Synthesis and Crystal Structure of Dinuclear Cadmium(II) Complex with Dipodal Ligand

Abstract

During the last four decades, the chemistry of macrocyclic and non-cyclic polyethers has attracted an increasing attention because of their selective complexation, cation transport and enzyme chemistry. [1][2][3][4][5] In the field of coordination chemistry, generally, non-cyclic, crown-type polyether affords the low complexation ability because of its conformational freedom while macrocyclic polyethers such as 18-crown-6 show the excellent complexing ability. However, the open chain oligoethylene glycols, so-called podands, with rigid aromatic donor end-groups at the both ends of the oligo(ethylene glycol) backbone have been reported on the considerable enhancement of complexing stabilities.4c Especially, the 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (L) has been spotlighted as a key podand because of its attractive characteristics to form a pseudo cyclic complex with metal ion by the intra-stacking interaction between two quinoline end-groups. 6 According to our and other's works on complexation of L against the transition metal ions, 7 L was also found to form the stable complexes with Ag + or Hg 2+ ions in solid state owing to two quinoline end-groups of L.Recently, we have reported the unique pseudo-cyclic Cd(II) complexes [Cd(L)(H2O)(CH3OH)](ClO4)2 (1a) and [Cd(L) (H 2 O)(NO 3 )](NO 3 ) (1b), in which the dipodal receptor (L) with quinoline end-groups wrapped around the cadmium atom in a helical mode, obtained by self-assembly of the dipodal ligand (L) and CdX2 (X = ClO4 and NO3) ( Figure S1 in Supporting Information).8 As a part of ongoing efforts for the complexation of L against transition metal ions, we prepared another Cd(II) complex with chloride anion. Herein, we report crystal structure and thermal behavior of dinuclear Cd(II) complex (2). Fig. 1. In the asymmetric unit of 2, there are two crystallographically independent Cd atoms which adopt the distorted pentagonal bipyramidal geometries with seven-coordinate number, being bound to three O and one N donors of L and three Cl atoms. The O3N donors of L and one bridging Cl atom (Cl3