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Title: A study of the Group 1 metal tetra-aza macrocyclic complexes [M(Me(4)cyclen)(L)](+) using electronic structure calculations
Authors: Bhakhoa, H
Rhyman, L
Lee, EP 
Mok, DKW 
Ramasami, P
Dyke, JM
Issue Date: 2017
Publisher: Royal Society of Chemistry
Source: Dalton transactions : an international journal of inorganic chemistry, 28 Nov. 2017, v. 46, no. 44, p. 15301-15310 How to cite?
Journal: Dalton transactions : an international journal of inorganic chemistry 
Abstract: 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(Me(4)cyclen)(L)](+), was initiated by results of an experimental study which prepared some Group 1 metal cyclen complexes, namely [Li(Me(4)cyclen)(H2O)][BArF] and [Na(Me(4)cyclen) (THF)][BArF] 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(Me(4)cyclen)(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(Me(4)cyclen)(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(Me(4)cyclen)(H2O)](+) and [Na(Me(4)cyclen)(THF)](+) with the corresponding geometrical parameters derived from the crystal structures [Li(Me(4)cyclen)(H2O)](+)[BArF]- and [Na(Me(4)cyclen)(THF)](+)[BArF]-is obtained. Bonding analysis indicates that the stability of the [M(Me(4)cyclen)(L)](+) structures originates mainly from ionic interaction between the Me(4)cyclen/L ligands and the M+ centres. The experimental observation that [M(Me(4)cyclen)(L)](+)[BArF](-) 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 [Me(4)cyclenH][BArF] is investigated using DFT and explicitly correlated calculations, and explained by considering production of [Me(4)cyclenH](+) by a hydrolysis reaction, involving traces of water, which competes with [M(Me(4)cyclen)(L)](+) formation. [Me(4)cyclenH](+) formation dominates for M+ = K+, Rb+, and Cs+ whereas formation of [M(Me(4)cyclen)(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(Me(4)cyclen)](+) complexes and it is hoped that this work will encourage experimentalists to prepare and characterise other [M(Me(4)cyclen)(L)](+) complexes.
ISSN: 1477-9226
EISSN: 1477-9234
DOI: 10.1039/c7dt03002a
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