ARTICLE | doi:10.20944/preprints202208.0217.v1
Subject: Chemistry, Inorganic & Nuclear Chemistry Keywords: Ruthenium; crystal structures; ferromagnetic coupling; molecular magnetism; single-ion magnet.
Online: 11 August 2022 (11:41:41 CEST)
Two mononuclear Ru(III) complexes of formula trans-[RuCl4(Hgua)(dmso)]·2H2O (1) and trans-[RuCl4(Hgua)(gua)]·3H2O (2) [Hgua = protonated guanine (gua), dmso = dimethyl sulfoxide] have been synthesized and characterized magnetostructurally. Compounds 1 and 2 crystallize in the monoclinic system with space groups P21/n and Pc, respectively. Each Ru(III) ion in 1 and 2 is six-coordinate and bonded to four chloride ions and one (1) or two (2) nitrogen atoms from guanine molecules and one sulfur atom (1) of a dmso solvent molecule, generating quasi regular octahedral geometries in both cases. In their crystal packing, the Ru(III) complexes are self-assembled mainly through an extended network of N-H⋯Cl hydrogen bonds and π⋯Cl type intermolecular interactions, forming novel supramolecular structures based on this paramagnetic 4d metal ion. Variable-temperature dc magnetic susceptibility measurements performed on microcrystalline samples of 1 and 2 show a different magnetic behavior. While 1 is a ferromagnetic compound at low temperature, 2 exhibits a behavior typical of noninteracting mononuclear Ru(III) complexes with S = 1/2. Ac magnetic susceptibility measurements reveal slow relaxation of the magnetization in the presence of external dc fields only for 2, hence indicating the occurrence of field-induced single-ion magnet (SIM) phenomenon in this mononuclear guanine-based Ru(III) complex.
ARTICLE | doi:10.20944/preprints202103.0662.v1
Subject: Chemistry, Analytical Chemistry Keywords: thymine; gadolinium; contrast agent; magnetic resonance; metal complexes; crystal structure; relaxivity
Online: 26 March 2021 (12:13:33 CET)
The paramagnetic gadolinium(III) ion is used as contrast agent in magnetic resonance (MR) imaging to improve the lesion detection and characterization. It generates a signal by changing the relaxivity of protons from associated water molecules and creates a clearer physical distinction between the molecule and the surrounding tissues. New gadolinium-based contrast agents displaying larger relaxivity values and specifically targeted might provide higher resolution and better functional images. We have synthesized the gadolinium(III) complex of formula [Gd(thy)2(H2O)6](ClO4)3·2H2O (1) [thy = 5-methyl-1H-pyrimidine-2,4-dione or thymine], which is the first reported compound based on gadolinium and thymine nucleobase. 1 has been characterized through vis-IR, SEM-EDAX and single-crystal X-ray diffraction techniques, and its magnetic and relaxometric properties have been investigated by means of SQUID magnetometer and MR imaging phantom studies, respectively. On the basis of its high relaxivity values, this gadolinium(III) complex can be considered a suitable candidate for contrast enhanced magnetic resonance imaging.