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Structural characterization is developed to determine crystallographic site-specific metal disorder. Anomalous scattering at the Zn and Cu edges is used for determining that there is no Zn occupation of the intralayer Cu sites within the kagome layer, however there is Cu present on the Zn intersite, which has led to a structural formula of ([Zn.sub.0.85][Cu.sub.0.15])[Cu.sub.3][(OH).sub.6][Cl.sub.2].

MnCl2(urea)2 is a new linear chain coordination polymer that exhibits slightly counter-rotated Mn2Cl2 rhomboids along the chain-axis. The material crystallizes in the noncentrosymmetric orthorhombic space group Iba2, with each Mn(II) ion equatorially surrounded by four Cl- that lead to bibridged ribbons. Urea ligands coordinate via O atoms in the axial positions. Hydrogen bonds of the Cl···H-N and O···H-N type link the chains into a quasi-3D network. Magnetic susceptibility data reveal a broad maximum at 9 K that is consistent with short-range magnetic order. Pulsed-field magnetization measurements conducted at 0.6 K show that a fully polarized magnetic state is achieved at Bsat = 19.6 T with another field-induced phase transition occurring at 2.8 T. Zero-field neutron diffraction studies made on a powdered sample of MnCl2(urea)2 reveal that long-range magnetic order occurs below TN = 3.2(1) K. Additional Bragg peaks due to antiferromagnetic (AFM) ordering can be indexed according to the Ib′a2′ magnetic space group and propagation vector τ = [0, 0, 0]. Rietveld profile analysis of these data revealed a Néel-type collinear ordering of Mn(II) ions with an ordered magnetic moment of 4.06(6) μB (5 μB is expected for isotropic S = 5/2) oriented along the b-axis, i.e., perpendicular to the chain-axis that runs along the c-direction. Owing to the potential for spatial exchange anisotropy and the pitfalls in modeling bulk magnetic data, we analyzed inelastic neutron scattering data to retrieve the exchange constants: Jc = 2.22 K (intrachain), Ja = −0.10 K (interchain), and D = −0.14 K with J > 0 assigned to AFM coupling. This J configuration is most unusual and contrasts the more commonly observed AFM interchain coupling of 1D chains. [ABSTRACT FROM AUTHOR]

Examines the long-range magnetic properties of Magnesium [N(CN)[sub 2]] [sub 2](pyz) {pyz = pyrazine}. Use of direct current magnetization, alternating current susceptibility, specific heat and neutron diffraction measurements; Properties of the crystallographic and antiferromagnetic structures; Evidence of spin-flop to paramagnetic transition in magnesium ion.

Structural characterization, exploiting X-ray scattering differences at elemental absorption edges, is developed to quantitatively determine crystallographic site-specific metal disorder. We apply this technique to the problem of Zn-Cu chemical disorder in ZnCu3(OH)6Cl2. This geometrically frustrated kagomé antiferromagnet is one of the best candidates for a spin-liquid ground state, but chemical disorder has been suggested as a mundane explanation for its magnetic properties. Using anomalous scattering at the Zn and Cu edges, we determine that there is no Zn occupation of the intralayer Cu sites within the kagomé layer; however there is Cu present on the Zn intersite, leading to a structural formula of (Zn0.85Cu0.15)- Cu3(OH)6Cl2. The lack of Zn mixing onto the kagomé lattice sites lends support to the idea that the electronic ground state in ZnCu3(OH)6Cl2 and its relatives is nontrivial. [ABSTRACT FROM AUTHOR]