Crystal and magnetic structures and magnetic properties of selenate containing natrochalcite, A(I)M(II)2(H3O2)(SeO4)2 where A = Na or K and M = Mn, Co, or Ni.

The synthesis of a series of selenate containing natrochalcite, A(I)M(II)(2)(H(3)O(2))(SeO(4))(2) where A = Na or K and M = Mn, Co, or Ni (here labeled as AMH and AMD for the hydrogenated and deuterated compounds, respectively), the X-ray crystal structure determinations from single crystals (Ni) and powder (Mn), magnetic properties, and magnetic structures of the cobalt analogues are reported. The nuclear crystal structures for NaNiH, KNiH, and KMnH are similar to those reported for the cobalt analogues (NaCoH and KCoH) and consist of chains of edge-sharing octahedra (MO(6)) which are connected by H(3)O(2) and SeO(4) to form layers which are in turn bridged by the alkali, in an octahedral coordination site, to form the 3D-framework. The magnetic properties are characterized by antiferromagnetic interaction at high temperatures and antiferromagnetic ordering at low temperatures (NaCoH, 3.5 K; KCoH, 5.9 K; KNiH, 8.5 K; and KMnH, 16 K), except for KNi(2)(H(3)O(2))(SeO(4))(2) which displays a weak ferromagnetic interaction and no long-range ordering above 2 K. The neutron magnetic structures of the cobalt analogues, studied as a function of temperature, are different for the two cobalt salts and also different from all the known magnetic structures of the natrochalcite family. Whereas the magnetic structure of NaCoD has a k = (0, 0, 0), that of KCoD has one consisting of a doubled nuclear cell, k = (0, 0, 1/2). Both compounds have four magnetic sublattices related to the four cobalt atoms of the nuclear unit cell. In NaCoD the moments are in the bc-plane, M(y) = 2.51(2) µ(B) and M(z) = 1.29(4) µ(B), with the major component along the cobalt chain and the resultant moment, 2.83(3) µ(B), making an angle of 27° with the b-axis. The sum of the moments within the cell is zero. For KCoD the moment at each cobalt site has a component along each crystallographic axis, M(x) = 2.40(3), M(y) = 1.03(3), M(z) = 1.59(8) giving a total M = 2.49(3) µ(B). Within one nuclear cell the moments are fully compensated. The moments corresponding to the cobalt atoms of the second nuclear cell comprising the magnetic unit cell are oriented in opposite directions.

Existence of two concomitant magnetic structures below T(Néel) for the natrochalcite, NaFe(II)2(H3O2)(MoO4)2.

A comparative study of the magnetic properties and magnetic structures of the natrochalcite, NaFe(2)(D(3)O(2))(MoO(4))(2) (FeD) to those of the isostructural NaCo(2)(D(3)O(2))(MoO(4))(2) (CoD) and NaNi(2)(D(3)O(2))(MoO(4))(2) (NiD) is presented. The structural change is a shrinking of the unit cell in the order of the ionic radii of the transition metal, FeD > CoD > NiD. While NiD and CoD are canted-antiferromagnets with T(N) = 28 and 21 K, respectively, FeD is an anisotropic 2D-Ising antiferromagnet (T(N) = 17 K) with a spin-flop field of 14 kOe at 2 K and the presence of a hysteresis loop reaching only (1)/(4) of the saturation magnetization in 70 kOe. The critical field decreases almost linearly on warming to T(N). The neutron diffraction patterns of FeD below T(N) display numerous magnetic Bragg peaks which cannot be assigned to any one magnetic structure but fits well to two superposed sets, one with a temperature independent line width and has a propagation vector k(1) = (0, 0, 0) while for the other there is a clear dependence and k(2) = (0, 0, ½). In the k(1) = (0, 0, 0) magnetic structure the moments are parallel to each other within one chain and lie along the a-axis but are antiparallel to those in neighboring chains. In contrast CoD and NiD, for which k = (0, 0, 0), have their moments aligned along the b-axis and ac-plane, respectively. The second magnetic structure, k(2) = (0, 0, ½), is characterized by four sublattices, two per layer, where the moments are in the ab-plane and canted with a resultant along the a-axis which is compensated by those of the adjacent layers. For the k(2) = (0, 0, ½) structure, the scattering coherent length decreases, and the moments tend progressively toward the a-axis upon increasing temperature. The coexistence of two concomitant magnetic structures is unprecedented for compounds containing transition metal moment carriers.

Synthesis, magnetic properties, and magnetic structure of a natrochalcite structural variant, KM(II)2D3O2(MoO4)2 (M = Mn, Fe, or Co).

We report the syntheses, crystal structures, and magnetic properties of KMn(2)(H(3)O(2))(MoO(4))(2) (MnH), KMn(2)(D(3)O(2))(MoO(4))(2) (MnD), KFe(2)(H(3)O(2))(MoO(4))(2) (FeH), KFe(2)(D(3)O(2))(MoO(4))(2) (FeD), KCo(2)(H(3)O(2))(MoO(4))(2) (CoH), and KCo(2)(D(3)O(2))(MoO(4))(2) (CoD), and the magnetic structures of MnD and FeD. They belong to the structural variant (space group I2/m) of the mineral natrochalcite NaCu(2)(H(3)O(2))(SO(4))(2) (space group C2/m) where the diagonal within the ac-plane of the latter become one axis of the former. The structure of MnD, obtained from Rietveld refinement of a high-resolution neutron pattern taken at 300 K, consists of chains of edge-sharing octahedra bridged by MoO(4) and D(3)O(2) to form layers, which are connected to K through the oxygen atoms to form the three-dimensional (3D)-network. The X-ray powder diffraction patterns of the other two compounds were found to belong to the same space group with similar parameters. The magnetic susceptibilities of MnH and FeH exhibit long-range ordering of the moments at a Néel temperature of 8 and 11 K, respectively, which are accompanied by additional strong Bragg reflections in the neutron diffraction in the ordered state, consistent with antiferromagnetism. Analyses of the neutron data for MnD and FeD reveal the presence of both long- and short-range orderings and commensurate magnetic structures with a propagation vector of (½, 0, ½). The moments are antiferromagnetically ordered within the chains with alternation between chains to generate four nonequivalent nuclear unit cells. For MnD the moments are perpendicular to the chain axis (b-axis) while for FeD they are parallel to the b-axis. The overall total is a fully compensated magnetic structure with zero moment in each case. Surprisingly, for KCo(2)(D(3)O(2))(MoO(4))(2) neither additional peaks nor increase of the nuclear peaks' intensities were observed in the neutron diffraction patterns below the magnetic anomaly at 12 K which was identified to originate from a small quantity of a ferromagnetic compound, Co(2)(OH)(2)MoO(4).

Synthesis, magnetic structure, and properties of a layered cobalt-hydroxide ferromagnet, Co5(OH)6(SeO4)2(H2O)4.

The synthesis and nuclear and magnetic structures from the powder diffraction of Co(II)(5)(OH)(6)(SeO(4))(2)(H(2)O)(4) and its deuterated analogues as well as their infrared spectral, thermal, and magnetic properties are reported. The nuclear structure consists of brucite-like cobalt hydroxide layers connected by ...OSeO(3)-Co(H(2)O)(4)-O(3)SeO... bridges. The two independent cobalt atoms within the layer are arranged in chains along the b axis creating an anisotropy within each layer. The interlayer distance (10.718 A) is the only parameter to increase compared to the sulfate analogue (10.273 A). The infrared spectra and thermal properties are similar to those reported for the sulfate analogue. Due to the ferromagnetic exchange between the nearest-neighbor cobalt atoms within the layer, satisfying the Goodenough-Kanamori rule, and the weak interlayer exchange, an overall ferromagnet is obtained. The ferromagnetic order at 9 K was confirmed by the ac susceptibilities, the saturation magnetization, and most importantly the enhancement of some Bragg diffraction peaks below the Curie temperature. The moments of all the cobalt atoms were found to be aligned along the b axis with a moment of 3.25(8) mu(B) each giving the best fit. The increase in layer distance and the electron density by replacing sulfur by selenium lowers the Curie temperature.

4-Benzyl-pyridinium hydrogen selenate.

The structure of the title salt, C(12)H(12)N(+)·HSeO(4) (-), consists of infinite parallel two-dimensional planes built of 4-benzyl-pyridinium and hydrogen selenate ions that are mutually connected by strong O-H⋯O and N-H⋯O hydrogen bonds. There are no contacts other than normal van der Waals inter-actions between the layers.