Change in molecular shapes of the trinuclear CuII2ZnII complexes on Schiff base reduction: structural and theoretical investigations

Two new trinuclear heterometallic complexes, [(CuL1)2Zn(N3)(μ1,3-N3)]·H2O (1) and [(CuL2)2Zn(N3)(μ1,3-N3)] (2), have been synthesized using [CuL1] and [CuL2] as metalloligands (where H2L1 = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine and H2L2 = N,N′-bis(2-hydroxybenzyl)-1,4-butanediamine). Both complexes were characterized by elemental analysis, different spectroscopic methods and X-ray crystallography. Complexes 1 and 2 possess similar trinuclear angular structures, in which two terminal five-coordinated metalloligands ([CuL1] and [CuL2], respectively) are connected to central Zn(II) through μ2-phenoxido bridges and of the two azido ions, one is terminally coordinated to the Zn atom while the other forms a bridge (μ1,3-N3) between two terminal Cu(II) ions. The molecular structures of 1 and 2 are very different from their unreduced analogues, 1A and 1B, reported previously. Both the reported complexes are trinuclear and the azide ions are terminally coordinated to central Zn(II) in the bent structure of 1B, whereas two end-on bridging azido ions (μ1,1-N3) between the central Zn(II) and terminal Cu(II) metal ions make the shape of 1A linear. These differences have been rationalized by theoretical calculations using the BP86-D3/def2-TZVP level of theory. Moreover, the existence of intramolecular spodium bonds has been investigated in both compounds (1 and 2) where the (μ1,3-N3) bridge acts as an electron donor.