Metal–organic frameworks constructed from an [MS4Cux]x−2 (M = W, Mo) unit: isomerization of the cluster unit induced by temperature

Abstract

An [MS₄Cu_x]^x−2 cluster unit (M = W, Mo, x = 1, 2,…6) is a kind of heterothiometallic unit of versatile connectivities and geometries for building metal–organic frameworks (MOFs) of intriguing structures and properties. We here report two MOFs based on the [WS₄Cu_x]^x−2 unit and a MOF based on the [MoS₄Cu_x]^x−2 unit with 9,10-di(pyridin-4-yl)anthracene (dpa). 1 contains penta-nuclear [WS₄Cu₄]²⁺ units, which act as tetrahedral nodes and are linked by dpa ligands into a 5-fold interpenetrated diamondoid network. 2 contains an unprecedented [WS₄Cu₆]⁴⁺·I⁻·[WS₄Cu₆]⁴⁺ unit where two hepta-nuclear [WS₄Cu₆]⁴⁺ units are bridged by an I⁻ ion, which acts as a 7-connector node, leading to a 3D network with the rare hxg-d topology. 3 is built from penta-nuclear [MoS₄Cu₄]²⁺ units and dpa ligands and is isostructural to 1. The structural difference between 1 and 2 should come from the isomerization of the [WS₄Cu_x]^x−2 unit in the synthesis processes, and we found that temperature was much more important than other factors, such as solvent, the halide anion of the Cu^I salt and the ratio of [NH₄]₂WS₄ to Cu^I salt, for the isomerization of the [WS₄Cu_x]^x−2 unit in the formation of 1 and 2.