A di-μ-phenoxo bridged zinc dimer with unfamiliar spatial arrangement

A curious dimeric complex, Zn2(H2SB)2 · 3H2O · Me2CO [H4SB: N,N′-bis(2,5-dihydroxybencylidene)-1,4-diaminobutane], was synthesised by self-assembly reaction between H2SB2− and Zn2+ ions electrochemically generated. Interestingly, the zinc ions reside in chemically identical N2O3 coordination environments, but adopting two different geometries: trigonal bipyramidal and square based pyramidal. This peculiar molecule is non-centrosymmetric, but owns a pseudo twofold axis normal to the centre of the Zn2O2 metallacycle. This unfamiliar arrangement of the dimer leads to keep both tetra-methylene spacers at the same side of the plane formed by the metallacycle, resulting in a cavity where both zinc ions appear uncovered.