Synthesis, Magnetic Properties, and Magnetic Structure of a Natrochalcite Structural Variant, KM^II₂D₃O₂(MoO₄)₂ (M = Mn, Fe, or Co)

Abstract

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).

Existence of Two Concomitant Magnetic Structures Below TNéelfor the Natrochalcite, NaFeII2(H3O2)(MoO4)2

“…However, for the KM 2 (H 3 O 2 )(MoO 4 ) 2 , M = Mn, Fe, or Co, only the former two exhibit antiferromagnetic ordering and k = ( 1 / 2 , 0, 1 / 2 ) structures with antiparallel alignment of moments along different directions within the edge-sharing chains. The cobalt complex is paramagnetic at all temperatures above 1.6 K …”

“…By using alkali metal ions, divalent transition metal cations of the first row for their octahedral coordination, and tetrahedral anions TO 4 , where T is S, Se, or Mo, we and other scientists have synthesized a wide variety of materials. − While many have natural equivalents, such as Antlerite, Brochantite, or Natrochalcite, there are several that are not known in nature. The selection of high purity starting materials results in transition metal pure materials, which are highly suitable for the study of their magnetic properties unlike the naturally occurred minerals that often contain mixtures of several cations. − Furthermore, by working in heavy water it is possible to replace the hydrogen atoms in the structures by deuterium, thus providing excellent samples for studies by neutron diffraction …”

“…Both have an idle spin for the copper atom at the center of the trimeric unit. The other set for which a wider range of structures have been observed is that belonging to the natrochalcite structure based on NaCu 2 (H 3 O 2 )(SO 4 ) 2 . − All the components in this structure are potentially replaceable, for example, Na by K, Rb, Cs, Tl, Ag, NH 4 ; Cu by Mn, Fe, Co, Ni, and S by Se, Mo. − Previous studies on the molybdate series, NaM 2 (H 3 O 2 )(MoO 4 ) 2 , M = Co or Ni, reveal collinear antiferromagnetic k = (0, 0, 0) structures for both with the moments along the b -axis for Co and along the ac -plane for Ni . However, for the KM 2 (H 3 O 2 )(MoO 4 ) 2 , M = Mn, Fe, or Co, only the former two exhibit antiferromagnetic ordering and k = ( 1 / 2 , 0, 1 / 2 ) structures with antiparallel alignment of moments along different directions within the edge-sharing chains.…”

“…10 However, for the KM 2 (H 3 O 2 )(MoO 4 ) 2 , M = Mn, Fe, or Co, only the former two exhibit antiferromagnetic ordering and k = ( 1 / 2 , 0, 1 / 2 ) structures with antiparallel alignment of moments along different directions within the edge-sharing chains. The cobalt complex is paramagnetic at all temperatures above 1.6 K. 17 To complement these studies as well as to understand the unusual alkali-metal dependence, we have studied the third member of the first series, NaFe II 2 (H 3 O 2 )(MoO 4 ) 2 . First to our surprise, the crystals were easily synthesized in good yield and also without contamination with magnetic iron oxides.…”

Spectroscopic characterization of extra‐framework hydrated proton complexes with the extremely strong hydrogen bonds in microporous silicate minerals

“…8,9 Numerous synthetic selenates and sulfates with the mineral-like structures including the compounds [(H 5 O 2 )(H 3 O)(H 2 O)][(UO 2 )(SeO 4 ) 2 ], 10 K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)], 11 and (H 5 O 2 )[Al(H 2 O) 2 (SO 4 ) 2 ] 12 contain Zundel cation. The structural and vibrational behavior of the H 3 O 2 À anion has been studied in natrochalcite-type compounds MCu 2 (H 3 O 2 )(ZO 4 ) 2 (M = Na, K; Z = S, Se) 13 as well as KM 2 (H 3 O 2 )(MoO 4 ) 2 (M = Mn, Fe, Co) 14 and NaFe 2 (H 3 O 2 )(MoO 4 ) 2 . 15 The possible presence of hydronium, H 3 O + , Zundel cation, H 5 O 2 + , Eigen cation, H 9 O 4 + , and larger hydrated proton complexes with the general formula H 2n+1 O n + in natural minerals was supposed already in the sixties.…”