H-Bonds, π-Stacking and (Water)O-H/π Interactions in (µ4-EDTA)Bis(Imidazole) Dicopper(II) Dihydrate

Jeannette Belmont-Sánchez,Juan Niclós-Gutiérrez,Alfonso Castiñeiras,Josefa González-Pérez,Antonio Frontera,María García-Rubiño

doi:10.3390/cryst11010048

Jeannette Belmont-Sánchez, Juan Niclós-Gutiérrez + Show 4 more

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https://doi.org/10.3390/cryst11010048

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Abstract

We synthesized and studied the polymeric compound {[Cu2(µ4-EDTA)(Him)2] 2H2O}n (1). The single-crystal structure is reported along with an in depth characterization of its thermal stability (TGA), spectral properties (FT-IR, Vis-UV and RSE), and magnetic behavior. The crystal consists of infinite 2D-networks built by centrosymmetric dinuclear motifs, constructed by means of a bridging anti,syn-carboxylate group from each asymmetric unit. Each layer guides Him ligands toward their external faces. They are connected by intermolecular (Him)N-H···O(carboxylate) bonds and antiparallel π–π stacking between symmetry related pairs of Him ligands, and then pillared in a 3D-network with parallel channels, where disordered water molecules are guested. About half of the labile water is lost from these channels over a wide temperature range (r.t. to 210 °C) before the other one, most strongly retained by the cooperating action of (water)O1-H(1A)···O(carboxylate) and (water) O1-H(1B)···π(Him) interactions. The latter is lost when organic ligands start to burn. ESR spectra and magnetic measurements indicated that symmetry related Cu(II) centers connected by the bridging carboxylate groups behave magnetically not equivalently, enabling an exchange interaction larger than their individual Zeeman energies.

Highlights

Ethylenediaminetetraacetic acid (H4 EDTA) and its different anionic forms generate an enormous diversity of metal chelate complexes
As a part of a program on ternary copper(II) complexes with amino-polycarboxylate chelators and five or six-membered N-heterocyclic ligands related to structural formulas of purine nucleic basis, here we report the synthesis, crystal structure, physical properties, and density functional theory (DFT) calculations of {[Cu2 (μ4 -EDTA)(Him)2 ]·2H2 O}n (1)
The noncovalent interaction (NCI) index [28,29] and quantum theory of atoms-inmolecules (QTAIM) [30,31] analyses were calculated using the wavefunction generated by Gaussian-16 as input for the AIMAll program [32]

Summary

Introduction

Ethylenediaminetetraacetic acid (H4 EDTA) and its different anionic forms generate an enormous diversity of metal chelate complexes. The ability of EDTA to form up to five stable five-membered chelate rings around a metal center is only one among all these possibilities, frequently enriched in structurally well documented compounds where μEDTA bridging forms increases its denticity. EDTA anion as a bridging μ-chelator for two metallic centers (M), generating M2 (μEDTA) motifs which can form dinuclear complex molecules, as well as polymeric networks of different dimensionalities. In these compounds, at least a tridentate role for each halfEDTA should be expected, where each M center should be chelated by a N,N-methyleneaminodiacetate(2-) group, -CH2 -N(CH2 CO2 - ) (here after a mida group). The highest μn -EDTA denticity in these kind of compounds has been reported for the Ba(II) derivative, [Ba2 (μ12 -EDTA)]

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