Synthesis, crystal structures, and spectroscopic characterization of the neutral monomeric tetrahedral [M(Diap)2(OAc)2] · H2O complexes (M = Zn,Cd; Diap = 1,3-diazepane-2-thione; OAc = acetate) with N–H⋯O and O–H⋯O intra- and intermolecular hydrogen bondi

The title complexes, [M(Diap)2(OAc)2] · H2O (M = Zn,Cd; Diap = 1,3-diazepane-2-thione; OAc = acetate) with an MO2S2 configuration, have been characterized by X-ray crystallography as well as FT-IR, 1H and 13C NMR spectroscopy. In these complexes, the metal atoms lie in a pseudo-tetrahedral environment and are coordinated by the thione sulfur atoms of two neutral 1,3-diazepane-2-thione ligands and one oxygen atom from each of two monodentate acetate anions. In both complexes, there are two intramolecular N–H⋯O hydrogen bonds, each being between one NH group of a Diap ligand and the uncoordinated O atom of an OAc ligand. The water molecule is also involved in hydrogen bonds, as an acceptor and as a donor twice, linking together three symmetry-related complexes. The Cd complex undergoes a structural phase transition from a monoclinic form at 150 K with Z′ = 2 to a smaller monoclinic cell at room temperature with Z′ = 1 without loss of crystallinity. The Zn complex does not exhibit an equivalent phase transition, and at 150 K is isostructural with the room-temperature form of the Cd complex. All three crystallographically independent molecules found for the Cd complex (two at low temperature and one at room temperature) have essentially the same structure except for small changes in the conformations of the ligands. Tetrahedral coordination with monodentate carboxylate ligands is common for Zn complexes of this kind, but is unusual for Cd complexes, and is the result of the bulky Diap ligands.

Graphical abstractThe title Zn and Cd complexes are isostructural; although a distorted tetrahedral arrangement is well known for Zn complexes of this kind, it is unusual for Cd complexes, and is a result of the bulky thione ligand, a sterically demanding analogue of thiourea.Figure optionsDownload full-size imageDownload as PowerPoint slide