Low Carbonyl-coordination Number Compound Of 3D Binuclear Transiton Metal:A Theoretical Study

Transition metal carbonyl compounds play an irreplaceable role in modern coordination chemistry and metal organic chemistry,which have become one of the most important topics in the field of chemistry research.In recent years,with the developing of experimental conditions and computer technology,more and more complex transition metal carbonyl compounds have been confirmed and studied.However,few studies have been conducted on low-coordination binuclear transition metal carbonyl compounds.Therefore,at the calculation level of BP86/6-311g?d?,this paper systematically studied the point groups,ground states,electronic states,geometric structures,vibration frequency and infrared intensity of low-energy structures of TM₂CO₂?TM=Sc-Zn?and TM₂CO₃?TM=Sc-Zn?systems.The main contents are as follows:?1?In the two systems of TM₂?CO?₂?TM=Sc-Zn?and TM₂?CO?₃?TM=Sc-Zn?,by comparing the energy of the C-O unseparated structure and the C-O separated structure,we found that the C-O separated structure has the lowest structural energy for the structure containing the early transition metal atoms with fewer d electrons.For the late transition metal atoms with more d electrons,the C-O unseparated structure energy is the lowest.?2?In the two systems of TM2?CO?2?TM=Sc-Zn?and TM2?CO?3?TM=Sc-Zn?,we compared the energy gap between the C-O unseparated structure and the C-O separated structure in the structure of the early transition metal atom containing fewer d electrons,and found that the energy gap gradually decreased with the increase of the number of d electrons.?3?In the two systems of C-O unseparated TM2?CO?2?TM=Sc-Zn?and TM2?CO?3?TM=Sc-Zn?,by comparing the C-O bond length and C-O stretching vibration frequency,we find that for the structure with fewer d electrons,the C-O bond length and C-O stretching vibration frequency are far from the C-O bond length and C-O stretching vibration frequency in the single CO molecule.The C-O bond length and C-O stretch vibration frequency of the structure of the transition metal atom with large number of d electrons are more similar to those of the C-O bond length and C-O stretch vibration frequency of the CO molecule alone,but there are still differences.The C-O bond length and C-O stretch vibration frequency are close to that of the C-O stretch vibration frequency in the structure of Cu atom and Zn atom which are fully occupied by the electrons in the 3d orbital.?4?We analyzed the TM-TM distances in the two systems TM2?CO?2?TM=Sc-Zn?and TM₂?CO?₃?TM=Sc-Zn?,and compared with the TM₂ molecules alone and others have been discovered and the TM-TM bond lengths in carbonyl compounds containing TM-TM metal multiple bonds were compared and found to be low coordination TM2?CO?2?TM=Sc-Zn?and TM2?CO?3?TM=Sc-Zn?.There is a relatively short distance between TM-TMs,and strong correlation interactions are expected.?5?In TM₂?CO?₂?TM=Sc-Zn?and TM₂?CO?₃?TM=Sc-Zn?systems,the relative stability of the structure and the CO stretching vibration frequency have the same change law,because the strength of the coordination bond between the metal atom and the carbonyl ligand in the transition metal carbonyl compound plays a crucial role in the stability of the structure.When a transition metal atom possesses less d electrons,it is difficult to form an effective feedback?bond with the carbonyl ligand;When the transition metal atom has more d electrons,it can be better with the the electron transfer of carbonyl ligand and forms a stronger feedback?bond,and the synergistic effect of the feedback?bond and the?bond further promotes the stability of the carbonyl complex.