Solution, Solid, and Gas Phase Studies on a Nickel Dithiolene System: Spectator Metal and Reactor Ligand.

The syntheses of cationic nickel complexes using N,N'-dimethyl piperazine 2,3-dithione (Me2Dt0) and N,N'-diisopropyl piperazine 2,3-dithione (iPr2Dt0) ligands are reported. These ligands were used in synthesizing bis and tris(dithione)Ni(II) complexes as tetrafluoroborate or hexafluorophosphate salts, i.e., [Ni(iPr2Dt0)2][BF4]2 ([1a][BF4]2), [Ni(iPr2Dt0)2][PF6]2 ([1a][PF6]2), [Ni(Me2Dt0)2][BF4]2 ([1b][BF4]2), [Ni(iPr2Dt0)3][BF4]2 ([2a][BF4]2), and [Ni(iPr2Dt0)3][PF6]2 ([2a][PF6]2), respectively. Complex [2a][PF6]2 was isolated from a methanolic solution of [1a][PF6]2. Compound [1a][BF4]2 crystallizes in a trigonal crystal system (space group, P31/c) and exhibits unique packing features, whereas [2a][BF4]2 crystallizes in a monodinic (P21/n) space group. Cyclic voltammograms of [1a][BF4]2 and [1b][BF4]2 are indicative of four reduction processes assodated with stepwise single-electron reduction of the ligands. Spectroelectrochemical experiments on [1a][BF4]2 exhibit an intervalence charge transfer (IVCT) transition as a spectroscopic signature of the mixed-valence [Ni(iPr2Dt0)-(iPr2Dt1-)]- spedes. Analysis of this IVCT band suggests that this ligand based mixed valence complex, [Ni(iPr2Dt0)-(iPr2Dt1-)]-, behaves more like a traditional dass II/IU metal based mixed-valence complex. The density functional theory (DFT) and time dependent DFT calculations provide a theoretical framework for understanding the electronic structures and the nature of exdted states of the target compounds that are consistent with their spectroscopic and redox properties. Vibrational spectra of [1a]2+ and [2a]2+ were investigated as discrete spedes in the gas phase using infrared multiple photon dissodation (IRMPD) spectroscopy. [ABSTRACT FROM AUTHOR]