No abstract

No abstract

This Account reports recent progress in the study of some approximately 20 heterometal derivatives of [Mo3S4(H2O)9]4+ with reference also to W and Se analogues. Single cubes (3:1) and corner-shared double cubes (6:1), as well as dimers of the 3:1 single cubes, are considered. A classification of the heterometals as subtypes A, B, and C is introduced.

Cuboidal cluster complexes having M 4 Q 4 cores made up of transition and main group metals (M), and non-metallic e.g. chalcogenide elements (Q), constitute a rapidly expanding area of inorganic chemistry. Extensive preparation, structural and reactivity studies have been carried out on the Group 6 metals (M ‫؍‬ Mo, W) and chalcogenide (Q ‫؍‬ S, Se, Te) clusters, and are the main focus of this perspective. The aqueous solution chemistry provides an important reference point in considering redox and other relevant properties.

Reaction of Scenedesmus obliquus plastocyanin with excess [Ru(trpy)(L)(H2O)]2+ (trpy = 2,2‘:6‘,2‘‘-terpyridine; L = 2,2‘-bipyridine, 4,4‘-(CH3)2-2,2‘-bipyridine, 4,5,4‘,5‘-(CH3)4-2,2‘-bipyridine) affords Ru(trpy)(L)(His59)Pc as the main product. These RuPc derivatives are luminescent with λmax(emission) ∼ 650 nm and lifetimes of (Cu+) in the range 110−140 ns. Photogenerated *Ru2+PcCu2+ is quenched by *Ru2+ → Cu2+ electron transfer (ET) to produce Ru3+PcCu+; intramolecular ET was monitored by transient absorption at 590 (Cu+ → Cu2+) and 424 nm (Ru3+ → Ru2+). The Cu+ to Ru3+ ET rate constants (k ET) are as follows:  2.9(2) × 107 s-1 (L = bpy); 2.3(2) × 107 s-1 (L = dmbpy); and 1.9(2) × 107 s-1 (L = tmbpy). Activationless rates (−ΔG° ∼ λ ∼ 0.70−0.75 eV) are consistent with coupling-limited tunneling through a β sheet at an estimated Cu−Ru distance of 15.6 Å (calcd k ET = 107 s-1 for a tunneling decay constant of 1.1 Å-1). Biphasic Cu+ → Ru3+ ET kinetics (k ET > 107 and ∼104 s-1) were observed after flash-quench generation of Ru3+PcCu+ in acidic solutions. The slow phase kinetics are markedly temperature and pH dependent:  the activation parameters (ΔH ⧧ = 43.1 kJ/mol; ΔS ⧧ = −17 J/(K·mol) for L = bpy) suggest that the trigonal low-pH form of Cu+ reorganizes to the tetrahedral form prior to oxidation to the blue Cu2+ state.