A Quantum Chemical Study on Hexanuclear Cluster Halides of Rare Earth Elements and Their Interstitial Compounds

The electronic structures of rare earth cluster halides R(R_6X_(12)) and their interstitial compounds R_7X_(12)Zwere studied by the DV-X_(?) method (R=Sc,Y,Pr,Gd or Er;X=Cl,Br or I;Z=B,C,N,Fe,Co or Ru).Theresults show that because f electrons in empty rare earth cluster are screened,their orbitals are more difficult tooverlap each other,a deficiency of skeleton orbitals in cluster causing the system to be unstable.They are easilycondensed into chain compound R_2X_3 or R_5X_8.If a light atom of main group is embedded into octahedralcluster,bonding orbitals formed from interstitial atom and rare earth cluster strengthen clusterskeleton bond in the system to reach structural stability.If embedded atom belongs to transition metal,bondingorbitals composed of that of interstitial atom and rare earth cluster take the place of original cluster skeletonorbitals to form heteronuclear metal cluster (or double-coordination compound).     

过渡金属氮化物TinNm小团簇结构中的定域键

Ti、N形成的小团簇TinNm,当n＋m≤4时,一般出现线形和平面构型;当n＋m=5或6时,TinNm团簇异构体既有线形结构,也有平面结构,还有少数立体结构。线形结构大多形成强弱交替的定域键。平面结构中Ti—N键,随着原子数的增加,逐渐从共价键向离子键过渡,Ti失去电子增多,N得到电子也增多。而立体构型中大多形成离域键,验证了Anderson理论。