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Aza-macrocyclic complexes of Group 1 cations:synthesis, structures and density functional theory study

Aza-macrocyclic complexes of Group 1 cations:synthesis, structures and density functional theory study
Aza-macrocyclic complexes of Group 1 cations:synthesis, structures and density functional theory study
The Group 1 complexes, [M(Me6[18]aneN6)][BArF] (M = Li–Cs; Me6[18]aneN6 = 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane; BArF = tetrakis{3,5-bis(trifluoromethyl)-phenyl}borate), are obtained in high yield by reaction of the macrocycle with M[BArF] in anhydrous CH2Cl2 solution, and characterised spectroscopically (1H, 13C{1H}, 7Li, 23Na, and 133Cs NMR), by microanalysis and, for M = Li, K, and Rb, by single crystal X-ray analysis. The structures show N6-coordination to the metal ion; the small ionic radius for Li+ leads to a puckered conformation. In contrast, the K+ ion fits well into the N6 plane, with the [BArF]? anions above and below, leading to two K+ species in the asymmetric unit (a hexagonal planar [K(Me6[18]aneN6)]+ cation and a ‘[K(Me6[18]aneN6)(?1-BArF)2]? anion’, with long axial K?F interactions). The Rb+ ion sits above the N6 plane, with two long axial Rb?F interactions in one cation and two long, mutually cis Rb?F interactions in the other. The unusual sandwich cations, [M(Me3tacn)2]+ (M = Na, K; distorted octahedral, N6 donor set) and half-sandwich cations [Li(Me3tacn)(thf)]+ (distorted tetrahedron, N3O donor set), [Li(Me4cyclen)(OH2)]+, and [Na(Me4cyclen)(thf)]+ (both distorted square pyramids with N4O donor sets) were also prepared (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, Me4cyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane). Density functional theory (DFT) calculations, using the BP86 and B3LYP functionals, show that the accessibility of the [M(Me3tacn)2]+ sandwich cations depends strongly on the M+ ionic radius, such that it is sufficiently large to avoid steric clashing between the Me groups of the two rings, and small enough to avoid very acute N–M–N chelate angles. The calculations also show that coordination to the Group 1 cation involves significant donation of electron density from the p-orbitals on the N atoms of the macrocycle, rather than purely electrostatic interactions.
1472-7773
13853-13866
Dyke, John
46393b45-6694-46f3-af20-d7369d26199f
Levason, William
e7f6d7c7-643c-49f5-8b57-0ebbe1bb52cd
Light, Mark
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Pugh, David
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Reid, Gillian
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Bhakhoa, Hanusha
1a26ab2f-484e-4e54-803c-0e35af679ead
Ramasami, Ponnadurai
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Rhyman, Lydia
d025e9f5-e723-49fd-ad1c-0a0508e6eb8a
Dyke, John
46393b45-6694-46f3-af20-d7369d26199f
Levason, William
e7f6d7c7-643c-49f5-8b57-0ebbe1bb52cd
Light, Mark
cf57314e-6856-491b-a8d2-2dffc452e161
Pugh, David
9ec61267-ae4d-40d8-bebf-0d603e2588d3
Reid, Gillian
37d35b11-40ce-48c5-a68e-f6ce04cd4037
Bhakhoa, Hanusha
1a26ab2f-484e-4e54-803c-0e35af679ead
Ramasami, Ponnadurai
5401f300-4ad3-4d35-8762-822768d6bd0c
Rhyman, Lydia
d025e9f5-e723-49fd-ad1c-0a0508e6eb8a

Dyke, John, Levason, William, Light, Mark, Pugh, David, Reid, Gillian, Bhakhoa, Hanusha, Ramasami, Ponnadurai and Rhyman, Lydia (2015) Aza-macrocyclic complexes of Group 1 cations:synthesis, structures and density functional theory study. Journal of the Chemical Society, Dalton Transactions, 44 (31), 13853-13866. (doi:10.1039/c5dt01865j).

Record type: Article

Abstract

The Group 1 complexes, [M(Me6[18]aneN6)][BArF] (M = Li–Cs; Me6[18]aneN6 = 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane; BArF = tetrakis{3,5-bis(trifluoromethyl)-phenyl}borate), are obtained in high yield by reaction of the macrocycle with M[BArF] in anhydrous CH2Cl2 solution, and characterised spectroscopically (1H, 13C{1H}, 7Li, 23Na, and 133Cs NMR), by microanalysis and, for M = Li, K, and Rb, by single crystal X-ray analysis. The structures show N6-coordination to the metal ion; the small ionic radius for Li+ leads to a puckered conformation. In contrast, the K+ ion fits well into the N6 plane, with the [BArF]? anions above and below, leading to two K+ species in the asymmetric unit (a hexagonal planar [K(Me6[18]aneN6)]+ cation and a ‘[K(Me6[18]aneN6)(?1-BArF)2]? anion’, with long axial K?F interactions). The Rb+ ion sits above the N6 plane, with two long axial Rb?F interactions in one cation and two long, mutually cis Rb?F interactions in the other. The unusual sandwich cations, [M(Me3tacn)2]+ (M = Na, K; distorted octahedral, N6 donor set) and half-sandwich cations [Li(Me3tacn)(thf)]+ (distorted tetrahedron, N3O donor set), [Li(Me4cyclen)(OH2)]+, and [Na(Me4cyclen)(thf)]+ (both distorted square pyramids with N4O donor sets) were also prepared (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, Me4cyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane). Density functional theory (DFT) calculations, using the BP86 and B3LYP functionals, show that the accessibility of the [M(Me3tacn)2]+ sandwich cations depends strongly on the M+ ionic radius, such that it is sufficiently large to avoid steric clashing between the Me groups of the two rings, and small enough to avoid very acute N–M–N chelate angles. The calculations also show that coordination to the Group 1 cation involves significant donation of electron density from the p-orbitals on the N atoms of the macrocycle, rather than purely electrostatic interactions.

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Accepted/In Press date: 15 June 2015
e-pub ahead of print date: 18 June 2015
Published date: 21 August 2015
Organisations: Chemistry

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Local EPrints ID: 383081
URI: http://eprints.soton.ac.uk/id/eprint/383081
ISSN: 1472-7773
PURE UUID: e376c0e2-98b1-4e8c-9e65-71580db8afa2
ORCID for John Dyke: ORCID iD orcid.org/0000-0002-9808-303X
ORCID for William Levason: ORCID iD orcid.org/0000-0003-3540-0971
ORCID for Mark Light: ORCID iD orcid.org/0000-0002-0585-0843
ORCID for Gillian Reid: ORCID iD orcid.org/0000-0001-5349-3468

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Date deposited: 27 Oct 2015 13:45
Last modified: 18 Feb 2021 16:52

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Author: John Dyke ORCID iD
Author: William Levason ORCID iD
Author: Mark Light ORCID iD
Author: David Pugh
Author: Gillian Reid ORCID iD
Author: Hanusha Bhakhoa
Author: Ponnadurai Ramasami
Author: Lydia Rhyman

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