Pyramidal coordination

The alkoxides and aryloxides, particularly of yttrium have excited recent interest. This is because of their potential use in the production of electronic and ceramic materials,in particular high temperature superconductors, by the deposition of pure oxides (metallo-organic chemical vapour deposition, MOCVD). They are moisture sensitive but mostly polymeric and involatile and so attempts have been made to inhibit polymerization and produce the required volatility by using bulky alkoxide ligands. M(OR)3, R = 2,6-di-terr-butyl-4-methylphenoxide, are indeed 3-coordinate (pyramidal) monomers but still not sufficiently volatile. More success has been achieved with fluorinated alkoxides, prepared by reacting the parent alcohols with the metal tris-(bis-trimethylsilylamides) ... 

An analysis of the water molecule configurations in hydrates of the amino adds, peptides, carbohydrates, purines, pyrimidines, nucleosides and nucleotides is presented in Ihble 22.1. The key to the 12 different observed configurations is given in Ihble 22.2. The water molecules, which are involved only in two-center bonds constitute 63% of the total number of bonds, the others are donors or acceptors of three-center bonds. Similar proportions are observed in all three different classes of molecules. Thq only possibly significant difference is a trend toward more three-coordinated pyramidal configurations with the nucleosides and nucleotides. 

Similar stacking of AsSi coordination pyramids and PbSg octahedra in lengen-bachite probably produces the (pseudo-) hexagonal configuration of its H component (Makovicky and Leonardsen, unpublished work). 

Thiolates and Related Systems. Lanthanide thiolates have only been characterized in detail recently. Monomeric species have been obtained using bulky Ugands, such as the three-coordinate (pyramidal) Sm(SC6H2-t-Bu-2,4,6)3 (Figure 19) ... 

Another common tin geometry in bivalent tin compounds is a distorted four-coordinate pyramidal arrangement in this... 

Certain bivalent tin salts have solubilities in nonaqueous solvents, e.g. tin(ll) chloride is soluble in many organic solvents, including alcohols, acetone, THF, and pyridine, probably to give rise to three-coordinate pyramidal [SnCl2-L]-type complexes. Other selected solubilities are SnBr2 in methanol, pyridine, or THF and tin(II) formate in H0(CH2)30H. Bivalent tin species are also solnble in acetonitrile solution, to give [Sn(MeCN) ] + (n = 2, 3, or 6), and in liquid ammonia, to give [Sn(NH2)3] . 

In neutral 1,3-diphospholes (22) the second heteroatom is a three-coordinate pyramidal phosphorus atom which is not at all or only very weakly conjugated to the remaining Jt-system. Full cyclic conjugation occurs only in their anions, that is, in the 1,3-diphospholide anions. The same applies to the 1,3-benzodiphospholides (3) and their anions. The known monocyclic and fused 1,3-heterophospholes and 1,3-diphospholes are shown in Table 1. 

All known X-ray diffraction data indicate that in penta-coordinated pyramidal vanadium chelates the vanadium atom lies out of the basal plane of the ligand macrocycle, i,e.j the plane of the four pyrrole nitrogen atoms. The distance from vanadium... 

In the Sn(ii) complex [Li2(/Li3-OBu )2(Ar-OBu )4Sn2] the lithiums are four-coordinated but the tin atoms are three-coordinated (pyramidal) with a Li206Su2 cage built from two eco-norcubane Sn2Li203 units sharing a Li202 four-membered ring." In the Sn(iv)... 

Indium(i) and thallium(i) are also involved in the structures of heterometaiiic aikoxides. For example in the binuclear complex [Tl(/r-OBu )3Sn] both metals are three-coordinated (pyramidal). 

In the organometallic alkoxo complex [ (cod)Rh 2(/z-OEt)4Sn(OEt)2] (cod = cyclooctadiene), the distorted octahedral Sn(iv) has cw-terminal ethoxo ligands. The dinuclear complex [ClSn(/u,-OBu )2Al(OBn )2] has three-coordinated (pyramidal) Sn(n) and distorted tetrahedral... 

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