Missing Link in the Ligand-Field Photolysis of [Mo(CN)₈]^4-:  Synthesis, X-ray Crystal Structure, and Physicochemical Properties of [Mo(CN)₆]^2-

Abstract

Photoinduced dissociation of two Mo-CN bonds in [Mo(CN)8]4- affords the octahedral complex anion [Mo(CN)6]2-. This hexacyanomolybdate(IV) ion is also obtainable from tetracyanooxomolybdate via a thermal substitutional synthetic route. The anion represents the missing link in the ligand-field photolysis of octacyanomolybdate(IV); it is characterized by means of single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility measurements as well as IR, Raman, 1H and 13C NMR, and electronic spectroscopy.

How can [MoIV(CN)6]2−, an apparently octahedral (d)2complex, be diamagnetic? Insights from quantum chemical calculations and magnetic susceptibility measurements

“…In fact, our calculations will suggest that [Mo(CN) 6 ] 2À tends to adopt a non-octahedral, trigonalprismatic structure, which may be presumably the primary factor leading to stabilization of the low-spin state. The relative spin-state energetics of [Mo(CN) 6 ] 2À will be studied with a number of DFT and wave function theory methods. Finally, the magnetic properties will be theoretically simulated and compared with the experimental magnetic susceptibility data for a wide range of temperatures.…”

“…6 For the octahedral complex of Mo(IV) one would rather expect the triplet ground state ( 3 T 1g ; arising from two d electrons in the t 2g manifold) and thus, obviously, a paramagnetic character. The purpose of this paper is to elucidate this paradoxical result by means of quantum chemical calculations and interpretation of magnetic susceptibility measurements.…”

“…7,8 It is thus important to thoroughly understand their electronic properties and relation thereof to the molecular structure, particularly for cases as puzzling as the present one. Therefore, in this paper we shall consider various effects that might be responsible for the unexpected diamagnetism of [Mo(CN) 6 ] 2À , including a possibility of magnetic coupling between the neighboring anions in the crystal structure of 1, effects of the spin-orbit coupling, and distortions from the ideal octahedral geometry. In fact, our calculations will suggest that [Mo(CN) 6 ] 2À tends to adopt a non-octahedral, trigonalprismatic structure, which may be presumably the primary factor leading to stabilization of the low-spin state.…”

“…Therefore, in this paper we shall consider various effects that might be responsible for the unexpected diamagnetism of [Mo(CN) 6 ] 2À , including a possibility of magnetic coupling between the neighboring anions in the crystal structure of 1, effects of the spin-orbit coupling, and distortions from the ideal octahedral geometry. In fact, our calculations will suggest that [Mo(CN) 6 ] 2À tends to adopt a non-octahedral, trigonalprismatic structure, which may be presumably the primary factor leading to stabilization of the low-spin state. The relative spin-state energetics of [Mo(CN) 6 ] 2À will be studied with a number of DFT and wave function theory methods.…”

“…Finally, the magnetic properties will be theoretically simulated and compared with the experimental magnetic susceptibility data for a wide range of temperatures. 6 ] 2À were carried out using Turbomole 9 and Gaussian 09 10 packages. The structures were optimized and harmonic frequencies were computed (to verify the character of stationary points and to yield zero-point energies and thermal vibrational corrections to the Gibbs free energy) at the DFT:BP86/def2-TZVP 11 level in Turbomole.…”