Bridged stmctures complexes

The crystal stmcture of [(OEP)Fe]2(A<-ONNO) demonstrates one example of a iram-hyponitrite bridge bimetaUic complex proposed as an intermediate in the reduction of NO to N2O, except that our system is composed of two heme bimetaUic centers instead of the proposed heme and nonheme bimetallic centers. Regardless, we note here that the [(OEP)Fe]2(/<-ONNO) complex is, to date, the only reported crystal structure of a trares-hyponitrite bridge bimetaUic porphyrin complex. Key stmctural features of the crystal structure are worthy of note. 

Summary The synthesis of intramolecularely Jt-stabilized silylium ions such as 7-sila-norbomadienyl- and 2-silanorbomyl cations was attempted. While benzo-7-sila-norbomadienyl cation 7 could not be detected at room temperature in hydrocarbon solvents, its donor-acceptor complex 8 was identified by NMR spectroscopy. In contrast, persistent 2-silanorbomyl cations could be synthesized and characterized by NMR spectroscopy and modem quantum chemical methods. Silanorbomyl cations 5 and 25 are stable at room temperature and have a bridged stmcture in which the silicon adopts a [3+2] coordination. 

Metallocene Catalysts. Polymerization of cycloolefins with Kaminsky catalysts (combinations of metallocenes and methylaluminoxane) produces polymers with a completely different stmcture. The reactions proceeds via the double-bond opening in cycloolefins and the formation of C—C bonds between adjacent rings (31,32). If the metallocene complexes contain bridged and substituted cyclopentadienyl rings, such as ethylene(hisindenyl)zirconium dichloride, the polymers are stereoregular and have the i j -diisotactic stmcture. 

Symmetrical diaLkyl peroxides are commonly named as such, eg, dimethyl peroxide. For unsymmetrical diaLkyl peroxides, the two radicals usually are hsted ia alphabetical order, eg, ethyl methyl peroxide. For organomineral peroxides or complex stmctures, ie, where R and R are difficult to name as radicals, the peroxide is named as an aLkyldioxy derivative, although alkylperoxy is stUl used by many authors. CycHc peroxides are normally named as heterocychc compounds, eg, 1,2-dioxane, or by substitutive oxa nomenclature, eg, 1,2-dioxacyclohexane however, when the two oxygens form a bridge between two carbon atoms of a ring, the terms epidioxy or epiperoxy are frequendy used. The resulting polycycHc stmcture has been called an endoperoxide, epiperoxide, or transaimular peroxide. 

Sohd uranium—phosphate complexes have been reported for the IV and VI oxidation states, as well as for compounds containing mixed oxidation states of U(IV) and U(VI). Only a few sohd state stmctures of U(IV) phosphates have been reported, including the metaphosphate U(P03)4, the pyrophosphate U(P202), and the orthophosphate, CaU(PO4)2. The crystal stmcture of orthorhombic CaU(POis similar to anhydrite (194). Compounds of the general formula MU2(PO4)3 have been reported for M = Li, Na, and K, but could not be obtained with the larger Rb and Cs ions (195). In the sohd state, uranium(IV) forms the triclinic metaphosphate, U(P03)4. Each uranium atom is eight-coordinate with square antiprismatic UOg units bridged by... 

Dinitrog en Complexes. The relative iaertness of molecular nitrogen is well known, however, some Cp —Zr compounds coordinate dinitrogen and substantially iacrease its reactivity. The nitrogen molecule can be coordinated either ia a terminal position or as a bridge ia dimeric stmctures. 

Structure. The CO molecule coordinates in the ways shown diagrammaticaHy in Figure 1. Terminal carbonyls are the most common. Bridging carbonyls are common in most polynuclear metal carbonyls. As depicted, metal—metal bonds also play an important role in polynuclear metal carbonyls. The metal atoms in carbonyl complexes show a strong tendency to use ak their valence orbitals in forming bonds. These include the n + 1)5 and the n + l)p orbitals. As a result, use of the 18-electron rule is successflil in predicting the stmcture of most metal carbonyls. 

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