A tale of crystal engineering of metal complexes derived from a special ligand family having a cosmopolitan compartment

Abstract

The journey of the syntheses and studies of the structures and properties of metal complexes derived from double-compartment 3-ethoxysalicylaldehyde-diamine (H 2 L OEt ) ligands was started in 1995, as per the CSD version 1.15 (2012) record. After dealing with mainly mononuclear complexes in the early years, the "metallo-ligand as reactant" approach was started in 2002 with the reporting of a Cu II Gd III compound, with the aim to explore the magnetic properties of 3d-4f systems. It was realized within a few years that the O(phenoxo) 2 O(ethoxy) 2 compartment has strong potential to interact with water molecule(s) due to the formation of bifurcated hydrogen bonds, resulting in the stabilization of the mononuclear inclusion products and two-component and even three-component cocrystals. "Metallo-ligand as reactant" was reacted with several metal ions from various parts of the periodic table (s, p, 3d, d 10 , 4f, 5f) as well as with possible hydrogen bond donors, such as an ammonium ion, diprotonated diamines, dicarboxylic acids and aquated proton (perchloric acid). A number of cocrystals, supramolecular dimers, a new type of hydrate isomerism, systems with interesting topologies and systems showing resemblances of entirely different types of metal ions have been obtained. Eventually, we can call the H 2 L OEt a special ligand family and the O(phenoxo) 2 O(ethoxy) 2 compartment a cosmopolitan compartment. This highlight deals with the metal complexes derived from 3-ethoxysalicylaldehyde-diamine ligands from a crystal engineering perspective.

Syntheses, structures and catecholase activity of two cobalt(III) complexes derived from N,N′-ethylenebis(3-ethoxysalicylaldiimine): A special host–guest system from a special ligand

“…As already mentioned, a number of mononuclear M III compounds are known from H 2 L OEt ligands [1,19,[24][25][26]57,58,[61][62][63][64][65][66][67][68][69][70]. Fig.…”

“…Many mono/di/oligonuclear metal complexes have been reported from the following types of acyclic Schiff base ligands: (i) Single-compartment ligands (H 2 L Single ), obtained on [2+1] condensation of salicylaldehyde/2-hydroxyacetophenone/2-hydroxypropiophenone and a diamine [1][2][3][4][5][6][7][8][9][10][11]; Double-compartment ligands H 2 L OMe [1,[12][13][14][15][16][17][18] and H 2 L OEt [1,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] ligands, obtained on [2+1] condensation of 3-methoxysalicylaldehyde and 3-ethoxysalicylaldehyde, respectively, and a diamine. It has been established that H 2 L OEt ligands are something special because its O(phenoxo) 2 O(ethoxy) 2 compartment is strongly potential to act as a hydrogen bond acceptor with hydrogen bond donors such as water [1,[19][20][21][22][23][24][25]…”

“…It has been established that H 2 L OEt ligands are something special because its O(phenoxo) 2 O(ethoxy) 2 compartment is strongly potential to act as a hydrogen bond acceptor with hydrogen bond donors such as water [1,[19][20][21][22][23][24][25][26][27][28][29][30][31], aquated proton [32,33], ammonium ion [22] and diprotonated diamine [34,35]. The metal complexes derived from H 2 L OEt ligands include mononuclear host-guest systems, dinuclear systems, double/triple/quadruple-decker compounds, supramolecular dimers and finite/infinite cocrystals [1,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”

“…It is worth mentioning that a number of the metal compounds derived from H 2 L OEt ligands are weak interaction directed selfassemblies [1,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and thus lie in the domain of general perspectives of crystal engineering [36][37][38][39]. In spite of our extensive works on H 2 L OEt ligands [1,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and in spite of our observation of a number of interesting self-assemblies over a decade, we have been hopeful that some more new types of weak interaction directed systems can be stabilized with this family of special ligands and therefore we are yet in the process of continuous development.…”

“…The metal complexes derived from H 2 L OEt ligands include mononuclear host-guest systems, dinuclear systems, double/triple/quadruple-decker compounds, supramolecular dimers and finite/infinite cocrystals [1,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. It is worth mentioning that a number of the metal compounds derived from H 2 L OEt ligands are weak interaction directed selfassemblies [1,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and thus lie in the domain of general perspectives of crystal engineering [36][37][38][39]. In spite of our extensive works on H 2 L OEt ligands [1,[19][20][21][22][23][24]…”