Coordination geometry tris

Figure 15.16 Coordination geometries of bis- and tris-l,2-dithiolene complexes (see text).

Properties of nickel poly(pyrazol-l-yl)borate complexes such as solubility, coordination geometry, etc., can be controlled by appropriate substituent groups on the pyrazol rings, in particular in the 3- and 5-positions. Typical complexes are those of octahedral C symmetry (192)°02-604 and tetrahedral species (193). In the former case, two different tris(pyrazolyl)borate ligands may be involved to give heteroleptic compounds.602,603 Substituents in the 5-position mainly provide protection of the BH group. Only few representative examples are discussed here. 

A,A A"-tris[(2S)-2-hydroxypropyl]-1,4,7-triazacyclononane (LH3) forms the air-stable mangane-se(II) species [MnLH3][MnCl4] when conditions are such that the ligand remains fully protonated. The X-ray structure indicates the presence of a trigonal prismatic coordination geometry." ... 

The coordination geometry of these Cu(III) complexes is presumed to be square planar, indicative of high field d complexes. This has been demonstrated in the crystal structure of deprotonated tri-a-aminobutyric acid, Cu "(H 2Aib3), in which the copper-donor atom bonds were found to be 0.12-0.17 A shorter than for the corresponding Cu(II) complex... 

For anions, it is tempting to try and attribute a preferential coordination geometry analogous to that so well established for various metal cations. In many cases simple anions such as the halides exist in approximately tetrahedral or octahedral environments, but it is clear from the diversity of examples reviewed herein that anion coordination geometry is highly flexible and may be adjusted to fit the properties of the various host systems. 

Such a reader might find relief in differential geometry, the mathematical study of multiple coordinate systems. There are many excellent standard texts, such as Isham s book [I] for a gentle introduction to some basic concepts of differential geometry, try [Si]. A text that discusses covariant and contravariant tensors is Spivak s introduction to differential geometry [Sp, Volume I, Chapter 4]. For a quick introduction aimed at physical calculations, try Joshi s book [Jos]. 

---