title: Combined Mössbauer spectral and density functional theory determination of the magnetic easy-axis in two high-spin iron(II) 2-pyrazinecarboxylate complexes.
abstract: A combination of density functional theory (DFT) calculations and Mössbauer spectroscopy has been used to determine that the magnetic easy-axis is coincident with its crystallographic c-axis in [Fe(pca)(2)(py)(2)] x py, where pac is the 2-pyrazinecarboxylate ligand. This easy-axis bisects the approximately axial O-Fe-O coordination axes of molecules adjacent to each other along the b-axis. In {[Fe(pca)(2)(H(2)O)] x H(2)O}(n) the easy magnetic axis is not coincident with any of its crystallographic axes nor with the Fe-O(water) coordination axis, but is coincident with one of the Fe...Fe axes in the crystal structure. The DFT calculations, which use the B3LYP functional and the 6-311++G(d,p) basis set, yield s-electron probability densities and electric field gradient tensors for the iron(II) ion that are in excellent agreement with the observed iron-57 Mössbauer spectral isomer shifts and quadrupole interactions. The gas phase results are very similar for calculations based either on the X-ray structures of the two complexes or on their optimized structures; the optimized structures indicate that the iron to ligand bond distances increase in the absence of any solid-state lattice interactions. The results of a normal coordinate vibrational mode analysis of the two optimized structures are compared with the observed infrared spectra.
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology, University of Missouri, Rolla, Missouri 65409-0010, USA. glong@mst.edu
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Long
authors.forename: Stefania
authors.initials: S
authors.lastname: Tanase
authors.forename: Françoise
authors.initials: F
authors.lastname: Remacle
authors.forename: Ganga
authors.initials: G
authors.lastname: Periyasamy
authors.forename: Fernande
authors.initials: F
authors.lastname: Grandjean
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D008956:Models, Chemical; D008958:Models, Molecular; D011719:Pyrazines / Q000737:chemistry*; D015204:Spectroscopy, Mossbauer
chemical_list: D002264:Carboxylic Acids; D005296:Ferrous Compounds; D008024:Ligands; D011719:Pyrazines