Matouzenko Galina S., Bousseksou Azzedine, Lecocq Sylvain, van Koningsbruggen Petra J., Perrin Monique, Kahn Olivier, Collet André
Stéréochimie et Interactions moléculaires (UMR CNRS and ENS-Lyon No. 117; chaire de l'Institut universitaire de France), École normale supérieure de Lyon, 46, allée d'Italie, 69364 Lyon cedex 07, France, Laboratoire de chimie de coordination (UPR CNRS No. 8241), 205, route de Narbonne, 31077 Toulouse cedex, France, and School of Chemistry, Queen's University of Belfast, Belfast, BT9 5AG, Northern Ireland, Laboratoire de reconnaissance et organisation moléculaire (ESA Q5078), Université Claude Bernard-Lyon 1, 69622 Villeurbanne cedex, France, and Laboratoire des sciences moléculaires, Institut de chimie de la matière condensée de Bordeaux (UPR CNRS No. 9048), 33608 Pessac, France.
Inorg Chem. 1997 Dec 3;36(25):5869-5879. doi: 10.1021/ic971174t.
Three polymorphic modifications A-C of [Fe(II)(DPPA)(NCS)(2)], where DPPA = (3-aminopropyl)bis(2-pyridylmethyl)amine is a new tetradentate ligand, have been synthesized, and their structures, magnetic properties, and Mössbauer spectra have been investigated. For polymorph A, variable-temperature magnetic susceptibility measurements as well as Mössbauer spectroscopy have revealed the occurrence of a rather gradual HS if LS transition without hysteresis, centered at about 176 K. The same methods have shown that polymorph B is paramagnetic over the temperature range 4.5-295 K, whereas polymorph C exhibits a very abrupt S = 2 if S = 0 transition with a hysteresis. The hysteresis width is 8 K, the transitions being centered at T(c) downward arrow = 112 K for decreasing and T(c) upward arrow = 120 K for increasing temperatures. The crystal structures of the three polymorphs have been solved by X-ray diffraction at 298 K. Polymorph A is triclinic, space group P&onemacr; with Z = 2, a = 8.710(2) Å, b = 15.645(2) Å, c = 7.985(1) Å, alpha = 101.57(1) degrees, beta = 112.59(2) degrees, and gamma = 82.68(2) degrees. Polymorph B is monoclinic, space group P2(1)/c with Z = 4, a = 8.936(2) Å, b = 16.855(4) Å, c = 13.645(3) Å, and beta = 97.78(2) degrees. Polymorph C is orthorhombic, space group Pbca with Z = 8, a = 8.449(2) Å, b = 14.239(2) Å, and c = 33.463(5) Å. In the three polymorphs, the asymmetric units are almost identical and consist of one chiral complex molecule with the same configuration and conformation. The distorted [FeN(6)] octahedron is formed by four nitrogen atoms belonging to DPPA and two provided by the cis thiocyanate groups. The two pyridine rings of DPPA are in fac positions. The main differences between the structures of the three polymorphs are found in their crystal packing. The stabilization of the high-spin ground state of polymorph B is tentatively explained by the presence of two centers of steric strain in the crystal lattice resulting in the elongation of the Fe-N(aromatic) distance. The observed hysteresis in polymorph C seems to be due to the existence of an array of intermolecular contacts in the crystal lattice making the spin transition more cooperative than in polymorph A.
已合成了[Fe(II)(DPPA)(NCS)₂]的三种多晶型变体A - C，其中DPPA = (3 - 氨丙基)双(2 - 吡啶甲基)胺是一种新型四齿配体，并对其结构、磁性和穆斯堡尔谱进行了研究。对于多晶型变体A，变温磁化率测量以及穆斯堡尔光谱显示，在约176 K处发生了相当平缓的高自旋（HS）到低自旋（LS）转变，且无磁滞现象。相同方法表明，多晶型变体B在4.5 - 295 K温度范围内呈顺磁性，而多晶型变体C表现出非常陡峭的S = 2到S = 0转变且伴有磁滞现象。磁滞宽度为8 K，降温时转变中心温度T(c)向下箭头 = 112 K，升温时转变中心温度T(c)向上箭头 = 120 K。通过在298 K下的X射线衍射解析了这三种多晶型变体的晶体结构。多晶型变体A为三斜晶系，空间群P&onemacr;，Z = 2，a = 8.710(2) Å，b = 15.645(2) Å，c = 7.985(1) Å，α = 101.57(1)°，β = 112.59(2)°，γ = 82.68(2)°。多晶型变体B为单斜晶系，空间群P2(1)/c，Z = 4，a = 8.936(2) Å，b = 16.855(4) Å，c = 13.645(3) Å，β = 97.78(2)°。多晶型变体C为正交晶系，空间群Pbca，Z = 8，a = 8.449(2) Å，b = 14.239(2) Å，c = 33.463(5) Å。在这三种多晶型变体中，不对称单元几乎相同，均由一个具有相同构型和构象的手性络合物分子组成。扭曲的[FeN₆]八面体由属于DPPA的四个氮原子和由顺式硫氰酸根基团提供的两个氮原子构成。DPPA的两个吡啶环处于面式位置。这三种多晶型变体结构的主要差异在于它们的晶体堆积。多晶型变体B的高自旋基态的稳定化初步解释为晶格中存在两个空间应变中心，导致Fe - N(芳香)距离伸长。在多晶型变体C中观察到的磁滞现象似乎是由于晶格中存在一系列分子间接触，使得自旋转变比多晶型变体A更具协同性。
