Contrary to expectations based on the spectrochemical series, H2O is found to be a significantly weaker field ligand than OH- in the magnetochemical series ranking of ligand field strengths based on the spin states of iron(III) tetraphenylporphyrin complexes. The preparation and characterization of the [Fe(H2O)(TPP)]+ ion and the spectroscopic identification of Fe(OH)(TPP) have made this assessment possible. These two species were previously thought to be unattainable because of the facile formation of the well-known μ-oxo dimer, (TPP)Fe-O-Fe(TPP). However, the special characteristics of single equivalents of water under high acidity, relevant to metalloenzyme active sites and superacidity, make them accessible in benzene solution. Their 1H NMR β-pyrrole chemical shifts at -43 and +82 ppm indicate admixed-intermediate S = 3/2, 5/2 and high S = 5/2 spin states for the aqua and hydroxo species, respectively. The X-ray crystal structure of the aqua complex has been determined for [Fe(H2O)(TPP)] [CB11H6Cl6] and is consistent with the high degree of S = 3/2 character indicated by the NMR measurement, Mossbauer spectroscopy (ΔE(q) = 3.24 mm·s-1), and magnetic susceptibility (μ(eff) = 4.1 μ(B)). The anhydrous precursor to these species is the 'nearly bare' iron(III) porphyrin complex Fe(CB11H6Br6)(TPP). Judged by its magnetic parameters (δ(pyrrole) = -62 ppm, ΔE(q) = 3.68 mm·s-1, μ(eff) = 4.0 μ(B)) it attains the long sought essentially 'pure' S = 3/2 spin state. The magnetochemical ranking of ligand field strengths in five-coordinate high-spin and admixed-intermediate-spin iron(III) porphyrins is useful because it more closely reflects the intuitive field strengths of crystal field theory than does the usual spectrochemical ranking, which is controlled largely by π effects in octahedral low-spin d(π)6 complexes.

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)(C6H6)][CB11H6Br6] · 3.5C6H6 (1), [Fe(TPP)(C7H8)][CB11H6Cl6] · 2C7H8 (2), [Fe(TPP)(C8H10)][Ag(CB11H6Br6)2] · arene (3), and [Fe(TPP)(C60)][F20-BPh4] · 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.

Discrete forms of repetitive thought (RT), such as worry and reflection, can be characterized along basic dimensions of valence (positive vs. negative) and purpose (searching vs. solving). In addition, people can be characterized as high or low in their tendency to engage in RT. This dimensional model has been demanding to assess, and a smaller number of items that could stand in for a large battery would make measurement more accessible. Using four samples (N = 1,588), eight items that assess RT valence, purpose, and total in a circumplex model were identified. Across these and other samples, the dimensions were adequately reliable and valid with regard to assessment via large RT battery, other measures of RT, and depressive symptoms. The accessibility of dimensional assessment of RT using this smaller number of items should facilitate work on questions about the qualities of RT that predict mental and physical health.