Clegg Jack K, Lindoy Leonard F, McMurtrie John C, Schilter David
Centre for Heavy Metals Research, School of Chemistry, University of Sydney, NSW 2006, Australia.
Dalton Trans. 2005 Mar 7(5):857-64. doi: 10.1039/b418870e. Epub 2005 Feb 1.
A range of 1,3-aryl linked, bis-beta-diketone derivatives (LH2) has been employed to synthesise neutral bis(ligand), dinuclear complexes incorporating square-planar copper(II) and tris(ligand) dinuclear helical derivatives containing octahedral iron(III). The 1H NMR spectra of the free ligands contain singlet peaks at ca. 16.2 ppm, indicative of enolic protons, confirming that the (bis) enol tautomer is present in solution. An X-ray structure of a ligand from the series incorporating tert-butyl terminal substituents confirms that the same tautomer persists in the solid and that the relative orientation of the bis-beta-diketone fragments is such that the coordination vectors lie at approximately 120 degrees to each other. The planar, dinuclear copper complexes form 1 : 2 adducts with pyridine and 4-(dimethylamino)pyridine, confirmed by X-ray structures, that incorporate five-coordinate metal centres. Based on this behaviour, the prospect of linking copper centres in the dinuclear complexes using the difunctional heterocyclic bases, 4,4'-bipyridine, 4,4'-trans-azopyridine and pyrazine as co-ligands has been probed. However, 4,4'-bipyridine was observed to coordinate through only one of its heterocyclic nitrogen atoms in the solid state to form a 1 : 2 ([Cu2(L)2]: 4,4'-bipyridine) adduct, analogous to the structures obtained with the above mono-functional nitrogen bases. Nevertheless, an X-ray structure determination shows that the related difunctional base, 4,4'-trans-azopyridine, coordinates in a bridging fashion via both its heterocyclic nitrogen atoms on alternate sides of each planar [Cu2(L)2] unit to produce an infinite one dimensional metallo chain. In contrast, with pyrazine, a new neutral, discrete assembly of type [Cu4(L)4(pyrazine)2] is formed. The X-ray structure shows that two planar dinuclear complexes are linked by two pyrazine molecules in a sandwich arrangement such that the coordination environment of each copper ion is approximately square pyramidal with the overall tetranuclear structure thus taking the form of a 'dimer of dimers'.
一系列1,3 - 芳基连接的双β - 二酮衍生物（LH2）已被用于合成包含平面正方形铜（II）的中性双（配体）双核配合物以及含有八面体铁（III）的三（配体）双核螺旋衍生物。游离配体的1H NMR谱在约16.2 ppm处含有单峰，表明存在烯醇质子，证实（双）烯醇互变异构体存在于溶液中。该系列中一个含有叔丁基末端取代基的配体的X射线结构证实相同的互变异构体在固态中也存在，并且双β - 二酮片段的相对取向使得配位向量彼此间夹角约为120度。平面双核铜配合物与吡啶和4 - （二甲基氨基）吡啶形成1 : 2加合物，X射线结构证实其包含五配位金属中心。基于此行为，已探究了使用双官能杂环碱4,4'-联吡啶、4,4'-反式偶氮吡啶和吡嗪作为共配体连接双核配合物中铜中心的可能性。然而，观察到4,4'-联吡啶在固态中仅通过其一个杂环氮原子配位，形成1 : 2（[Cu2(L)2] : 4,4'-联吡啶）加合物，类似于用上述单官能氮碱得到的结构。尽管如此，X射线结构测定表明相关的双官能碱4,4'-反式偶氮吡啶通过其两个杂环氮原子在每个平面[Cu2(L)2]单元的交替侧以桥连方式配位，生成无限一维金属链。相比之下，与吡嗪形成了一种新型的中性离散组装体[Cu4(L)4(吡嗪)2]。X射线结构表明两个平面双核配合物通过两个吡嗪分子以夹心排列相连，使得每个铜离子的配位环境近似为方锥型，整体四核结构因此呈“二聚体的二聚体”形式。
