La7Os4C9의 전자구조와 화학결합

Abstract

고체 화합물 La7Os4C9 속에 있는 [Os4C9]21‑ 사슬의 전자구조와 화학결합을 extended Hückel 계산 결과에 의해서 논의하였다. 탄소 원자는 물론 (C2)2‑ 분자의 결합 특성은 비교적 큰 Os-C 상호작용을 나 타내었고 특히 (C2)2‑ 분자의 결합길이 증가는 Fermi level 바로 아래에 Os-C2(1 πg) 결합 밴드의 존재로 인 해서 반결합 1πg 오비탈에 부분적인 전자점유가 일어나기 때문인 것으로 해석된다. In the recently synthesized rare earth transition metal carbide <TEX>$La_7O_{s4}C_9$</TEX> one finds one-dimensional organometallic <TEX>$[O_{s4}C_9]^{21-}$</TEX> polymers embedded in a <TEX>$La^{3+}$</TEX> ionic matrix. The electronic structure of the polymeric <TEX>$[O_{s4}C_9]^{21-}$</TEX> chain was investigated by density of states (DOS) and crystal orbital overlap population (COOP), using the extended Huckel algorithm. A fragment molecular orbital analysis is used to study the bonding characteristics of the <TEX>$C_2$</TEX> units in <TEX>$La_7O_{s4}C_9$</TEX> containing <TEX>$C_2$</TEX> units and single C atoms as well. The title compound contains partially filled Os and carbon bands leading to metallic conductivity. As the observed distances already indicated, the calculations show extensive Os-C interactions. The C-C bond distance in the diatomic <TEX>$C_2$</TEX> units (<TEX>$d_{C-C}$</TEX>=131 pm) in the solid is significantly increased relative to <TEX>$<TEX>${C_2}^{2-}$</TEX>$</TEX> or acetylene, because antibonding <TEX>$1{\pi}_g$</TEX> orbitals are partially filled by the Os-<TEX>$C_2(1\;{\pi}_g)$</TEX> bonding contribution found at and below the Fermi level.