Trimer structure

Figure 7.26 Dimer and trimer structures of ortho-quinone methides.

An X-ray crystal-structure determination (370) revealed that mixed, nickel coordination exists in the trimeric complex, [Ni(S2CPh)2]3. The trimeric structure is similar to that found (371) in [Pd(PhCS2>]. The structure contains one molecule of type A linked centrosymmetrically through short Ni-S bridges to two molecules of type B, the three molecules being closely parallel (XXVII). Bonamico and co-workers (372)... 

A structurally related tetrameric macroheterocycle is compound 13 that is prepared in a one-pot synthesis (yield 64%) from salicylaldehyde and (3-aminophenyl)boronic acid in methanol (Fig. 4). Due to its insolubility it has been characterized only by mass spectrometry. If a substitutent is introduced at the imine function (R = Me, Ph), trimeric structures (14 and 15) are... 

Such a trimeric structure is almost completely disrupted but present as a monomer for regenerated bR in lipid bilayer of the liquid crystalline phase (Figure 34A and B). As demonstrated in Figure 34B, the 13C NMR... 

Di-f-butyltin oxide has a trimeric structure (102). Arylboronic acids can condense into trimeric structures and can displace tin sectors from 102, as shown in reaction 35. The structure of these compounds was elucidated by X-ray crystallography289. 

FIGURE 5-1 3 (A, B) Structure of a glutamate transporter. This bacterial glutamate transporter provides the first high-resolution model of a glutamate transporter [88]. The X-ray data indicate a trimeric structure. (A) A view of the trimer extracellularly and perpendicular to the bilayer. 

Komiyama at al. have prepared two oligonuclear Zn(II) complexes (22 and 23) and tested their hydrolytic activity toward different diribonucleotides [45,46] (catalytic turnover was not demonstrated). The dimer and trimer structures of the active species were confirmed by measuring the hydrolytic activity as a function of Zn/L ratio, which show sharp maxima at the expected 2/1 and 3/1 ratios, respectively. The oligomer complexes have high ribonuclease activity (e.g. the hydrolysis of UpU is accelerated more than 4 and 5 orders of magnitude by 22 and 23, respectively), whereas the effect of the monomer complex 24 was not... 

D-correlation spectra were collected. This information was used with empirical spectral simulations of proton and carbon spectra to elucidate the structures. The necessary information was thus provided to demonstrate that multiple dimer-like structures were formed through bonding of residual synthetic precursor to each of the hydroxyl sites of the drug substance itself. Three distinct dimers were identified. These species were tracked by LC-NMR, and two were shown to interconvert over time. Analogous trimer structures were also evident at lower levels. 

Figure 9.6 Trimer structure repeated in the two-dimensional network of closo-[3-Ru(C6H6)-8-HS-1,2-C2B9Hio]. (Reproduced with permission from ref. 8.)...

Other xanthylium salt structures in which one of the catechin A-rings was substituted with an hydroxyl (in 6 or 8 position) or an ethylcarboxy group (in C8) were proposed on the basis of their NMR and MS data and postulated to result from condensation of the formylcatechin derivatives. Finally, carboxymethine-linked trimeric structures containing xanthylium and quinonoidal moieties were postulated for pigments showing absorbance maxima at 560 nm, on the basis of their mass signals at m/z 959 and 961 in the positive ion mode. ... 

Aluminum methoxide Al(OMe)3 is a solid which sublimes at 240 °C in vacuum. Aluminum isopropoxide melts in the range 120-140 °C to a viscous liquid which readily supercools. When first prepared, spectroscopic and X-ray evidence indicates a trimeric structure which slowly transforms to a tetramer in which the central Al is octahedrally coordinated and the three peripheral units are tetrahedral.162,153 Intramolecular exchange of terminal and bridging groups, which is rapid in the trimeric form, becomes very slow in the tetramer. There is MS and other evidence that the tetramer maintains its identity in the vapour phase.164 Al[OCH(CF3)2]3 is more volatile than Al[OCH(Me)2]3 and the vapour consists of monomers.165 Aluminum alkoxides, particularly Al(OPr )3, have useful catalytic applications in the synthetic chemistry of aldehydes, ketones and acetals, e.g. in the Tishchenko reaction of aldehydes, in Meerwein-Pondorf-Verley reduction and in Oppenauer oxidation. The mechanism is believed to involve hydride transfer between RjHCO ligands and coordinated R2C=0— A1 groups on the same Al atom.1... 

The structures of the trinuclear species Cr3(OH)45 + and the two tetranuclear species a- and /7-Cr4(OH)6< + have not been established. Linear as well as cyclic trimeric structures (structures 4a, 4b, and 5 in Fig. 1) have been considered (27, 37), as has another cyclic structure such as that shown in Fig. 10. However, the kinetic, thermodynamic, spectroscopic, and magnetic properties appear to provide no evidence to favor the one rather than the other (27). The number of possible... 

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