ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The X-Ray structures of the 1:1 copper(II) complexes with racemic and opticall active (+)-(R,R)-(2,6-bis(pyrrolidin-2-yl)pyridine ((+)-bpp; (+)-I) were determined. Whereas the perchlorate 1 of racemic complex contains the monomeric units with perfect C2 symmetry, the sulfate of the optically active compound crystallizes as a coordination polymer composed of sequences of three different five-coordinate units linked by sulfate bridges around a threefold screw axis (see 2). Formation of the 1:2 complexes of nickel(II) with (±)-bpp is shown to be highly stereoselective. Acidimetric titrations and CD measurements indicate that the equilibrium mixture contains 99% of the meso-complex 3 belonging to the point group S4 and only 0.5% of each enantiomer of the C2-symmetric optically active forms. The S4 symmetry of meso-[Ni{(+)-bpp}{(-)-bpp}]ClO4)2 (3) was confirmed by X-ray analysis. The formation of binary complexes of cobalt(II), zinc(II), and cadmium(II) with (±)-bpp shows an excess of 28, 34, and 8%, respectively, of the meso-form over the statistical amount. CD and UV/VIS measurement show a pH-dependent high spin/low spin equilibrium between the octahedral [Ni(bpp)(H2O)3]2+ and the square-planar [Ni(bpp)OH]+ in aqueous solution.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19930760136
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