Di- and tri-valent metal complexes with tris-amide-functionalised 1,4,7-triazacyclononane chelators
Di- and tri-valent metal complexes with tris-amide-functionalised 1,4,7-triazacyclononane chelators
The reactions of a series of divalent 3d metal ions (Co, Ni, Cu, Zn) with two tris-amide functionalised tacn ligands, {PhNHC(O)CH2}3-tacn (1) and {iPrNHC(O)CH2CH2}3-tacn (2), in alcohol solution are described. The resulting complexes, [M(1)](NO3)2 and [M(2)](NO3)2 are characterised by elemental analysis, mass spectrometry, IR, UV-vis, 1H and 13C{1H} NMR spectroscopy, as appropriate, and by single crystal X-ray analysis for four representative examples. In all cases the ligands behave as hexadentate chelators to the divalent metal ion, with N3O3 donor sets through the tacn N-donor atoms and the O-bound carboxamide pendant arms. However, the reaction of 1 with Co(NO3)2·6H2O produces the Co(iii) complex, [Co(1-H)](NO3)2, via air oxidation. The X-ray crystal structure of this complex confirms a distorted octahedral N4O2 coordination environment at cobalt(iii) through the three facial tacn amine groups, the anionic N atom from one deprotonated amide group, and two O-bound carboxamides. In comparison, the coordination of 1 towards the trivalent group 13 nitrates, M(NO3)·9H2O (M = Ga and In) at room temperature in MeOH yields the distorted octahedral [M(1)](NO3)3 salts initially (from NMR and IR spectroscopy and elemental analysis data) as colourless solids. However, they are less stable than the divalent complexes, undergoing slow amide hydrolysis in MeOH at room temperature over several hours, or more rapidly with heating. This process occurs more readily with Ga(iii) than with the less Lewis acidic In(iii) analogue. The crystal structure of one hydrolysis product, [Ga(3)](NO3), is also reported (3 = {PhNHC(O)CH2-tacn-(CH2CO2)2}2−), in which two amide arms from 1 are converted to carboxylates.
4061-4071
O’Callaghan, Charley
c789466d-1c1f-4b19-9a5e-cb9a750a2a8a
Greenacre, Victoria K.
c665a38b-0b1a-4671-ac75-bf0679dd1c57
Reid, Gillian
37d35b11-40ce-48c5-a68e-f6ce04cd4037
O’Callaghan, Charley
c789466d-1c1f-4b19-9a5e-cb9a750a2a8a
Greenacre, Victoria K.
c665a38b-0b1a-4671-ac75-bf0679dd1c57
Reid, Gillian
37d35b11-40ce-48c5-a68e-f6ce04cd4037
O’Callaghan, Charley, Greenacre, Victoria K. and Reid, Gillian
(2025)
Di- and tri-valent metal complexes with tris-amide-functionalised 1,4,7-triazacyclononane chelators.
New Journal of Chemistry, 49 (10), .
(doi:10.1039/d4nj05327c).
Abstract
The reactions of a series of divalent 3d metal ions (Co, Ni, Cu, Zn) with two tris-amide functionalised tacn ligands, {PhNHC(O)CH2}3-tacn (1) and {iPrNHC(O)CH2CH2}3-tacn (2), in alcohol solution are described. The resulting complexes, [M(1)](NO3)2 and [M(2)](NO3)2 are characterised by elemental analysis, mass spectrometry, IR, UV-vis, 1H and 13C{1H} NMR spectroscopy, as appropriate, and by single crystal X-ray analysis for four representative examples. In all cases the ligands behave as hexadentate chelators to the divalent metal ion, with N3O3 donor sets through the tacn N-donor atoms and the O-bound carboxamide pendant arms. However, the reaction of 1 with Co(NO3)2·6H2O produces the Co(iii) complex, [Co(1-H)](NO3)2, via air oxidation. The X-ray crystal structure of this complex confirms a distorted octahedral N4O2 coordination environment at cobalt(iii) through the three facial tacn amine groups, the anionic N atom from one deprotonated amide group, and two O-bound carboxamides. In comparison, the coordination of 1 towards the trivalent group 13 nitrates, M(NO3)·9H2O (M = Ga and In) at room temperature in MeOH yields the distorted octahedral [M(1)](NO3)3 salts initially (from NMR and IR spectroscopy and elemental analysis data) as colourless solids. However, they are less stable than the divalent complexes, undergoing slow amide hydrolysis in MeOH at room temperature over several hours, or more rapidly with heating. This process occurs more readily with Ga(iii) than with the less Lewis acidic In(iii) analogue. The crystal structure of one hydrolysis product, [Ga(3)](NO3), is also reported (3 = {PhNHC(O)CH2-tacn-(CH2CO2)2}2−), in which two amide arms from 1 are converted to carboxylates.
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d4nj05327c
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Accepted/In Press date: 6 February 2025
e-pub ahead of print date: 8 February 2025
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Local EPrints ID: 499965
URI: http://eprints.soton.ac.uk/id/eprint/499965
ISSN: 1144-0546
PURE UUID: 01ca4c5d-f69e-4ced-b0ca-4e0b6278b46f
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Date deposited: 09 Apr 2025 18:56
Last modified: 22 Aug 2025 02:19
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Author:
Charley O’Callaghan
Author:
Victoria K. Greenacre
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