Theoretical Studies On The Binuclear Homoleptic Rhodium Carbonyls

Transition metal carbonyls acted as an important part of organic metal compound have absorbed the whole world's attraction to study their structure and character with theoretical method. The binuclear homoleptic rhodium carbonyls Rh2(CO)n (n = 8, 7, 6, 5) have been examined using three density functional theory (DFT) methods, i.e., BP86, B3LYP, and MPW1PW91. The Stuttgart double-ζbasis set with an effective core potential (ECP) were used for the rhodium atoms. The effective core approximation includes scalar relativistic contributions, which may become significant for the heavy transition metal atoms. For the C and O atoms, the all-electron DZP basis sets are used. Three energetically low-lying equilibrium structures of Rh2(CO)8 were found, i.e., one doubly bridged C2v singlet structure and two unbridged singlet structures with D3d and D2d symmetry. The doubly bridged structure is the global minimum predicted to lie 15 kJ/mol below the D2d structure and 27 kJ/mol below the D3d structure. For Rh2(CO)7 the global minimum is either a singlet C2v unbridged structure or a singlet doubly bridged Cs structure within 8 kJ/mol depending upon the theoretical method. For Rh2(CO)6, the global minimum is either a singlet doubly bridged D2 structure or a singlet unbridged D2d structure depending upon the method. Triplet structures for Rh2(CO)7 and Rh2(CO)6 are predicted to be of high energies relative to the low energy singlet structures. For Rh2(CO)5 the C2v singlet singly bridged structure lies below the C2 or C2v triplet structures. This paper also used theoretical method to forecast the frequency of those structure, and the analysis of CO frequency substantiate the presumed structure. Through compared the calculated data with experimental ones, we can further prove the accuracy of theoretical computation.