Bringing an important macrocycle into a polyoxometalate matrix: synthesis, crystal structure, spectroscopy and electrochemistry of [Co<SUP>III</SUP>(transdiene)(Cl)<SUB>2</SUB>]<SUB>2</SUB>[Mo<SUB>6</SUB>O<SUB>19</SUB>], [Ni<SUP>II</SUP>(transdiene)][W<SUB>6</SUB>O<SUB>19</SUB>]·DMSO·DCM and [Zn<SUP>II</SUP>(transdsiene)(Cl)]<SUB>2</SUB>[W<SUB>6</SUB>O<SUB>19</SUB>]

Three polyoxometalate based ion pair solids (1-3), in which CoIII (d6), NiII (d8) and ZnII (d10) complexes of a tetra-aza macrocycle, Me6-trans-[14]-diene act as the cationic moieties, have been reported. The title complexes, formulated as [Co (C16H32N4)(Cl)2]2[Mo6O19] (1), [Ni(C16H32N4)][W6O19]·DMSO·DCM (2) and [Zn(C16H32N4)(Cl)]2[W6O19] (3) (C16H32N4 = Me6-trans-[14]-diene), are the first crystallographic paradigms where transition metal complexes of a Schiff condensed tetra-aza macrocycle have been associated with an isopolyanion, [M6O19]2- (M = Mo(VI) and W(VI)). Compounds 1-3 have been characterized through routine spectroscopic analyses including elemental analysis and their structures have been unambiguously determined through single crystal X-ray crystallography. The molecules of compound 1 assemble obeying P11̅(#2) space symmetry, whereas those of compounds 2 and 3 follow the higher symmetrical ensemble P21/c (#14). The ESR spectral studies of compounds 1-3 have revealed their diamagnetic (low-spin) nature. The last part of this article describes the electrochemical properties of the title compounds