Pyridine bonding

Figures 2.a-c show the pyridine adsorption results. Bronsted acidity is manifested by the bands at 1440-1445,1630-1640 and 1530-1550 cm . Bands at 1600-1630 cm are assigned to pyridine bonded to Lewis acid sites. Certain bands such as the 1440-1460 and 1480-1490 cm can be due to hydrogen-bonded, protonated or Lewis-coordinated pyridine species. Under continuous nitrogen purging, spectra labeled as "A" in Figures 2a-c represent saturation of the surface at room temperature (90 25 unol pyridine/g found in all three tungsta catalysts) and "F" show the baseline due to the dry catalyst. We cannot entirely rule out the possibility of some extent of weakly bound pyridine at room temperature. Nevertheless, the pyridine DRIFTS experiments show the presence of Brpnsted acidity, which is expected to be the result of water of reduction that did not desorb upon purging at the reduction temperature. It is noted that, regardless of the presence of Pt, the intensity of the DRIFTS signals due to pyridine are...

Infrared spectra of pyridine adsorbed on dehydrated TS-1 and Ti-MCM-41 of comparable Ti content indicated the presence of only Lewis acid sites (Fig. 13). The infrared absorptions at 1595 and 1445 cm-1 are attributed to hydrogen-bonded pyridine (Si/Ti-OH—pyridine) and those at 1580 and 1485 cm-1 to pyridine bonded to weak Lewis acid sites (Fig. 12). Brpnsted sites, if present,... 

The separation of the same charged compounds were also accomplished on an ethyl-pyridine bonded silica surface and 30 0% methanol/C02 mobile phases without the need of added sulfonate modifier. Anionic compounds did not elute from the ethyl-pyridinium surface that lead the authors to hypothesize that the surface was positively charged. To further test this hypothesis, the separation of the same compounds on a strong anion exchange column, silica-based propyltri-methylammonium cationic surface, which exhibits are permanent positive charge was attempted. The same retention order was observed on the strong cation exchange surface. 

The rate law for the oxidation of [Ru(NH3)5(FlL)] + (HE = isonicotinamide) by I2 in acidic solution contains two terms, one depending on P2] and one depending on [I3 ] and [Ru complex]. An outer-sphere electron-transfer mechanism is proposed for each term. Reduction of [Ru (NFl3)5L] + (TIL = nicotinamide or isonicotinamide) to [Ru (NH3)5L]+ is accompanied by an isomerization from the amide-bonded L to pyridine-bonded FIL. Bromine oxidation of... 

Figure 10 X-Ray data for 7-hydroxy-6-methyl-7,6-borazarothieno[3,2-c]pyridine (bond lengths in A)...

The Co(II) compounds are usually low-spin, five-coordinate monomeric species, LCo(DH)2(II) (II). However, L2Co(DH)2 low-spin compounds can be isolated (II). These latter materials are known to be five coordinate in solution and have EPR and visible spectra and magnetic moments ( 2 BM) identical to those of LCo(DH)2 (12). The X-ray structure of neither type of solid is known when L = P-donor ligand but the bis(pyridine) compound has been characterized structurally (13) and exhibits long Co-N(pyridine) bonds of 2.25 A. 

The concept of a molecular lock using the dual character of a Pt(II)-pyridine coordination bond has been shown [95JA4175] utilization of the labile nature of the Pd(II)-pyridine bond has realized the quantitative self-assembly of [2]-catenane 27 from two related monocyclic counterparts. The catenane with M = Pd(II) is in rapid equilibrium whereas with M = Pt(II), the catenane is locked, but can be unlocked with added salt and heating or relocked by removing of the salt and cooling. 

Fig.5 step C At the mixing interface HjO-acelonc, water molecules meet a Mn3-complex species and attack the acetyl- and pyridine bonds hydrolyzing the whole structure. A buffer effect is established. 

The self-assembly of Pt(II) analogue lb with 2 was very slow due to the inactivity of the Pt(II)-pyridine bond. Thus, upon treatment of lb with 2, a kinetically distributed oligomeric mixture was initially formed. However, the mixture gradually turned into the thermodynamically most stable molecular square 3b after heating the solution for a few weeks at 100 °C. The use of bis-nitrate salt of 2, instead 2 itself, dramatically increased the reaction rate as well as the yield (79-81%). Similar improvements in reaction rate and yield were observed by the addition of NaNOj to the reaction. A significant difference in stability was found between 3a and 3b. The addition of la to 3a in D2O resulted in dissociation of 3a to give a mixture of 3a (ca. 50%) and two acyclic components which have la and 2 in 1 2 and 2 3 ratios. In a striking contrast, 3b remained intact even upon the addition of lb, as its structure had been locked by the inert Pt-Py bond. The square complex 3b was also found to show inclusion properties similar to 3a (Table 1). 

Bond order cannot be the determining factor, because the bond orders of pyridine and benzene are — to the best of our knowledge — identical 88). Furthermore, carbenes 81 and 82 show opposite selectivities, even though they both have the opportunity of adding to a 3,4-pyridine bond. The same goes for the pair 80, 82. 

Table 3. Characteristic frequencies for ammonia and pyridine bonded...

Dibutoxy-2,3-di(4-pyridyl)-8,11,15,18,22,25-hexakis (hexyl)-phthalocyaninato zinc, 40, was shown to form a coordinating polymer in the solid state (Figure 27). Each zinc atom has square pyramidal coordination and the apical Zn-pyridine bonds Unk the molecules in an infinite polymer chain. Such a chain is reminiscent of that reported for zinc 5,10,15-triphenyl-20-pyridylporphyrin. The behavior of 40 in solution was shown to be solvent dependent. In dichloromethane, it forms aggregates that break down into the monomeric Pcs in THF. Addition of pyridine to the solution evidently also breaks down the aggregates. 

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