Physical study

3 Physical Studies. - Ag H INEPT n.m.r. studies of intramolecular core rearrangements are reported for Ag2Ru4 clusters.Substitution reactions on RUC03 clusters have been monitored by Co and n.m.r. spectroscopy. Applications are recorded of ID heteronuclear NOE difference spectroscopy in assignment of % and n.m.r. parameters of dinuclear fulvalene complexes. 

Numerous physical studies of poly(l-pyrazolyl)borate complexes have been carried out, some as part of structure determinations, others to study different phenomena inherent in the complexed transition metal. 

The process is repeated to average the pz environments and also involving inversion of the B(pz)2Pd boat. Examples of this type of exchange are fairly common and were found in anumber of RB(pz 3 complexes of Pd(II) Rh(I) Pt(II) Cu(l) 

In octahedral compounds such as Co[B(pz)j2 or [B(pz)4Mo(CO)j] the fourth, uncoordinated pz group maintains its separate NMR identity. This can be seen particularly well in the Co(II) complex, where the peaks range from —5500 to -t-6960 Hz (at 60 MHz) because of contact shifts. The fact that the pz groups show up as a 3 1 pattern implies a low barrier to rotation of the uncoordinated pz moiety about the B—N bond, thus making the environments of all 5-protons averaged. 

A large number of poly(l-pyrazolyl) borate complexes had their structure determined by X-ray crystallography these are listed in Table 8. It should be remembered, however, that in some instances the structure in solution will have a different denticity of the poly(l-pyrazolyl)borate ligand than that found in the crystal. 

Various dinuclear complexes involving Mo have been reported. They include [(HB pz-3,5-(CH3)2 3Mo(NO)I]20, where the Mo 0—Mo bond is bent at a 171° angle and also [HB(pz)3Mo(CO)2]2S, which was prepared from 

Because of the limited solubility of metal phthalocyanines, the spectra are limited to the solid state. Most authors have used Nujol or halocarbon mulls, but Sidorov and Kotlyar (328) sublimed the complexes onto potassium chloride or bromide disks. The disks and samples were maintained at a temperature of about 100°C, as a result of which thin layers of the a modification were always produced. The /3 polymorphs were obtained by taking the disks and subjecting them to a temperature of 280°-300°C in vacuo for several hours, whereupon the a— j3 transformation took place. The infrared spectra were then remeasured. The spectral characteristics of the a and 6 forms are almost independent of the central metal ion. In- 

Certain of the absorption bands are central ion-sensitive (lines 13, 17, 23 and 27-31). These all follow approximately the same sequence, namely, Mg = Zn Cu Fe Co Ni. There appears to be no especial significance to this order. A similar effect is observed in the Nujol mull spectra, but it is probably not valid to compare the two sets of data in view of the different manner in which they were obtained. Using band number 13, the Nujol mull data follow the order Pb Sn(II) Sn(IV) U02 Al(III) Ge(IV) Ru(II) Si (170, 177, 195, 196, 220, 295). This order is not 

Assignments op NH and ND Vibrations in Metal-Free Phthalocyanine and Its JV-Deuterated Derivatives  

By far the most detailed thermodynamic studies have been made by Berezin, who has looked at the equilibria existing in concentrated sulfuric acid. Linstead s group were the first to observe that some of the metal phthalocyanines were demetallated in concentrated sulfuric acid, whereas others appeared indefinitely stable (10). It was shown that all phthalocyanines which resisted attack were of metals whose radii were of the right size to fit nicely into the space available at the center of the ligand. Berezin has since put these observations on a more quantitative basis (19, 21, 26). Labile complexes (i.e., those which are demetallated instantly or fairly rapidly in concentrated sulfuric acid) include those of the alkali metals, alkaline earth metals, Be, Mg, Cd, Hg, Sb(III), Pb, Sn(II), Mn(II), and Fe(III). Stable complexes (demetallated very slowly in acid) include those of Zn, Al, Cl2Sn(IV), OV(IV), Co(II), Rh(II), Os(IV), Ni(II), Pd(II), Pt(II), and Cu(II). The actual rates of decomposition vary widely thus, while calcium and magnesium phthalocyanines are demetallated very rapidly, silver and lead phthalocyanines react fairly slowly (19). The rates of decomposition in 1 M sulfuric acid increase in the sequence (19) Fe(III) 

Values for the rate constant k are listed in Table XI. The constant kv is independent of the concentration of sulfuric acid within the range 15-18 M, and the reaction is irreversible. 

It is true that the results of some investigations in the past led to the conclusion that dimeric species were present in sodium silicate solutions. Thus measurements of dif- 

However, it is possible that the lower diffusion rate ascribed to SijOj might be due to HSiOj hydrogen-bonded to water molecules, or to a loosely hydrogen-bonded [OjSi, ) SiO,] complex and not to the formation of an oxygen-bonded dimeric ion. In any case, the exact nature of the dimer ions in silicate solutions, if present, remains to be determined. 

Most investigators, especially since 1950, indicate that in aqueous 3.3 1 ratio sodium silicate solutions there are few dimer and trimer ions and the silica is distributed between monomer ions, HSiOs or SiOj , and three-dimensional polymer. ions or charged particles. There is some evidence that a minor amount of cyclic tetramer ion may also be present. 

Even in 1928, Harman (34) concluded from conductivity, transfer numbers, activity coefficients, hydrolysis, osmotic activity, freezing point data, phase relations, and diffusion experiments that there are only two simple silicates, NajSiOj and NaHSiOa, and that silicates in the SiO rNajO ratio range of 2 1 to 4 1 become increasingly colloidal.  

Viscosity studies by Main (35) led to the conclusion that above a ratio of 2 SiO 1 NajO, colloidal aggregates of some type were present, along with simple silicate ions. Hk gg (36) reached similar conclusions from potentiometric measurements. 

Alkane eliminations frcan p-alkylldene complexes have been monitored 36 

Electrochemical studies of redox processes of a number of cluster 

2- PrNCH2CH,N Pr ligand , and a neutron difiiraction study of [H,OS o(CO)2J[PPN]2 at 20K which allowed the direct location of the hydrido ligands  

Compounds with Homomiclear Transition Metal Bonds 

1 Group 4.- As in 1990, there appears to be no reports of direct metal-tnetal bonds in organometallic complexes of this group. 

Magnetic susceptibilities of osmium clusters show the evolution of metallic behaviour for high nuclearity species. Electrochemical measurements have been made on several cluster systems, including 

Measured heats of hydrogenation of metal-metal bonded complexes (M2(CO)gCp2] are -3.3, +6.3 and -1.5 kcal/mol, for M Cr, Ifo and W, respectively. Further studies of reactions of gas phase transition metal cluster ions with hydrocarbons have been reported.  

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Newton, one of the greatest physicists of all time, is said to have spent more time on his alchemist efforts and experimentation than on his physical studies. Was this only scientific fascination, or had his... 

Pieces of coal are mixtures of materials somewhat randomly distributed in differing amounts. The mineral matter can be readily distinguished from the organic, which is itself a mixture. Coal properties reflect the individual constituents and the relative proportions. By analogy to geologic formations, the macerals are the constituents that correspond to minerals that make up individual rocks. For coals, macerals, which tend to be consistent in their properties, represent particular classes of plant parts that have been transformed into coal (40). Most detailed chemical and physical studies of coal have been made on macerals or samples rich in a particular maceral, because maceral separation is time consuming. 

Although physical studies of the electronic structure of surfaces have to be performed under UHV conditions to guarantee clean uncontaminated samples, the technique does not require vacuum for its operation. Thus, in-situ observation of processes at solid-gas and solid-liquid interfaces is possible as well. This has been utilized, for instance, to directly observe corrosion and electrode processes with atomic resolution [5.2, 5.37]. 

Selenium biochemistry. Chemical and physical studies. J. D. Odom, Struct. Bonding (Berlin), 1983,... 

The complexes of the 1,1-dithio ligands with the Group I transition metals have been studied in considerable detail, and have been extensively reviewed by Coucouvanis (1). Interest in the synthetic chemistry of these complexes has been maintained over recent years, but a large proportion of the work on these complexes has been concerned with physical studies, particularly by esr spectroscopy. 

Odom JD (1983) Selenium Biochemistry. Chemical and Physical Studies. 54 1-26 Oehme 1, see Wolfbeis OS (1996) 85 51-98... 

M. F. Fingas, B. Kolokowski, and E. J. Tennyson. Study of oil spill dispersants effectiveness and physical studies. In Proceedings Volume, pages 265-287.13th Environ Can Arctic Mar Oil Spill Program Tech Semin (Edmonton, Canada, 676-6/8), 1990. 

For M. capsulatus (Bath), values of +350 and -25 mV, for Ex° and E2°, respectively, vs NHE were obtained from redox titrations by measuring the appearance and disappearance of the EPR signal of Hmv (37). Problems were encountered in producing high yields of Hmv from this organism for use in physical studies, despite the large difference between Ex and E2°, and so the potentials were remeasured. In the latter experiments, two sets of electron-transfer mediators were used,... 

Physical studies of the hydroxylase have established the structural nature of the diiron core in its three oxidation states, Hox, Hmv, and Hred. Although the active site structures of hydroxylase from M. tri-chosporium OB3b and M. capsulatus (Bath) are similar, some important differences are observed for other features of the two MMO systems. The interactions with the other components, protein B and reductase, vary substantially. More structural information is necessary to understand how each of the components affects the others with respect to its physical properties and role in the hydroxylation mechanism and to reconcile the different properties seen in the two MMO systems. The kinetic behavior of intermediates in the hydroxylation reaction cycle and the physical parameters of intermediate Q appear similar. The reaction of Q with substrate, however, varies. The participation of radical intermediates is better established with the M. triehosporium... 

Lemus, R. L. Lee, C. H. Skibo, E. B. Studies of extended quinone methides. Synthesis and physical studies of purine-like monofunctional and bifunctional imidazo[4,5-g]quinazo-line reductive alkylating agents. J. Org. Chem. 1989, 54, 3611-3618. 

Bouanchaud DH, Hellio R, Bieth G, et al. 1975. Physical studies of a plasmid mediating tetracycline resistance and hydrogen sulfide production in Escherichia coli. Mol Gen Genet 140(4) 355-359. 

Ligand (119) yields nickel complexes of type [Ni2L](BF4)4 (low spin) and [Ni2L(NCS)4].2H20 (high spin). For each of these complexes, physical studies indicate that the macrocycle circumscribes the two nickel ions such that each ion is surrounded by four sulfur donors in a planar array. 

Recent chemical and physical studies of this laboratory gave support to the consideration that a flavanone type moiety can reasonably be considered to be present in bagasse lignin (111). 

Reaction of 1 with benzaldehyde and zinc chloride gave a diastereomeric mixture (6) of R- and 5-2,3-O-benzylidene derivatives (4a and 4b). The former (4a) would be identical to the acetal described by Zinner et al. (3) as 2,4-O-benzylidene-D-ribono-1,5-lactone. This structure was further established as 4a, by chemical and physical studies of the product obtained on reaction of 1 with benzaldehyde dimethyl acetal (7). The 2,3-O-benzylidene derivative, obtained by Garegg et al. (8) on reaction of 1 with a,a-dichlorotoluene in pyridine, has the same properties as compound 4a, which would indicate the -configuration for the acetal carbon. 

In addition to these physical studies at the Bureau, Tipson was able to return to his synthetic interests, both alone and in collaboration with other staff members. He was especially pleased to prepare D-talose in crystalline form, an accomplishment that had eluded Emil Fischer. Pursuing his longstanding interest in the reaction of sulfonic esters with iodide and following an earlier observation that the tetratosyl ester of erythritol is converted into butadiene by the action of sodium iodide and zinc, he demonstrated (with A. Cohen) that nonterminal unsaturation may be conveniently introduced into alditol derivatives by reaction of contiguous secondary sulfonates with sodium iodide and zinc dust in boiling A.A-dimethylformamide. This Tipson-Cohen reaction subsequently proved of great utility in other hands for the conversion of more complex carbohydrate structures into vicinal dideoxy derivatives. 

After the reaction has taken place we make a physical study of what has happened and, there again, we carry on physical operations (14) ... 

Previous work on the synthesis of TTF (tetrathiafulvalene) containing polymers has been reported by at least seven groups of researchers. Most of this work concerns condensation 6,7,8,9 polymers or polymers made from vinyl substituted TTF molecules . Without exception, the polymers produced by these methods have been largely unacceptable for subsequent physical study because of their brittle,intractable, highly insoluble nature. Only by reaction of a suitably monofunctionalized TTF derivative with the preformed polymer poly(vinylbenzylchloride) has it been found possible — to prepare soluble TTF homopolymers with more manageable physical properties. 

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