Using HgX2 units (X=Cl, CN) to increase structural and magnetic dimensionality in conjunction with (2,2′-bipyridyl)copper(II) building blocks

Abstract

A series of complexes containing (bipy)nCuCl2 units (bipy=2,2′-bipyridyl; n=1,2) and linear, neutral Hg(CN)2 or HgCl2 building blocks have been synthesized and structurally characterized. Generally, the Lewis acidic HgX2 moieties accept chloride ligands from the copper(II) center, in some cases increasing the structural and magnetic dimensionality of the system as a result. [Cu(bipy)2(μ-Cl)2Hg(CN)2] (1) is a molecular complex in which the chloride ligands bridge the copper(II) and mercury(II) centers. [Cu(bipy)2Hg2Cl6]2 (2) contains two copper(II) centers connected by an [Hg4Cl12]4− bridge, that was generated by chloride migration from the harder copper(II) to the softer, highly Lewis acidic HgCl2 group. N-cyano coordination from Hg(CN)2 in {[Cu(bipy)Hg(CN)2Cl2]2Hg(CN)2} (3) generates a “Chinese-kite” type Cu2Hg2 rectangular cluster. The clusters are connected to form a 1D chain by Hg(CN)2 groups, that accept bridging chloride ligands from adjoining clusters. The crystallization of (bipy)CuCl2/Hg(CN)2-containing complexes from aqueous NH4OH yields 1D {[Cu(bipy)(OH)(Cl)]2Hg(CN)2}·2H2O (4) which is composed of [(bipy)Cu(OH)(Cl)]2 units bridged by Hg(CN)2 moieties. The variable temperature magnetic susceptibility of 3 can be fitted to the theoretical expression for a 1D antiferromagnetic chain of S=1/2 centers with alternating interaction pathways (J=−0.92 cm−1, α=0.17, g=2.26). For 4, μeff increases with decreasing temperature to a maximum and then decreases; fitting with the Bleaney–Bowers model for copper(II) dimers with weak antiferromagnetic interdimer interactions yielded J=56.3 cm−1, zJ′=−0.06 cm−1 and g=2.23. Complexes 3 and 4 are examples of coordination polymers with the rarely used Hg(CN)2 building block.