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)

Reaction of tetrabutylammonium aminosquarate (1-amino-2-methoxycyclobutenedionate) with MCl2. xH(2)O (M = Mn, Co) and tetraethylammonium aminosquarate with M(NO3)(2). xH(2)O (M = Ni, Cu, Zn) in N,N-dimethyl-formamide (dmf) afforded the series of complexes M(C4O4)(OH2)(2)(dmf)(2). The complexes are isomorphous and crystallise in the space group P2(1)/c, with the exception of the copper analogue which crystallises in P2(1)/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.