Trigonal complexes

Scheme 1 Electronic states involved in the absorbtion bands in the region of the first singlet—triplet intersection for octahedral, tetragonal and trigonal complexes of nickel(II).336 Solid arrows denote spin-allowed absorbtion transitions, dotted arrows connect pairs of interacting levels. (reprinted with permission from ref. 336 1998, American Chemical Society).

The bonding mode is dependent on the nature of the metal centre as well as the steric or electronic properties of the imido substituent. For example, the M(CO)5 unit in the (AO-trigonal complex [W(CO)5 S(NMe)2 ] undergoes a 1,3-shift between the two nitrogen donors, whereas the tert-butyl forms a N,N -chelated [W(CO)4 S(NtBu)2 ] complex, as is also observed with main-group metal halides, e.g., [SnCl4 E(NtBu)2 ] (E=S, Se).153... 

The stress dependence of the transition frequency of the 1561 cm-1 mode of the As—H complex is shown in Fig. 21. The solid lines are given by fits to the data using the expressions shown in Table I with the parameters shown in Table III. The splittings and polarization data are well explained by an Ax stretching mode of a trigonal complex. (The weaker component expected for [111] stress and E//F was not resolved.)... 

A dynamic model with tunneling hydrogen (Joos etal., 1980) and a static model (Broeckx et al., 1980 Ham, 1988) have been proposd to explain the experimental findings. Space here is far too limited to discuss all the features of the two models and their relative merits. Suffice it to state that both models can explain certain properties of this complex. At the same time, both models have some shortcomings. The static model, which is based on a trigonal complex, is clearly too limited and cannot explain all... 

Starting from this rotated set complex orbitals and (t)3 multiplet operators may be constructed in a way which is entirely analogous to the treatment of Sect. 2. Hence the multiplets in Table 2 can be used equally well for trigonal complexes, keeping in mind that the axis of quantization is now the z axis. This implies that the subduction rules for real components in Eq. 15 have to be replaced by the appropriate S03 j. O j D3 subduction rules. In order to obtain the real forms of the (t2)3 basis functions the resulting expressions have to be multiplied once again by the pseudoscalar quantity of A2 symmetry. The appropriate product rules have been given by Ballhausen [59], For the individual orbital functions one obtains ... 

Fig. 7. A trigonal complex displaying displacement of the olefin along the double bond.

Tetragonal structures may also be obtained for models of Cu-alcohol dehydrogenase [39]. When the fourth ligand is uncharged, they are less stable than the corresponding trigonal complexes (in accordance with the crystal structure). However, with OH (which is involved in the reaction mechanism of the enzyme)... 

Type 1 Tetrahedral Complex Type 2 Trigonal Complex... 

Fig. 1. Projection drawing of the trigonal complex containing three planar ligands. The heavy lines represent the ligands, whose molecular planes have been rotated by 45° relative to the XY-plane, defined by the central ion and the ligating atoms. The (-f) and (—) mean above and below the XY-plsne. The projection in this way has the full symmetry D3 of the complex.

Ligands of the type 2,ll-bis(di-R-phosphinomethyl)benzo[c]-phenanthrene (bpbp) form trigonal complexes with metals such as Cu, Ag, Pd, Au, eta Two extreme conformations exist for these complexes in the P (parallel) cqnformer the CH2 - P vectors point to the same side of the mean bpbp plane, whereas in the A (anti-parallel) conformer they point to opposite sides of this plane. 

Bu4N]+ cation with [Me4N] induces formation of the dimeric tetrahedral structure preferentially over the mononuclear trigonal complex (54). 

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