Doubly-linked 1D coordination polymers derived from 2 ∶ 2 metallamacrocyclic Ni(ii) complexes with bipodal acylthiourea and exo-bidentate N-donor bridging ligands: toward potentially selective chemical sensors?

Abstract

The square planar 2 ∶ 2 metallamacrocyclic Ni(II) complex of 3,3,3′,3′-tetraethyl-1,1′-isophthaloylbis(thiourea) readily forms coordination polymers by axial coordination of various exo-bidentate N-donor linkers: pyrazine, 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethane and 1,2-di(4-pyridyl)ethylene. Steric constraints, together with coordination limited to the axial directions, result in the self-assembly of double-linked 1D ladder structures. One compound in particular, with the bridging ligand 1,2-di(4-pyridyl)ethylene, is found to exist as a quasi-polymer, realising only one-third of its potential linkages. On exposure to various solvents, this compound appears to undergo complete polymerisation, both rapidly and fully reversibly with an associated colour change, making it a potential chemical sensor.