Subramanian P S, Suresh E, Dastidar P, Waghmode S, Srinivas D
Silicate and Catalysis Division, Central Salt & Marine Chemicals Research Institute, Gijubhai Badheka Marg, Bhavnagar 364 002, India.
Inorg Chem. 2001 Aug 13;40(17):4291-301. doi: 10.1021/ic010182d.
Weak molecular and magnetic exchange interactions in ternary copper(II) complexes, viz., [Cu(L-phe)(phen)(H(2)O)]ClO(4) (1), [Cu(L-phe)(bpy)(H(2)O)]ClO(4) (2), and [Cu(L-his)(bpy)]ClO(4).1.5H(2)O (3), where L-phe = L-phenylalanine, L-his = L-histidine, phen = 1,10-phenanthroline, and bpy = 2,2'-bipyridine, have been investigated. Single-crystal X-ray structures reveal that complex 2 crystallizes in a monoclinic space group P2(1), with unit cell parameters a = 7.422(7) A, b = 11.397(5) A, c = 12.610(2) A, beta = 102.10(5) degrees, V = 1043.0(11) A(3), Z = 2, R = 0.0574, and R(w) = 0.1657. Complex 3 crystallizes in a monoclinic space group C2, with a = 18.834(6) A, b = 10.563(4) A, c = 11.039(3) A, beta = 115.23(2) degrees, V = 1986.6(11) A(3), Z = 4, R = 0.0466, and R(w) = 0.1211. Molecules of 2, in the solid state, are self-assembled via weak intra- and intermolecular pi-pi stacking and H-bonding interactions. Molecules of 3 exhibit intermolecular dimeric association with the Cu.Cu separation being 3.811 A. X-ray structures and (1)H NMR studies reveal conformational isomerism in both solid and liquid states of complexes 1 and 2. The aromatic side chain of L-phe in 1 and 2 adopts either a "folded" (A) or an "extended" (B) conformation. Variable-temperature (1)H NMR and spin lattice relaxation measurements point out interconversion between conformations A and B at temperatures above 323 K. The change in molecular conformation induces a change in the electron density at the site of copper and band gap energy between HOMO and LUMO orbitals. Interestingly, in spite of paramagnetic nature, complexes 1 and 2 are amenable for both EPR and (1)H NMR spectroscopic studies. Single-crystal EPR spectra of 2 in three orthogonal planes are consistent with three-dimensional magnetic behavior. Intramolecular exchange dominates the dipolar interactions. The EPR spectra of 3 correspond to weak magnetic interactions between associated dimeric units. The structural and magnetic resonance investigations together reveal that the weak pi-pi stacking interactions are the electronic pathways for magnetic interactions in 1-3.
已对三元铜（II）配合物，即[Cu（L-苯丙氨酸）（邻菲罗啉）（H₂O）]ClO₄（1）、[Cu（L-苯丙氨酸）（2,2'-联吡啶）（H₂O）]ClO₄（2）和[Cu（L-组氨酸）（2,2'-联吡啶）]ClO₄·1.5H₂O（3）中的弱分子和磁交换相互作用进行了研究。其中L-苯丙氨酸 = L-phenylalanine，L-组氨酸 = L-histidine，邻菲罗啉 = 1,10-phenanthroline，2,2'-联吡啶 = bpy。单晶X射线结构表明，配合物2结晶于单斜空间群P2(1)，晶胞参数a = 7.422(7) Å，b = 11.397(5) Å，c = 12.610(2) Å，β = 102.10(5)°，V = 1043.0(11) ų，Z = 2，R = 0.0574，R(w) = 0.1657。配合物3结晶于单斜空间群C2，a = 18.834(6) Å，b = 10.563(4) Å，c = 11.039(3) Å，β = 115.23(2)°，V = 1986.6(11) ų，Z = 4，R = 0.0466，R(w) = 0.1211。固态下配合物2的分子通过弱的分子内和分子间π-π堆积以及氢键相互作用自组装。配合物3的分子表现出分子间二聚体缔合，铜-铜间距为3.811 Å。X射线结构和¹H NMR研究表明，配合物1和2在固态和液态下均存在构象异构现象。1和2中L-苯丙氨酸的芳香侧链采取“折叠”（A）或“伸展”（B）构象。变温¹H NMR和自旋晶格弛豫测量表明，在高于323 K的温度下，构象A和B之间会发生相互转换。分子构象的变化会导致铜位点处的电子密度以及HOMO和LUMO轨道之间的带隙能量发生变化。有趣的是，尽管配合物1和2具有顺磁性，但它们仍适用于EPR和¹H NMR光谱研究。配合物2在三个正交平面上的单晶EPR光谱与三维磁行为一致。分子内交换主导偶极相互作用。配合物3的EPR光谱对应于相关二聚体单元之间的弱磁相互作用。结构和磁共振研究共同表明，弱π-π堆积相互作用是1 - 3中磁相互作用的电子通道。
