Trapping of a Four‐Coordinate Zinc Salphen Complex Inside a Crystal Matrix

Abstract

A remarkable twosome: Four-coordinate square-planar complexes based on [Zn(salen)] derivatives are conveniently captured inside a crystal matrix using a supramolecular protecting strategy (see figure). The four-coordinate species is accompanied by a five-coordinate complex that binds an axial ligand able to hydrogen bond to an N-heterocycle positioned in the axial region of the coordinative unsaturated derivative. The size of the N-heterocycle is a decisive stabilization parameter.

Substrate-dependent allosteric regulation by switchable catalytic molecular tweezers

“…The zinc atoms coordinated to the salphen ligands adopt a distorted square pyramidal geometry with apical oxygen atoms from water or hydroxyl ligands at Zn-O distances of 2.046 and 1.957 Å, respectively. In both cases, the Zn atoms are located above the average N 2 O 2 plane of the ligand (0.66 and 0.41 Å) with average Zn-O, Zn-N distances of 1.961 Å and 2.076 Å, respectively, in agreement with previously reported Zn-salphen complexes [68][69][70] . The packing of the tweezers generated large channels with disordered solvent molecules that could not be successfully modeled resulting in a rather high R factor (10.9%).…”

A DFT Study on the Mechanism of the Cycloaddition Reaction of CO2 to Epoxides Catalyzed by Zn(Salphen) Complexes

“…However, in the case of ZnA C H T U N G T R E N N U N G (salphen)s, hexa-coordination is an extremely rare phenomenon and is only observed in condensed solid phases. [27] Furthermore, we [28] and others [29] have clearly demonstrated that penta-coordination in ZnA C H T U N G T R E N N U N G (salphen)s is highly favored both in the solid state as well as in solution phases as supported by crystallographic evidence, UV/Vis titration data, Job plot analyses and fitting 1:1 complex-ligand binding models by using multivariate data analysis. [30] Therefore, the consideration of penta-coordination in the ZnA C H T U N G T R E N N U N G (salphen) case seems to give a reasonable starting point in the mechanisms discussed below.…”

Facile Synthesis of Substituted Mono‐, Di‐, Tri‐ and Tetra‐2‐aryl‐2,3‐dihydro‐1H‐perimidines

“…[10] We are particularly attracted to diamino-aryl scaffolds that are able to induce a planar geometry around the ligated metal ion, and have reported on the unusual properties of Zncentred salphen complexes [salphen = N,NЈ-salicylidene-1,2-diaminophenyl]. [11] We envisioned that 1,8-diaminonaphthalene would be a useful starting point for the creation of other types of geometrically planar ligands that, upon ligation of Zn ions, should be able to amplify the arsenal of intriguing structures potent as a molecular building block. Molecular modelling studies [12] revealed that indeed a rather planar geometry may be obtained and therefore we set out to prepare the corresponding salen complex derived from 1,8-diaminonaphthalene using conditions that have previously been proven to be successful for salphen deriva-tives.…”