3(-), NCO(-)). As indicated by DC magnetic susceptibility measurements, this substitution induced higher ferromagnetic couplings in complexes 2 and 3, leading to higher ground spin states compared to that of 1. Variable-field experiments have shown that the ground state is not well isolated from excited states, as a result of which it cannot be unambiguously determined. AC susceptometry has revealed out-of-phase signals, which suggests that these complexes exhibit a slow relaxation of magnetization that follows Arrhenius behavior, as observed in single-molecule magnets, with energy barriers of 41 K for 2 (tau 0=3.4 x 10(-12) s) and 44 K for 3 (tau 0=2.0 x 10(-11) s). Slow magnetic relaxation has also been observed by zero-field 57Fe Mössbauer spectroscopy. Characteristic integer-spin electron paramagnetic resonance (EPR) signals have been observed at X-band for 1, whereas 2 and 3 were found to be EPR-silent at this frequency. 1H NMR spectrometry in CD3CN has shown that complexes 1-3 are stable in solution.

“…For Sb(N 3 ) 3 , the reciprocal lattice was initially indexed as a hexagonal cell with cell constants of a = 7.2046 (10), c = 19.439(4) ä, V = 873.8(2) ä 3 , and Z = 6. An alternate setting with a smaller rhombohedral cell was obtained by using the transformation matrix { [25] and refined by the least-squares method on F 2 , SHELXL-97, [26] incorporated in the SHELXTL Suite 5.10 for Windows NT. [27] All atoms were refined anisotropically.…”

mentioning

confidence: 99%

First Structural Characterization of Binary As^IIIand Sb^IIIAzides

Haiges

Vij

Boatz

et al. 2004

The highly explosive molecules As(N(3))(3) and Sb(N(3))(3) were obtained in pure form by the reactions of the corresponding fluorides with (CH(3))(3)SiN(3) in SO(2) and purification by sublimation. The crystal structures and (14)N NMR, infrared, and Raman spectra were determined, and the results compared to ab initio second-order perturbation theory calculations. Whereas Sb(N(3))(3) possesses a propeller-shaped, pyramidal structure with perfect C(3) symmetry, the As(N(3))(3) molecule is significantly distorted from C(3) symmetry due to crystal packing effects.