Five-fold interpenetrated strongly hydrogen bonded rhomboid grid layers constructed from the aggregation of neutral coordination complexes with long pendant aromatic dicarboxylate and organodiimine ligands

Abstract

Combination of cobalt or zinc chloride, 4,4′-dipyridylamine (dpa) and 4,4′-biphenyldicarboxylic acid (H₂BPDC) under hydrothermal conditions has afforded the neutral coordination complexes {[Co(Hdpa)₂(BPDC)₂]·2H₂O} (1) and [Zn(dpa)₂(HBPDC)₂] (2). The pendant cationic termini of the Hdpa ligands and anionic uncoordinated BPDC carboxylate groups allow each molecular unit of 1 to engage in strong charge-separated N–H⋯O hydrogen bonding interactions to four neighboring molecules, thereby creating a two-dimensional (2-D) hydrogen bonded (4,4) rhomboid grid motif with extremely large ∼42 Å × ∼25 Å apertures. Intra-layer void space is minimized by the interpenetration of four other identical hydrogen bonded rhomboid grids. Although the pendant carboxylate groups in 2 are protonated, strong O–H⋯N hydrogen bonding occurs, resulting in a supramolecular interaction pattern virtually identical to that of 1. To the best of our knowledge complexes 1 and 2 represent the first observations of a five-fold interpenetrated 2-D hydrogen bonded rhomboid grid supramolecular architecture. Adjacent layers further connect into three dimensions (3-D) by either weaker hydrogen bonding mechanisms mediated by water molecules of crystallization (1) or crystal packing forces (2).