A rational approach of modulating the easy-plane magnetic anisotropy of mononuclear pentagonal bipyramidal Co single molecule magnets (SMMs) has been revealed in this paper. A class of three new pentagonal-bipyramidal complexes with formulas [Co(Hdaps)(MeOH)] (1), [Co(Hdaps)(NCS)(MeOH)]·(ClO)·(MeOH) (2), and [Co(Hdaps)(NCS)]·(MeOH) (3) (Hdaps = 2,6-bis(1-salicyloylhydrazonoethyl) pyridine) were studied. In these complexes, the axial positions are successively replaced by different O and N donar ligands in a systematic way. Detailed magnetic measurements disclose the existence of large easy-plane magnetic anisotropy and field-induced slow magnetic relaxation behavior. Both experimental and ab initio theoretical calculations display that easy-plane magnetic anisotropy is maintained upon variation of coordination environments. Nevertheless, the magnitude of the D value was found to be increased in the case of weaker axially coordinated σ-donor ligands and a more symmetrical equatorial ligand. Additionally, the detailed investigation of field and temperature dependence of relaxation time revealed that quantum tunnelling of magnetization is the predominant process for slow magnetic relaxation and the Raman process is significant which explicates the thermal dependence. Magnetic dilution experiments have been performed to eliminate the possible influence of intermolecular interactions on magnetic behaviors of adjacent Co centers.

This paper explores the quantum fluid dynamical ͑QFD͒ representation of the time-dependent Schrödinger equation for the motion of a wave packet in a high dimensional space. A novel alternating direction technique is utilized to single out each of the many dimensions in the QFD equations. This technique is used to solve the continuity equation for the density and the equation for the convection of the flux for the quantum particle. The ability of the present scheme to efficiently and accurately describe the dynamics of a quantum particle is demonstrated in four dimensions where analytical results are known. We also apply the technique to the photodissociation of NOCl and NO 2 where the systems are reduced to two coordinates by freezing the angular variable at its equilibrium value.

The reaction of Fe(NCS) 3 prepared in situ in MeOH with 5-X-SalEen ligands (5-X-SalEen = condensation product of 5-substituted salicylaldehyde and N-ethylethylenediamine) provided three Fe(III) complexes, [Fe(5-X-SalEen) 2 ]NCS; X=Me (1), X=Br (2), X=OMe (3). All the complexes reveal similar structural features but a very different magnetic profile. Complex 1 shows a gradual spin crossover while complexes 2 and 3 show a sharp spin transition. The T 1/2 for complex 2 is 237 K while for complex 3 it is much higher with a value of 361 K. The spin transition temperature is shifted towards higher temperature with increasing electron-donation ability of the ligand substituents. This experimental observation has been rationalized with DFT calculations. UV-Vis and cyclic voltammetry studies support the fact that the electron density on the ligand increases from Me to Br to OMe substituents. To understand the change in spin states, temperature-dependent EPR spectra have been recorded. The spin state equilibrium in the liquid state has been probed with Evans NMR spectroscopic method, and thermodynamic parameters have been evaluated for all complexes.