Article pubs.acs.org/IC
Crystal and Magnetic Structures and Magnetic Properties of Selenate Containing Natrochalcite, AIMII2(H3O2)(SeO4)2 Where A = Na or K and M = Mn, Co, or Ni Wassim Maalej,†,‡ Serge Vilminot,*,† Gilles André,§ Zakaria Elaoud,‡ Tahar Mhiri,‡ and Mohamedally Kurmoo*,∥ †
Département de Chimie des Matériaux Inorganiques, IPCMS, UMR 7504 (CNRS-UdS), 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 02, France ‡ Laboratoire de l’Etat Solide, Faculté des Sciences, Université Sfax, route de Skoura km 3,5, 3000 Sfax, Tunisia § Laboratoire Léon Brillouin, CEA-CNRS, CEA Saclay, 91191 Gif-sur-Yvette, France ∥ Laboratoire DECOMET, CNRS-UMR 7177, Institut de Chimie de Strasbourg, Université de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg Cedex 1, France S Supporting Information *
ABSTRACT: The synthesis of a series of selenate containing natrochalcite, AIMII2(H3O2)(SeO4)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 Xray 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 (MO6) which are connected by H3O2 and SeO4 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 KNi2(H3O2)(SeO4)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, My = 2.51(2) μB and Mz = 1.29(4) μB, with the major component along the cobalt chain and the resultant moment, 2.83(3) μB, 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, Mx = 2.40(3), My = 1.03(3), Mz = 1.59(8) giving a total M = 2.49(3) μB. 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.
1. INTRODUCTION The sequence of events in the study of magnetism and magnetic structures using neutron diffraction started with magnetic minerals and especially oxides of the general structural families, viz, rocksalt, spinel, rutile, and perovskite.1 For these materials, the structures are composed of only polyhedra of magnetic ions.2 The next sets of materials to be studied were those containing polyhedra of both magnetic and nonmagnetic ions and for the latter the natural salts contain sulfate, borate, phosphate and arsenate.3 These were expanded synthetically with other ones, such as vanadate, selenate, and others.3,4 Very few studies have been performed on sulfate until © 2012 American Chemical Society
the rise of interest in understanding the frustration in magnetism, consequent to the presence of structural triangular motifs, where there were major developments on jarosites and kagome layered systems.5 The few magnetic structure studies on minerals containing octahedral magnetic transition metals and tetrahedral nonmagnetic anions prompted us to study first Antlerite, a product of pollution, which gives the statue of liberty its green coloration, and its selenate analogue.6,7 This led to the Received: October 19, 2011 Published: January 20, 2012 1953
dx.doi.org/10.1021/ic202273e | Inorg. Chem. 2012, 51, 1953−1962
Inorganic Chemistry
Article
Table 1. Summary of Crystal and Magnetic Structures and Magnetic Properties of Some Natrochalcitesa space group - crystal form
Θ/K
TNéel / K [canting angle/°]
NaCu2(H3O2)(SO4)2 NaNi2(H3O2) (MoO4)2 NaCo2(H3O2) (MoO4)2 NaFe2(H3O2) (MoO4)2
C2/m - SC C2/m - P
+9.9 −12.9(3)
3.3 28 [0.30]
0, 0, 0
yes
yes
0.5(1)
0
1.65(6)
13 14a
C2/m - SC
−47(1)
21 [0.17]
0, 0, 0
yes
yes
0
2.95(2)
0
14a
C2/m - SC
−24.7(3)
17
0, 0, 0 0, 0, 1/2
yes
no
3.09(3) 0.83(2)
0 2.48(4)
0.41(3) 0
14c
KCo2(H3O2) (MoO4)2 KFe2(H3O2) (MoO4)2 KMn2(H3O2) (MoO4)2 NaCo2(H3O2) (SeO4)2 NaNi2(H3O2) (SeO4)2 KCo2(H3O2)(SeO4)2 KNi2(H3O2)(SeO4)2 KMn2(H3O2) (SeO4)2
I2/m - P
−17.1(3)
compound
I2/m - P
k(x, y, z)
LRO
SRO
Mx / μB
My / μB
Mz / μB
ref
14b 11
1/2, 0, 1/2
yes
no
0
3.55(3)
0
14b
I2/m - P
−52.6(2)
8.2
1/2, 0, 1/2
yes
yes
3.90(3)
0
1.57(9)
14b
C2/m - SC
−15.5(3)
3.5
0, 0, 0
yes
yes
0
2.51(2)
1.29(4)
this work
C2/m - SC
+1.5(2)
C2/m - SC C2/m - SC C2/m - P
−26.1(6) −11.2(4) −30.9(7)
this work 5.9 8.5 16
0, 0, 1/2
yes
no
2.40(3)
1.03(3)
1.59(8)
this work this work this work
Θ = Weiss constant; k(x, y, z) = propagation magnetic vector; LRO = long-range magnetic ordering; SRO = short-range magnetic ordering; Mi = magnetic moment along the i-axis obtained from neutron diffraction; SC = single crystal; P = powder. a
antiferromagnetic ordering with the exception of a couple (Table 1).13,14 The exceptions do not show any long-range ordering at temperatures above 2 K. In another couple of cases canting of the moments were detected in the magnetic properties. The Néel transition temperatures vary widely and unsystematically. Most surprising is the variety and unpredictable magnetic structures that have been observed and the unprecedented observation of two concomitant magnetic structures for the 2D-Ising antiferromagnet, NaFe2(D3O2)(MoO4)2.14c The present study was undertaken in search of clues to the unexpected inconsistencies in the magnetic properties and magnetic structures. Here, we present the crystal structures of three unknown ones, two from single crystal data (NaNiH and KNiH) and one from powder data (KMnH), the magnetic properties as a function of temperature and field, and the magnetic structures of the two cobalt analogues (NaCoD and KCoD) for which deuterated samples were obtained in the required quantity. With the exception of KNiH all the compounds exhibit longrange magnetic ordering above 2 K. The two cobalt compounds have magnetic structures belonging to two different propagation vectors, k = (0, 0, 0) for NaCoD and k = (0, 0, 1/2) for KCoD.
observation that Antlerite has a simple magnetic structure (k = 0, 0, 0), but with an idle moment on the central copper of the trimer within the structure. In contrast, the selenate analogue displays a very unusual and rarely observed cycloidal magnetic structure becoming commensurate at the lowest temperatures with a vector k = kx, 0, 0 where kx = 1/7.7 This work then followed those of the antiferromagnet brochantite [Cu4(OH)6(SO4)],8 the ferrimagnet lindgrenite [Cu3(OH)2(MoO4)2]9 and three sets of synthetic compounds, M3(OH)2(SO4)2(H2O)2,10 K2M3(OH)2(SO4)3(H2O)2,11 and Co5(OH)6(TO4)2(H2O)412 where M = Mn, Fe, Co, Ni and T = S or Se. The first of these sets are canted antiferromagnets, the second are ferrimagnets, and the last are ferromagnets. The last family of compounds that we are studying is that of natrochalcite, AM2(H3O2)(TO4)2.13,14 The synthesis and crystal chemistry using X-ray, and in some cases neutron diffraction, of the mineral natrochalcite, AM2(H3O2)(TO4)2, family are well documented,13−20 but their magnetic properties and magnetic structures remained unknown until the reported antiferromagnetism of NaCu2(D3O2)(SO4)2 (TN = 3.3 K) and NaM2(H3O2)(MoO4)2 (M = Ni (TN = 21 K) and Co (TN = 28 K)).13,14 Previous works were concerned principally with the syntheses, characterization, and identification of the geometry and function of the H3O2 anion. It has been demonstrated that a wide range of salts can be prepared with A of varying sizes (Na, K, Cs, Rb, Tl, NH4, and Ag), M of the divalent transition metals (Mn, Fe, Co, Ni, Cu, and Zn), and the central atom of the tetrahedral anion (T) being S, Se, or Mo.13−20 Although the known salts contain principally divalent metals, one has been reported to contain trivalent iron. Such a variety of possible cations (A, M, and T) in the three crystallographic sites provide a handful of materials for systematically studying their influence on the magnetic properties and magnetic structures as a function of cationic sizes, spin, and magnetic anisotropy.14,20 Previous work on the molybdate family and the present one on the selenate family indicate that all display long-range
2. EXPERIMENTAL SECTION Synthesis. All the compounds were prepared by hydrothermal technique using a fill factor of 1/3 of the 125-mL capacity Teflon-lined stainless steel autoclaves. As the transition metal selenates are not available commercially, we have prepared them by the reaction of MnCO 3 ·4H 2 O, CoCO3·4H2O, or NiCO3·2Ni(OH)2 with an excess of selenic acid (H2SeO4, 40 wt % water solution). When the resulting solutions were slowly evaporated at room temperature MnSeO4·2H2O, CoSeO4·4H2O, or NiSeO4·6H2O were obtained. If the solutions were kept at 60 °C the monohydrated salts, MSeO 4·H 2 O, were obtained. The formulas and 1954
dx.doi.org/10.1021/ic202273e | Inorg. Chem. 2012, 51, 1953−1962
Inorganic Chemistry
Article
Table 2. Summary of the Single-Crystal X-ray Data for NaNiH and KNiH formula formula weight temperature (K) a (Å) b (Å) c (Å) β (°) V (Å3) Z system space group F (000) Dcalcd (g·cm−3) radiation, λ (Å) μ (mm−1) hkl range θ range (°) measured reflections unique reflections unique I > 2σ(I) Rint (%) R1 (all data) (%) wR2(Fo2) (all data) (%) GoF (%) residual electron density
NaNiH
KNiH
Se2H3NaO10Ni2 NaNi2(H3O2)(SeO4)2 461.31 173 8.8476(4) 6.2451(3) 7.4883(4) 114.531(1) 376.41(3) 2 monoclinic C2/m 436 4.07 Mo Kα1, 0.71069 1.48 −11
