Subject square-pyramidal

The deep violet color of pentaphenylbismuth and certain other pentaarylbismuth compounds has been the subject of considerable speculation. It has been shown by x-ray diffraction (173) that the bismuth atom in pentaphenylbismuth is square—pyramidal. WeU-formed crystals are dichromic, appearing violet when viewed in one plane but colorless in another plane. The nature of the chromophore has been suggested to be a charge-transfer transition by excitation of the four long equatorial bonds ... 

The V02+ phthalocyanine [VO(pc)] has been the subject of patents as it is useful in photoelectrophoretic and xerographic imaging.887 It can exist in at least three solid phases888 and the structure of so-called phase II was determined.889 It is composed of sheets of parallel and overlapping [VO(pc)] molecules and no discrete dimer pair exists. The vanadium is five-coordinate and square pyramidal, and is 0.575 A above the plane of the four nitrogens. The V—N distances do not differ significantly with a mean of 2.026 A the V=0 distance is 1 1.580 A. 

Unlike the position for most of the preceding configurations, the spectra of some Co11 complexes of low symmetry are fairly well defined and can be interpreted in terms of transitions between the d-orbitals.38 A number of square-planar and square pyramidal complexes have been the subject of detailed study.150-156 However, there is often a lack of agreement between the interpretations of different workers. 

The structurally established t/ -pyramidal complexes are all classifiable as square pyramidal with SO2 at the apex. This category is unquestionably the most extensive of all presently known M-SO2 complexes (see Appendix). The first examples were prepared by Vaska by direct addition of SO2 to Ma(CO)(PPh3)2 (M = Rh, Ir) As with most pyramidal M-SO2 complexes, this reaction is reversible, the starting materials being obtained when the adducts are subjected to high vacuum. 

In terms of applications, the subjects of chemical equivalence and symmetry still deserve honorable mention in that one can use the relative number and NMR multiplicity to assign structure, e.g., trigonal bipyramidal, (7), vs. square pyramidal, (8), in ML5 complexes (especially where L is a spin 7= 1/2 donor). 

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