| Popis: |
Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 2 : 1 adducts of the N,N′- bidentate aromatic base 1,10-phenanthroline (' phen ') with lead(II) nitrate and perchlorate . [( phen )2Pb(NO3)2] is monoclinic, P21/n, a 18.104(4), b 7.733(2), c 16.688(3) Ǻ, β 98.17(2)′, Z = 4, R being 0.036 for No = 3381 independent 'observed' reflections, while [( phen )2Pb(ClO4)2] is triclinic, Pī , a 13.134(4), b 12.342(4), c 7.771(3) Ǻ, α 94.34(3), β 101.49(3), γ 93.91(2)′, Z = 2, R being 0.056 for No 3473. The two systems are mononuclear with eight-coordinate PbN4O4 coordination environments incorporating a pair of O,O'- bidentate anions. Stereochemical calculations, based on valence shell electron pair repulsion (VSEPR) theory, have been performed for coordination complexes of the general type [M( bidentate A)n( bidentate B)4-n] (n = 1 or 2) and for several types of lead(II) complex thought to contain sterically active lone pairs of electrons. Expected deviations from ideal stereochemistry have been successfully predicted and for many of the complexes studied there is good agreement between the observed and calculated stereochemistry. In the particular case of these lead(II)/ phen complexes it appears to be necessary to invoke steric interactions of the a-hydrogen atoms in addition to a sterically active lone pair. |
