Solvent-driven structural diversities in Zn^II coordination polymers and complexes derived from bis-pyridyl ligands equipped with a hydrogen-bond-capable urea backbone

Abstract

A new series Zn^II metal–organic compounds [both coordination complexes (CCs) and coordination polymers (CPs)] derived from bis-pyridyl ligands equipped with hydrogen-bonding functionality such as urea have been synthesized and characterized by single crystal X-ray crystallography. Out of the six compounds reported herein, [{Zn(μ-3bpmu)Cl₂}] (CP1), [{Zn(μ-3bpmu)Cl₂}·benzene] (CP2), [{Zn(μ-3bpmu)Cl₂}·p-xylene] (CP3), and [{Zn(μ-4bpmu)Cl₂}·p-xylene] (CP4) are coordination polymers, whereas [{Zn₂(μ-3bpu)₂Cl₄}·p-xylene] (CC1) and [{Zn₂(μ-3bpu)₂Cl₄}·benzene] (CC2) are coordination complexes. The solvent of crystallization has profound effect on the supramolecular architecture of the resultant coordination compounds; while crystallization in the presence of aromatic solvents resulted in guest occluded crystals (CP2–CP4, CC1, and CC2), crystallization using only polar solvents produced crystals devoid of guests. Aromatic solvents appear to have induced the formation of metallamacrocycle in CC1 and CC2.