화학공학소재연구정보센터
Inorganic Chemistry, Vol.35, No.12, 3667-3674, 1996
Stereochemical Analysis of Palladium(II) Complexes of the Selenium Coronands 1,5,9,13-Tetraselenacyclohexadecane and 1,5,9,13,17,21-Hexaselenacyclotetracosane
Crystal structures for [Pd(16Se4)][BF4](2) (1) (16Se4 = 1,5,9,13-tetraselenacyclohexadecane) and [Pd(16Se4)][BF4]Cl (2) both contain the [Pd(16Se4)](2+) ion which has square-planar coordination about Pd and a stereochemistry (denoted c,c,c) in which all of the selenium nonbonding valence electron pairs are mutually cis with respect to the coordination plane. In both structures the conformation adopted by the cation deviates slightly but significantly from molecular mm (C-2v) symmetry. The asymmetry is most clearly resolved for 2, in which the Pd-Se bond lengths vary significantly (2.444(1)-2.463(1) Angstrom). For 1 : T = 295 K; fw = 764.2; space group Pnma; Z = 4; a = 12.356(1) Angstrom; b = 10.397(1) Angstrom; c = 16.233(2) Angstrom; V = 2193.7 Angstrom(3); R(F) = 0.036 for 997 data (I-0 greater than or equal to 2.5 sigma(I-0)) and 131 variables. For 2 : T = 295 K; fw = 712.8; space group P (1) over bar; Z = 2; a = 7.2377(4) Angstrom; b = 10.7784(7) Angstrom; c = 12.9523(9) Angstrom; alpha = 76.607(6)degrees; beta = 86.020(6)degrees; gamma = 85.186(5)degrees; V = 978.17 Angstrom(3); R(F) = 0.023 for 2134 data (I-0 greater than or equal to 2.5 sigma(I-0)) and 214 variables. The Se-77,H-1,C-13, and H-1-C-13 correlated NMR spectra for 1 in D2O solution were fully assigned. At room temperature, [Pd(16Se4)](2+) occurs in D2O solution predominantly as the c,t,c and c,c,c stereoisomers. Variable temperature NMR spectroscopic results demonstrate that at an elevated temperature (389 K) configurational interconversion is rapid on the H-1-NMR time scale.