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Issue 3, 2018
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Fe(II) and Co(II) N-methylated CYCLEN complexes as paraSHIFT agents with large temperature dependent shifts

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Abstract

Several complexes of Co(II) or Fe(II) with 1,4,7,10-tetraazacyclododecane (CYCLEN) appended with 1,7-(6-methyl)2-picolyl groups are studied as 1H NMR paraSHIFT agents (paramagnetic shift agents) for the registration of temperature. Two of the complexes, [Co(BMPC)]2+ and [Fe(BMPC)]2+, contain methyl groups only on the methyl picolyl pendents. Two other complexes, [Co(2MPC)]2+ and [Fe(2MPC)]2+, contain picolyl groups and also methyl groups on the macrocyclic amines. All macrocyclic complexes are in high spin form as shown by solution magnetic moments in the range of 5.0–5.9μBM and 5.3–5.8μBM for Co(II) and Fe(II) complexes, respectively. The 1H NMR spectra of both of the Fe(II) complexes and one of the Co(II) complexes are consistent with a predominant diastereomeric form in deuterium oxide solutions. The highly shifted methyl proton resonances for [Co(2MPC)]2+ appear at 164 and −113 ppm for macrocycle and pendent picolyl methyls and show temperature coefficients of −0.58 ppm °C−1 and 0.49 ppm °C−1, respectively. Fe(II) complexes have less shifted methyl proton resonances and smaller temperature coefficients. The 1H resonances of [Fe(2MPC)]2+ appear at 105 ppm and −46 ppm with corresponding temperature coefficients (CT) of −0.29 ppm °C−1 and 0.22 ppm °C−1, respectively. The relatively narrow linewidths of [Fe(2MPC)]2+, however, produce superior CT/FWHM values of 0.44 and 0.31 °C−1 for the N-methyl and picolyl proton resonances where FWHM is the full width at half maximum of the 1H resonance. The crystal structure of [Co(BMPC)]Cl2 shows a six-coordinate Co(II) bound to the macrocyclic amines and two pendent picolyl groups. The distorted trigonal prismatic geometry of the complex resembles that of an analogous complex containing four 6-methyl-2-picolyl groups, in which only two picolyl pendents are coordinated.

Graphical abstract: Fe(ii) and Co(ii) N-methylated CYCLEN complexes as paraSHIFT agents with large temperature dependent shifts

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Publication details

The article was received on 10 Oct 2017, accepted on 11 Dec 2017 and first published on 11 Dec 2017


Article type: Paper
DOI: 10.1039/C7DT03812G
Citation: Dalton Trans., 2018,47, 916-924
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    Fe(II) and Co(II) N-methylated CYCLEN complexes as paraSHIFT agents with large temperature dependent shifts

    P. B. Tsitovich, T. Y. Tittiris, J. M. Cox, J. B. Benedict and J. R. Morrow, Dalton Trans., 2018, 47, 916
    DOI: 10.1039/C7DT03812G

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