Nickel(II) complexes self-assembled from hexamethylenetetramine and isomeric nitrobenzoates: structural diversity and supramolecular features

Abstract

Three new nickel(II)-hmt complexes [Ni(2-nbz)₂(μ₂-hmt)(H₂O) ₂]_n (1), [Ni(3-nbz)₂(hmt) ₂(H₂O)₂]•2(3-nbzH) (2) and [Ni(4-nbz) ₂(μ ₂-hmt)(H₂O) ₂]_n (3) bearing isomeric nitrobenzoates [2-nbz = 2-nitrobenzoate, 3-nbz = 3-nitrobenzoate, 4-nbz = 4-nitrobenzoate and hmt = hexamethylenetetramine] have been synthesised by self-assembly and crystallographically characterised. Compounds 1 and 3 are zigzag chain 1D polymers whereas complex 2 is a monomer. Various weak forces, i.e. –NO₂–π, π–π and CH–π interactions play a key role in stabilizing the structures of 1, 2 and 3, which are further extended into the distinct 1D (2), 2D (1) or 3D (3) H-bonded networks via the intermolecular O–H⋯N (1–3) and O–H⋯O (3) interactions involving the H₂O ligands and hexamethylenetetramine and/or nitrobenzoate moieties. The H-bonded 2D and 3D networks in 1 and 3 have been topologically classified as trinodal 3,4,6-connected or 3,4,4-connected nets with the 3, 4, 6L6 or sqc69 topologies, respectively.