Spin density of the hexacyanochromate(III) ion measured by polarized neutron diffraction

Abstract

A polarized neutron diffraction experiment on Cs2KCr(CN)6 yielded 437 unique magnetic structure factors, which were analyzed in terms of valence orbital or alternatively multipole populations on all atoms. Apart from a small population on the potassium atom, the spin density is described by a model corresponding to octahedral symmetry in the Cr(CN)63" ion with 3d and 4p orbitals on the chromium atom and (sp)" and pT orbitals on carbon and nitrogen atoms. The chromium configuration is t2g2- 30(3,eg0•12(4)4p°-83(7) with the 3d orbitals expanded 8% radially relative to the free ion. The ligand atom and orbital populations are C" = -0.044 (8), C" = -0.044 (5), N, = -0.034 (7), and N, = 0.087 (4). This complex spin density pattern is incompatible with molecular orbital theories of bonding that do not accommodate spin polarization effects, for example restricted Hartree-Fock. There is negative spin in the ligand framework and net positive spin in the orbitals and in the metal 3d orbitals, with the 3dr (t2g) population less than the free-ion value of 3.00. These features are compatible with a model involving back-bonding in the expected direction, which delocalizes spin from the t2g to ligand orbitals, together with spin polarization of about the same magnitude in the Cr-CN -bond. An approximate unrestricted calculation by the DVmethod shows fair agreement with our results, particularly in the cyanide ligand region. These results indicate that in this strongly covalent ion the electron-electron correlation effects on the spin distribution are of the same magnitude as the covalence effects.

Bimetallic Molecular-Based Magnetic Materials

“…Theoretical calculations beyond the SCF approximation on [Cu(pba0H}]2-predict negative spin densities around the carbon atoms of the oxamato groups. Such negative spin densities were found through polarized neutron diffraction in the trivalent hexacyanometallates [M(CN)6]3- [13][14][15].…”

Organometallic Compounds of Chromium, Molybdenum and Tungsten without Carbonyl Ligands

“…165 The former study shows that the [Cr(CN) 6 ] 3 " ion is substantially octahedral. To a first approximation the complex ion consists o f a Cr(t 2g 3 e g°) atom surrounded by six free ion-like cyanide ions.…”

Probing the Local Magnetic Structure of the [FeIII(Tp)(CN)3]− Building Block Via Solid‐State NMR Spectroscopy, Polarized Neutron Diffraction, and First‐Principle Calculations

“…[9][10][11][12][13] Af ew years ago, we undertook af undamental study of the [Fe III (Tp)(CN) 3 ] À building block with the aim of gaining a deeper understanding of its properties by probing the magnetism at the local level. [19][20][21] To gain information on the ligand spindensity distribution, experimentald iffractiona nalysist echniques can be also combined with quantum chemistry. The rationalization of these macroscopic magnetic properties is then commonlya ddressed by phenomenological approaches based on spin Hamiltonian models.…”