Solvent-induced structural changes in complexes of 1,2-bis(3-(3-pyridyl) pyrazolyl)ethane

A series of complexes have been obtained using the flexible ditopic ligand 1,2-bis(3-(3-pyridyl)pyrazolyl)ethane (L^Et) 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 depending on its geometry. Three different cobalt(ii) complexes of the general form [Co(L^Et) 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(L ^Et)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(L^Et)Cl₂] (5) is also presented. The structures of the metal complexes are contrasted with that of the free ligand.