Interplay of supramolecular organization, metallophilic interactions, phase changes, and luminescence in four polymorphs of IrI(CO)2(OC(CH3)CHC(CH3)N(p-tol)).

Four polymorphs of IrI(CO)2(OC(CH3)CHC(CH3)N(p-tol)) have been characterized by single crystal X-ray crystallography. While all contain the same molecular unit with no significant structural variations within the molecules, all show different degrees of metallophilic interactions between the planar molecules. Three of these (the amber, the pale yellow, and the orange forms) are stable at room temperature, while the fourth, the L. T. orange form, is only obtained by cooling the orange polymorph. At 77 K, the amber, pale yellow, and L. T. orange polymorphs show intense luminescence. The variations in the luminescence among the polymorphs are considered in the context of the structural differences between them and the nature of the metallophilic interactions between the iridium centers. These results demonstrate how subtle variations in molecular organization can affect the physical properties of planar d8 transition metal compounds, which are an important class of lumiphores.

A reversible polymorphic phase change which affects the luminescence and aurophilic interactions in the gold (I) cluster complex, [mu3-S(AuCNC7H13)3](SbF6).

Crystallographic examination of [mu3-S(AuCNC7H13)3](SbF6) shows that it undergoes a reversible phase change from orthorhombic to monoclinic upon cooling. At 190 K, the structure shows that two cations self-associate to form a pseudo-octahedral array of six gold atoms connected by both intra- and interionic aurophilic interactions. On cooling, the clusters become less symmetric, and in one, the interionic Au...Au separations increase, while they decrease in the second cluster. The luminescence of crystalline [mu3-S(AuCNC7H13)3](SbF6) shows corresponding changes in emission, with two emissions of similar lifetimes but with different excitations at 77 K, but only a single emission at 298 K. In contrast, [mu3-S(AuCNC6H11)3](PF6), which has a similar structure to that of the high-temperature form of [mu3-S(AuCNC7H13)3](SbF6), does not undergo a phase change or change in its luminescence upon cooling.

Electron and hydrogen-atom self-exchange reactions of iron and cobalt coordination complexes.

Reported here are self-exchange reactions between iron 2,2'-bi(tetrahydro)pyrimidine (H(2)bip) complexes and between cobalt 2,2'-biimidazoline (H(2)bim) complexes. The (1)H NMR resonances of [Fe(II)(H(2)bip)(3)](2+) are broadened upon addition of [Fe(III)(H(2)bip)(3)](3+), indicating that electron self-exchange occurs with k(Fe,e)(-) = (1.1 +/- 0.2) x 10(5) M(-1) s(-1) at 298 K in CD(3)CN. Similar studies of [Fe(II)(H(2)bip)(3)](2+) plus [Fe(III)(Hbip)(H(2)bip)(2)](2+) indicate that hydrogen-atom self-exchange (proton-coupled electron transfer) occurs with k(Fe,H.) = (1.1 +/- 0.2) x 10(4) M(-1) s(-1) under the same conditions. Both self-exchange reactions are faster at lower temperatures, showing small negative enthalpies of activation: DeltaH++(e(-)) = -2.1 +/- 0.5 kcal mol(-1) (288-320 K) and DeltaH++(H.) = -1.5 +/- 0.5 kcal mol(-1) (260-300 K). This behavior is concluded to be due to the faster reaction of the low-spin states of the iron complexes, which are depopulated as the temperature is raised. Below about 290 K, rate constants for electron self-exchange show the more normal decrease with temperature. There is a modest kinetic isotope effect on H-atom self-exchange of 1.6 +/- 0.5 at 298 K that is close to that seen previously for the fully high-spin iron biimidazoline complexes.(12) The difference in the measured activation parameters, E(a)(D) - E(a)(H), is -1.2 +/- 0.8 kcal mol(-1), appears to be inconsistent with a semiclassical view of the isotope effect, and suggests extensive tunneling. Reactions of [Co(H(2)bim)(3)](2+)-d(24) with [Co(H(2)bim)(3)](3+) or [Co(Hbim)(H(2)bim)(2)](2+) occur with scrambling of ligands indicating inner-sphere processes. The self-exchange rate constant for outer-sphere electron transfer between [Co(H(2)bim)(3)](2+) and [Co(H(2)bim)(3)](3+) is estimated to be 10(-)(6) M(-1) s(-1) by application of the Marcus cross relation. Similar application of the cross relation to H-atom transfer reactions indicates that self-exchange between [Co(H(2)bim)(3)](2+) and [Co(Hbim)(H(2)bim)(2)](2+) is also slow, < or =10(-3) M(-1) s(-1). The slow self-exchange rates for the cobalt complexes are apparently due to their interconverting high-spin [Co(II)(H(2)bim)(3)](2+) with low-spin Co(III) derivatives.