Lanthanide-Containing Molecular and Supramolecular Polymetallic Functional Assemblies Jean-Claude G. Bu ¨nzli* ,† and Claude Piguet* ,‡ Institute of Molecular and Biological Chemistry, Swiss Federal Institute of Technology, BCH 1402, CH-1015 Lausanne, and the Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, 30 quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland Received January 21, 2002 Contents I. Introduction 1 II. Lanthanide Ions as Functional Centers in Elaborate Molecular Edifices 3 A. Redox Centers and Lewis Acids 3 B. Optical, Spectroscopic, and Magnetic Probes 5 III. Synthesis of Elaborated Lanthanide-Containing Edifices 8 A. Lock-and-Key Principle in Monometallic Lanthanide Complexes 9 B. Induced Fit Principle in Monometallic Lanthanide Complexes 10 C. Planning Discrete Lanthanide-Containing Polymetallic Assemblies 11 D. Innovative Synthetic Routes to Lanthanide-Containing Polymetallic Assemblies 17 IV. Functional Polymetallic Assemblies Triggered by Intermetallic Communications 18 A. Edifices Containing 4f- and s-Block Ions 18 B. Edifices Containing 4f- and d-Block Ions 19 1. Communication Based On Orbital Overlap 19 2. Electrostatic Communication 19 3. Mechanical Coupling 21 C. Edifices Containing Two (or More) 4f-Block Ions 22 1. Communication Based On Orbital Overlap 22 2. Electrostatic Communication 22 3. Mechanical Coupling 23 V. Toward Programmed Functional Extended Networks 24 A. Clusters 24 B. Self-Assembled Supramolecular Polymetallic Edifices 25 C. One-Dimensional Arrays 25 D. Two-Dimensional Arrays 27 E. Three-Dimensional Arrays 27 VI. Outlook 28 VII. Acknowledgments 29 VIII. References 29 I. Introduction As a result of the different degrees of stabilization experienced by the 4f, 5d, and 6s orbitals occurring upon ionization of the neutral metal, the lanthanides (La-Lu, Z ) 57-71) exist almost exclusively in their trivalent state Ln(III) ([Xe]4f n , n ) 0-14) in coordi- nation complexes or supramolecular assemblies. 1 Except for some arene compounds involving bulky substituted benzenes or cyclo-octatetraenes, 2 cova- lence plays a minor role in Ln-ligand dative bonds and the nature of the coordination sphere is con- trolled by a subtle interplay between electrostatic interactions and interligand steric constraints. 3 Vari- able coordination numbers (6 e CN e 12) and geometries are thus observed in lanthanide com- plexes, leading to limited success in the design of molecular architectures with predetermined struc- tures. 3,4 Although rigid or semirigid receptors may help to control the coordination sphere according to the lock-and-key and induced fit concepts, 5 detailed studies of lanthanide solvates with water or aceto- nitrile suggest that trivalent lanthanides display a tendency to adopt nine-coordinate tricapped trigonal prismatic (TTP) arrangements around the metal ion in the solid state. In solution, the picture is a little more subtle: 6 in water, for instance, large Ln(III) ions at the beginning of the series (Ln ) La-Nd) adopt TTP geometries, which are gradually transformed into eight-coordinate square antiprismatic (SAP) arrangements for small Ln(III) ions (Ln ) Tb-Lu), equilibria between CN ) 8 and CN ) 9 being observed for Ln ) Nd-Tb. 7 The systematic contrac- tion of the ionic radii observed when going from Ln ) La to Lu (often referred to as the lanthanide contraction) 8 explains this trend and increases elec- trostatic bonding for heavier lanthanides, but this variation is so smooth and limited (15% contraction between La and Lu and ≈1% between two successive lanthanides) that selective recognition and incorpora- tion into organized supramolecular architectures remains challenging. 5 A rational access to extended polymetallic lanthanide-containing assemblies with predictable and controlled geometries is consequently very limited, and pioneer work in this field has focused on poorly characterized intricate mixtures of complexes in solution which are ‘transformed’ into well-defined solid-state clusters or networks through crystallization processes involving a rich palette of † Institute of Molecular and Biological Chemistry, Lausanne. E-mail: Jean-Claude.Bunzli@epfl.ch. ‡ Department of Inorganic, Analytical and Applied Chemistry, Geneva. E-mail: Claude.Piguet@chiam.unige.ch. 10.1021/cr010299j CCC: $39.75 © xxxx American Chemical Society PAGE EST: 31.8 Published on Web 00/00/0000