Four Decades of the Chemistry of Planar Hypercoordinate Compounds

• Published in: Angewandte Chemie International Edition Vol. 54; no. 33; pp. 9468 - 9501
• Main Authors: Yang, Li-Ming, Ganz, Eric, Chen, Zhongfang, Wang, Zhi-Xiang, Schleyer, Paul von Ragué
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 10.08.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Bonding; Cages; Carbon; Chemical elements; coordination numbers; Electronics; Evolution; Hypercoordination; Magnetic properties; Methane; nonclassical molecules; planar coordination; theoretical chemistry; nonclassical molecules; theoretical chemistry; Hypercoordination; planar coordination; coordination numbers
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201410407

The idea of planar tetracoordinate carbon (ptC) was considered implausible for a hundred years after 1874. Examples of ptC were then predicted computationally and realized experimentally. Both electronic and mechanical (e.g., small rings and cages) effects stabilize these unusual bonding arrangements. Concepts based on the bonding motifs of planar methane and the planar methane dication can be extended to give planar hypercoordinate structures of other chemical elements. Numerous planar configurations of various central atoms (main‐group and transition‐metal elements) with coordination numbers up to ten are discussed herein. The evolution of such planar configurations from small molecules to clusters, to nanospecies and to bulk solids is delineated. Some experimentally fabricated planar materials have been shown to possess unusual electrical and magnetic properties. A fundamental understanding of planar hypercoordinate chemistry and its potential will help guide its future development. Where the great plains begin: Planar hypercoordinate chemistry has emerged as an exciting field with the discovery of unique molecules with unusual bonding configurations. Starting with planar tetragonal carbon, molecules of increasing complexity and hypercoordinate bond numbers from four up to ten have been predicted, and some have been synthesized. This Review covers the evolution and rapid growth of the field of planar hypercoordinate chemistry over the last four and a half decades.