Solvent-Induced Structural Changes in Complexes of 1,2-Bis(3-(3-pyridyl)pyrazolyl)ethane

Abstract

A series of complexes have been obtained using the flexible ditopic ligand 1,2-bis(3-(3-pyridyl)pyrazolyl)ethane (LEt) with M(SCN)2 (M = Co, Fe) and ZnCl2. The ligand is observed to exist in a variety of conformations with rotations around the ethane spacer and around the pyridyl/pyrazole bond. The bridging length of the ligand (i.e., distance between pyridyl nitrogen atoms) varies by 3.5 Å depending on its geometry. Three different cobalt(ii) complexes of the general form [Co(LEt)2(SCN)2]·Solv (where Solv is a variable number/type of non-coordinated solvent) have been structurally characterized and form a series of solvent dependant supramolecular isomers. When Solv = 2MeCN a (4,4)-sheet is formed (1), however, when Solv = H2O an alternate ‘collapsed’ (4,4)-sheet is observed (2). Changing the solvent to two molecules of N,N-dimethylformamide (DMF) leads to a radical change in structure with a one-dimensional (1D) polymer formed (3) that contains two bridging ligands between adjacent metal atoms (i.e., maintaining the same metal/ligand ratio as in the (4,4)-sheet structures). A monomeric thiocyanate complex [Fe(LEt)2(SCN)2(H2O)2] (4) is reported in which the bispyridyl ligands are terminal and partake in an extended hydrogen-bonded network. A 1D polymer [Zn(LEt)Cl2] (5) is also presented. The structures of the metal complexes are contrasted with that of the free ligand.