Satcher Joe H., Olmstead Marilyn M., Droege Michael W., Parkin Sean R., Noll Bruce C., May Leopold, Balch Alan L.
Lawrence Livermore National Laboratory, Livermore, California 94550, and Departments of Chemistry, University of California Davis, Davis California, 95616, and The Catholic University of America, Washington, D.C. 20064.
Inorg Chem. 1998 Dec 28;37(26):6751-6758. doi: 10.1021/ic9802404.
The synthesis and characterization of novel tetranuclear and octanuclear iron(III) complexes with structures based on a nearly square arrangement of four iron ions are reported. Reaction of ferric nitrate, sodium acetate, and the unsymmetrical binucleating ligand HBMDP, where HBMDP is N,N,N'-tris((N-methyl)-2-benzimidazolylmethyl)-N'-methyl-1,3-diamino-2-propanol, in acetone/water yields the tetranuclear iron complex Fe(4)(&mgr;-O)(2)(&mgr;-BMDP)(2)(&mgr;-OAc)(2), which exhibits coordination number asymmetry. The structure of Fe(4)(&mgr;-O)(2)(&mgr;-BMDP)(2)(&mgr;-OAc)(2)(3)(OH).12H(2)O has been determined by single-crystal X-ray diffraction. Each (&mgr;-BMDP) ligand spans two iron(III) ions and causes these ions to become structurally distinct. Within this binuclear unit one iron atom is five-coordinate with distorted square pyramidal geometry and an N(2)O(3) donor set, while the other iron is six-coordinate with distorted octahedral geometry and an N(3)O(3) donor set. Two of these binuclear units are linked through a pair of oxo and acetato bridges to form the centrosymmetric tetranuclear complex. The coordinatively nonequivalent iron atoms exhibit distinct Mössbauer spectroscopic parameters and produce a pair of doublets at 80 K. The iron(III) centers are coupled antiferromagnetically with a room-temperature moment of 1.9 &mgr;(B) per iron with J = -103.3 cm(-)(1), zJ' = -105.9 cm(-)(1). The properties of the unsymmetric cation Fe(4)(&mgr;-O)(2)(&mgr;-BMDP)(2)(&mgr;-OAc)(2) are similar to those observed for binuclear iron proteins with comparable coordinative inequivalence. Efforts to increase the solubility of Fe(4)(&mgr;-O)(2)(&mgr;-BMDP)(2)(&mgr;-OAc)(2) by metathesis with sodium tetrafluoroborate resulted in the isolation of crystals of a new octanuclear iron species, Fe(8)(&mgr;-O)(4)(&mgr;-BMDP)(4)(OH)(4)(&mgr;-OAc)(4)(3)(OH).2CH(3)CN.8H(2)O( )()(2), which has also been characterized by single-crystal X-ray diffraction. The asymmetric unit consists of an Fe(2)(&mgr;-O)(&mgr;-BMDP)(&mgr;-OAc)(OH) group which is externally bridged via the oxo ions to form a molecular square with four of the eight iron ions at the corners. Both iron sites are six-coordinate with distorted octahedral geometry. One has an N(2)O(4) donor set; the other has an N(3)O(3) donor set.
报道了基于四个铁离子近似正方形排列结构的新型四核和八核铁（III）配合物的合成与表征。硝酸铁、醋酸钠与不对称双齿配体HBMDP（其中HBMDP为N,N,N'-三[（N-甲基）-2-苯并咪唑基甲基]-N'-甲基-1,3-二氨基-2-丙醇）在丙酮/水中反应生成四核铁配合物Fe(4)(μ-O)(2)(μ-BMDP)(2)(μ-OAc)(2)，该配合物表现出配位数不对称性。Fe(4)(μ-O)(2)(μ-BMDP)(2)(μ-OAc)(2)(3)(OH)·12H(2)O的结构已通过单晶X射线衍射确定。每个（μ-BMDP）配体跨越两个铁（III）离子，使这些离子在结构上变得不同。在这个双核单元中，一个铁原子为五配位，具有扭曲的四方锥几何构型和N(2)O(3)供体集，而另一个铁为六配位，具有扭曲的八面体几何构型和N(3)O(3)供体集。这两个双核单元通过一对氧桥和醋酸根桥相连形成中心对称的四核配合物。配位不等价的铁原子表现出不同的穆斯堡尔光谱参数，并在80 K时产生一对双峰。铁（III）中心反铁磁耦合，每个铁在室温下的磁矩为1.9 μ(B)，J = -103.3 cm(-)(1)，zJ' = -105.9 cm(-)(1)。不对称阳离子Fe(4)(μ-O)(2)(μ-BMDP)(2)(μ-OAc)(2)的性质与具有类似配位不等价性的双核铁蛋白所观察到的性质相似。通过与四氟硼酸钠复分解来提高Fe(4)(μ-O)(2)(μ-BMDP)(2)(μ-OAc)(2)溶解度的努力导致分离出一种新的八核铁物种Fe(8)(μ-O)(4)(μ-BMDP)(4)(OH)(4)(μ-OAc)(4)(3)(OH)·2CH(3)CN·8H(2)O的晶体，其也已通过单晶X射线衍射表征。不对称单元由一个Fe(2)(μ-O)(μ-BMDP)(μ-OAc)(OH)基团组成，该基团通过氧离子外部桥连形成一个分子正方形，八个铁离子中的四个位于角上。两个铁位点均为六配位，具有扭曲的八面体几何构型。一个具有N(2)O(4)供体集；另一个具有N(3)O(3)供体集。
