Coordination tetrameric

Crystal structure determination has also been done with -butyllithium. A 4 1 n-BuLi TMEDA complex is a tetramer accommodating two TMEDA molecules, which, rather than chelating a lithium, link the tetrameric units. The 2 2 -BuLi TMEDA complex has a structure similar to that of [PhLi]2 [TMEDA]2. Both 1 1 -BuLi THF and 1 1 -BuLi DME complexes are tetrameric with ether molecules coordinated at each lithium (Fig. 7.2). These and many other organolithium structures have been compared in a review of this topic. ... 

Figure 16.13 Structures of some tetrahalides of Se and Te (a) Sep4 (gas), (b) crystalline Sep4, and schematic representation of the association of the pseudo-tbp molecules (see text), (c) coordination environment of Te in crystalline Tep4 and schematic representation of the polymerized square pyramidal units, (d) the tetrameric unit in crystalline (TeCl4)4, and (e) two representations of the tetrameric molecules in Te4li6 showing the shared edges of the Telg octahedral subunits.

LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

Figure 27-10 Anhydrous acetates of Pd" and Pt" (a) trimeric [Pd(02CMe)2h involving square-planar coordinated Pd but no metal-metal bonding (average Pd -Pd = 315pm), and (b) tetrameric [Pt(02CMc)2]4 involving octahedrally coordinated Pt and metal-metal bonds (average Pt-Pi = 249.5 pm). llie four bridging ligands in the Pt,j plane are much more labile than the others.

Polymerization of alkynes by Ni" complexes produces a variety of products which depend on conditions and especially on the particular nickel complex used. If, for instance, O-donor ligands such as acetylacetone or salicaldehyde are employed in a solvent such as tetrahydrofuran or dioxan, 4 coordination sites are available and cyclotetramerization occurs to give mainly cyclo-octatetraene (cot). If a less-labile ligand such as PPhj is incorporated, the coordination sites required for tetramerization are not available and cyclic trimerization to benzene predominates (Fig. A). These syntheses are amenable to extensive variation and adaptation. Substituted ring systems can be obtained from the appropriately substituted alkynes while linear polymers can also be produced. 

It melts at 86.5°C and boils at 227°C. The tetrameric structure (Figure 1.1) is one adopted by a number of pentafluorides with m-bridges completing the 6-coordination. 

Tilley and co-workers reported the isolation of coordinatively unsaturated complexes Cp Ru(L)Cl (Cp =/j -C-sMes, L = PCy3 and P Pr ) by a simple reaction with the tetrameric species fCp RuCI]4. This synthetic pathway has allowed us... 

Cronje, S., Raubenheimer, H.G., Spies, H.S.C., Esterhuysen, C., Schmidbaur, H., Schier, A. and Kruger, G.J. (2003) Synthesis and characterisation of N-coordinated pentafluorophenyl gold(I) thiazole-derived complexes and an unusual self-assembly to form a tetrameric gold(I) complex. Dalton Transactions, (14), 2859-2866. 

The crystal structures of many organolithium compounds have been determined.44 Phenyllithium has been crystallized as an ether solvate. The structure is tetrameric with lithium and carbon atoms at alternating corners of a highly distorted cube. The lithium atoms form a tetrahedron and the carbons are associated with the faces of the tetrahedron. Each carbon is 2.33 A from the three neighboring lithium atoms and an ether molecule is coordinated to each lithium atom. Figures 7.2a and b show, respectively, the Li-C cluster and the complete array of atoms, except for hydrogen 45 Section 6.2 of Part A provides additional information on the structure of organolithium compounds. 

Triply bridging carbonates between three zinc centers have been identified in nine different X-ray structures deposited in the CSD 458,461,465-467 For example, a binuclear ft-OH zinc complex with a tetradentate /V-donor ligand absorbs atmospheric carbon dioxide to a triply bridged carbonate.468 Examples are also known where the metal atoms are in varying coordination environments. The complex cation [Zn3(bipyridine)6(/U3-C03)(H20)2]4+ contains one penta- and two hexacoordinate zinc centers.469 A tetrapodal compartmental ligand forms a tetrameric complex with zinc that contains the carbonate bridging between three of the four zinc centers.470... 

Neutral benzol,3,2-diazaphospholes or their tetrameric cycloaddition products react with hard Lewis acids to give N-coordinated Lewis acid-base complexes [13, 80, 81] this reaction can be used to disassemble the otherwise stable oligomers into monomeric units at ambient temperature. 

Iodo (trimethyl) platinum (IV) is a yellow crystalline product which decomposes at 190 to 195°. It is soluble in most nonpolar solvents and essentially insoluble in polar media such as water and acetone. In benzene solution, the iodo derivative is tetrameric.6 X-ray investigations have shown that in chloro-(trimethyl) platinum four platinum atoms describe a tetrahedron as do the four chlorine atoms, and the two tetrahedra are interpenetrating so as to give a cubic array of platinum and chlorine atoms. Each platinum atom is bonded to three chlorine atoms and to three terminal methyl groups. Some of the trimethylplatinum derivatives of organic chelate ligands are dimeric and in these structures the platinum is again six-coordinate.7... 

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