Forschungsbericht  Research Report Recent Advances in the Chemistry of “Clusters” and Coordination Polymers of Alkali, Alkaline Earth Metal and Group 11 Compounds Katharina M. Fromm*, Estelle D. Gueneau, Adeline Y. Robin, William Maudez, Jorge Sague, and Re ´mi Bergougnant Basel/Switzerland, University, Department of Chemistry Received February 2 nd , 2005. Abstract. This contribution gives an overview on the different sub- jects treated in our group. One of our fundamental interests lies in the synthesis and study of low-dimensional polymer and molecular solid state structures. We have chosen several synthetic approaches in order to obtain such compounds. Firstly, the concept of cutting out structural fragments from a solid state structure of a binary compound will be explained on behalf of BaI 2 . Oxygen donor ligands, used as chemical scissors on BaI 2 , allow obtaining three-, two-, one- and zero-dimensional derived compounds depending on their size and concentration. Thus, a structural genealogy tree for BaI 2 can be established. This method, transferred to alkali halides using crown ethers and calix[n]arenes as delimiting ligands, leads us to the subject of one-dimensional ionic channels. A second chapter deals with the supramolecular approach for the synthesis of different dimensional polymer structures derived from alkaline earth metal iodides, and based on the combination of me- tal ion coordination with hydrogen bonding between the cationic complexes and their anions. Under certain circumstances, rules can be established for the prediction of the dimensionality of a given compound, thus contributing to the fundamental problem of struc- ture prediction in crystal engineering. A third part describes a fundamentally new synthetic pathway for generating pure alkaline earth metal cage compounds as well as alkali and alkaline earth mixed metal clusters. In a first step, differ- ent molecular precursors, such as solvated alkaline earth metal hal- Introduction We got interested in the non-aqueous chemistry of alkali and alkaline earth metal elements for several reasons: i) the chemistry of alkali and alkaline earth metal compounds in water can best be described as ionic whereas not much was known about their behaviour in organic solvents; ii) alkali * Prof. Dr. K. M. Fromm University of Basel Department of Chemistry Spitalstrasse 31 CH-4056 Basel Tel. : +41 61 267 1004 Fax: +41 61 267 1021 E-mail: katharina.fromm@unibas.ch www.unibas.ch Z. Anorg. Allg. Chem. 2005, 631, 1725-1740 DOI: 10.1002/zaac.200500079  2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1725 ides are investigated as a function of the ligand size and reactivity. They are then reacted with some alkali metal compound in order to partially eliminate alkali halide and to form the clusters. The so obtained unique structures of ligand stabilized metal halide, hydroxide and/or alkoxide and aryloxide aggregates are of interest as potential precursors for oxide materials. Approaches to two synthetic methods of the latter, sol-gel and (MO)-CVD, are investi- gated with our compounds. In order to generate single source precursors for oxide materials, we started to investigate transition metal ions, especially Cu and Ag, using multitopic ligands. This has led us into the fundamental problematic of “crystal engineering” and solid state structure pre- diction and we found ourselves confronted to numerous interesting cases of polymorphism and pseudo-polymorphism. Weak interac- tions, such as π-stacking, H-bonding and metal-metal interactions, and solvent, counter ion and concentration effects seem to play important roles in the construction of such low-dimensional struc- tures. Finally, the physical properties of some of our compounds are de- scribed qualitatively in order to show the wide spectrum of possibil- ities and potential applications for the chemistry in this field. Keywords: Alkali metals; Alkaline earth metals; Coordination polymers; Clusters; Cage compounds; Structural investigations; Structure prediction and alkaline earth metal clusters - in the sense of aggre- gates or cage compounds - were observed as by-products in metallation reactions in organic chemistry which encour- aged us to make such compounds on purpose; iii) we wanted to know whether there is an analogy in the clusters of group 1 and 2, and transition metal clusters, i. e. of group 11; iv) concerning the “covalent” polymers, the principle of cutting out structural fragments from a solid state structure with chemical scissors was to be tested; v) single source precursors for the chemical vapour deposition or sol-gel technique in the synthesis of oxide materials are scarce; and vi) we wanted to contribute to the problem of structure prediction in the case of supramolecular coordination poly- mers. Applications for such alkali and alkaline earth metal compounds can be found in many fields, such as metall- ation reactions and superbases in organic chemistry, bio- mineralization and biomimetics as far as biology is con-