Group coordination complexes

Under general headings such as Cobalt(III) complexes and Ammines, used for grouping coordination complexes of similar types having names considered unsuitable for individual headings, formulas or names of specific compounds are not usually given. Hence it is imperative to consult the Formula Index for entries for specific complexes. 

Under other general headings, such as CcbaUlJH) complexes and Ammines, used for grouping coordination complexes of nmilar types having names considered... 

Some of the oxidation states given above, especially the higher oxidation states (7, 6) and oxidation state 0, are found only when the metal atom or ion has attached to it certain groups or ligands. Indeed the chemistry of the transition elements is so dominated by their tendency to form coordination complexes that this aspect of their behaviour must be considered in some detail. 

Simple nickel salts form ammine and other coordination complexes (see Coordination compounds). The octahedral configuration, in which nickel has a coordination number (CN) of 6, is the most common stmctural form. The square-planar and tetrahedral configurations (11), iu which nickel has a coordination number of 4, are less common. Generally, the latter group tends to be reddish brown. The 5-coordinate square pyramid configuration is also quite common. These materials tend to be darker in color and mostiy green (12). 

Many complexes have more than one coordination mode of BH4 featured in their structure, e.g. [U ()9 -BH4)()9 -BH4)2(dmpe)2]. Likewise, whereas [M(BH4)4] are monomeric 12-coordinate complexes for M = Zr, Hf, Np, Pu, they are polymeric for M = Th, Pa, U the coordination number rises to 14 and each metal centre is coordinated by two r) -BH4 and four bridging r) -BH4 groups. It is clear that among the factors which determine the mode adopted are the size of the metal atom and the steric requirements of the co-ligands. Many of the complexes... 

The molecule has an almost linear N3 group and an angle C-N-N of 112.4° (Fig. II.4a).( ) The (linear) azide ion, N3", is isoelectronic with N2O, CO2, OCN", etc. and forms numerous coordination complexes by standard ligand replacement reactions. Various coordination modes have been established, including end-on bridging... 

There is one striking group of exceptions to the otherwise almost unbroken success of Kepert s approach. No model predicated solely upon the repulsions between monodentate ligands (or between bonds) can account for the planarity of some four-coordinate complexes. Yet hundreds of planar (f complexes like [Ni(CN)4] or [PtCl4] are known. Clearly, Kepert s model is to be augmented and we discuss this matter further in Chapter 7. 

Similar to the four- and five-coordinate complexes 120-126, for RCo (dioxime-BR2)2L 127 and Fe(dioxime-BR2)LL 128 different conformations are possible in solution and in the solid state, in which the substituents of the boron atoms may adopt cis- or trans-configurations and in which the alkyl group R may have a parallel or an antiparallel orientation with respect to the BR2 substituents [173-180]. 

In an excellent review by Roesky et al. in 1994 [70a] a vast number of examples for coordination complexes of cyclic phosphazanes and phosphazenes and other related systems have already been compiled. In the following section, an attempt is made to cover the latest features of group 13 systems along with some earlier examples with phosphorus-nitrogen based systems other than pyridyl phosphanes. 

This review deals with the chemistry and coordination complexes of isoelectronic analogues of common oxo-anions of phosphorus such as PO3, POl", RPOl" and R2POy. The article begins with a discussion of homoleptic systems in which all of the 0x0 ligands are replaced by imido (NR) groups. This is followed by an account of heteroleptic phosphorus-centered anions, including [RN(E)P(/<-NR )2P(E)NR]2-, [EP(NR)3]3-, [RP(E)(NR)2] and [R2P(E)(NR )] (E=0,S, Se, Te). The emphasis is on the wide variety of coordination modes exhibited by these poly-dentate ligands, which have both hard (NR) and soft (S, Se or Te) centers. Possible applications of their metal complexes include new catalytic systems, coordination polymers with unique properties, and novel porous materials. 

The lipophilicity of the TRISPHAT anion 8 also confers to its salts an affinity for organic solvents and, once dissolved, the ion pairs do not partition in aqueous layers. This rather uncommon property was used by Lacour s group to develop a simple and practical resolution procedure of chiral cationic coordination complexes by asymmetric extraction [134,135]. Selectivity ratios as high as 35 1 were measured for the enantiomers of ruthenium(II) trisdiimine complexes, demonstrating without ambiguity the efficiency of the resolution procedure [134]. 

The complexes Fe(CNR)4(CN)2 (R = H, CH3, C2H5) are reported to form 1 2 complexes with boron trihalides (65). In these complexes the BX3 group coordinates to the cyanide nitrogen, giving the ligand group [CNBXj] . A mention of a similar complex was made earlier 161). 

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