Crystal structures of zinc(II) complexes with β-hydroxypyridinecarboxylate ligands: examples of structure-directing effects used in inorganic crystal engineering

Abstract

The coordination properties of four hydroxypyridinecarboxylates, designed for the treatment of iron-overloading conditions as bidentate O,O′-donor ligands, have been studied with ZnII in the solid state. The coordination compounds [Zn(A1)2(H2O)2] (1), [Zn(A2)2(H2O)] (2), [Zn(A3)2(H2O)]·2H2O (3) and [Zn2(B1)4(H2O)2]·4H2O (4), where the ligands are 1-methyl-4-oxidopyridinium-3-carboxylate (A1, C7H6NO3), 1,6-dimethyl-4-oxidopyridinium-3-carboxylate (A2, C8H8NO3), 1,5-dimethyl-4-oxido-pyridinium-3-carboxylate (A3, C8H8NO3) and 1-methyl-3-oxidopyridinium-4-carboxylate (B1, C7H6NO3), have been synthesized and analysed by single-crystal X-ray diffraction. The ligands were chosen to probe (i) the electronic effects of inverting the positions of the O-atom donor groups (i.e. A1 versus B1) and (ii) the electronic and steric effects of the addition of a second methyl group in different positions on the pyridine ring. Two axially coordinated water molecules resulting in a six-coordinated symmetrical octahedron complement the bis-ligand complex of A1. Ligands A2 and A3 form five-coordinated trigonal bipyramidal complexes with one additional water molecule in the coordination sphere, which is a rarely reported geometry for ZnII complexes. Ligand B1 shows a dimeric structure, where the two Zn2+ dications have slightly distorted octahedral geometry and the pyridinolate O atom of the neighbouring complex bridges them. The coordination spheres of the Zn2+ dications and the supramolecular structures are discussed in detail. The packing arrangements of 1–3 are similar, having alternating hydrophilic and hydrophobic layers, however the similarity is broken in 4. The obtained coordination geometries are compared with their previously determined CuII analogues. The study of the individual complexes is complemented with a comprehensive analysis of ZnII complexes with oxygen donor ligands with data from the Cambridge Structural Database.

Gradual Changes in the Aromaticity in a Series of Hydroxypyridine-Carboxylic Acid Derivatives and Their Effect on Tautomerism and Crystal Packing

“… a Ring (1) is the pyridine ring. Cg(1)···Cg(1): distance between ring Centroids (Å), Cg(1)_Perp: perpendicular distance of Cg(1) on neighbouring ring (Å), α: Dihedral angle between planes (o). b Data for B1 were taken from ref . …”

“…In our previous studies, we investigated the complexation properties of selected 3HPC and 4HPC derivates with copper(II) 6 and with zinc(II). 7 The bis-ligand complexes with…”

“…Their favorable properties include low toxicity, no redox activity, and high complex stability. , The effect of aromaticity on the proton dissociation process is important because this proton is replaced by the metal ion during chelation therapy. In our previous studies, we investigated the complexation properties of selected 3HPC and 4HPC derivates with copper­(II) and with zinc­(II) . The bis-ligand complexes with [O – ,O carb – ]­[ O – ,O carb – ] equatorial coordination crystallized in all cases, but the electron distribution in the ligand influences the type of the axial coordination of the metal center in dimeric complexes.…”