Mercury (II) chloride adducts of flexible double betaines: influence of different quaternary ammonio side groups in the adipic acid skeleton

Abstract

Two new mercury (II) complexes containing flexible double betaine and chloride ligands, [{2Hg 3(L 1)Cl 6·Hg 2Cl 4} n ]( 1) and [{Hg 3(L 2)Cl 6} n ] ( 2), ( −O 2CCH (N +R 3)CH 2CH 2 CH( N + R 3) CO 2 −, N + R 3=( CH 3) 3( L 1); N + C 5 H 5 ( L 2), crystallize in the same monoclinic space group P2 1 n with a11.767(2), b17.466(3), c17.235(3) A ̊ , β96.85(3)°, V3517(2) A ̊ 3, Z2 and a11.015(2), b10.071(3), c11.435(3) A ̊ ,β100.02(3)°, V1249.2(6) A ̊ 3, Z2 , respectively. The complexes have two-dimensional structures with different metal-betaine molar ratio, metal coordination, ligation mode of carboxylate groups, and disposition of the flexible double betaine backbone due to different positively-charged side groups attached to the 2,5-positions of adipic acid. Complex 1 comprises two kinds of molecules, of which the metal-betaine molar ratio in the unsymmetric molecule is 3:1 while that in the symmetric molecule is 2:1. A layer structure is formed by arraying two unsymmetric molecules and one symmetric molecule alternatively, which are linked by the weak Hg…Cl and Hg…O bonds. Each mercury (II) atom is coordinated by two chloride atoms and a carboxylate oxygen atom in a distorted T-shaped fashion, and the carboxylate groups coordinate the metal atoms in the unidentate mode and μ-O bridging mode. In complex 2, the metal-betaine molar ratio is 3:1 with an inversion center at the mid-point of the betaine ligand. One of the two crystallographically independent mercury (II) atoms is coordinated in a distorted T-shaped fashion, whereas the other one is coordinated by two chloride atoms and two carboxylate oxygen atoms in a novel square-planar coordination about mercury (II) to generate a chain structure, which is further linked by the weak Hg…Cl and Hg…O bonds to complete a layer network. The carboxylate groups coordinate the metal atoms in an uncommon skew- syn μ- O, O′ bridging mode.