Combined Experimental and Theoretical Study on Redox-Active d8 Metal Dithione鈥揇ithiolato Complexes Showing Molecular Second-Order Nonlinear Optical Activity

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• 作者：Luca Pilia ; Davide Espa ; Alberto Barsella ; Alain Fort ; Christodoulos Makedonas ; Luciano Marchi貌 ; Maria Laura Mercuri ; Angela Serpe ; Christiana A. Mitsopoulou ; Paola Deplano
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：October 17, 2011
• 年：2011
• 卷：50
• 期：20
• 页码：10015-10027
• 全文大小：1190K
• 年卷期：v.50,no.20(October 17, 2011)
• ISSN：1520-510X

文摘

Synthesis, characterization, NLO properties, and theoretical studies of the mixed-ligand dithiolene complexes of the nickel triad [M(II)(Bz₂pipdt)(mnt)] (Bz₂pipdt = 1,4-dibenzyl-piperazine-3,2-dithione, mnt = maleonitriledithiolato, M(II) = Ni, 1, Pd, 2, Pt, 3) are reported. Molecular structural characterization of 1鈥?b>3 points out that four sulfur atoms are in a slightly distorted square-planar geometry. While the M鈥揝 bond distances are only slightly different, comparison of the C鈥揅 and C鈥揝 bonds in the C₂S₂MS₂C₂ core allows us to point out a significant difference between the C鈥揅 and the C鈥揝 distances in Bz₂pipdt and mnt. These findings suggest assigning a dithiolato character to mnt (pull ligand) and a dithione one (push ligand) to Bz₂pipdt. Cyclic voltammetry of 1鈥?b>3 exhibits two reversible reduction waves and a broad irreversible oxidation wave. These complexes are characterized in the visible region by a peak of moderately strong intensity, which undergoes negative solvatochromism. The molecular quadratic optical nonlinearities were determined by the EFISH technique, which provided the following values 渭尾_位 (10^鈥?8 esu) = 鈭?436 (1), 鈭?450 (2), and 鈭?950 (3) converted in 渭尾₀ (10^鈥?8 esu) = 鈭?63 (1), 鈭?84 (2), and 鈭?22 (3), showing that these complexes exhibit large negative second-order polarizabilities whose values depend on the metal, being highest for the Pt compound. DFT and TD-DFT calculations on 1鈥?b>3 allow us to correlate geometries and electronic structures. Moreover, the first molecular hyperpolarizabilities have been calculated, and the results obtained support that the most appealing candidate as a second-order NLO chromophore is the platinum compound. This is due to (i) the most extensive mixture of the dithione/metal/dithiolato orbitals, (ii) the influence of the electric field of the solvent on the frontier orbitals that maximizes the difference in dipole moments between the excited and the ground state, and (iii) the largest oscillator strength in the platinum case vs nickel and palladium ones.