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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 23 (2018) pp 210-215

Unraveling the Mysterious Square Planar Complexes

Linda S. Hill and Erwin Boschmann

Department of Chemistry and Chemical Biology’ IUPUI, 402 N. Blackford Street, Indianapolis, IN 46202-3374,,
Received July 9, 2018. Accepted August 13, 2018.

Published: 10 October 2018

Abstract. Unless forced by a locked ring system, symmetry considerations, steric factors, or valence shell electron pair repulsions, four mono-dentate ligands will naturally settle into the tetrahedral configuration thereby allowing for longer ligand-ligand distances compared to the square planar configuration. Driven by crystal field stabilization energies, there are, however, four-ligand complexes which prefer the square planar arrangement. We have conducted a systematic study of the conditions leading to such configurations and find it instructive to study the crystal field stabilization energy differences vs. d configurations. Not only can the structures of existing four-ligand complexes be understood, but those of as yet unknown species may be predicted as well.

Key Words: Laboratories and Demonstrations; inorganic chemistry; square planar complexes; prediction of planarity; crystal field stabilization energy; crystal field stabilization energy differences

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