Linear dimerization

The structure of a non-hydrolyzed dimer, cA-[(2,2 -bipyridine)palladium(II)]2(/i-l,3-N03)2 2+ is shown in Figure 45.521 The dimerized m-( 2.2-bi pyridine) Pd11 units aggregate into a dimer-to-dimer linear conformation through direct metal—metal interaction522 and tt-tt stacking.523 Notably, the dimer was first reported to be linked by double nitrato-bridges (/x-l,3-N03)2 in a cofacial... 

There are a number of papers which report the use of Si NMR in studies of the structures of various soluble silicates and alkali silicate glasses. (93, 97-103) Early workers concluded that in soluble sodium metasilicate solutions only simple monomeric silicate structures are present. (104) The presence of polymeric structures was subsequently identified using Raman spectroscopy (105-107) and trimethylsilylation experiments. (108) Marsmann (97) first reported the existence of dimer, linear trimer, tricyclic, and polymeric structures based on Si NMR... 

We have confirmed these assignments for Q Q, and a species by recording the Si NMR spectra of the unhydrolyzed, pure compounds of dimer, linear trimer (CH30)8Si302, and a mixture of linear and branched tetramer (CH3O) 1081403 (Table I). The values are in excellent agreement with the results of Marsmann et al. (15) and previous work in our laboratory (12). We have used these assignments for the kinetics calculations discussed in the next section. 

The pattern is that increasing temperature and pressure results in progressive polymerization Ceo -> dimers linear polymer —> 2D-polymer - 3D-polymer -y superhard phase [46] . The final material is interesting because hardness tests reveal that that this material is approximately two-thirds as hard as diamond but with a resistivity very... 

G3.2 Synthesis, structure and spectrometry of metal-metal dimers, linear chains and dimer chains [Nyholm Lecture]... 

Fig. 3.5. The energy spectrum of the valence and conduction molecular-orbital states for a dimerized, linear chain. A particle-hole excitation and its degenerate counterpart, connected by the paxticle-hole transformation, are shown. 2A is the charge gap, shown as a function of inverse chain length in Fig. 3.6.

Fig. 3.6. The charge gap, 2A, for dimerized, linear chains versus the inverse chain length, and the square of the inverse chain length (inset). As AT cx) the charge gap scales as 1/N. [5 = 0.1.)...

The following two examples deliver some insight into the current status of research and give an impression of the large potential on-surface reactions have to offer. Grill, Hecht, and coworkers utilized a reaction based on Ullmann coupling to obtain from brominated porphyrins adsorbed onto Au(lll) dimers, linear chains, or a 2D network depending on the number of bromine atoms (one, two, and four, respectively) attached to the porphyrin monomers. The porphyrins are activated either directly on the Au... 

It may be concluded that they are formed by cyclization of dimerized linear precursors, as shown in Figure 21.20b, while the formation of trefoil knots isomers of single rings is not observed. 

Mulder and Damen [114] hydrolyzed TEOS with water under acidic conditions (r = 1). Raman and Si NMR spectral comparisons of the non-OH substituted dimers, trimers, and tetramers isolated by fractional distillation allowed assignments of some of the Raman bands observed during the initial stages of the hydrolysis and condensation reactions. The principal symmetric Si04 stretch vibrations of TEOS and the non-OH substituted dimer, linear trimer, and linear tetramer are 654,600, 576, and 545 cm", respectively. No evidence of the cyclic trimer was observed, in contrast to the results of Balfe and Martinez [108] and Kelts and Armstrong [106],... 

Other examples were described by Chapiro and DeUeu The authors paid attention to the unusual behavior of polymerization of AA in different solvents. It is well known that organic adds form dimeric complexes by hydrogen bonds. The authors assumed that molecarles of AA can take four forms as free monomer, cyclic dimer, linear oligomer, and monomer assodated with polymeric template, depending on the nature of the solvent used, temperature, and concentration. 

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