Solvent control: dinuclear versus tetranuclear complexes of a bis-tetradentate pyrimidine-based ligand

Abstract

A new bis-tetradentate acyclic amine ligand L^Et has been synthesized from 4,6-bis(aminomethyl)-2-phenylpyrimidine and 2-vinylpyridine. Dinuclear complexes, Mn^II₂L^Et(MeCN)(H₂O)₃(ClO₄)₄ (1), Fe^II₂L^Et(H₂O)₄(BF₄)₄ (2), Co^II₂L^Et(H₂O)₃(MeCN)₂(BF₄)₄ (3), Ni^II₂L^Et(H₂O)₄(BF₄)₄ (4), Ni^II₂L^Et(H₂O)₄(ClO₄)₄·8H₂O (4′), Cu^II₂L^Et(BF₄)₄·MeCN (5), Zn^II₂L^Et(BF₄)₂(BF₄)₂·½MeCN (6), were obtained from 1 : 2 reactions of L^Et and the appropriate metal salts in MeCN, whereas in MeOH tetranuclear complexes, Mn^II₄(L^Et)₂(OH)₄(ClO₄)₄ (7), Fe^II₄(L^Et)₂(F)₄(BF₄)₄·H₂O (8), Co^II₄(L^Et)₂(F)₄(BF₄)₄·3H₂O (9), Ni^II₄(L^Et)₂(F)₄(BF₄)₄·4H₂O (10), Cu^II₄(L^Et)₂(F)₄(BF₄)₄·3H₂O (11) and Zn^II₄(L^Et)₂(F)₄(BF₄)₄ (12), result. Six complexes have been structurally characterized: in all cases each L^Et 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(L^Et)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, Cu^II₂ → Cu^I₂, and this occurs at a more positive potential [E_m = +0.11 V (E_pc = −0.03 and E_pa = +0.26 V) vs. 0.01 M AgNO₃/Ag] than for either of the dicopper(II) complexes of the analogous pyrazine-based ligands.