Trigonal ligands

When copper is bound to one sulfur atom of a cysteine and two nitrogens of two histidines in an essentially tetrahedrally distorted - trigonal ligand environment (type I copper proteins), the excited levels are low in energy, and the values are reduced to about 5 x 10 ° s (29). Examples are blue copper proteins, like ceruloplasmin and azurin, and copper(II) substituted liver alcohol dehydrogenase (30-32). 

The ideal NiAs structure consists of a close-packed-hexagonal anion sublattice with cations in the octahedral interstices, which form a simple-hexagonal sublattice. Along the c axis the octahedral sites share common faces both above and below, so that the cations are arranged in linear chains with optimum conditions for cation- -cation interactions via I>i orbitals, each octahedral-site cation seeing a trigonal ligand field (see Fig. 77). Whether the IYi electrons are... 

Sun et al. have used the flexible trigonal ligand 36 to form a smaller M3L2 cage compound with zinc acetate [78]. This system represents one of the first such compounds to be formed and subsequently analysed in the solid state. The cage was shown to complex camphor with a binding constant of 117 M-1 (D20). Fur-... 

The extent of mixing of different spin-orbital states expressed by the angle (x) is determined by the ratio of the trigonal ligand field splitting parameter A (positive if [Pg.193]

An interesting series of structures based on the rutile net illustrates the relationship between interpenetration and self-penetration. The compounds are constructed using octahedral metal ions and the trigonal ligands tcm [tricyanomethanide, C(CN) ] and dca [dicyanamide, N(CN)2 ]. It is important to note that dca is a smaller ligand than tcm. Thus, while the compounds M(tcm)2 have two interpenetrating rutile-related networks,the... 

Fig. 3. Ti(urea)gl3 single crystal. Temperature dependence of P and Px- The solid curves are the smoothed experimental data, the dashed line is calculated for py, the dotted line is calculated for pj, from the theory for the term with Dg = 1700cm" J=-600cm fc = 0.45, A = 75cm" , C7 g < 50 cm fc is the orbital angular momentum reduction factor, A is the splitting of the term, 17 q is a trigonal ligand field parameter [73F6].

Complexes of titanium(III) can be made from the trichloride— these are either approximately octahedral, 6-coordinate (for example TiClj.SL (L = ligand) and [TiCljfHjOj, formed when TiCls dissolves in aqueous hydrochloric acid), or 5-coordinate with a trigonal bipyramid structure. 

The copper(I) ion, electronic stmcture [Ar]3t/ , is diamagnetic and colorless. Certain compounds such as cuprous oxide [1317-39-1] or cuprous sulfide [22205-45 ] are iatensely colored, however, because of metal-to-ligand charge-transfer bands. Copper(I) is isoelectronic with ziac(II) and has similar stereochemistry. The preferred configuration is tetrahedral. Liaear and trigonal planar stmctures are not uncommon, ia part because the stereochemistry about the metal is determined by steric as well as electronic requirements of the ligands (see Coordination compounds). 

The concept of heterotopic atoms, groups, and faces can be extended from enantiotopic to diastereotopic types. If each of two nominally equivalent ligands in a molecule is replaced by a test group and the molecules that are generated are diaster-eomeric, then the ligands are diastereotopic. Similarly, if reaction at one face of a trigonal atom generates a molecule diastereomeric with that produced at the alternate face, the faces are diastereotopic. 

A number of transition-metal complexes of RNSO ligands have been structurally characterized. Three bonding modes, r(A,5), o-(5)-trigonal and o (5 )-pyramidal, have been observed (Scheme 9.1). Side-on (N,S) coordination is favoured by electron-rich (et or j °) metal centers, while the ff(S)-trigonal mode is preferred for less electron-rich metal centres (or those with competitive strong r-acid co-ligands). As expected ti (N,S)... 

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