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

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 H NMR paraSHIFT agents (paramagnetic shift agents) for the registration of temperature. Two of the complexes, [Co(BMPC)] and [Fe(BMPC)], contain methyl groups only on the methyl picolyl pendents. Two other complexes, [Co(2MPC)] and [Fe(2MPC)], 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 5.0-5.9μ and 5.3-5.8μ for Co(ii) and Fe(ii) complexes, respectively. The H 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)] appear at 164 and -113 ppm for macrocycle and pendent picolyl methyls and show temperature coefficients of -0.58 ppm °C and 0.49 ppm °C, respectively. Fe(ii) complexes have less shifted methyl proton resonances and smaller temperature coefficients. The H resonances of [Fe(2MPC)] appear at 105 ppm and -46 ppm with corresponding temperature coefficients (CT) of -0.29 ppm °C and 0.22 ppm °C, respectively. The relatively narrow linewidths of [Fe(2MPC)], however, produce superior CT/FWHM values of 0.44 and 0.31 °C for the N-methyl and picolyl proton resonances where FWHM is the full width at half maximum of the H resonance. The crystal structure of [Co(BMPC)]Cl 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.