1. Eduard-Zintl-Institut für Anorganische and Physikalische Chemie, Technische Universität Darmstadt, Petersenstrasse 20, D-64287 Darmstadt, Germany, Polymer Research, BASF SE, D-67056 Ludwigshafen, Germany, and School of Chemical Engineering and Analytical Science, University of Manchester, P.O. Box 88, Sackville Street, Manchester M60 1QD, U.K.