The reaction of Mn (CO)<sub>5</sub>Br with Thionicotinic acid in a 1:1 molar ratio in acetone in the presence NaBPh<sub>4</sub> yields selectively only one of the possible two isomers. Repeated experiment shows that the isolated products appeared to be cis based on X-ray crystallographic and infrared spectroscopic data. This contrasts with the general belief that a trans-isomer is more stable than cis. To address this issue, we have used density functional theory (DFT) calculations to estimate and compare the energy of formation and thereby the stability of these two geometrical isomers. Specifically, B3LYP (hybrid density functional), TPSSh (meta-hybrid density functional) theory and split valence triple zeta basis set, def2-TZVP, were used for geometry optimization and electronic properties calculations. Results of these DFT calculations suggests that the cis isomeric complex I is energetically more stable than the trans isomeric complex II. The energy differences between cis-complex I and trans-complex II is -2.34 kcal/mole (B3LYP/def2-TZVP) and -3.55 kcal/mole (TPSSh/def2-TZVP). Our results from both the experimental and theoretical studies will be discussed during the presentation.

Synthesis, x-ray studies, and theoretical structural analysis of a binuclear manganese tricarbonyl thionicotinic acid complex

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