Three-coordination, idealized geometries

For the spherically symmetric Cu d" ion, the common geometries are two-coordinate linear, three-coordinate trigonal planar, and four-coordinate tetrahedral. Some distortions from these ideal geometries are observed, particularly with chelating ligands a fairly small number of pentacoordinate Cu complexes have been isolated and characterized as well. Cu compounds are diamagnetic and colorless, except where the color results from charge-transfer bands or a counterion. Cu complexes are often fairly readily oxidized to Cu compounds the electron-transfer kinetics of several systems have been studied. ... 

Ag(I) is a d10 ion and, like Au(I), can be two-, three- or four-coordinate with appropriate ligands. The idealized geometries are linear, trigonal planar and tetrahedral, but distortions from the ideal are observed in the solid state and in non-homoleptic complexes where greater silver s character is conferred on the bonds to selected elements. The chemical shift values generally increase with coordination number, other things being equal,... 

Reaction of the orange solution of 54 with N3(l-Ad) in hexanes afforded dark red crystals of 3,5- Pr2-Ar Fe(N-Ad)2 (59) [144] (Fig. 16). It is noteworthy that 59 was the only isolated product when variable molar ratios of N3(l-Ad) to 54 were attempted. It is notable not only because it is the first stable Fe(V) imide, but it is also a very rare example of a well-characterized Fe(V) molecular species of any kind [147]. The iron has a planar three-coordinate geometry with interligand angles that have a maximum deviation of only ca. 1.4° from the idealized 120° trigonal planar value. The coordination planes at the imido nitrogens are almost coincident (maximum deviation 7.2°) with the central C(l)Fe(l)N(l)N(2) plane. 

The zinc atom has almost ideal tetrahedral coordination geometry, with bond angles ranging from 115.37(10)° to 123.60(9)°. The zinc-carbon bond (1.964(3) A) has a similar length as in the neutral [MeZn(OBut)]4 tetramer,106 in which zinc is also tetrahedrally surrounded by one alkyl group and three oxygen atoms. 

---