Electrochemical evidence for reversible five-membered electron transfer chains in octahedral chromium complexes

Abstract

The spin Hamiltonian parameters of [Cr(NH3)5X]Z, where X is H20, C1-, Br-, NCS-, or NO3-, and of cis-[Cr(NH3)4XY]Z, where XY is HzO-CI-or C20d2-, have been determined at 295 and 77 K. Some complexes showed considerable variations in the parameters with temperature. For [Cr(NH3)jH20]Z3, where Z is NO3-or clod-, the effect of the counterion on the parameters was investigated. It appeared that the counterion had a considerable influence. Within a tetragonal ligand field model the spin Hamiltonian parameters were calculated by means of second-order perturbation theory. It was found that there was reasonable agreement between the calculated and experimental axial zero-field parameter D if the ligands did not have large spin-orbit constants.

Homoleptic and heteroleptic complexes of chromium(III) containing 4′-diphenylamino-2,2′:6′,2″-terpyridine ligands

“…The synthesis of related pairs of homoleptic and heteroleptic coplexes containing a {Cr(tpy) 2 [29]. [33].…”

“…Although large numbers of metal complexes containing 2,2':6',2''-terpyridine (tpy) metalbinding domains have been reported in the past 80 years, those with chromium(III) remain underexplored since the homoleptic [Cr(tpy) 2 ] n (n = +3, +2, +1, 0, -1) complexes were described in the 1960s [1,2,3,4,5,6]. In 2012, Sproules, Wieghardt and coworkers proposed that in the series [Cr(tpy) 2 ][PF 6 ] n with n = 3, 2 1, 0, all one-electron redox processes are ligand-based with the chromium centre remaining in the +3 oxidation state [7].…”

Metal complexes with non-innocent ligands

“…For example, the metal atom in [Ru(bipy) 3 ] 2+ (bipy is 2,2 H -bipyridyl) is oxidised at the potential of +1.26 V, whereas a series of reduction steps involve the ligand, because the metal d(p) orbital (HOMO) and the ligand p* orbital (LUMO) differ substantially in energy. 4 In contrast, [Cr(bipy) 3 ] 3+ is involved in a series of reduction reactions, 5 which are much more difficult to interpret, because the metal-and ligand-centred orbitals involved in redox processes are comparable in energy. In actuality, the metal atom of [Cr(bipy) 3 ] 3+ is reduced in the first step to form [Cr II (bipy) 3 ] 2+ , and the successive two-electron reduction occurs at the p* orbital of the ligand to give a species described as [Cr II (bipy) 2 3 ] 2+ , but the term`non-innocent' is applicable only to the latter complex.…”

Characterization of metal complexes of 1,10-phenanthroline, 2,2′-bipyridine, and their derivatives by fast atom bombardment mass spectrometry

“…The interest in coorplaces. dination and related compounds stems from their use in the Experimental fields of catalysis (7)(8)(9), chemical analysis (7)(8)(9), medicine were purchased mass spectrometry has been limited, (2,15) because many of from G. Frederic Smith Chemical Co., and used without further purification. Other complexes given in Table 1 were synthesized using them are involatile and thermally labile, although even convenstandard methods (6).…”