Retention of Cs–Cl bond induces coordination polymer formation over trinuclear chiral assembly of copper(ii) complexes of l-leucine derived ligand

Abstract

The use of caesium is a less trodden path in terms of the synthesis of coordination polymers. The chemical similarity and mild toxic nature of caesium salts does not provide much impetus to work with these compounds compared to their potassium analogues. However, are the potassium and caesium salts really close in terms of coordination polymer formation? The result presented in this manuscript shows that while neither potassium halides or potassium nitrate inhibit the formation of a trinuclear chiral assembly of a copper(II) complex from a mononuclear Cu(II) complex, caesium chloride preferentially forms a coordination polymer while keeping the Cs-Cl bond intact. Under the same conditions, caesium nitrate does not inhibit the assembly formation. Structural characterization of {[CsCl{Cu (HL L-leu ) 2 }(H 2 O)]} n (2) showed it to be a two-dimensional coordination polymer in the ab plane, where pentacoordinated Cu(HL L-leu ) 2 complex units (HL L-leu = reduced Schiff base of L-leucine and the salicylaldehyde condensation product) were interconnected through the formation of Cu-Cl-Cs bonds. Multitudes of intermolecular H-bonds were observed as well. The use of KCl, KBr, KI or CsNO 3 in lieu of CsCl to the [Cu(HL L-leu ) 2 (CH 3 CN)] (1) facilitated the formation of the trinuclear assembly, [M{Cu(HL L-leu ) 2 } 3 ]X, where M = K + or Cs + and X = Cl, Br, I or NO 3 depending on the salt used. The Cu(HL L-leu ) 2 units in these assemblies are hexacoordinated Cu(II) complexes.

Water-soluble chiral coordination polymers of Li+, Na+, K+, and Ba2+ with an anionic iron(iii) complex of a l-threonine derivative and a significant red shift of visible spectra with Al3+ salt

“…Earlier, our interest was in forming larger chiral assemblies from rigid metal complexes of relatively flexible amino acidderived ligands. [30][31][32][33]39,40 Other forms of assemblies, such as coordination networks, were mostly ignored because of their poor solubility in most common solvents, which limited experiments with guest molecules. 31 However, we did find that bis-complexes of Cu(II) and Ni(II) with amino acid derived ligands themselves can act as ligands to alkali metal ions, but the structural motif of the complex was not suitable for network formation.…”

“…31 However, we did find that bis-complexes of Cu(II) and Ni(II) with amino acid derived ligands themselves can act as ligands to alkali metal ions, but the structural motif of the complex was not suitable for network formation. 30,32 Here, we have built a new coordinatively saturated bis-Iron(III) complex with an extra negative charge. It has multiple phenolates and carboxylates on the different faces of the octahedron to promote multidirectional network formation.…”

“…They show strong and sharp asymmetric carboxylate stretches 1600-1628 cm −1 , the same region where reported complexes with similar ligands (1580-1630 cm −1 ) were observed. [30][31][32][33]39,40 All four complexes are soluble in water and methanol and could be recrystallized in crystalline from either of the solvents. The crystals were dried inside a vacuum desiccator for several days before analysis and bulk measurements.…”

“…This phenomenon of opposite conformation preference at chiral carbon C8A and amine N1A has been observed in all the characterized complexes of this type of ligand. [30][31][32]39,40 The deviation of bond angles from ideal 90°and 180°(Table 2 and Table S1 †) indicates that the geometry is slightly distorted. In particular, the axial Fe carboxylate -Fe-O carboxylate angle at 160.14( 9)°( O2a-Fe-O2b in Fig.…”

“…Earlier, we observed that the Ni(II) and Cu(II) complexes of reduced Schiff bases of salicylaldehyde and amino acids bind to Na + or K + through carboxylate oxygen atoms of the complexes. [30][31][32] The ligand was a L-leucine derivative. Phukan et al reported the structures of Na + , K + and Ca 2+ salts of an achiral iron(III) complex where binding occurs through carboxylates.…”