Anchoring of boron halides BX (X: F, Cl, and Br) on transition metal (M: Cr, Mo, W) carbonyl complexes M(CO)5 (M: Cr, Mo, W): structure, bonding, and energy decomposition studies based on theoretical calculations

Abstract

This study investigates the structural and electronic properties of hexacarbonyl [M(CO)₆] (M = Cr, Mo, W) and haloborylene-substituted complexes [M(CO)₅BX] (X = F, Cl, Br) using the density functional theory (DFT) computation at the B3LYP-D3(BJ)/def2-SVP method. The M-C bond lengths are found to follow the order: W–C (2.090 Å in W(CO)₅BBr) > Mo-C (2.055 Å) > Cr-C (1.906 Å in Cr(CO)₅BCl). Substituting BX leads to a decrease in bond lengths and an increase in bond strength for Cr complexes, while Mo and W complexes show opposite trends. The M-B bond lengths increase from Cr (1.886 Å in Cr(CO)₅BBr) to W (2.115 Å in W(CO)₅BF), indicating a correlation with atomic radii and electronic interactions. Vibrational spectroscopy shows C-O stretching frequencies ranging from 2080 to 2210 cm⁻¹, with Cr(CO)₆ at 2208 cm⁻¹, while B-X stretching frequencies range from 1045 to 1456 cm⁻¹. The Wiberg bond order (WBO) analysis indicates strong bonding in Mo(CO)₅BCl (WBO = 1.234) and weaker bonds in bromide complexes, consistent with intrinsic bond strength values. A charge decomposition analysis reveals significant back-donation in Cr(CO)₅BBr, while Mo(CO)₆ favors σ-donation. Thermodynamic calculations show that bromide complexes exhibit high stability with negative entropy changes and elevated heat capacities. Quantum chemical parameters reveal that Cr(CO)₆ has the highest HOMO–LUMO gap (5.475 eV), whereas W(CO)₅BBr shows the smallest (4.372 eV), indicating greater reactivity. QTAIM analysis shows consistent electron density (ρ = 0.291–0.292 a.u.) and a Laplacian value of − 0.232, confirming similar electronic distributions. This comprehensive analysis elucidates the structural stability, bonding characteristics, and electronic properties of these complexes, providing insights into their potential catalytic applications.