from WorldWideScience.org

1

1999-06-01

Resumo em inglês This article describes the progress of a group of investigation on thermochemistry, which started in 1972. A homemade calorimeter was employed to provide quantitative support to the information on interative effect between lanthanide cations and halides or pseudohalides, in non-aqueous solvents, previously derived from conductometric titrations. However, the features of this instrument were not able to detect the thermal effects. Therefore, the great input to the group ca (mais) me from the acquisition of an LKB commercial apparatus, by the University in 1975. Considering the historical development of the coordination chemistry in Brazil, which was previously dedicated to strutural features of adducts, without focusing the energetic envolved in any coordinationcompound. Since starting the thermochemistry study, numerous masters and doctoral thesis covering more than a hundred adducts and a reasonable number of chelates, were presented systematizing data in order to understand the behavior of this kind of coordination compounds (C. Airoldi and A. P. Chagas, Coord. Chem. Rev. 1992, 119, 29). This knowledge enabled an extension of the study to include some heterogeneous systems formed by natural or synthetic materials like immobilized silica gel, lamellar phosphate, phosphonate or sulphate compounds, clays, polysaccharides, chrysotile, soils, etc. Many students are now engaged as staff members in Universities, Research Instituitions or other private institutions, developing many activities. Due to a multiplying effect on the formation of researchers, the group is now reaching the fourth generation.

2

1999-01-01

Resumo em português Os deslocamentos químicos de RMN 13C de carbonos a , b , g e d de 17 conjuntos de haletos (F, Cl Br e I) alifáticos, inclusive compostos mono, bi e tricíclicos, podem ser reproduzidos por uma equação linear de duas constantes e duas variáveis do tipo : d R-X = A*d R-X1 + B*d R-X2 onde A e B são constantes obtidas por regressão multilinear a partir de deslocamentos químicos de 13C; d R-X, o deslocamento químico de 13C do composto com halogênio (R-X); d R-X1 e d (mais) R-X2 deslocamentos químicos de outros haletos. Para brometos (R-X) alifáticos a melhor correlação foi obtida com os dados de fluoretos (R-X1) e iodetos (R-X2) com R2 de 0,9989 e desvio médio absoluto (DM) de 0,39ppm. Para cloretos (R-X) a melhor correlação foi com dados de brometos (R-X1) e iodetos (R-X2) com R2 de 0,9960 e DM de 0,76ppm. Para fluoretos (R-X) a melhor correlação foi com brometos (R-X1) e iodetos (R-X2) com R2 de 0,9977 e DM de 1,10ppm e para iodetos (R-X) foi com fluoretos (R-X1) e brometos (R-X2) com R2 de 0,9972 e desvio médio absoluto de 0,60 ppm. Resumo em inglês The 13C NMR chemical shifts of the a , b , g and d carbons of 17 sets of aliphatic halides (F, Cl, Br and I ), including mono, bi and tricyclic componds, can be reproduced by a linear equation composed with two constants and two variables: d R-X = A * d R-X1 + B* d R-X2, where A and B are constants derived from multilinear regression of 13C chemical shifts observed; d R-X, the chemical shifts of aliphatic halide (R-X) and d R-X1, d R-X2 the chemical shifts of other halide (mais) s. Were observed better correlation for aliphatic bromides (R-X) by using data of aliphatic fluorides (R-X1) and aliphatic iodides (R-X2), resulting R2 of 0.9989 and average absolute deviation (AVG) of 0.39 ppm. For the clorides (R-X), the better correlation were observed by using data of bromides (R-X1) and iodides (R-X2), R2 of 0.9960 and AVG of 0.76ppm. For the fluorides (R-X) were observed better correlation with data of bromides (R-X1) and iodides (R-X2), R2 of 0.9977 and AVG of 1.10 ppm. For the iodides (R-X) were observed better correlation with data of fluorides (R-X1) and bromides (R-X2), R2 of 0.9972 and AVG of 0.60.

3

1999-04-01

Resumo em inglês In this work are presented two modified forms of Kapustinskii equation that could be used to estimate the values of the lattice enthalphies for adducts: DM Hm o=(-n.z+ .z- .10(2)/D).(1-d*/D) .K and DM Hm o=(-n.z+ .z-.10(2)/d).(1-d*/d).K.d. Two new parameters related with steric effects and donor power of the ligands, J anddare introduced. The proposed equations were tested for 49 adducts (mainly from the zinc group halides). The difference between experimental (calorimetric) and calculated values (using the proposed equations) values are less than 5% for 41 of the tested adducts.

4

1998-07-01

Resumo em inglês An empirical equation: deltaD HmO = t i/2.2(2-n) is obtained and tested for 102 adducts (mainly adducts with zinc group halides). In the equation, t i is the Kelvin temperature of the beginning of the thermal decomposition of the adduct, (obtained by thermogravimetry), and n is the number of ligands. For 1/3 of the tested adducts the difference between experimental and calculated values was less than 5%. For about 1/3 of the adducts that difference exceeds 15%.