Insights into Single-Molecule-Magnet Behavior from the Experimental Electron Density of Linear Two-Coordinate Iron Complexes.

A breakthrough in the study of single-molecule magnets occurred with the discovery of zero-field slow magnetic relaxation and hysteresis for the linear iron(I) complex [Fe(C(SiMe))] (1), which has one of the largest spin-reversal barriers among mononuclear transition-metal single-molecule magnets. Theoretical studies have suggested that the magnetic anisotropy in 1 is made possible by pronounced stabilization of the iron d orbital due to 3d -4s mixing, an effect which is predicted to be less pronounced in the neutral iron(II) complex Fe(C(SiMe)) (2). However, experimental support for this interpretation has remained lacking.

Predictive concept for lone-pair distortions - DFT and vibronic model studies of AXn-(n-3) molecules and complexes (A = NIII to BiIII; X = F-I to I-I; n = 3-6).

The stereochemical and energetic consequences of the lone-pair effect in the title molecules and complexes have been studied by DFT calculations based on a vibronic coupling concept. The anionic complexes were examined as bare entities and, more realistically, in a polarizable charge-compensating solvent continuum. The tendency for distortions of AX3 compounds away from the high-symmetry parent geometry becomes more pronounced the larger the chemical hardness of a molecule and its constituents is; on the other hand, anionic complexes AXn-(n-3) (n = 4-6) become softer and less susceptible to distortion as compared to the corresponding AX3 molecule, the larger the coordination number and the anionic charge are.