Galet Ana, Gaspar Ana Belén, Muñoz M Carmen, Levchenko Georgii, Real José Antonio
Institut de Ciència Molecular/Departament de Química Inorgànica, Universitat de València, Edifici de Instituts de Paterna, Apartat de Correus 22085, 46071 València, Spain.
Inorg Chem. 2006 Nov 27;45(24):9670-9. doi: 10.1021/ic060729u.
The crystal structure of [Fe(bt)2(NCS)2] (A) was determined by X-ray diffraction at 293 and at 150 K in order to analyze the structural changes associated with the spin transition. The space group is P1 with Z = 2 at both temperatures. Lattice constants are as follows: a = 8.5240(4), b = 11.0730(6), c = 12.5300(8) at 293 K and a = 8.1490(4), b = 11.4390(5), c = 12.1270(6) at 150 K. The iron(II) atom lies at the center of a distorted [FeN6] defined by two bt ligands arranged in a cis conformation. The two remaining coordination positions are occupied by two isothiocyanate anions. The average bond lengths of 2.159(4) A (293 K) and 1.951(2) A (150 K) clearly indicate the change in spin configuration. The trigonal distortion parameter phi has a value of 9.6 degrees and 5.5 degrees at 293 and 150 K, respectively. For A, DeltaV = DeltaV(SCO) = 28 A(3) per formula unit and is accompanied by a hysteresis of 10 K. chi(M)T vs T curves at atmospheric pressure for A show an abrupt spin transition with Tc downward arrow = 176 K and Tc upward arrow = 187 K. The thermodynamic parameters associated with the spin transition are DeltaH = 8.4 +/- 0.4 kJ mol(-1) and DeltaS = 46.5 +/- 3 J K mol(-1). The thermal dependence of the magnetic susceptibility at different pressures, 0.1-0.91 GPa, points out an unusual behavior, which can only be understood in terms of a crystallographic phase transition or a change in the bulk modulus of the complex. Polymorph B crystallizes in the C2/c space group with an average Fe-N bond length of 2.168(2) A and phi = 14.7 degrees at 293 K. B remains in the HS configuration even at pressures of 1.06 GPa.
通过X射线衍射在293K和150K下测定了[Fe(bt)₂(NCS)₂]（A）的晶体结构，以分析与自旋转变相关的结构变化。两个温度下的空间群均为P1，Z = 2。晶格常数如下：293K时，a = 8.5240(4)，b = 11.0730(6)，c = 12.5300(8)；150K时，a = 8.1490(4)，b = 11.4390(5)，c = 12.1270(6)。铁（II）原子位于由两个呈顺式构象排列的bt配体所定义的扭曲[FeN₆]的中心。其余两个配位位置由两个异硫氰酸根阴离子占据。平均键长在293K时为2.159(4) Å，在150K时为1.951(2) Å，这清楚地表明了自旋构型的变化。三角畸变参数phi在293K和150K时分别为9.6度和5.5度。对于A，每个化学式单位的ΔV = ΔV(SCO) = 28 ų，并伴有10K的磁滞现象。A在大气压下的χ(M)T对T曲线显示出一个突然的自旋转变，Tc向下箭头 = 176K，Tc向上箭头 = 187K。与自旋转变相关的热力学参数为ΔH = 8.4 ± 0.4 kJ mol⁻¹和ΔS = 46.5 ± 3 J K mol⁻¹。在0.1 - 0.91 GPa不同压力下磁 susceptibility的热依赖性指出了一种异常行为，这只能通过晶体学相变或配合物的体积模量变化来理解。多晶型物B在C2/c空间群中结晶，在293K时平均Fe - N键长为2.168(2) Å，phi = 14.7度。即使在1.06 GPa的压力下，B仍保持高自旋构型。
