混電子價三核鈷錯化合物與鉻-鉻金屬五重鍵之電子密度分析

Abstract

In this work, a combined experimental and theoretical study was applied to achieve the bond characterization on a Hofmann-water-type clathrates complex, a mixed-valence tri-cobalt complex and a quintuple bonded di-chromium complex. The first one is [Mn(H2O)2Ni(CN)4](H2O)3 (MnNi) in which the manganese and nickel atom is coordinated in octahedral and square planar environments, respectively. The second one is Co3(u-admtrz)4(u-OH)2(CN)6.2H2O (Co3), admtrz = 3,5-dimethyl-4- amino-1,2,4-triazole) containing three cobalt atoms with CoIII(LS)-CoII(HS)-CoIII(LS) mixed valence and spin state. The third one is a quintuple bonded binuclear Cr complex, Cr2(Dipp)2 (Cr2) (Dipp- = ArdippNC(H)-NArdipp and Ardipp = 2,6-i-Pr2-C6H3). The Cr atoms are coordinated in low covalent and low coordination number situation which were stabilized by two bridging Dipp ligands. This complex has the shortest Cr-Cr distance of 1.75 Å so far. These three complexes were investigated by high resolution single-crystal X-ray diffraction. Bond characterizations of the three molecules are described in terms of topological properties associated with bond critical points (BCPs), Fermi-hole function, source function, electron localization function (ELF) and natural bonding orbital (NBO) analysis. According to topological properties, Ni-C and CoIII-C bonds are characterized as polarized covalent bond and NBO analysis reveals that the effective bond order (eBO) of CoIII-C is closed to 0.9 with mainly interaction. The other metal-ligand bonds; Mn-N, Mn-O, Co-OH and Co-N are characterized as dative bond. The Laplacian density reveals different shape of inner-valence shell charge concentration (i-VSCC) of two distinct cobalt atoms. Different techniques including “near edge X-ray absorption structure” (NEXAS), “X-ray emission spectrum” (XES) and magnetic properties were used to clarify the spin state of Co3. The Cr-Cr quintuple bond is confirmed with one ds, two dp and two dd interactions by Fermi-hole function and NBO analysis with effective bond order of 4.40. The molecular orbitals of these five bonding orbitals indicate that they are predominantly contributed by 3d orbitals of Cr(I) metal ions. The electron density distribution shows significant overlap between two Cr atoms and the electron density at BCP of Cr-Cr bond is 1.7 e/Å, which is a quite high value for a metal-metal bond. The local source function also indicates that the electron density at BCP of Cr-Cr bond is higher than 80% contributed by the quintuple bonded Cr atoms. The topological properties will be discussed with the di-Cr complexes which have Cr-Cr fBO= 4 and 4.5. The detail discussion between experimental and theoretical results of those three compounds will be given.