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σ-Aromaticity in Trinuclear and Tetranuclear Transition Metal Carbonyl Clusters: A Comprehensive Magnetic and
Chhanda Paul1, Sumit Satish Kadam1, Shanti Gopal Patra1
1Department of Chemistry, National Institute of Technology Silchar, Silchar, Cachar, Assam, India.
None:
This study investigates the presence of σ-aromaticity in a series of trinuclear and tetranuclear metal carbonyl clusters with the general formulas [M3(CO)12], [M4(CO)16], [M4(CO)15], and [M4(CO)14], (where M = Fe, Ru, and Os), and isolobal trinuclear clusters [M3(CO)12]3- (where M = Mn, Tc, Re), and [M3(CO)12]3+ (where M = Co, Rh, Ir). Density functional theory was employed for all the geometry optimisation. Aromaticity was assessed using magnetic criteria, specifically nucleus-independent chemical shifts (NICS) and gauge-including magnetic-induced ring currents (GIMIC). Our findings indicate that all cluster types exhibit σ-aromaticity. Among all the clusters studied, the [Fe3(CO)12] cluster displayed exceptionally strong σ-aromaticity, evidenced by highly negative NICS values and a significant diatropic current, as confirmed by GIMIC analysis. Further analysis, utilising NICS-scan, and electron density of delocalised bonds, confirmed the presence of pronounced σ-delocalisation in these metal carbonyl clusters.
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