CHARACTERIZATIONS OF NOVEL BINUCLEAR ALKALINE-EARTH METAL COMPOUNDS: M2(ηn-N5)2 (M=Be AND Mg, n = 1, 2; M=Ca, n = 2, 5)

摘要: The first structural characterization for the twelve binuclear alkaline-earth metal compounds M2(ηn-N5)2 (M=Be, Mg; n = 1, 2) and Ca2(ηn-N5)2(n 2, 5) have been optimized with local energy minimum by density functional theory (DFT). most energetically favored structures in M2(ηn-N5)2(M=Be, Mg, Ca) are of D2d symmetry Be2(η1-N5)2, Mg2(η2-N5)2 Ca2(η2-N5)2 metal–metal distances 2.03 A Be-Be, 2.77 Mg-Mg 3.72 Ca-Ca, which significantly shorter than experiment values weakly bound bare diatomic Be2, Mg2 Ca2.1,2Ca2(η5-N5)2 (D5d or D5h) is only stable specie sandwiched structure, bearing an even Ca-Ca distance 3.66 A, lying 24 kcal/mol higher structure. dissociation enthalpies to two M(ηn-N5) fragments predicted be 72.6–73.1, 41.2–43.8, 27.4–29.7 kcal/mol, respectively, implying a substantial bonding. Natural bond orbital (NBO) analysis suggests that bonds σ-bond. natural charge alkali earth atom species larger +0.88, consistent +1 oxidation state atoms. Nucleus-independent chemical shift (NICS) confirm planar exhibits characteristics aromaticity these species.