A Systematic Density Functional Theory Investigation On The Geometrical And Electronic Properties Of Binary Nickel Carbonyl Compounds

Transition metal carbonyls,which consist of transition metal and CO ligands,play an important role in modern coordination chemistry and organometallic chemistry.They are widely used in various chemical processes such as homogeneous and heterogeneous catalysis,organicmetallic synthesis and decomposition.The synthesis,detection,structure characterization and reactivity of these compounds have been the focus of research in transition metal chemistry.In this thesis,we systematically studied binary mononuclear,dinuclear,and trinuclear nickel carbonyls using different density functionals,focusing on their electronic structures,geometric structures,thermochemical stability and vibration frequencies of these complexes,and their structural evolution.These results can help us in the understanding of chemical adsorption of CO molecules on metal surface and metal-metal bond interaction.Firstly,we have studied the mononuclear nickel carbonyl system Ni(CO)n0/-1(n =1-3).Their geometrical structures,electron affinities,vibrational frequencies,bond lengths,and binding energies were predicted using different density functional theory(DFT)methods and compared with available experimental data reported in literatures.The comprehensive comparisons between theoretical results and experimental data have shown confirmable reliability of the B3LYP/Ni/Stuttgart + 2f1g/C,O/aug–cc–p VTZ method.In addition,we have performed Franck-Condon simulations for the photoelectron spectra of Ni(CO)n-(n = 1-3)on the basis of the optimized geometries and theoretical frequencies.The simulations have well reproduced the spectra and further calibrated the aforementioned B3 LYP predictions.Then,the binuclear system Ni2(CO)n0/-1(n = 1-6)were investigated and their ground-state structures were obtained.Theoretical results show that Ni2(CO)and Ni2(CO)2have two degenerate isomers,which are singlet and triplet with similar structures,respectively.The carbonylation process of neutral nickel dimer is as follows.The first and second CO are terminally attached tothe same nickel atom,forming unbridged Ni2(CO)and Ni2(CO)2,respectively.The Ni2(CO)3 have two terminal CO attached to different nickel atoms and one bridging CO group,forming single-bridged structure [Ni(CO)1Ni(?-CO)Ni(CO)1].On the base of the Ni2(CO)3,the forth CO bridged attaches to the nickel dimer,forming dibridged Ni2(CO)4.The fifth and sixth CO groups are terminally attached to different nickel center,forming dibridged Ni2(CO)5 and Ni2(CO)6.For negative charged binuclear nickel carbonyls,the first three CO groups are terminally coordinated to the same nickel atom.For Ni2(CO)4-,the dibridged [(CO)1Ni(?-CO)2Ni(CO)1]– is formed,structurally similar to the neutral Ni2(CO)4.The Ni2(CO)5-has two degenerate isomers,i.e.,dibridged[(CO)1Ni(?-CO)2Ni(CO)2]– and monobridged [(CO)2Ni(?-CO)1Ni(CO)2]–.The Ni2(CO)6-also has two energy degenerate isomers,unbridged [(CO)3Ni Ni(CO)3]–and dibridged[(CO)2Ni(?-CO)2Ni(CO)2]–.For both the neutral and negative charged dinuclear nickel carbonyls Ni2(CO)n0/-1(n = 1-6),the theoretical results show that the CO groups prefer to terminally coordinate to binuclear metals,CO group of bridged coordination occurs in n =1-6 and forms two bridge carbonyl groups at most.Finally,we have studied the trinuclear system Ni3(CO)n(n = 1-6),and obtained their ground state structures.It's found that they possess nickel triangulation core.The Ni3(CO)n(n = 1-3)all have two degenerate isomers,which are singlet and triplet with similar structures,respectively.Ni3(CO)4 have four energy degenerate isomers,including an open chain like [(OC)1Ni(?-CO)Ni(?-CO)Ni(CO)1] and three structures with nickel triangulation core,Ni3(CO)(?-CO)3,Ni3(CO)2(?-CO)2,Ni3(CO)4.The carbonylation of nickel trimer can be divided into two strategy.The first and second CO are terminally attached to the same nickel atom to form Ni3(CO)and Ni3(CO)2,respectively.For Ni3(CO)3,the third CO are terminally attached to adjacent nickel atom to form [Ni Ni(CO)2Ni(CO)] structure.Based on the Ni3(CO)4-[Ni3(CO)(?-CO)3],the fifth and sixth CO groups are terminally attached to different nickel center,forming [Ni3(CO)2(?-CO)3],[Ni3(CO)3(?-CO)3].Our results show that trinuclear nickel carbonyls take Ni3 three membered ring as the core,and the CO ligandsare terminally attached to the vertex of Ni3 triangle,orbridged attached to the Ni3 triangle edge.