The DFT Study On Structures And Second-order Nonlinear Optical Properties Of Closo-Metallacarborane Half-sandwich Complexes

Metallacarboranes are a class of inorganic polyhedral clusters containing carbon, boron,hydrogen, and metal atoms in various combinations. One typical of them is the sandwichcomplexes that whose structures are similar with ferrocenes. Metallacarboranes are becominga subject of growing interest for chemical workers owing to their unique combination offeatures and properties including the rigidity of the cages, hydrophobicity, and the chemicaland thermal stability due to delocalized charge. Process in this field has been discussed in anumber of experimental and theoretical reviews. In recent years, metallacarboranes are foundto be good candidates as the nonlinear optics （NLO） materials for their well performed NLOproperties, as well as the relative optical transparency. This work employed the quantumchemistry calculation method with the FF method to calculate the NLO properties offerradicarbollide and rhenacarborane half-sandwich complexes. The results show that:（1） The nonlinear optical （NLO） properties of a series of sandwich complexes which arecoordinated by7,10,12vertexes ferradicarbaboranes and1,2,4,5-Me₄C₆H₂（dur₁）,1,2,3,4-Me₄C₅H（dur₂） were investigated by density functional theory （DFT） CAM-B3LYPmethod. The results indicate that the vertexes of ferradicarbaboranes and the substituteposition of nitryl both affect the molecular geometry and then affect the NLO properties of themolecules. The dipole moment and the polarizability are both enhanced with the increase ofthe vertexes of ferradicarbaboranes. The HOMO-LUMO energy gaps of molecules with10vertexes ferradicarbaboranes are relatively smaller, so the first hyperpolarizabilities（tot）values of them are larger than the molecules with12and7vertexes ferradicarbaboranes.When replacing of the atom H of Fe（Ⅱ） para-position by nitro, the totvalues of moleculesare larger than the non-substitution molecules；However, the atom H of Fe（Ⅱ） ortho-positionis substituted by nitro, the totvalues of molecules are smaller than the non-substitutionmolecules. In the studied molecules, the carboranes can act as either electronic donor oracceptor.（2） Three sets of n-legged piano stool shaped （-Re（CO）3or-Re（CO）3I）12-vertexrhenacarborane half-sandwich complexes （n=3or4） have been investigated by densityfunctional theory （DFT）. Natural bond orbital （NBO） analysis shows that introducing iodine（I） atom changes the bond formations between rhenium （Re） ion and carborane cage or3/4-legged piano stools. The redox-switchable second-order nonlinear optics （NLO）properties of sets1and3are different, notably, the total first hyperpolarizability （βtot） ofcomplex231eis about20times larger than that of its parent complex3. Furthermore,time-dependent density functional theory （TDDFT） calculations were employed to accountfor the redox-switchable NLO properties, the plots of frontier molecular orbitals （FMOs） andelectron density difference maps （EDDM） visually indicate that the intramolecularinteractions among I atom, Re ion and carborane cage contribute to the redox property of set3.