Supramolecular hydrogen-bonded networks formed from copper(II) carboxylate dimers

The well-known copper carboxylate dimer, with four carboxylate ligands extending outwards towards the corners of a square, has been employed to generate a series of crystalline compounds. In particular, this work centres on the use of the 4-hydroxybenzoate anion (Hhba) and its deprotonated phenolate form 4-oxidobenzoate (hba2) to obtain complexes with the general formula [Cu-2(Hhba) (4-x)(hba)xL(2-)y]x, where L is an axial coligand (including solvent molecules), x = 0, 1 or 2, and y = 0 or 1. In some cases, short hydrogen bonds result in complexes which may be represented as [Cu-2(Hhba)(2)(H(0.5)hba)(2)L-2]. The main focus of the investigation is on the formation of a variety of extended networks through hydrogen bonding and, in some crystals, coordinate bonds when bridging coligands (L) are employed. Crystals of [Cu-2(Hhba)(4)(dioxane)(2)]center dot(4)(dioxane) consist of the expected Cu dimer with the Hhba anions forming hydrogen bonds to 1,4-dioxane molecules which block network formation. In the case of crystals of composition [Et4N][Cu-2(Hhba)(2)(H(0.5)hba)(2)(CH3OH)(H2O)]center dot(2)(dioxane), Li[Cu-2(Hhba)(2)(H(0.5)hba)(2)(H2O)(2)]center dot(3)(dioxane)center dot 4H2O and [Cu2(Hhba)(2)( H(0.5)hba)(2)(H(0.5)DABCO)(2)]center dot 3CH3OH (DABCO is 1,4-diazabicyclo[2.2.2]octane), square-grid hydrogen-bonded networks are generated in which the complex serves as one type of 4-connecting node, whilst a second 4-connecting node is a hydrogen-bonding motif assembled from four phenol/ phenolate groups. Another two-dimensional (D-2) network based upon a related square-grid structure is formed in the case of [Et4N]2[Cu2(Hhba)2(hba)2(dioxane) (2)][Cu-2(Hhba)(4)(dioxane)(H2O)]center dot CH3OH. In [ Cu-2(Hhba)(4)(H2O)(2)]center dot(2)(Et4NNO3), a square-grid structure is again apparent, but, in this case, a pair of nitrate anions, along with four phenolic groups and a pair of water molecules, combine to form a second type of 4-connecting node. When 1,8-bis(dimethylamino)naphthalene (bdn, 'proton sponge') is used as a base, another square-grid network is generated, i.e. [Hbdn](2)[Cu-2( Hhba)(2)(hba)(2)(H2O)(2)] center dot(3)(dioxane)center dot H2O, but with only the copper dimer complex serving as a 4-connecting node. Complex three-dimensional networks are formed in [Cu-2(Hhba)(4)(O-bipy)] center dot H2O and [Cu-2(Hhba)(4)(O-bipy)(2)]center dot(2)(dioxane), where the potentially bridging 4,40- bipyridine N,N-0- dioxide (O-bipy) ligand is employed. Rare cases of mixed carboxylate copper dimer complexes were obtained in the cases of [Cu-2(Hhba)(3)(OAc)(dioxane)]center dot 3.5(dioxane) and [Cu-2(Hhba)(2)(OAc)(2)(DABCO)(2)]center dot 10(dioxane), with each structure possessing a 2D network structure. The final compound reported is a simple hydrogen-bonded chain of composition (H(0.5)DABCO)(H(1.5)hba), formed from the reaction of H(2)hba and DABCO.