Solvent control: dinuclear versus tetranuclear complexes of a bis-tetradentate pyrimidine-based ligand†
Abstract
A new bis-tetradentate acyclic amine ligand LEt has been synthesized from 4,6-bis(aminomethyl)-2-phenylpyrimidine and 2-vinylpyridine. Dinuclear complexes, MnII2LEt(MeCN)(H2O)3(ClO4)4 (1), FeII2LEt(H2O)4(BF4)4 (2), CoII2LEt(H2O)3(MeCN)2(BF4)4 (3), NiII2LEt(H2O)4(BF4)4 (4), NiII2LEt(H2O)4(ClO4)4·8H2O (4′), CuII2LEt(BF4)4·MeCN (5), ZnII2LEt(BF4)2(BF4)2·½MeCN (6), were obtained from 1 : 2 reactions of LEt and the appropriate metal salts in MeCN, whereas in MeOH tetranuclear complexes, MnII4(LEt)2(OH)4(ClO4)4 (7), FeII4(LEt)2(F)4(BF4)4·H2O (8), CoII4(LEt)2(F)4(BF4)4·3H2O (9), NiII4(LEt)2(F)4(BF4)4·4H2O (10), CuII4(LEt)2(F)4(BF4)4·3H2O (11) and ZnII4(LEt)2(F)4(BF4)4 (12), result. Six complexes have been structurally characterized: in all cases each LEt is bis-tetradentate and provides a pyrimidine bridge between two metal centres. As originally anticipated, complexes 1, 4′ and 6 are dinuclear, while 9, 10 and 12 are revealed to be tetranuclear, with two M2(LEt)4+ moieties bridged by two pairs of fluoride anions. Weak to moderate antiferromagnetic coupling between the metal centres is a feature of complexes 2, 3, 4, 8, 9 and 10. The dinuclear complexes 1–6 undergo multiple, mostly irreversible, redox processes. However, the pyrimidine-based dicopper(II) complex 5 undergoes a two electron quasi-reversible reduction, CuII2 → CuI2, and this occurs at a more positive potential [Em = +0.11 V (Epc = −0.03 and Epa = +0.26 V) vs. 0.01 M AgNO3/Ag] than for either of the dicopper(II) complexes of the analogous pyrazine-based ligands.