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The special symposium was held within the 92^nd Conference & Exhibition of the Canadian Society for Chemistry (CSC). The academic program honoring the scientific achievements of Ronald J. Gillespie consisted of two days of invited lectures. The symposium created a forum where leading international experts discussed new developments, across a broad front, in chemical bonding and molecular structure. The symposium introduction during the first session was given by Prof. Peter E. A. Robinson from the University of Toronto who spoke about Ron Gillespie's influence on models of molecular structure based on ligand close packing. The sessions were attended by 61 to 140 individuals, including faculty, industrial researchers, graduate and undergraduate students.

Foreign Speakers Provided Travel Support, in Part, by PRF:

István Hargittai (Budapest University of Technology and Economics, Budapest, Hungary) – Molecules in Symmetry

The dramatic success of the VSEPR model occurred in predicting the shapes of molecules where there were lone pairs of electrons and where electron domains participating in bonding were not equivalent. Thus, the highest symmetry does not necessarily occur in any given structure. Five-fold symmetry used to be forbidden in crystal structures, but that constraint has been removed since the discovery of quasi-crystals. As for VSEPR, the lowest-energy arrangements are distinguished by small amounts of energy, which is the origin of Berry-pseudorotation, essential in many biological systems. Correlating function and symmetry often presents a challenge.

Rüdiger Mews (University of Bremen, Bremen, Germany) – Hexafluoroarsenate: A weakly coordinating anion and a versatile ligand

Following the footsteps of Professor Gillespie, the system, AsF₅/SO₂, was applied to syntheses in inorganic nometal and organometallic chemistry. Due to the poor donor properties of the AsF₆^- anion in organometallic and nonmetallic salts, almost no interactions between anions and cations are observed. In SO₂ solutions of M[AsF₆]_n (n = 1-3) and weak donors (e.g., NSF₃, OPF₃. OPCl₃), the hexafluoroarsenate anion competes with the solvent and the donors for coordination sites, showing a very versatile coordination chemistry. 32 coordinating possibilities exist for this hexadentate ligand, many of them have been experimentally verified.

Herbert W. Roesky (Institut für Anorganische Chemie, Göttingen, Germany) - Preparation and Reactions of Compounds with Low-Valent Elements of Carbon Analogues.

The chemistry of aluminum(l) and structural characterized LAl (L is a B-diketiminate ligand) had been previously studied. LAl exhibits a broad chemistry. Consequently, L ligands were used for the preparation of LSiCl, LGeCl, LGeF. LGe-GeL, LGeH, and LGe(OH). The latter two compounds show a diverse chemistry. LGeH reacts with alkynes, carbon dioxide, diazomethane derivatives, ammonia and sulfur. The congener of LGeH, the LSnH, reacts with aldehydes, ketones and carbon dioxide, The resulting products of the reactions with LGeH and LSnH were discussed in detail.

Sebastian Riedel (Freiburg University, Freiburg, Germany) -How Far Can We Go? Main-Group Ligands for Stabilizing High Oxidation

High oxidation states of transition-metals and main-group elements serve in many fields of chemistry as potent catalysts, oxidants and fluorinating agents. These important properties go along with the ligands which are able to stabilize these high oxidation states, namely fluorine and oxygen. The maximum oxidation states for the early transition metals of the 5d row follow the group number up to group 8 as in the case of OsO₄. The trends of the later metals tend to be less clear-cut. To investigate the remaining highly oxidized transition metal species, high-level quantum-chemical calculations in combination with matrix-isolation techniques can be applied.

Bernard Silvi (Université Pierre et Marie Curie, Paris, France) - How Reciprocal VSEPR Enables the Prediction of Electron Density Transfers in Organic Reactions

The first Hohenberg and Kohn theorem establishes that the external potential, i.e., the nuclear potential in molecules and solids, is a unique functional of the electronic density and reciprocally. This proof also holds for pair densities and therefore related properties such as the arrangement of the bonding and non bonding domains are determined by the nuclear geometries. The “reciprocal VSEPR” rules provide the possible arrangements consistent with any arbitrary nuclear geometry. Several textbook organic reactions, namely substitutions and cyclisations were studied. For all, of the ELF analysis confirms the findings of the “reciprocal VSEPR” approach.

Other Invited Speakers Supported from Other Sources

Ronald J. Gillespie (McMaster University, Hamilton, ON) - Molecular Compactness, the Methyl Tilt, Molecular Conformations and the Anomeric Effect

Richard Bader (McMaster University, Hamilton, ON) - My Years with Ron

David Brown (McMaster University, Hamilton, ON) - Acid-Base Bonds in Solids and Liquids

Tristram Chivers (University of Calgary, AB, Canada) - New Aspects of Chalcogen-Chalcogen Bonding

Karl O. Christe (University of Southern California, Los Angeles, CA) - Recent Progress on the Christe/Dixon Quantitative Scale of Lewis Acidity

Alan H. Cowley (University of Texas at Austin, TX) - Recent Adventures in Low-Coordinate, Low-Valent Group 13 and Group 15 Chemistry

Michael Gerken (University of Lethbridge, Lethbridge, AB) - Solid-State NMR Spectroscopy of Xenon Fluorides: Structural Characterization and Trends in Lewis Acidity

Risto Laitinen (University of Oulu, Oulu, Finland) - Reversible Dissociation of Solid (Se₆I₂)[AsF₆]₂·2SO₂ in Liquid SO₂

Josef Michl (University of Colorado at Boulder, Boulder, CO) - Electronic Structure and Reactivity of the CB₁₁ Cage

Jack Passmore (University of New Brunswick, Fredericton, NB) - Understanding Some Group 16 and 17 Main-Group Containing Species with Geometries that Do Not Obey VSEPR Theory Rules

Joseph S. Thrasher (University of Alabama, Tuscaloosa, AL) - Non-VSEPR Structures from Sulfur-Fluorine Chemistry and Advances in Superacid Chemistry

Heikki M. Tuononen (University of Jyväskylä, Jyväskylä, Finland) - When Does an Allene Become a Carbene?

Other Speakers

Rene T. Boeré (University of Lethbridge, Lethbridge, AB) Nucleophile-Induced Transformations of S, N and C, N, S Cages

Gary J. Schrobilgen (McMaster University, Hamilton, ON) - Recent Synthetic and Structural Developments in Krypton and Xenon Chemistry: From Linear NgF₂ (Ng = Kr, Xe) to Non-Octahedral XeF₆

Ignacio Vargas-Baca (McMaster University, Hamilton, ON) - Crossing the Boundaries between van der Waals Interactions, Secondary Bonding Interactions and Hypervalent Bonds