Research Interests


Keywords: Clusters, Crystal Engineering, Alkali Metals, Alkaline Earth Metals, Group 11 Elements Cu, Ag, Au, Supramolecular Chemistry, Oxide Materials, Anti-microbial Biomaterials


One of the more fundamental research themes in our group concerns the approach to “cut out” excerpts from solid state structures. In three-dimensional binary starting compounds with bond lengths of different length scale (as for instance in BaI2, where we have Ba-I distances varying from 3.4 to 4.2 Å), we can use chemical scissors in form of oxygen donor ligands to cut out three-, two- and one-dimensional compounds in which parts of the initial structure are maintained, whereas other bonds have been cut. Depending on the strength of the ligand and its concentration, we were able to derive for instance a structural genealogy tree for BaI2, cutting the structure down as far as to the molecular level. (Angew. Chem. 1997, 109, 24, 2876-2878, Angew. Chem. Int. Ed. Engl. 1997, 36, 24, 2799-2801; Acta Cryst. Sect. C, 2000, 56, 1179-1180; Z. Anorg. Allg. Chem., 2001, 627, 1626-1630)

0-dimensional BaI2(thf)5 1-dimensional BaI2(thf)3 2-dimensional BaI2(OH2)(OC3H6)

Aggregates of alkali and alkaline earth metals were so far obtained mostly as secondary products in organic metallation reactions. We got interested in such compounds because they can be valuable precursors for oxide materials. A more fundamental aspect is the analogy to transition metal clusters. An in our group newly developed synthesis allows isolation of a number of pure alkali and alkaline earth metal clusters, but also mixed metal aggregates. Some of them are useful in the sol-gel technique, others are volatile and yield halide and carbonate-free oxides after thermal treatment. (Chem. Comm. 1999, 17, 1659-1660, Chem. Commun. 2000, 2187-2188; J. Am. Chem. Soc., 2003, 125(12), 3593-3604.)

BaLiO
Ca7I6(OH)8(thf)12 [IBa(OtBu)4{Li(thf)}4(OH)]

The coordination geometry of alkaline earth metal iodide adducts is difficult to predict. We study such compounds in order to gain insight into the coordination behaviour of alkaline earth metal iodides in organic solvents with donor functions, such as THF and polyethers. Contrarily to the expected trans-iodides, we were also able to isolate cis-compounds with small I-M-I angles of ca. 90°, just as it is known for complexes of transition metal halides. (Angew. Chem. 1997, 109, 24, 2876-2878, Angew. Chem. Int. Ed. Engl. 1997, 36, 24, 2799-2801; Cryst. Eng. Comm., 2002, 4(57), 318-322; Chimia, 2003, 57(4), 175-178; Eur. J. Inorg. Chem. 2003, 18, 3440-3444;)

BaLiO
trans-[BaI2(thf)5] cis-[SrI2(diglyme)2]

This part of our research deals with the problem of structure prediction. Using 2+ charged complexes of alkaline earth metal ions, featuring at least one water molecule in its coordination sphere with otherwise innocent O-donor ligands, we are able to predict the dimensionality of the formed supramolecular array. (Z. Anorg. Allg. Chem. 2000, 7, 1685-1691; Polyhedron, 2000, 19, 1783-1789; Chem. Eur. J., 2001, 7, 2236-2244)

1-dim
1-dimensional, polar [Ca(H2O)2(diglyme)2]I2

Using calix[n]arenes and crown ethers as scaffolds, we firstly obtained molecular compounds, either polar structures at the molecular level, or alkali metal clusters. We also build up channel structures through which protons, alkali or alkaline earth metal cations can be transported. This is a rather recent project in our group and is interesting for charge transport mimics of biological systems with possible applications in miniaturization of "cables". (Z. Anorg. Allg. Chem., 2002, 628, 171-178; Chem. Eur. J. 2003, 9(2), 509-514; Cryst. Growth & Design, 2005, 5(5), 1691-1694)

li2 K8 H-Kana
Li2(Calix[4]arene-2H)(H2O)2(THF) K8(Calix[4]arene-4H)2(THF)10 (H3O)(DB18C6)(H2O)I3

In our channel systems, but also in our coordination networks, we are interested in the synthesis, isolation and characterization of water molecules in form of clusters and chains. Thus, we are interested in water exchange reaction using D2O to replace H2O and to study the speed and mechanism of such transport. (Z. Anorg. Allg. Chem., 2002, 628, 171-178; Cryst. Growth & Design, 2005, 5(5), 1691-1694)

wasclu
A (H2O)10-cluster held by two calix[8]arenes

Using ditopic ligands, we are able to generate mostly one-dimensional coordination networks with copper and silver ions. They are interesting from many point of views: polyelectrolytes, starting materials for mixed metal compounds due to the ligand's different donor type atoms, as materials in coatings for disinfectant surfaces. (Cryst. Eng. Comm., 2003, 5(71), 405-410; Cryst. Eng. Comm., 2004, 6(60), 336-343; Z. Anorg. Allg. Chem., 2005, 631, 1725-1740; A. Y. Robin, J. L. Sagué, K. M. Fromm, Cryst. Eng. Comm., 2006, 8, 403-416)

Cu-chaine
1-dimensional chain of [Cu(L)Cl]

More generally, we are interested in polymorphism and pseudo-polymorphism, supramolecular isomerism and crystal engineering. In this field, many challenges remain that are related with the real structure prediction at the solid state, including weak inter-molecular forces (H-bonds, pi-stacking, metal-metal contacts, van der Waals interactions etc.) and the process of crystallisation itself, which could be regarded as a very complicated process of self-assembly. (Cryst. Eng. Comm., 2003, 5(71), 405-410; Cryst. Eng. Comm., 2004, 6(60), 336-343; Z. Anorg. Allg. Chem., 2005, 631, 1725-1740; Chem. Commun., 2005, 36, 4548-4550)

rinag flech aghel

Polymorphism and supramolecular isomerism for [Ag(L)]ClO4

Silver is one of the most powerful anti-microbial agents.We therefore investigate the deposition of our silver compounds on biologically relevant materials. Our alkali and alkaline earth metal compounds are tested for their potential use as precursors in oxide materials' synthesis (Z. Anorg. Allg. Chem., 2005, 631, 1725-1740)

fig17 sup
Artificial hip stems Meissner Effect of superconductors