Antiferromagnetic Intrachain Interactions Research Articles

Molecular structure and magnetic properties of copper(II), manganese(II) and iron(II) croconate tri-hydrate

The compounds M IIC 5O 5·3H 2O with M=Cu ( I), Mn ( II), Fe ( III), were prepared and characterized by means of structural and magnetic measurements. The crystals are orthorhombic, space group Pbca, with a=11.770(2), b=8.085(2), c=15.571(2) Å for I, a=12.063(3), b=8.213(2), c=15.652(3) Å. for II, a=11.999(2), b=8.158(1), c=15.536(4) Å for III; Z=8. The previously reported structures of I and II, refined in this work, and the novel structure of III were solved by direct methods and least-squares refinement of structural parameters led to conventional R factors of 0.029, 0.025 and 0.025 for I, II and III, respectively. The overall structure is similar for the three compounds and consists of infinite one-dimensional chains of metal ions bridged by croconate ligands acting in a monodentate and bidentate fashion. The magnetic properties of I, II and III are reported and discussed on the basis of intrachain and interchain exchange couplings and, for III, of single-ion axial zero-field splitting contributions. Weak antiferromagnetic intrachain interactions via the croconate dianion ( J=0.99(3), 0.22(1) and ⩽0.54 cm −1 for I, II and III, respectively) appear to be responsible of most of the observed magnetic behavior.

Crystal structure and magnetic properties of the linear chain organic-intercalated chromium(II) compound: Tetramethylammonium trichlorochromate(II), [(CH 3) 4N]CrCl 3

The crystal structure and magnetic properties of [(CH 3) 4N]CrCl 3, TMCrC, are reported. The material crystallizes in the space group P6 3 m(C 6h su2) of the hexagonal system, with two molecules in a unit-cell of dimensions: a = b = 9.129(3) Å, c = 6.512(2) Å. The structure consists of linear one-dimensional chains of chromium atoms with three bridging chlorine atoms between them. The compound shows one-dimensional magnetic behaviour with antiferromagnetic intra-chain exchange interactions ( J k = −15.2 K) . At low temperatures ( T N = 7 K) antiferromagnetic three-dimensional order is observed.

Magnetic properties and superexchange in single chloride-bridged copper(II) chain compounds

Magnetic susceptibility data have been measured in the temperature range 1.75 to 60 K for the following structurally characterized, single chloride-bridged copper(II) chain compounds: dichlorobis(dimethyl sulphoxide)copper(II), dichlorobis(imidazole)copper(II), aquo(caffeine)dichlorocopper(II), and dichloro[2-(2′-methylaminoethyl)pyridine]copper(II). The first two compounds exhibit antiferromagnetic intrachain interactions with exchange coupling constants of –6.1 and –2.1 cm–1, respectively, while the second two compounds exhibit ferromagnetic interactions with J values of 0.48 and 1.58 cm–1 respectively. Except for dichlorobis(imidazole)copper(II), which undergoes long-range magnetic ordering below 7.7 K, the exchange coupling constants become more negative as the angle at the chloride bridge increases from 113.6° in dichloro[2-(2′-methylaminoethyl)pyridine]copper(II) to 144.6° in dichlorobis(dimethyl sulphoxide)copper(II).

The Magnetic Properties of Cu(NO3)2·C4H4N2

The magnetic and thermal properties of Cu(NO 3 ) 2 · C_4H_4N_2 have been investigated. As expected from crystal structure, the Heisenberg linear chain like properties have been found and the antiferromagnetic intrachain interaction is determined as |J|/k\cong5.5 K. Long range ordered state has not been found down to 0.18 K (0.04|J|/k).