Structural Flexibility of Metal Chelate Complexes and Its Relation to Supramolecular Chemistry

Abstract

This article is in memory of Professor Jack D. Dunitz, whose laboratory I visited in 1979. I hope I have passed on to my own students some of the ideas and inspiration that Jack gave so generously.Crystal structures of metal chelate and related complexes in the Cambridge Structural Database have been analyzed, with respect to their use as components in supramolecular metal-organic compounds. In β-diketonate complexes, the distribution of angles between ligands is relatively broad; other ligands, such as 2,2'-bipyridine, yield significantly narrower distributions. According to the principle of structure correlation, these distributions reflect the ease of distorting the various families of complexes. A comparison through density functional theory calculations also indicates that angular distortions require significantly less energy for M(β-diketonate) 3 than for M(2,2'-bipyridine) 3 . The differences are likely to affect the construction of supramolecular systems from different combinations of metals and ligands, including the likelihood that the desired structures will be obtained.

Structural Information on Supramolecular Copper(II) β-Diketonate Complexes from Atomic Force Microscopy and Analytical Ultracentrifugation

“…In our previous work with copper molecular squares (Figure ), only squares (Cu 4 L 4 ) were formed, rather than the hexagons (Cu 6 L 6 ) that were expected based on the angle of ca. 120° between the β-diketonates. , Thus, β-diketonates are somewhat flexible in the way they bind to Cu 2+ ; we have recently shown that metal β-diketonates are among the most flexible among common chelates in their coordination geometry …”

“…37,38 Thus, β-diketonates are somewhat flexible in the way they bind to Cu 2+ ; we have recently shown that metal β-diketonates are among the most flexible among common chelates in their coordination geometry. 42 The new supramolecular complexes do not form crystals suitable for X-ray analysis; also, their mass spectra do not provide useful information concerning the size of the molecules formed. In this work, we use atomic force microscopy (AFM) and analytical ultracentrifugation (AUC) to provide additional information about the structure of the new supramolecular Cu(II) complexes.…”

“… 37 , 38 Thus, β-diketonates are somewhat flexible in the way they bind to Cu 2+ ; we have recently shown that metal β-diketonates are among the most flexible among common chelates in their coordination geometry. 42 …”