Square-planar mixed ligand nickel dithiolenes as second order non-linear chromophores: synthesis and characterisation of [Ni(Me2pipdt)(dddt)]

The novel [Ni(Me₂pipdt)(dddt)] complex based on the Me ₂pipdt (1,4-dimethylpiperazine-3,2-dithione) and dddt (5,6-dihydro-1,4-dithine-2,3-dithiolate) ligands has been synthesised and characterised. Structural data, vibrational marker, solvatochromic behaviour of the typical absorption in the near infrared region, and approximate theoretical calculations suggest that an unbalanced electron distribution at the dithiolene core occurs in the ground and excited states. In particular, the dddt ligand gives a prevailing contribution to the HOMO, and Me₂pipdt to the LUMO. The charge-transfer character of the HOMO-LUMO transition makes this complex a potential second-order non-linear optic chromophore.