Molecular recognition between 4′-(4-biphenylyl)-4,2′:6′,4″-terpyridine domains in the assembly of d9 and d10 metal ion-containing one-dimensional coordination polymers

Abstract

Assembly of [{Zn2(μ-OAc)4(1)}n] from reaction of zinc(II) acetate and 4′-(4-biphenylyl)-4,2′:6′,4″-terpyridine (1) using 1:1, 2:1 and 1:2 ratios of Zn(II): 1 is independent of the conditions tested. Free ligand 1 is a rare example of a compound that crystallizes with five independent molecules in the unit cell (Z′=5). Single crystal X-ray diffraction confirms that [{Zn2(μ-OAc)4(1)}n] is a one-dimensional coordination polymer in which 1 bridges {Zn2(μ-OAc)4} nodes. Each polymer chain has a zigzag configuration and chains associate through face-to-face π stacking of pairs of biphenyl domains and pairs of tpy units. The solid state structure of [{Zn2(μ-OAc)4(1)}n] is compared to those of related compounds. Moving from zinc(II) to copper(II) has little effect on the assembly of a coordination polymer with 1, and [{Cu2(μ-OAc)4(1)}n] is isostructural with [{Zn2(μ-OAc)4(1)}n]. With cadmium(II) acetate, a ladder-like polymer chain forms which contains {Cd2(μ,κ3-O,O′:O′-OAc)2(κ2-O,O′-OAc)2} nodes. The electronic absorption and emission properties of 1, [{Zn2(μ-OAc)4(1)}n], [{Cu2(μ-OAc)4(1)}n] and [{Cd2(μ,κ3-O,O′:O′-OAc)2(κ2-O,O′-OAc)2(1)2}n] are discussed. Binding zinc(II) or cadmium(II) red-shifts the ligand-based solid state emission, while the latter is quenched by coordination to copper(II); solution electronic spectroscopic data are consistent with dissembly of the polymer chain.