Mapping the Stereochemistry and Symmetry of Tetracoordinate Transition‐Metal Complexes

Abstract

A continuous shape and symmetry study of tetracoordinate transition-metal complexes is presented, in an attempt to provide a systematic description of the stereochemistry of the metal coordination sphere in this important family of compounds. A tetrahedron/square-planar symmetry map has been developed, the main distortion paths of the ideal geometries are presented, and the applicability of a sawhorse shape measure is discussed. More than 13,000 structural data sets have been analyzed and the corresponding stereochemistries assigned from the values of their tetrahedral and square-planar symmetry measures. A good number of structures that are quite distant from the two ideal geometries can be adequately described as snapshots along the spread pathway for their interconversion, making use of the corresponding path deviation function. Further analysis of the structural data by metal electron configuration or by the denticity and conformation of the ligands provide general rules to describe the stereochemical preferences of tetracoordinate transition metal centers.

Using hinged ligands to target structurally flexible copper(ii) MOFs

“…MOF 1 undergoes slight structural changes upon desolvation but is probably best described as a 2 nd generation material, while MOF 2 is perhaps better considered as a 1 st 25 generation material (non-recoverable structural collapse) despite showing some porosity following its structural change. As shown in our previous and current work, the implementation of a methylene 'hinge' backbone impacts favourably on structural flexibility in MOF materials, however, this work also highlights 30 that the flexibility is governed by the need for alterations in the coordination geometry around the metal ion coordinated by the 'hinge' donors. Importantly, this study also demonstrates that this class of hinged ligands can form metal nodes exclusively from one type of donor, giving rise MOF materials containing two 35 distinct structural nodes.…”

“…A 77 K N2 isotherm performed in 1 ac revealed a marginal gas 30 uptake of (3.2 cm 3 /g at P/Po = 0.94), while adsorption of CO2 at 195K gave a type I isotherm with a maximum uptake of 32.5 cm 3 /g at P/Po = 0.95 ( Figure SI 3). The BET and Langmuir surface areas were calculated from the 195 K CO2 isotherm using the criteria detailed by Walton and Snurr, 46 This isotherm profile and uptake is consistent with a combination of unsaturated Cu 2+ sites and a small pore volume ( Figure 5).…”

“…The latter were considered as Cu(I) centres as a tetrahedral geometry is far more common for d 10 transition metals and CHN analysis supported the inclusion of only one nitrate anion per tetrahedral copper centre. 30 Four molecules of ligand bcpdmpm complete the coordination requirements of the two copper(II) paddlewheel clusters, while each ligand chelates to a tetrahedral copper(I) centre via di-pyrazolyl methane motif (Figure 4a). The coordination of the paddlewheel copper(II) could not be located in the difference map.…”

“…37,38 Nonetheless, examples of mixed valence Cu(II)/Cu(I) coordination polymers are relatively rare, 39 and a majority of these examples contain CN -or SCN -co-ligands. 40,41 Based on literature precedent and the yield of the reaction (63%), the 30 identity of the reducing agent is likely to be ethanol. The in-situ reduction is further supported by the angles about the tetrahedral copper centres of 2 which compare favourably to the bond angles of a known Cu(I) complex [Cu(bpy)2]ClO4 42 (Table SI 1).…”

Hoch oder niedrig? Zur Erlaubtheit von Spinzuständen in der Übergangsmetallchemie

“…Bei den genannten Verbindungen kommt es zu einer unterschiedlich stark ausgeprägten "Umbrella"-Verzerrung des Tetraeders. Diese unterscheidet sich von der häufiger auftretenden Spreizung, [36] die letztlich in einen quadratisch-planaren Komplex übergeht. Solche Verzerrungen können auf die Summe der E-M-E-Winkel (S) kalibriert werden, die 328.48 für den idealen Tetraeder, 300.28 für den Nikkel(iv)-Komplex und 264-2988 für die Komplexe der dreizähnigen Liganden beträgt.…”