Determination of d-Orbital Populations in a Cobalt(II) Single-Molecule Magnet Using Single-Crystal X-ray Diffraction

Abstract

The tetrahedral cobalt(II) compound (PhP)[Co(SPh)] was the first mononuclear transition-metal complex shown to exhibit slow relaxation of the magnetization in zero external magnetic field. Because the relative populations of the d orbitals play a vital role in dictating the magnitude of the magnetic anisotropy, the magnetic behavior of this complex is directly related to its electronic structure, yet the exact role of the soft, thiophenolate ligands in influencing the d-electron configuration has previously only been investigated via theoretical methods. To provide detailed experimental insight into the effect of this ligand field, the electron density distribution in this compound was determined from low-temperature, single-crystal X-ray diffraction data and subsequent multipole modeling. Topological analysis of the electron density indicates significant covalent contributions to the cobalt-sulfur bonds. The derived d-orbital populations further reveal a fully occupied d orbital, minor d orbital population, and nearly equal population of the d , d, and d orbitals. Notably, we find that an electrostatic interaction between Co(II) and one hydrogen atom from a thiophenolate group in the xz plane increases the energy of the d orbital, leading to the nearly equal population with d and strong magnetic anisotropy.

Field-induced slow relaxation of magnetization in the S = 3/2 octahedral complexes trans-[Co{(OPPh2)(EPPh2)N}2(dmf)2], E = S, Se: effects of Co–Se vs. Co–S coordination

“…22,31 It should be stressed that the tetrahedral S = 3/2 (PPh 4 ) 2 [Co(SPh) 4 ] complex 32,33 bearing a Co(II)S 4 core, was the first mononuclear 3d metal complex to exhibit slow relaxation of its magnetization in the absence of a Direct Current (DC) magnetic field. [34][35][36][37] Along these lines, tetrahedral [Co{(EP i Pr 2 ) 2 N} 2 ], E = S, 38 Se, 38 Te, 39 complexes, bearing dichalcogenidoimidodiphosphinato ligands 40 and Co(II)E 4 cores, exhibit slow relaxation of their magnetization, which was also observed in the absence of DC magnetic field for the E = Se, Te, complexes. On the other hand, high-spin, S = 3/2, octahedral Co(II) complexes exhibit magnetic anisotropy that can be tuned through appropriate structural modifications, for instance axial elongation or compression of an octahedral coordination sphere, leading to axial anisotropy (very small Δ rh ) and the presence of either easy axis (Δ ax < 0) or easy plane (Δ ax > 0), of magnetization, respectively (Δ ax is the axial and Δ rh the rhombic crystal field parameter, vide infra).…”

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

“…[14] Indeed, the magnetic properties of molecular materials are mostly determined from bulk measurements that only give access to macroscopic behavior. [22,23] Another alternative experimental methodi sN MR spectroscopy. [15] For example, EPR spectroscopy can also provide interesting local information,s uch as the magnetic anisotropy of the ground state.…”

“…A large panel of complexes with various cyanido building blocks have already been investigated by this technique, but very approximate information was obtained on the spin‐density extension on the ligands . To gain information on the ligand spin‐density distribution, experimental diffraction analysis techniques can be also combined with quantum chemistry . Another alternative experimental method is NMR spectroscopy.…”

Aspherical and covalent bonding character of d electrons of molybdenum from synchrotron x-ray diffraction

“…The spatial and energetic structures of d-electrons have been largely investigated both experimentally and theoretically. The distribution of d-electrons in 3d-transition metals [4][5][6][7][8][9] and their complexes [10,11] have been observed by experimental charge density studies. Spectroscopic studies of 3d-transition metals [12][13][14] and their complexes [1,15,16] have also been carried out using optical [12,14,15,17], photoemission, [1,13,16,18] and x-ray absorption spectroscopies [19], among others.…”