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

A new bis-tetradentate acyclic amine ligand L-Et has been synthesized from 4,6-bis(aminomethyl)-2-phenylpyrimidine and 2-vinylpyridine. Dinuclear complexes, (Mn2LEt)-L-II(MeCN)(H2O)(3)(ClO4)(4) (1), (Fe2LEt)-L-II(H2O)(4)(BF4)(4) (2), (Co2LEt)-L-II(H2O)(3)(MeCN)(2)(BF4)(4) (3), (Ni2LEt)-L-II(H2O)(4)(BF4)(4) (4), (Ni2LEt)-L-II(H2O)(4)(ClO4)(4)center dot 8H(2)O (4 ), (Cu2LEt)-L-II(BF4)(4)center dot MeCN (5), (Zn2LEt)-L-II(BF4)(2)(BF4)(2)center dot 1/2MeCN (6), were obtained from 1 : 2 reactions of L-Et and the appropriate metal salts in MeCN, whereas in MeOH tetranuclear complexes, Mn-4(II)(L-Et)(2)(OH)(4)(ClO4)(4) (7), Fe-4(II)(L-Et)(2)(F)(4)(BF4)(4)center dot 5/2H(2)O (8), Co-4(II)(L-Et)(2)(F)(4)(BF4)(4)center dot 3H(2)O (9), Ni-4(II)(L-Et)(2)(F)(4)(BF4)(4)center dot 4H(2)O (10), Cu-4(II)(L-Et)(2)(F)(4)(BF4)(4)center dot 3H(2)O (11) and Zn-4(II)(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 M-2(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-II 2 -> Cu-2(I), and this occurs at a more positive potential [(Em) = +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.