Hydrogen-bonding interactions in the series of complexes [M(C4O4)(OH2)2(dmf)2] and [M(C4O4)(OH2)4] (M = Mn, Co, Ni, Cu, Zn)

Abstract

Reaction of tetrabutylammonium aminosquarate (1-amino-2-methoxycyclobutenedionate) with MCl₂·xH₂O (M = Mn, Co) and tetraethylammonium aminosquarate with M(NO₃)₂·xH₂O (M = Ni, Cu, Zn) in N,N-dimethylformamide (dmf) afforded the series of complexes M(C₄O₄)(OH₂)₂(dmf)₂. The complexes are isomorphous and crystallise in the space group P2₁/c, with the exception of the copper analogue which crystallises in P2₁/n. They all have chain structures that are similar to the squarates [M(C₄O₄)(OH₂)₄] and the complexes [Zn(C₄O₄)(OH₂)₂(dmso)₂] and [Ni(C₄O₄)(C₃N₂H₄)₂(OH₂)₂] and exhibit similar but subtly different hydrogen-bonding interactions to those observed in [Zn(C₄O₄)(OH₂)₂(dmso)₂]. Analysis of the hydrogen-bonding interactions in these complexes provides an insight into some additional factors that affect these interactions in transition metal squarates and their role in determining tertiary structure. The implications with respect to solid-state materials design are discussed.