| Gas-phase multiply charged metal complex cations serve as important models for the understanding of the chemistry of multiply charged metal cations.Since the effects of solvent molecules and counter-ions can be adjusted in the gas phase,fundamental understanding of the influences of metal cation and ligand on the structure,bonding and reactivity of multiply charged complexes can be provided at the molecular level.In contrast to the rich studies in condensed phase,the gas-phase chemistry of multiply especially triply and quadruply charged metal cations is far less investigated.This is mainly due to the fact that multiply charged metal cations tend to undergo electron or proton transfer reaction to form charge reducing products during ionization process without the stabilization effect of solvent molecules and counter-ions.Therefore,it is crucial to find suitable ligands that can form stable gas-phase complexes with multiply charged metal cations in order to reveal the chemical properties of these species in the gas phase.Doubly charged metal complex cations dominate the known examples of gas-phase multiply charged cations.These cations are composed of alkaline earth/transition metal cations and simple ligands,and their compositions as well as dissociation patterns have been elucidated.Less attention has been paid to the gas-phase transition/lanthanide metal trications coordinated with specific ligands.For tetrapositive metal complex cations,the fact that the 4th ionization energies of most metals lie substantially above the ionization energies of common ligands makes it a real challenge to observe these species in the gas phase.In this thesis,neutral diamide ligands are employed for the preparation of a series of multiply charged metal-diamide complex cations in the gas phase via electrospray ionization(ESI),and their structures and fragmentation behaviors are studied by both collision-induced dissociation(CID)and quantum chemical calculation.The major results are below:(1)A series of gas-phase triply charged lanthanide cations ligated by neutraldiamides with different heteroatoms have been observed,and their compositions,structures as well as fragmentation patterns are investigated.Abundant Ln(TMGA)33+,Ln(TMTDA)33+ and Ln(TMPDA)23+(TMGA = N,N,N',N'-tetramethyl glutaramide,TMTDA = N,N,N',N'-tetramethyl-3-thio-diglycolamide,TMPDA = N,N,N',N'-tetramethylpyridine-2,6-dicarboxamide)are observed with 1:3,1:3 and 1:2stoichiometries,and they possess C3,C3 h and S4 symmetries respectively in which Ln3+ is six-fold coordinate.The dissociation patterns of Ln(TMGA)33+ and Ln(TMTDA)33+ dependend on the reduction potentials of Ln(III)/Ln(II)in condensed phase: Eu(III)/Eu(II)(-0.36 V)>> Yb(III)/Yb(II)(-1.05 V)> Sm(III)/Sm(II)(-1.55V)> and the other Ln(III)/Ln(II)(<-2.00 V).It is therefore more facile for the gas-phase Eu3+ complex cations to undergo charge reduction during which Eu3+ is reduced to Eu2+.For a certain lanthanide element,the fragmentation behaviors among Ln(TMGA)33+,Ln(TMTDA)33+ and Ln(TMPDA)23+ depend on the nature of the ligands.(2)The coordination structures of a series of actinide-diamide complex cations in both gas phase and solution as well as the gas-phase dissociation behaviors have been investigated.According to the results of ESI-mass spectrometry and theoretical calculations,UO22+ mainly forms 1:2 complexes with TMGA,TMOGA,TMTDA and TMPDA in the gas phase.TMGA and TMTDA are bound to UO22+ in bidentate mode while TMOGA and TMPDA act as tridentate ligands,and the binding energy of UVIO2(TMPDA)2+ is 28.3 kcal/mol and 52.0 kcal/mol higher than those of the UVIO2(TMTDA)2+ and UVIO2(TMGA)2+ respectively.The coordination structures of these UO22+-diamide complexes in solution are the same as those in the gas phase revealed by the results from extended X-ray absorption fine structure measurement.UVIO2(TMGA)22+,UVIO2(TMTDA)22+ and UVIO2(TMPDA)22+ complexes fragment through the cleavages of Ccarbonyl-N,Ccarbonyl-Cmethylene/Ccarbonyl-Cpyridine,Cmethylidene-Cmethylidene/Cmethylidene-S bonds,which agree well with the radiolysis behavior of bare ligands under ? irradiation in solution.For Th4+,three TMPDA ligands are needed to stabilize it in the gas phase in the form of Th(TMPDA)34+,in which the thorium center is coordinated by six Ocarbonyl and three Npyridine atoms forming twistedtricapped trigonal prismatic geometry.The CID products of Th(TMPDA)34+ are barely observed.The absence of tetrapositive thorium complexes ligated by bidentate TMGA and TMTDA ligands in the gas phase suggests that the interaction of Th-Npyridine as well as previously characterzed Th-Oether play important roles in the stabilization of gas-phase Th4+.(3)Tetrapositive zirconium and hafnium complex cations are observed in the gas phase for the first time,and their reactivities as well as the factors affecting their gas-phase stabilities are investigated.It has been found that ESI of acetonitrile solutions of Zr(Cl O4)4/Hf(Cl O4)4 and TMPDA/TMOGA results in the formation of Zr(TMPDA)34+,Zr(TMOGA)34+,Hf(TMPDA)34+ and Hf(TMOGA)34+,where Zr4+ and Hf4+ are stabilized in the gas phase.The Zr4+ and Hf4+ centers in all these complexes are nine-coordinate.The major CID pattern for all these four complexes is proton transfer which is also supported by theoretical calculations.None of the Zr(TMTDA)34+?Zr(TMGA)34+?Hf(TMTDA)34+ or Hf(TMGA)34+ complex is found when the acetonitrile solutions of Zr(Cl O4)4/Hf(Cl O4)4 and TMTDA/TMGA are subjected to ESI.Both Zr4+ and Hf4+ are unsaturated with six-fold coordination in these complexes.As a result,other molecules such as water can enter the inner coordination shell which could cause hydrolysis and charge reduction of the complexes.No tetrapositive species are observed when either counter-ion is replaced by Cl-or solvent is replaced by methanol.This suggests that the deprotonation ability of solvent,the interaction between counter-ion and metal center,and the coordination mode of neutral ligand should be crucial to the stabilization of Zr4+ and Hf4+ in the gas phase. |
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