Cadmium halide coordination complexes of serpentine pentadentate ligands

Abstract

A series of morphologically distinct cadmium halide complexes were obtained from potentially pentadentate, serpentine ligands 2,6-bis([(2-pyridylmethyl)oxy]methyl)-pyridine (L) and 2,6-bis([(2-pyridylmethyl)thio]methyl)pyridine (L*). Methods were developed to isolate crystalline materials ranging from mononuclear [CdLCl2] (1) to zig-zag one-dimensional polymer {[CdL(μ-Cl)]2(CdCl4)}n·n(CH3CN) (2) for L and from one-dimensional helical polymers [CdL*Cl2]n (3) and [CdL*Br2]n (4) to dinuclear [CdL*(μ-Br)(CdBr3)]2 (toluene solvate 5a, ether solvate 5b) or three-dimensional polymer [((Cd(μ-Cl)2)2L*)2]n (6) for L*. Compounds 1 and 2 had pentagonal bipyramidal metal centers with L in a pseudo-planar spiral, pentadentate mode. In contrast, the complexes of L* had octahedral metal centers with a bis-N,S metal-bridging ligand binding mode linking Cd(halogen)2 units in polymeric complexes 3, 4, and 6, but a pentadentate Λ2/Δ2 ligand conformation in dinuclear complexes 5a and 5b. Interactions involved in supramolecular aggregation included offset π-π stacking interactions and edge-to-face σ-π interactions, as well as anion-π(pyridine) interactions, chalcogen–chalcogen interactions, halogen-chalcogen interactions and CH⋯X–Cd halide hydrogen bonds. Additional characterizations of the complexes included elemental analysis, solution 1H NMR spectroscopy, FTIR, TGA and PXRD.