Square pyramid coordination structures

Five-coordinate complexes are far more common than was once supposed and are now known for all configurations from d to d. Two limiting stereochemistries may be distinguished (Fig. 19.4). One of the first authenticated examples of 5-coordination was [VO(acac)2] which has the square-pyramidal 4 structure with the =0 occupying the unique apical site. However, many of the complexes with this coordination number have structures intermediate between the... 

The structural analyses reveal distorted square pyramidal coordination with a nearly linear Cl( 1)—Ru—Cl(2) angle (168.62 and 170.42 for 12 and 13,... 

As shown by ab initio studies with the anionic model species 49, the energy difference between the trigonal-bipyramidal (C2 symmetry) and the alternative square-pyramidal structure (C2v symmetry) is rather small (6.9 kJ mor1).40 From this result one may conclude that related zwitterionic A5S7-silicates, such as 47 and 48, should also have a chance to exist with a square-pyramidal /-coordination polyhedron in the solid state. The square-... 

Torardi et al, 1987 David et al, 1987). The structure is closely related to that of the superconducting copper oxide YBa2Cu307, consisting of square-pyramidally coordinated copper (Cu-O sheets) and square-planar copper (Cu-O chains). Excess oxygen in the lanthanum compound is located interstitially converting partially the chain copper to square-pyramidal and/or octahedral coordination. 

The structures of several Li+ complexes with crown-4 ethers have been solved. The complexes LiNCS(83),416 LiNCS(74),41 LiNCS(84)418 and LiNCS(85)419 all show Li+ to be square pyramidally coordinated by the four ring oxygen donors and the nitrogen from the... 

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