Macrocyclic tetramanganese(II) complexes with alkoxy and chloro or azido bridges; X-ray crystal structures of [Mn2(HL)(Cl)2]2(ClO4)2·2dmf·H2O and [Mn2(HL)(N3)2]2(ClO4)2·3MeCN (H2L = 1,7,14,20-tetramethyl-2,6,15,19-tetra-aza[7,7](2,6)pyridinophane-4,7-diol; dmf = dimethylformamide)