Structural insights and photophysical properties of mononuclear and pentanuclear Zn(II) acetate complexes with pyridyl-based thiazolyl-hydrazones

The solid state structures of zinc complexes with HLS1 and HLS3 ligands are reported, where HLS1 is 2-(2(pyridin-2-ylmethylene)hydrazinyl)-4-fenil-1,3-thiazole and HLS3 is 2-(2-(pyridin-2-ylmethylene)hydrazinyl)-4(4-methylphenyl)-1,3-thiazole. Structurally similar ligands form complexes of different structures with general formulas [Zn5(LS1)4(AcO)6] (1-AcO) and [Zn(LS3)(AcO)(H2O)] (3-AcO). The pentacoordinated complex 3-AcO exhibits NNN tridentate ligand coordination mode, with additional oxygen donor atoms from a water molecule and acetate anion. The structure of 1-AcO is unique as it is the first example of a pentanuclear complex with pyridyl-based thiazolyl-hydrazone ligands, containing an unprecedented centrosymmetric Zn3(AcO)6 cluster. Photophysical studies showed that 1-AcO is not photoactive, while 3-AcO displayed photoluminescent emission, attributed to ligand-based transitions as determined by time-dependent density functional theory (TD-DFT) calculations. This study underscores the role of molecular symmetry in predicting the photoactivity of at least Zn (II) complexes containing photo-inactive ligands.