Ni(II) andhs-Fe(II) Complexes of a Paramagnetic Thiazyl Ligand, and Decomposition Products of the Iron Complex, Including an Fe(III) Tetramer

Abstract

Synthesis and structural, magnetic and electrochemical characterization of the Ni(hfac) 2(pyDTDA) and the Fe(hfac) 2(pyDTDA) complexes are reported (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-; pyDTDA = 4-(2'-pyridyl)-1,2,3,5-dithiadiazolyl). Unlike the previously reported Mn(II) and Cu(II) complexes, but similar to the Co(II) complex, the Ni(II) and Fe(II) complexes are not dimerized in the solid state, allowing for magnetic coupling between the metal ion and paramagnetic ligand to be readily obtained from solid state magnetic measurements: Ni complex, J/k B = +132(1) K, using H = -2 J{ S Ni. S Rad} and g Ni = 2.04(2) and g Rad = 1.99(2); Fe complex, J/k B = -60.3(3) K, using H = -2 J{ S Fe. S Rad} and g av = 2.11(2). The iron complex is unusually unstable. A thermal decomposition product is isolated wherein the coordinated pyDTDA ligand appears to have been transformed into a coordinated 2-(2'-pyridyl)-4,6-bis(trifluoromethyl)pyrimidine. The iron complex also yields a solution decomposition product in the presence of air that is best described as an oxygen bridged iron(III) tetramer with two hfac ligands on each of three iron atoms and two oxidized pyDTDA ligands chelated on the fourth.

NMR relaxation and relaxivity parameters of MRI probes revealed by optimal wavelet signal compression of molecular dynamics simulations

“…Based on this context, in this work, we propose two Ni 2+ complexes as promising CAs in RMI, [Ni(ACAC) 2 (H 2 O) 2 ] and [Ni(TEA)] 2+ . The ligands chosen are important for the study, because they have OH − and H 2 O groups that can make hydrogen bonds with the free water molecules in the system . Figure shows the Ni 2+ complexes used in this work.…”

Coordination Complexes of a Neutral 1,2,4‐Benzotriazinyl Radical Ligand: Synthesis, Molecular and Electronic Structures, and Magnetic Properties

“…The coupling between the benzotriazinyl radicala nd the Fe II metal ion in complex 3 was found to be antiferromagnetic (À103 K) and significantly stronger than that reported for the related[Fe(pyDTDA)(hfac) 2 ]complex (À60 K). [19] As tructural comparison of complex 3 and [Fe(-pyDTDA)(hfac) 2 ]s hows that the keym etal-nitrogen bond lengths are not statistically differentb etween the two complexes: 2.140(3) and 2.158 (14) f or complex 3 and [Fe(pyDT-DA)(hfac) 2 ], respectively.H owever,a ccording to population analyses of the spin densities, the coordinating nitrogen atom in the radical 1 carries more spin density than that in the pyDTDA ligand, which offers ap lausible explanation for the observed coupling strengths.…”

“…For example, [Fe(hfac) 2 ]d oes not form as table coordination complex with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), [18] but does so when it is reacted with the 4-(pyrid-2-yl)-1,2,3,5-dithiadiazolyl (pyDTDA) radical ligand. [19] However,w hen sublimed, the complex [Fe(pyDT-DA)(hfac) 2 ]t hermally decomposes into ac oordinationc omplex that contains ad iamagnetic ligand. The coupling between the benzotriazinyl radicala nd the Fe II metal ion in complex 3 was found to be antiferromagnetic (À103 K) and significantly stronger than that reported for the related[Fe(pyDTDA)(hfac) 2 ]complex (À60 K).…”

Metal-radical coordination complexes of thiazyl and selenazyl ligands

“…Both the Mn II and Cu II complexes exhibit monomer/dimer equilibria in solution [68]. By contrast, crystalline Fe II and Ni II complexes are isostructural with the Co II complex, thus are not dimerized in the solid state [69]. Two unusual decomposition products of the Fe II complex were also isolated, one from thermolysis resulting in an Fe(hfac) 2 complex of 2-(pyrid-2-yl)-4,6-bis(trifluoromethyl)pyrimidine, and one from oxidation in air resulting in a tetranuclear Fe III cluster.…”