Theoretical Study On The Structure And Properties Of V_mF_n(m=1,2;2?n?7) Clusters

Transition metal-nonmetal mixed clusters have novel properties of photoelectricity,thermoelectricity,electrical conductivity,surface adsorption,superhalogenation,magnetism and nonlinear optics.Among transiton-metal,vanadium exhibits unique features such as variable valences,high melting point,paramagnetism and corrosion resistance.Meanwhile,typical non-metallic fluorine is easily combined with most metals to form various fluorides.Many researches on pure vanadium clusters have been carried out,but those on the mixed V_mF_n clusters are only insufficiently studied.In fact,systematic studies for the important V_mF_n may help to reveal the relationships between structures and performances and their changing rules,which are of special scientific significance.In this work,density functional theory?DFT?investigations on neutral and anionic V_mF_n?m=1,2;2?n?7?clusters are performed,and the geometric structures,relative stability as well as electronic and spectral?IR,Raman and UV-Vis?properties are systematically calculated with Gaussian 09.First,the geometrical structures and the related properties are calculated for VF_n^0,-?1?n?7?clusters.The ground state structures of neutral and anionic VF_n clusters are found to be largely similar to each other for n=1-4.And the electronic properties of VF_n clusters are related to the geometrical structures and the value of n.Particularly,the clusters for n?4 exhibit superhalogen property with very high adiabatic electron affinities?AEA?,VF₆ having the maximum.Analysis of the interactions between VF₆and Li indicates high stability of LiVF₆,where VF₆ acts like fluorine.Themagnetic moments are zero for VF₅ and VF₆^-and 1-4?_B for the others.The highest and next highest UV-Vis absorption peaks within 200-350nm for neutral and anionic clusters are mainly ascribed to the electronic transitions between F 2p and V 3d orbitals.The obvious absorption in visible region?500-800nm?for both neutral and anionic VF_n?n=1,3,4?and VF₂^-clusters indicate that these systems could be adopted as potential visible light photocatalysts.Second,V₂F_n?2?n?7?clusters arealsostudied.The spin-multiplicities of the ground state structures for V₂F_n^0,-?2?n?7?clusters are generally high.V₂F₆ has the highest stability.The calculations of AEA show that only V₂F₇ has super-halogenation property.The total magnetic moments of V₂F_n^0,-are in the range of 3 to 7?_B,which are mainly attributed to the contributionsfrom V with the unfilledd-shell.The atoms in thesymmetrical positions of the clusters exhibit the same local magnetic moments.The anisotropic response to external fields is the weakest and strongest forV₂F₂^-and V₂F₅^-,respectively.In addition,acomparative analysis of the V_mF_n?m=1,2;2?n?7?clusters reveals that the vibration peaks in the infrared and Raman spectra are largely attributed to the stretching vibration of F atoms.With the increase of the number m of V atoms,the total magnetic moment of the cluster roughly shows the increasing tendency,while the super-halogenation displays the decreasing rule.