草酸根桥联手性双核铜的合成、表征、结构与磁性

Synthesis,characterization,structures and magnetic properties of chiral oxalate-bridged dicopper(Ⅱ) complexes

分别以(8R,10R)-(-)-[4,5]-pineno-2,2′-bipyridine或(8S,10S)-(+)-[4,5]-pineno-2,2′-bipyridine(LRR和LSS)为手性配体合成双核铜络合物[Cu2(μ-ox)(LRR)2(H2O)2(ClO4)2](1)、[Cu2(μ-ox)(LRR)2(CH3COCH3)2(ClO4)2](1a)、[Cu2(μ-ox)(LSS)2(H2O)2(ClO4)2](2)和[Cu2(μ-ox)-(LRR)(LSS)(CH3COCH3)2(ClO4)2](3)(ox2-=草酸根),并探讨了其反应机理.由元素分析、电导率、紫外可见谱(UV-vis)、圆二色(CD)谱和晶体结构分析推测:该系列络合物具有草酸根桥联的双核结构,两个铜(II)离子与草酸根几乎成共平面;1a和3的晶体结构分析表明,每个Cu(II)的配位构型为拉长畸变八面体,双核分子中轴向的两个溶剂分子和两个高氯酸根互为反式配位.对映体络合物1和2的溶液CD光谱大致呈镜像对称,在可见区的极弱CD吸收峰可能源于LRR和LSS蒎烯基上的手性中心对Cu(II)d-d生色团的手性微扰产生的邻位效应.采用最小二乘法和Bleaney-Bowers方程对络合物1的变温磁化率测试数据进行拟合,求得交换积分J=-338.41(4)cm-1,表明铜(II)离子间有较强的反铁磁自旋交换作用.

The oxalato-bridged dicopper（Ⅱ） complexes [Cu2（μ-ox）（LRR）2（H2O）2（ClO4）2] （1）,[Cu2（μ-ox） （LRR）2（CH3COCH3）2（ClO4）2]（1a）,[Cu2（μ-ox）（LSS）2（H2O）2（ClO4）2] （2） and [Cu2（μ-ox）（LRR）（LSS）2 （CH3COCH3）2-（ClO4）2] （3） [LRR=（8R,10R）-（-）-[4,5]-pineno-2,2＇-bipyridine,LSS=（8S,10S）-（＋）-[4,5]-pineno-2,2＇-bipyridine;ox2-= oxalate] were first prepared.A possible mechanism for the formation of the chial dicopper（II） complexes was proposed.Based on elemental analysis,conductance measurement,UV-vis spectra,CD spectra and X-ray single-crystal diffraction,the oxalato-bridged structures of 1 and 2 were deduced to adopt two Cu（II） ions and the bridged oxalate lying in the nearly same plane.The crystal structures of 1a and 3 reveal that the coordination geometry around each Cu（II） ion is an elongated and distorted octahedron and two axial solvent molecules and two perchlorate ions are anti to each other respectively in both binuclear molecules.The solution CD spectra of 1 and 2 in the visible d-d range show very weak Cotton effects with peaks at 588 and 779 nm,which are approximately of mirror image,suggesting the optical activities may be derived from the vicinal effects of the chiragenic centers at the pinene group of LRR and LSS,respectively.The complex 1 has been characterized by variable-temperature magnetic susceptibility and the data was least-square fitted to the Blenaey-Bowers equation.The exchange integral J was found to be-338.41（4） cm-1,indicating a strong antiferromagnetic interaction between two copper（II） ions.