![]() 4 This trigonal deformation was reported to be sensitive to the environment of the complex. The influence of this reduction in the symmetry of 3+ on its vibrational spectrum was also examined in the solid state. 3 analyzed the electronic spectra of the hexaamminecobalt( III) complex cation in aqueous solution to obtain the spectral components attributed to the slight distortion from a regular octahedron around the central cobalt( III) ion and reported that the LC-BLYP/6-31G(d) optimized geometry of the complex in aqueous solution is a trigonally compressed octahedron under D 3d. 1,2 Considerable research effort has been made to understand the properties of Co complexes, particularly those derived from cobaltammines. Introduction Co complexes play various important roles in the chemistry of life processes and have been known for ages to impart blue color to ceramics. Co(NH 3) 6 3+ is less stable compared to Co(NH 3) 5NO 2 2+ and undergoes a slight geometrical distortion from D 3d to either D 3 or S 6 characterized by a stabilization energy of ∼750 cm −1 at CCSD(T)/6-31+G(d,p). The intramolecular-resonance-assisted hydrogen bonds (N–H⋯O and N–H⋯N), the orientation of NO 2, and the difference between Co–N and Co–O bond energies are identified as the key factors determining the relative stabilities of the linkage isomers. Pathway (1) through endo-nitrito is the most likely isomerization mechanism because of a lower energy barrier than pathway (2). The study of the ground-state potential energy surface of 2+ reveals that the nitro/ exo-nitrito isomerization reaction can proceed via the following two paths: (1) nitro → TS1 (38.16 kcal mol −1) → endo-nitrito → TS2 (9.68 kcal mol −1) → exo-nitrito and (2) nitro → TS3 (41.76 kcal mol −1) → exo-nitrito. Different techniques like atoms in molecules (AIM), electron localization function (ELF) and natural bonding orbital (NBO) were used to gain insight into the chemical bonds of the isomers and to identify the key factors influencing their relative stabilities. Nitro–nitrito isomerization in Co(NH 3) 5NO 2 2+ linkage isomers was investigated with a focus on the geometries, relative stabilities and chemical bonding using ωB97XD/6-31+G(d,p) to elucidate the photo-salient effect in NO 3Cl.
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