New Directions in the Coordination Chemistry of Verdazyl Radicals

A series of palladium and platinum complexes of verdazyl radicals were prepared to study the intermolecular magnetic exchange coupling. Reaction of bidentate verdazyl radicals with (RCN)2MCl2 (R = Me or Ph; M = Pd or Pt) yielded square planar (verdazyl)MCl2 complexes. The isolated complexes crystallized in either an infinite 1D array or as loosely associated pi-stacked dimer pairs. Molecules stacked with either M--M or M--N(verdazyl) close contacts. Molecules that stacked with a M-M close contact exhibited weak antiferromagnetic coupling. Molecules that stacked with a M-- N(verdazyl) close contact had coupling that was an order-of-magnitude weaker, but the type of exchange was also metal dependent. While the palladium complex exhibited weak antiferromagnetic coupling, the exchange in the analogous platinum complex was ferromagnetic. The difference between the two was attributed to increased spin leakage onto the platinum centre relative to palladium. The differing electronic behaviour of the two metals was evident in the data from EPR and UV/vis spectroscopies.;Ruthenium complexes of a verdazyl radical were prepared by the reaction of a bidentate verdazyl with Ru(L)2(MeCN)2 (L = acac or hfac). The complexes were isolated in two or more oxidation states and all characterized by FT-IR, UV/vis/NIR, and EPR spectroscopies, and their structures determined by X-ray crystallography. Experimental data was further explained and supported with time-dependant DFT calculations which were performed by Dr. A. B. P. Lever at York University, Toronto, Ontario. When the complex contained an electron-rich metal fragment, Ru(acac)2, noninnocent behaviour was observed. There was a large degree of orbital mixing, so that the spin distribution was approximately 56% ligand and 39% metal. The contrasting complex with the electron-poor fragment, Ru(hfac)2, behaved more innocently, the majority of charge was localized and the spin was calculated to be 89% ligand and only 11% metal.;Verdazyl-bridged diruthenium complexes were prepared from a bisbidentate verdazyl and Ru(L)2(MeCN)2 (L = acac or hfac) to study the effect of a neutral radical bridge on mixed-valence properties. Structural data from X-ray crystallography, spectroscopic data from EPR, FT-IR, and UV/vis/NIR spectroscopies, and comparison to the mononuclear ruthenium-verdazyl complexes were used to assess the charge distribution in these complexes. The complex in which the verdazyl ligand bridged two electron-rich metal centres exhibited a NIR absorption at approximately 1716 nm. Together, this long wavelength transition and the structural data indicate a delocalized electronic structure, [RuIII--vd---RuII ↔ RuII--vd·RuII ↔ RuII--vd--RuIII]. The EPR spectrum was also consistent with the delocalization of ligand spin onto the ruthenium centres. With the verdazyl bridging two electron-poor Ru(hfac)2 fragments, the spin is ligand-based and best described as RuII--vd ·RuII. Like the analogous mononuclear complexes, the dinuclear complexes were each isolated in their other accessible oxidation states, the acac complex in its 0, +1, and +2 states and the hfac complex in its -1, 0, and +1 states.