Tetracyanoethylene (TCNE): The Characteristic Geometries and Vibrational Absorptions of Its Numerous Structures

• Published in: Angewandte Chemie (International ed.) Vol. 45; no. 16; pp. 2508 - 2525
• Main Author: Miller, Joel S.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 10.04.2006; WILEY‐VCH Verlag
• Subjects: electron transfer; IR spectroscopy; structure elucidation; structure-property relationships; tetracyanoethylene
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.200503277

Tetracyanoethylene (TCNE) undergoes numerous reactions and is reported to exist in many structural motifs. Identification of these forms and motifs can be challenging. Nonetheless, the number of $\tilde \nu $CN absorptions and their frequencies provide insight with respect to the specific forms and charge on the TCNE fragment. Particularly informative is the average of the fundamental $\tilde \nu $CN bands, as well as the length of the central CC bond. This Review discusses the assignment of structure and formal charge for TCNE‐containing compounds. Scrutiny of previous assignments reveals some discrepancies which are discussed, and provides a basis for further study of TCNE structure–function relationships. Several multimetal complexes with bridging [TCNE]z units exhibit mixed valency and extensive delocalization. The scarcity of suitable model compounds, especially those with M d π–π* backbonding to the CN groups, have thwarted the detailed description of these valence ambiguous compounds; thus, new well‐characterized polynuclear compounds are needed. Good vibrations: For tetracyanoethylene (TCNE) many structural motifs are known and their identification is often difficult. The fundamental $\tilde \nu $CN vibrations as well as the length (d) and $\tilde \nu $CC values of the central CC bond can provide important information on bond order, structure, and charge state (see graph).