Chirality Sensing and Size Discrimination of Anions by Macrotricyclic Cyclen-Disodium Complexes

Molecular recognition and sensing of dicarboxylates and dicarboxylic acids

The recognition and detection of dicarboxylic acids and dicarboxylates is of significance for a wide variety of applications, including medical diagnosis, monitoring of health and of environmental contaminants, and in industry. Hence small molecule receptors and sensors for dicarboxylic acids and dicarboxylates have great potential for applications in these fields. This review outlines the challenges faced in the recognition and detection of these species, strategies that have been used to obtain effective and observable interactions with dicarboxylic acids and dicarboxylates, and progress made in this field in the period from 2014 to 2020.

A study of the Group 1 metal tetra-aza macrocyclic complexes [M(Me4cyclen)(L)]+ using electronic structure calculations

Metal-cyclen complexes have a number of important applications. However, the coordination chemistry between metal ions and cyclen-based macrocycles is much less well studied compared to their metal ion-crown ether analogues. This work, which makes a contribution to address this imbalance by studying complex ions of the type [M(Me₄cyclen)(L)]⁺, was initiated by results of an experimental study which prepared some Group 1 metal cyclen complexes, namely [Li(Me₄cyclen)(H₂O)][BAr^F] and [Na(Me₄cyclen)(THF)][BAr^F] and obtained their X-ray crystal structures [J. M. Dyke, W. Levason, M. E. Light, D. Pugh, G. Reid, H. Bhakhoa, P. Ramasami, and L. Rhyman, Dalton Trans., 2015, 44, 13853]. The lowest [M(Me₄cyclen)(L)]⁺ minimum energy structures (M = Li, Na, K, and L = H₂O, THF, DEE, MeOH, DCM) are studied using density functional theory (DFT) calculations. The geometry of each [M(Me₄cyclen)(L)]⁺ structure and, in particular, the conformation of L are found to be mainly governed by steric hindrance which decreases as the size of the ionic radius increases from Li⁺ → Na⁺ → K⁺. Good agreement of computed geometrical parameters of [Li(Me₄cyclen)(H₂O)]⁺ and [Na(Me₄cyclen)(THF)]⁺ with the corresponding geometrical parameters derived from the crystal structures [Li(Me₄cyclen)(H₂O)]⁺[BAr^F]^- and [Na(Me₄cyclen)(THF)]⁺[BAr^F]^- is obtained. Bonding analysis indicates that the stability of the [M(Me₄cyclen)(L)]⁺ structures originates mainly from ionic interaction between the Me₄cyclen/L ligands and the M⁺ centres. The experimental observation that [M(Me₄cyclen)(L)]⁺[BAr^F]^- complexes could be prepared in crystalline form for M⁺ = Li⁺ and Na⁺, but that experiments aimed at synthesising the corresponding K⁺, Rb⁺, and Cs⁺ complexes failed resulting in formation of [Me₄cyclenH][BAr^F] is investigated using DFT and explicitly correlated calculations, and explained by considering production of [Me₄cyclenH]⁺ by a hydrolysis reaction, involving traces of water, which competes with [M(Me₄cyclen)(L)]⁺ formation. [Me₄cyclenH]⁺ formation dominates for M⁺ = K⁺, Rb⁺, and Cs⁺ whereas formation of [M(Me₄cyclen)(L)]⁺ is energetically favoured for M⁺ = Li⁺ and Na⁺. The results indicate that the number and type of ligands, play a key role in stabilising the [M(Me₄cyclen)]⁺ complexes and it is hoped that this work will encourage experimentalists to prepare and characterise other [M(Me₄cyclen)(L)]⁺ complexes.

Can Cyclen Bind Alkali Metal Azides? A DFT Study as a Precursor to Synthesis

Can cyclen (1,4,7,10-tetraazacyclododecane) bind alkali metal azides? This question is addressed by studying the geometric and electronic structures of the alkali metal azide-cyclen [M(cyclen)N3] complexes using density functional theory (DFT). The effects of adding a second cyclen ring to form the sandwich alkali metal azide-cyclen [M(cyclen)2N3] complexes are also investigated. N3(-) is found to bind to a M(+) (cyclen) template to give both end-on and side-on structures. In the end-on structures, the terminal nitrogen atom of the azide group (N1) bonds to the metal as well as to a hydrogen atom of the cyclen ring through a hydrogen bond in an end-on configuration to the cyclen ring. In the side-on structures, the N3 unit is bonded (in a side-on configuration to the cyclen ring) to the metal through the terminal nitrogen atom of the azide group (N1), and through the other terminal nitrogen atom (N3) of the azide group by a hydrogen bond to a hydrogen atom of the cyclen ring. For all the alkali metals, the N3-side-on structure is lowest in energy. Addition of a second cyclen unit to [M(cyclen)N3] to form the sandwich compounds [M(cyclen)2N3] causes the bond strength between the metal and the N3 unit to decrease. It is hoped that this computational study will be a precursor to the synthesis and experimental study of these new macrocyclic compounds; structural parameters and infrared spectra were computed, which will assist future experimental work.

Chirality sensing and size recognition of N-Boc-amino acids by cage-type dimeric lanthanide complexes: chirality detection of N-Boc-aspartate anions via luminescence colour change

A mixture of chiral luminescent macrotricyclic-cyclen-Tb–Eu complexes enabled naked-eye discrimination of N-Boc-d- and l-aspartates via luminescence colour change.