Oxalates structure

The two novel structures described above are closely related. In the layered Sn(II) oxalate, the 20-membered aperture results from linkages between four-and six-coordinated Sn(II) atoms and the oxalate units. There is three-dimensional connectivity in the zinc oxalate, and yet there are certain similarities between its structure and that of the Sn(II) oxalate. An examination of the connectivity patterns between the oxalates and M2+ ions (M = Zn or Sn) in both solids reveals that the zinc oxalate can be derived from the tin oxalate structure by the replacement of the four-coordinated Sn(II) atoms with a hexa-coordinated Zn atom having two in-plane connectivities and one out-of-plane connectivity with the oxalate units as shown in Fig. 7.31. The out-of-plane connectivity is responsible for the three-dimensional nature of the structure in the zinc oxalate (Figs. 7.29 and 7.30). 

Figure 7.34. The hierarchy of zinc oxalate structures (a) monomer, (b) dimer, (c) onedimensional chain, (d) two-dimensional layer and (e) three-dimensional structure. Note the close relationships between them (Vaidhyanathan et al. [49]).

The metal-activated head to head dimerization of CS2 has been reported for Fe (224 MesCj—Ni, Cp—Ni (225), and Cp—Ti (226) carbonyl complexes. The ligands in the Fe and Cp—Ni complexes 360 and 362 are formally regarded as derivatives of ethenetetrathiol, whereas in the MesCj—Ni and Ti complexes 361 and 363 the highly delocalized r-elec-tron systems suggest a major contribution from a bis(dithiolene)-like te-trathio-oxalate structure. The bonding pattern drawn in 361 and 363 does... 

Fig. 15a and b. EXAFS determined copper oxalate structure a) ribbon structure of the chains b) 3D packing of the ribbons... 

In spite of these investigations, there is still considerable ambiguity regarding the mechanisms involved. Such studies are hampered by the very nature of the reaction subtle changes in the oxalate structure, chemical environment, and type of fluorophore can result in large variations in overall quantum yield and emission intensity versus time profiles. 

Fig. 9.8 Half-cell investigated ORR overpotential at a current density of 0.5 mA cm plotted versus mesopore surface areas of catalyst synthesized frran different transition metal oxalate structure-forming agents (reprinted from [59], with permission from Elsevier)...

Fig. 13. Framework aluminophosphate-oxalate structure, [H3NCH(CH3)CH2NH3]2 [Al4P602o(OH)4(C204)(H20)]. The aluminophosphate layers are connected through oxalate bridges (C-atoms are shown as circles) into a 3-D framework structure. This [010] projection shows the characteristic 12-member ring channels (PO4 tetrahedra are white, the AIO4 tetrahedra and AlOg octahedra are gray).

Oxides from the hydrothermal decomposition of thorium oxalate. Oxides prepared by the hydrothermal decomposition of the oxalate [27] at 300°C in a closed autoclave were found to be markedly different in their characteristic properties from the thermally prepared materials. The precipitation temperature of the oxalate had no effect on the final shape or size, and all evidence of the original oxalate structure had disappeared. Sedimentation particle-size analyses indicated particle sizes between 0.5 and 1 micron. 

Because of the structural requirements of the bielectrophile, fully aromatized heterocycles are usually not readily available by this procedure. The dithiocarbamate (159) reacted with oxalyl chloride to give the substituted thiazolidine-4,5-dione (160) (see Chapter 4.19), and the same reagent reacted with iV-alkylbenzamidine (161) at 100-140 °C to give the 1 -alkyl-2-phenylimidazole-4,5-dione (162) (see Chapter 4.08). Iminochlorides of oxalic acid also react with iV,iV-disubstituted thioureas in this case the 2-dialkylaminothiazolidine-2,4-dione bis-imides are obtained. Thiobenzamide generally forms linear adducts, but 2-thiazolines will form under suitable conditions (70TL3781). Phenyliminooxalic acid dichloride, prepared from oxalic acid, phosphorus pentachloride and aniline in benzene, likewise yielded thiazolidine derivatives on reaction with thioureas (71KGS471). 

Novolacs are usually made under acidic conditions. Oxalic, sulfuric, toluene sulfonic, phenyl sulfonic, methane sulfonic, hydrochloric, and phosphoric acids are the most common catalysts, though nearly any moderately strong acid will probably do. Often selection of the acid has significant effects on the resultant polymer structure or performance. Sometimes acids are selected for their volatility, as it may be necessary to distill the acid off in some processes. 

From their structures, it appears that the hydrolytic stability of macrocyclic lactones must necessarily be inferior to macrocyclic polyethers. Ease of synthesis of the cyclic esters is therefore one of the aspects which commend them to interest. It is probably for this reason that such lactones have not been made more often by the interesting approach of Kdgel and Schroder . These workers report the ozonolysis of dibenzo-18-crown-6 in a mixture of methanol and dichloromethane at —20°. Reduction of the ozon-ide at —75° using dimethylsulfide followed by warming and addition of acetone led to formation of 6 in 14% yield. The bis-oxalate had mp 164—165° from acetone, very similar to that of the starting crown. The transformation is illustrated below in Eq. (5.9). 

The crystal structure of many compounds is dominated by the effect of H bonds, and numerous examples will emerge in ensuing chapters. Ice (p. 624) is perhaps the classic example, but the layer lattice structure of B(OH)3 (p. 203) and the striking difference between the a- and 6-forms of oxalic and other dicarboxylic acids is notable (Fig. 3.9). The more subtle distortions that lead to ferroelectric phenomena in KH2PO4 and other crystals have already been noted (p. 57). Hydrogen bonds between fluorine atoms result in the formation of infinite zigzag chains in crystalline hydrogen fluoride... 

The crystal structures of the oxalates 806264 and K28n(C264)2.H26 show interesting features " ... 

Dioxides are known for all the actinides as far as Cf. They have the fee fluorite structure (p. 118) in which each metal atom has CN = 8 the most common preparative method is ignition of the appropriate oxalate or hydroxide in air. Exceptions are Cm02 and Cf02, which require O2 rather than air, and Pa02 and UO2, which are obtained by reduction of higher oxides. 

Several carboxylates, both simple salts and complex anions, have been prepared often as a means of precipitating the An ion from solution or, as in the case of simple oxalates, in order to prepare the dioxides by thermal decomposition. In K4[Th(C204)4].4Fl20 the anion is known to have a 10-coordinate, bicapped square antipris-matic structure (Fig. 31.8b). -diketonates are precipitated from aqueous solutions of An and the ligand by addition of alkali, and nearly all are sublimable under vacuum. [An(acac)4], (An = Th, U, Np, Pu) are apparently dimorphic but both structures are based on an 8-coordinate, distorted square antiprism. 

Hydrocarbon A has the formula C Hg- It absorbs 8 equivalents of H2 on catalytic reduction over a palladium catalyst. On ozonolysis, only two products are formed oxalic acid (H02CC02H) and succinic acid (H02CCH2CH2C02H). Write the reactions, and propose a structure for A. 

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

Oxalic acid, H2C204, is a poisonous compound found in rhubarb leaves. Draw the Lewis structure for oxalic acid. There is a single bond between the two carbon atoms, each hydrogen atom is bonded to an oxygen atom, and each carbon is bonded to two oxygen atoms. 

Some ligands have more than one atom with an unshared pair of electrons and hence can form more than one bond with a central metal atom. Ligands of this type are referred to as chelating agents the complexes formed are referred to as chelates (from the Greek chela, crab s claw). Two of the most common chelating agents are the oxalate anion (abbreviated ox) and the ethylenediamine molecule (abbreviated en), whose Lewis structures are... 

Write the I ewis structure, including resonance structures where appropriate, for (a) the oxalate ion, C2042 (there is a... 

---