Structural and Optical Properties of Metal-Nitrosyl Complexes

Area of Science:

• Computational Chemistry
• Inorganic Chemistry
• Quantum Chemistry

Background:

• Metal nitrosyl complexes, [M(CN)5(NO)]2- (M = Fe, Ru, Os), exhibit diverse electronic, structural, and optical properties.
• Understanding their conformational isomerism is crucial for predicting reactivity and properties.

Purpose of the Study:

• To investigate the electronic, structural, and optical properties of metal nitrosyl complexes.
• To analyze the conformational isomerism in both ground and excited electronic states.
• To elucidate the role of Spin-Orbit Coupling and electronic transitions in these properties.

Main Methods:

• Density Functional Theory (DFT) for energy profiles and structural optimizations.
• Time-Dependent DFT (TD-DFT) and MS-CASPT2 for electronic state analysis.
• Restricted Active Space Self-Consistent Field (RASSCF) wavefunction calculations.

Main Results:

• N-bound conformation is generally the most stable for [M(CN)5(NO)]2- complexes.
• Conformational isomerism is energetically unfavorable in the S0 state, with high energy barriers (>2 eV).
• Lowest spectral bands are assigned to Metal-to-Ligand Charge Transfer (MLCT) and Ligand-to-Ligand Charge Transfer (LLCT) transitions, with increasing MLCT character from Fe to Os.

Conclusions:

• The triplet ground state of the O-bound iron complex is a notable exception to the general stability trend.
• Excited-state conformational isomerism is governed by low-lying triplet states (T1 and T2).
• Spin-Orbit Coupling significantly influences the electronic and optical properties of these metal nitrosyl complexes.