Coordination Compounds Featuring Non-Toxic Chiral 1,4-Dicarboxylic Acids and Copper(II)

Ulli Englert,Jan Van Leusen,Marius Kremer

doi:10.3390/cryst10060485

Abstract

Six new coordination compounds of copper cations and 1,4-dicarboxylic acids have been synthesized and structurally investigated. Aspartic acid (H2asp), enantiopure, racemic and meso tartaric acid (H2tart), di-para-toluyltartaric acid (H2dptta) and dibenzoyltartaric acid (H2dbta) represent environmentally benign water-soluble proligands which may be deprotonated for oxygen coordination. Chelating ligands such as tetramethylethylenediamine (TMEDA) and 2-aminomethylpyridine (AMPY) efficiently reduce the dimensionality of the target compounds, and additional aqua ligands complete the coordination environments. In this line of argument, the discrete mononuclear complexes [Cu(AMPY)(asp)(H2O)] and [Cu(Hdbta)2(H2O)4] were obtained; for the latter, only a preliminary structure model can be presented which, however, agrees with the powder diffraction pattern of the bulk. From enantiopure and racemic tartaric acid and TMEDA the closely related chain polymers [CuII(H2tart)(TMEDA)(H2O)2)]n were obtained; the racemic compound consists of individual homochiral strands of opposite chirality. The high steric demand of di-para-toluyltartaric acid leads to one-dimensional [Cu(dptta)(EtOH)(H2O)2]n with coordinated ethanol (EtOH) in the distant Jahn–Teller site of the coordination sphere. Cu(II), meso-tartaric acid and TMEDA aggregate to a trinuclear coordination compound [CuII2CuI(H2tart)(Htart)(TMEDA)2]. Its peripheral cations show the expected Jahn–Teller geometry of Cu(II), but the unambiguous assignment of the oxidation state +I for central cation required susceptibility measurements: their results prove the presence of only two and only very weakly interacting divalent cations, separated by a diamagnetic center.

Highlights

Carboxylic acids represent classical ligands for Werner complexes: As early as 1953, Niekerk et al.investigated the crystal structures of Ni(II) [1], Zn(II) [2] and Cu(II) [3] acetate and established the monohapto, chelating and bridging coordination modes, respectively, for the carboxylato ligand in these solids
Carboxylic acids may act as bridging building blocks in coordination polymers (CPs) [4]
Among the many potentially attractive properties of CPs, we have focused on their dynamic responses to external stimuli such as temperature [5,6,7,8] or moisture [9,10] in previous publications

Summary

Introduction

Carboxylic acids represent classical ligands for Werner complexes: As early as 1953, Niekerk et al. Dicarboxylic acids are even more prone to act as bridging components than their monofunctional congeners and have been frequently employed for the construction of coordination polymers [39,40] and metal-organic frameworks [41]. In this contribution, we introduce six new coordination compounds in which dicarboxylic acids act as terminal ligands or as linkers between divalent Cu cations, and we address the influence of chirality and the effect of blocking ligands on their crystal structures.

Compound 1

Compound 2a

Compound 2b

Compound 2c

Compound 3a

Compound 3b

Conlusions

Data Collection

Structure Solution and Refinement

Powder Diffraction

Magnetic Measurements