Cluster complexes octahedral

For trinuclear cluster complexes, open (chain) or closed (cycHc) stmctures are possible. Which cluster depends for the most part on the number of valence electrons, 50 in the former and 48 in the latter. The 48-valence electron complex Os2(CO)22 is observed in the cycHc stmcture (7). The molecule possesses a triangular arrangement of osmium atoms with four terminal CO ligands coordinated in a i j -octahedral array about each osmium atom. The molecule Ru (00) 2 is also cycHc and is isomorphous with the osmium analogue. 

The oxidation state of the tetramanganese cluster, having octahedral geometry and N303 coordination, is Mn4Iv. Electrochemical investigation shows that the complex undergoes a reversible oxidation... 

The structural relationship between the molecular and solid-state compounds has been a hot issue in inorganic chemistry for some time (25-27). The extrusion (or excision) from preformed solid-state cluster compounds is one of the major synthetic methods of the preparation of cluster complexes (26). Use of cluster complexes as precursors to solid-state cluster compounds is the reverse reaction of excision. Both reactions utilize the structural similarity of the metal cluster units. The basic cluster units of polyhedra (deltahedra) or raft structures are triangles, and both molecular and solid-state clusters with octahedral, tetrahedral, and rhomboidal cores have been reported. Similarity of other properties such as electronic structures based on the cluster units is also important. The present review is concerned with the syntheses and structures of the cluster complexes of the group 6 metals and with their relationships to solid-state chemistry. 

The infrared and Raman spectra of the [Mo6SgL6] complexes have been reported (37) (Table III). The infrared spectra have an Mo—S stretching band at 378-390 cm-1, and the Raman spectra show a distinguishing sharp peak at 411-418 cm-1 that can be attributed to the Alg totally symmetric Mo—S stretching mode. The broad band at 836 cm-1 in the piperidine complex is most likely the first overtone of the band at 411 cm-1. The ligand-deficient propylamine and pyridine cluster complexes exhibit a broadened Mo—S band at 448 cm"1 that is described as due to the loss of the octahedral symmetry by loss of ligands (37). 

Geometrically, the main group element tends to retain a tetrahedral nearest neighbor environment, whereas the transition metal element tends to retain an octahedral environment. As a consequence, transition metal clusters with more than six metal atoms have a tendency toward ligand loss, leading to the formation of condensed clusters (multiple interstitial metal atoms). This leads eventually to close-packed structures that mimic bulk metal structures (see Polynuclear Organometallic Cluster Complexes). On the... 

Some solid-state metal hydrides are commercially (and in some cases potentially) very important because they are a safe and efficient way to store highly flammable hydrogen gas (for example, in nickel-metal hydride (NiMH) batteries). However, from a structural and theoretical point of view many aspects of metal-hydrogen bonding are still not well understood, and it is hoped that the accurate analysis of H positions in the various interstitial sites of the previously described covalent, molecular metal hydride cluster complexes will serve as models for H atoms in binary or more complex solid state hydride systems. For example, we can speculate that the octahedral cavities are more spacious in which H atoms can rattle around , while tetrahedral sites have less space and may even have to experience some expansion to accommodate a H atom. 

As discussed in section 2.8, relativistic effects on the valence electronic structure of atoms are dominated by spin-orbit splitting of (nl) states into (nlj) subshells, and stabilization of s- and p-states relative to d- and f-states. Here we examine consequences of relativistic interactions for cubo-octahedral metal-cluster complexes of the type [M6X8Xfi] where M=Mo, Nb, W and X=halogen, which have a well defined solution chemistry, and are building blocks for many interesting crystal structures. 

Cluster complexes that obey Cotton s strict definition such as [ Nb6 Cli8]K4 and [ Mo6 C1h]Cs2 have 16 and 24 electrons, respectively, for bonding interactions within the octahedral niobium and molybdenum clusters. In a VB picture, these electrons are consumed for eight two-electron-three-center (2e-3c) or 12 2e-2c bonds, situated in the eight triangular faces and the 12 edges of the respective octahedra. 

Isolated octahedral clusters are scarce. There appears to be only one example, Cs2Lu[ CLu6 Cli8], in which not only the CLue cluster is isolated but also the [ CLu jClig] cluster complex unconnected. The most prolific families with isolated clusters are the so-called 7-12 and 6 10 type compoimds, halides of the compositions ZR6 Xi2R and ZR jXio. These are mostly iodides for the 6-10 type, bromides are equally fi equent, perhaps a packing problem. ... 

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