No abstract

Benzene, toluene, p-xylene, and [60]fullerene are shown to be weak ligands to a hard metal such as iron(III) in Fe(TPP) + cation (TPP) tetraphenylporphyrinate). X-ray crystal structures of [Fe(TPP)-(C 6 H 6)][CB 11 H 6 Br 6 ]‚3.5C 6 H 6 (1), [Fe(TPP)(C 7 H 8)][CB 11 H 6 Cl 6 ]‚2C 7 H 8 (2), [Fe(TPP)(C 8 H 10)][Ag(CB 11 H 6 Br 6) 2 ]‚ arene (3), and [Fe(TPP)(C 60)][F 20-BPh 4 ]‚2.5dichlorobenzene (4) show distinctively short Fe‚‚‚C contacts, in the range 2.65-2.95 Å, which distinguish ligation from π-π cocrystallized solvation. Dihedral angles between the arene and metalloporphyrin planes are also diagnostic of ligand versus solvate roles. The essential features of the arene coordination can be faithfully reproduced using density functional theory. In contrast to alkali metal cation/π-arene interactions, a component of the covalent bonding can be recognized. In a broader context, this study suggests that solvents such as benzene should always be viewed as potential ligands in the presence of coordinatively unsaturated cations. The common use in supramolecular chemistry of the term "noncovalent" to describe entities with metal-ligand bonds is viewed as misleading.

Articles you may be interested inElectronic processes during ion-beam sputtering of metals studied by resonance laser ionization mass spectrometry AIP Conf.Electron spin resonance measurements have been made on a number of copper (II) and vanadyl porphyrins. The spectra recorded at a sample temperature of 77°K have low field components attributed to I:!.M = 2 transitions which provided evidence for the existence of dimer species in solution. In one case, namely copper hematoporphyrin(IX) dimethylester, a resonance centered at 950 G is thought to be due to a I:!.M = 3 transition arising from a trimer species. The theory of the ESR spectra of dipolar coupled S =! transition metal ions with particular reference to systems involving copper (II) and vanadyl ions is outlined. The treatment has been developed to the point which makes a computer simulation of the I:!.M = 1 and I:!.M = 2 transitions possible in the systems studied. An important product of this is the evaluation of the distance between the metal ions in the dimeric species. The variation of this distance in the metalloporphyrins studied is related to subtle changes in structure brought about by the various substituents in the macrocylic system as well as to the nature of the transition metal ion.

No abstract