Density Functional Study on the Structural, Frontier Orbital, Electronic, and Magnetic Properties of the Transitional Metal Clusters $Pd_5(CO)_n$ $(n=1$ to $6)$

Abstract

The generalized gradient approximation based on density functional theory is used to analyze the structural, electronic, and magnetic properties of the transition metal clusters $Pd_5(CO)_n$ $(n=1$ to $6).$ For $Pd_5CO,$ the most stable isomer is the singlet state structure with $C$ atom adsorbed on the hollow site in the form of $CO$ molecule, as same as the conclusion reported by Zanti et al (Eur. J. Inorg. Chem. 2009, 3904). In the most stable isomers of $Pd_5(CO)_2$ and $Pd_5(CO)_3,$ the first $CO$ molecule is adsorbed on the hollow site, while the second and the third $CO$ molecules are adsorbed on the bridge sites, whereas, for the most stable $Pd_5(CO)_n$ $(n=4,5,6),$ all $CO$ molecules are adsorbed on the bridge sites. It is known from the adsorption energy that $Pd_5(CO)_2$ should be the most possible adsorption product. The energy gap indicates that $Pd_5(CO)_n$ $(n=1$ to $6)$ have the enhanced dynamical stability compared to $Pd_5$, and $Pd_5(CO)_3$ should be most dynamically stable of all. The chemisorptions of $CO$ molecules onto the $Pd_5$ cluster are non-dissociative and the strength of $C-O$ bond becomes weaker while more $CO$ molecules are adsorbed. Along with the increase of the $CO$ molecules in $Pd_5(CO)_n$ $(n=1$ to $6),$ the ability for detaching electrons is weakened and that for obtaining electrons is improved. The magnetic moment of $Pd_5$ is $2μ_B,$ however, $Pd_5(CO)_n$ $(n=1$ to $6)$ have no magnetic moment.