Stibrany Robert T, Lobanov Maxim V, Schugar Harvey J, Potenza Joseph A
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854, USA.
Inorg Chem. 2004 Feb 23;43(4):1472-80. doi: 10.1021/ic030180o.
2,2'-Bis[2-(1-propylbenzimidazol-2-yl)]biphenyl), 4, and its bis complexes with Fe(II) and Mn(II) have been prepared and characterized structurally and spectroscopically. Ligand 4 adopts an open, "trans" conformation in the solid state with the benzimidazole (BzIm) groups on opposite sides of the biphenyl unit. In its complexes with metal ions, a "cis" conformation is observed, and 4 behaves as a geometrically constraining bidentate ligand with four planar groups connected by three "hinges". Reaction of 4 with Fe(II) or Mn(II) yielded isomorphous crystals (space group Pnn2) of Fe(II)(4)2.(ClO4)2 and Mn(II)(4)2.(ClO4)2, in which the M(II)(4)2 cations exhibit distorted-tetrahedral coordination geometries (N-M-N angles, 109 +/- 11 degrees ) enforced by rigid, chiral nine-membered M(4) rings in the twist-boat-boat conformation. Individually, the cations show R,R or S,S stereochemistry, and the crystals are racemates. Mn(II)(4)2.(ClO4)2 exhibits a quasi-reversible Mn(II) --> Mn(III) oxidation at E(1/2) = 0.64 V; the corresponding Fe(II) --> Fe(III) oxidation occurs at E(1/2) = 1.76 V. The electrochemical stability of the Fe(III) oxidation state in this system suggests the possibility of isolating an unusual pseudotetrahedral Fe(III)N(BzIm)(4) species. Ultraviolet spectra of the iron and manganese complexes are dominated by absorptions of the ligand 4 blue-shifted by approximately 2000-3000 cm(-1). Ligand-field absorptions were observed for the Fe(II) complex; those for the Mn(II) complex were obscured by tailing ultraviolet absorptions. Electron paramagnetic resonance and magnetic susceptibility measurements are consistent with a high-spin Mn(II) complex, while for the Fe(II) complex, the falloff of the magnetic moment with decreasing temperature is indicative of zero-field splitting with D approximately 4 cm(-1).
2,2'-双[2-(1-丙基苯并咪唑-2-基)]联苯（4）及其与Fe(II)和Mn(II)的双配合物已被制备，并通过结构和光谱进行了表征。配体4在固态时呈现开放的“反式”构象，苯并咪唑（BzIm）基团位于联苯单元的相对两侧。在其与金属离子的配合物中，观察到“顺式”构象，并且4表现为具有由三个“铰链”连接的四个平面基团的几何约束双齿配体。4与Fe(II)或Mn(II)反应生成了Fe(II)(4)2.(ClO4)2和Mn(II)(4)2.(ClO4)2的同构晶体（空间群Pnn2），其中M(II)(4)2阳离子呈现扭曲的四面体配位几何结构（N-M-N角，109±11°），这是由处于扭船-船式构象的刚性手性九元M(4)环所强制形成的。单个阳离子显示R,R或S,S立体化学，并且晶体是外消旋体。Mn(II)(4)2.(ClO4)2在E(1/2)=0.64 V处表现出准可逆的Mn(II)→Mn(III)氧化；相应的Fe(II)→Fe(III)氧化在E(1/2)=1.76 V处发生。该体系中Fe(III)氧化态的电化学稳定性表明有可能分离出一种不寻常的假四面体Fe(III)N(BzIm)(4)物种。铁和锰配合物的紫外光谱主要由配体4的吸收主导，其蓝移约2000 - 3000 cm(-1)。观察到了Fe(II)配合物的配体场吸收；Mn(II)配合物的配体场吸收被拖尾的紫外吸收所掩盖。电子顺磁共振和磁化率测量结果与高自旋Mn(II)配合物一致，而对于Fe(II)配合物，磁矩随温度降低而下降表明零场分裂，D约为4 cm(-1)。
