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

A study of the Group 1 metal tetra-aza macrocyclic complexes [M(Me4cyclen)(L)]+ using electronic structure calculations
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)][BArF] and [Na(Me4cyclen)(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(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)]+[BArF]− and [Na(Me4cyclen)(THF)]+[BArF]− 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)]+[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 [Me4cyclenH][BArF] 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.
0300-9246
Bhakhoa, Hanusha
1a26ab2f-484e-4e54-803c-0e35af679ead
Rhyman, Lydia
d025e9f5-e723-49fd-ad1c-0a0508e6eb8a
Lee, Edmond P.
f47c6d5d-2d1f-4f03-a3ff-03658812d80b
Mok, Daniel K. W.
1bbfba3e-c2e8-4225-8e07-cb6208ad83e1
Ramsami, Ponnadurai
31185a3a-be22-4c59-ad49-fad4799abee4
Dyke, John
46393b45-6694-46f3-af20-d7369d26199f
Bhakhoa, Hanusha
1a26ab2f-484e-4e54-803c-0e35af679ead
Rhyman, Lydia
d025e9f5-e723-49fd-ad1c-0a0508e6eb8a
Lee, Edmond P.
f47c6d5d-2d1f-4f03-a3ff-03658812d80b
Mok, Daniel K. W.
1bbfba3e-c2e8-4225-8e07-cb6208ad83e1
Ramsami, Ponnadurai
31185a3a-be22-4c59-ad49-fad4799abee4
Dyke, John
46393b45-6694-46f3-af20-d7369d26199f

Bhakhoa, Hanusha, Rhyman, Lydia, Lee, Edmond P., Mok, Daniel K. W., Ramsami, Ponnadurai and Dyke, John (2017) A study of the Group 1 metal tetra-aza macrocyclic complexes [M(Me4cyclen)(L)]+ using electronic structure calculations. Dalton Transactions. (doi:10.1039/C7DT03002A).

Record type: Article

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(Me4cyclen)(L)]+, was initiated by results of an experimental study which prepared some Group 1 metal cyclen complexes, namely [Li(Me4cyclen)(H2O)][BArF] and [Na(Me4cyclen)(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(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)]+[BArF]− and [Na(Me4cyclen)(THF)]+[BArF]− 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)]+[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 [Me4cyclenH][BArF] 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.

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FinalMetalMeCyclenPaperAUG2017 - Accepted Manuscript
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Accepted/In Press date: 13 October 2017
e-pub ahead of print date: 16 October 2017

Identifiers

Local EPrints ID: 415461
URI: https://eprints.soton.ac.uk/id/eprint/415461
ISSN: 0300-9246
PURE UUID: 9715d81d-35c6-4250-af41-b67f2764befa
ORCID for John Dyke: ORCID iD orcid.org/0000-0002-9808-303X

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Date deposited: 10 Nov 2017 17:30
Last modified: 20 Jul 2019 04:43

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