Article pubs.acs.org/crystal
Synthesis and Crystal Structure of New Carbonate Ca3Na2(CO3)4 Homeotypic with Orthoborates M3Ln2(BO3)4 (M = Ca, Sr, and Ba) Pavel N. Gavryushkin,*,†,‡ Vladimir V. Bakakin,§ Nadezhda B. Bolotina,∥ Anton F. Shatskiy,†,‡ Yurii V. Seryotkin,†,‡ and Konstantin D. Litasov†,‡ †
V.S. Sobolev Institute of Geology and Mineralogy, Russian Academy of Science, Siberian Branch, Novosibirsk 630090, Russia Novosibirsk State University, Novosibirsk 630090, Russia § Nikolaev Institute of Inorganic Chemistry, Russian Academy of Science, Siberian Branch, Novosibirsk 630090, Russia ∥ Shubnikov Institute of Crystallography RAS, Moscow 119333, Russia ‡
S Supporting Information *
ABSTRACT: Single crystals of the new double alkali carbonate Ca3Na2(CO3)4 were synthesized using a high-pressure large volume apparatus at 6 GPa by slow cooling of the stoichiometric carbonate mixture from 1400 to 1150 °C for 2.5 h. The structure was solved and refined to R = 0.044 using 7489 independent reflections: P1n1, Z = 8, a = 31.4421(8) Å, b = 8.1960(2)Å, c = 7.4360(2) Å, and β = 89.923(2)°. The structure is characterized by the maximal number of nonparallel sets of CO3 groups among carbonates. The compound is homeotypic with the orthoborates M3Ln2(BO3)4 (where M = Ca, Sr, Ba and Ln = Er, Sm, Nd, Pr, La, Y, Gd, Eu, Dy, Ho, and Bi). No homeotypic analogs have been found among carbonates. The structure is described as a packing of two-capped trigonal prisms formed by Na+ and Ca2+ cations and centered by CO3 triangles.
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(99.9%, Wako Co. Ltd.), Na2CO3 (25 mol %) and CaCO3 (75 mol %), was ground in an agate mortar under acetone and loaded as a powder into a graphite capsule 1 mm in diameter and 1.5 mm in length. The loaded capsule was dried at 150 °C for 5 h prior to the experiment. Single crystals of Ca3Na2(CO3)4 were synthesized by the annealing of the stoichiometric carbonate mixture at 6 GPa and 1000 °C for 30 h.6 The sample pressure was controlled by varying the oil pressure in the hydraulic system of the BARS apparatus. Sample heating was achieved using a tubular graphite heater, 13.0/12.0 mm in outer/inner diameter and 19.0 mm in height. The sample temperature was controlled using a PtRh(6/30) thermocouple. The details of high-pressure experiments can be found elsewhere.10 Data Collection and Structure Solution. A single crystal sample with dimensions of 0.08 × 0.1 × 0.08 mm was picked up under a polarizing microscope. The X-ray diffraction data were collected on the Oxford Diffraction Gemini R Ultra single-crystal diffractometer (CCDdetector, graphite-monochromatized Mo Ka radiation) using the ω-scan technique with a scan width of 1° per frame. Data reduction was performed with Oxford Diffraction CrysAlisPro. Jana2006 was used for structure solution and refinement.12 The structure was solved in the P1 space group using Superflip.13 The details of data collection and structure refinement are summarized in Table 1. Basic structural data including atomic coordinates, isotropic displacement parameters, and site occupancies are listed in Table 2. A mixed occupation is assumed because of unusually small values of the atomic displacement
INTRODUCTION Na−Ca double carbonates are of significant interest from both crystal-chemical and geological points of view. From a geological point of view, Na−Ca double carbonates constitute one of the most important classes of compounds which can control melting temperature of oxidized mantle domains and provide formation of mantle carbonatites and kimberlites.1−4 From a crystal-chemical point of view, this is a surprisingly poorly investigated class of carbonates with two big cations that can be homeotypic with orthoborates, which are intensively investigated due to their promising applications in laser optics.5 Our recent research on phase relations in the system Na2CO3−CaCO3 at 6 GPa reveals three new compounds: CaNa4(CO3)3, Ca3Na2(CO3)4, and Ca4Na2(CO3)5,6 in addition to the known Na2Ca(CO3)2 and Na2Ca2(CO3)3.7−9 In this paper, we present single crystal structure solution and analysis of one of these new high-pressure compounds, Ca3Na2(CO3)4 (see the Supporting Information for the .cif structure). This compound is the first known double carbonate with a ratio of M1+:M2+ = 2:3.
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EXPERIMENTAL SECTION Received: May 16, 2014 Revised: July 23, 2014
Synthesis. Single-phase aggregate was synthesized using the pressless multianvil apparatus BARS at IGM SB RAS (Novosibirsk, Russia).6,10,11 The stoichiometric mixture of pure carbonate reagents © XXXX American Chemical Society
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dx.doi.org/10.1021/cg500718y | Cryst. Growth Des. XXXX, XXX, XXX−XXX
Crystal Growth & Design
Article
The crystal-chemical formulas of orthoborates are almost the same as those for carbonate. For example, the crystal-chemical formula for Sr3Pr2(BO3)4 is as follows.14 Pr 2[8] Sr 2[8] Sr [7] B4[3] O 3(5) O 9 (4). The cation array of the Ca3Na2(CO3)4 structure is homeotypic to that of Gd5Si4-type structures,27 which are known for their giant magnetocaloric effect.28 The traditional structure description based on cation polyhedrons does not work well for these carbonate and borate structures. In our opinion, the most fruitful approach to the structure representation is the cation sublattice with anions filling the cavities,29 as first suggested by A. Vegas30 and applied for borates in our previous work.31,32 As structures of orthoborate family M3Ln2(BO3)4 have not yet been described in this way, we believe that the description will be useful, given the significant interest in these crystals among researchers.5 The homeotypic relations between compounds implies that all our crystal-chemical conclusions will be the same for both carbonate and orthoborates. According to the crystal-chemical formula, the total amount of cation bonds is 51. The balance of anionic bonds is the following: (5 × 3) + (4 × 9). One fourth of oxygen atoms are bonded to four additional Na or Ca atoms in addition to the indispensable bond with carbon, and three-fourth of oxygen atoms are bonded to three (Na, Ca) atoms. We analyzed the orthoborate structures and found that the typical coordination for such a set of bonds of the BO3 triangle is the eight-cornered polyhedron, typically a two-capped trigonal prism. Thus, the analysis of the crystal-chemical formula alone suggests that one can expect that the Ca, Na cation arrangement has main cavities of a two-capped trigonal prism shape (Figure 1). The arrangement of Na and Ca is based on the square− rhombic 32434 net perpendicular to [100] (Figure 2). There are eight such nets on the a period of the unit cell, alternating by the law ···AABBAABB···. They superimpose pairwise, forming right slabs. These slabs are shifted, alternately forming oblique interjacent slabs. Square prisms of right slabs are centered by additional (not belonging to the nets) (Na and Ca) cations (Figure 2). The described cation arrangement results in a partition of the space on two types of two-capped trigonal prisms related to the right and oblique slabs. These prisms are centered by CO3 triangles accordingly to the above reasoning. It is not hard to distinguish two-capped trigonal prisms in the right slabs. Their axes are parallel to the a axis of the structure (Figure 2). Both caps lie in the same slab and are associated with additional (not belonging to net) (Na and Ca) cations. The prisms share side faces, two other faces have caps. The slab is filled with prisms without cavities, except for the tetragonal pyramid cavities below and above additional cations. These cavities are included in one-capped trigonal prisms of underlying and overlying slabs, transforming them into twocapped prisms. These prisms are not easily distinguishable visually. They are “lying” prisms with axes parallel to the plane of the net (Figure 2). One cap of such a prism is located in the same slab and the other is in the adjacent slab. Each pair of prisms has a common square face, in the same way as the prisms of the right slab. The space of a slab is filled with these prisms almost completely, except for a certain amount of tetrahedral cavities. One of the most remarkable crystal-chemical features of the structure is probably the diversity of CO3 triangle orientations. Eight nonparallel sets of CO3 groups exist in the structure in total. For known carbonates, this is the maximum possible
Table 1. Parameters of Single Crystal Data Collection and Structure Refinement crystal data formula formula weight space group a (Å) b (Å) c (Å) β (deg) V (Å3) calculated density (g cm−3) F(000) μ (mm−1) data collection
Ca3Na2C4O12 (Z = 8) 406.3 P1n1 (#7; unique axis b, cell choice 2) 31.4421 (8) 8.1960 (2) 7.4360 (2) 89.923 (2) 1916.25 (8) 2.815 1616 1.9
instrument radiation type measured reflections independent reflections reflections with I > 3δ(I) hkl limits
Rint refinement R factors [I > 3δ(I)] R factors (all data) refined parameters residual electron density (e Å−3)
Xcalibur, Ruby, Gemini R Ultra Mo Kα radiation (λ = 0.7107 Å) 51005 15241 7140 −11 ≤ h ≤ 11 −49 ≤ k ≤ 48 12 ≤ l ≤ 12 0.05 based on F R = 0.0441; wR = 0.0465 R = 0.1003; wR = 0.0603 677 max 0.70, min −0.46
parameters (ADP) at X1−X6 sites. Such assumption improves the R-factor and makes ADP realistic. We failed, however, to refine Na/Ca ratios because of unavoidable correlation between ADPs and these ratios accompanied by a practically standing R-factor. For this reason, the Na:Ca ratios were fixed as 1:1.
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RESULTS AND DISCUSSION Structure Description. Interatomic Ca−O and Na−O distances vary in quite a wide range from 2.27 to 2.95 Å. This fact leads to an uncertainty in the determination of coordination numbers for Ca and Na. Hence, we propose the following crystal-chemical formula. Ca[9]Ca2[8]Na2[7]C4[3]O3(5)O9(4). The superscripts in square brackets and in parentheses indicate the coordination numbers of cations and anions, respectively. The deviation of the CO3 groups from the planarity varies in the range of 0.25°−7° and equal to 1.75° on the average. Our analysis of ICSD database shows that Ca3Na2(CO3)4 does not have homeotypic analogs among carbonates, even though there exists a family of homeotypic orthoborates with chemical formulas M3Ln2(BO3)4 (where M = Ca, Sr, Ba and Ln = Er, Sm, Nd, Pr, La, Y, Gd, Eu, Dy, Ho, Bi)5,14−25 and Eu5(BO3)4.26 Twenty-four representatives of these orthoborates are known up to now.23 In Figure 1, we compare the crystal structures of Ca3Na2(CO3)4 and Ba3Nd2(BO3)4. Both the a axes and the numbers of formula units of the listed borates are two times smaller than those of carbonate. The borates crystallized in the space group Pmnb (a nonconventional setting of Pnma, no. 62) or P21nb (a nonconventional setting of Pna21, no. 33) that contain P1n1, the space group of Ca3Na2(CO3)4 (Figure 2). B
dx.doi.org/10.1021/cg500718y | Cryst. Growth Des. XXXX, XXX, XXX−XXX
Crystal Growth & Design
Article
Table 2. Fractional Atomic Coordinates and Isotropic (Equivalent) Displacement Parameters (Å2) Ca1 Ca2 Ca3 Ca4 Ca5 Ca6 Ca7 Ca8 Ca9 Na1 Na2 Na3 Na4 Na5 X1 (Na,Ca) X2 (Na,Ca) X3 (Na,Ca) X4 (Na,Ca) X5 (Na,Ca) X6 (Na,Ca) C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 O12 O13 O14 O15 O16 O17 O18 O19 O20 O21 O22 O23 O24
x
y
z
Uiso
0.33172 (5) 0.67290 (5) 0.33529 (5) 0.67416 (5) 0.08522 (5) 0.92095 (5) 0.08203 (5) 0.92566 (5) 0.00401 (5) 0.31790 (9) 0.68936 (8) 0.06715 (7) 0.93865 (9) 0.00294 (9) 0.31631 (6) 0.68960 (7) 0.94019 (6) 0.06640 (7) 0.75248 (7) 0.25374 (8) 0.2534 (2) 0.7532 (4) 0.2542 (2) 0.7559 (4) 0.3557 (2) 0.6456 (2) 0.3578 (2) 0.6514 (2) 0.6055 (2) 0.4014 (2) 0.6102 (2) 0.3971 (2) 0.5031 (2) 0.50372 (16) 0.5038 (2) 0.50394 (16) 0.28800 (18) 0.21776 (16) 0.2569 (4) 0.71763 (18) 0.78858 (18) 0.7524 (2) 0.2174 (2) 0.2886 (2) 0.25382 (17) 0.7915 (2) 0.7238 (4) 0.7494 (2) 0.3524 (2) 0.33170 (18) 0.3837 (2) 0.6487 (2) 0.6671 (4) 0.6172 (2) 0.3596 (2) 0.3338 (2) 0.3831 (2) 0.64972 (18) 0.67805 (18) 0.62572 (18)
0.91952 (17) 0.92317 (17) 0.06638 (17) 0.06442 (18) 0.42588 (17) 0.43211 (16) 0.56843 (18) 0.57700 (18) 0.70699 (16) 0.4041 (4) 0.4062 (4) 0.0965 (4) 0.0933 (4) 0.2439 (2) 0.5971 (4) 0.5952 (4) 0.9040 (2) 0.9014 (4) 0.2134 (2) 0.2475 (4) 0.3818 (8) 0.3776 (9) 0.1235 (9) 0.0902 (9) 0.2892 (9) 0.2935 (8) 0.6936 (8) 0.7023 (9) 0.7929 (8) 0.7887 (8) 0.1950 (8) 0.1983 (8) 0.8870 (7) 0.1327 (5) 0.4114 (7) 0.6355 (7) 0.3101 (8) 0.3198 (7) 0.5304 (8) 0.3281 (7) 0.3237 (7) 0.4576 (7) 0.0638 (7) 0.0600 (8) 0.2779 (7) 0.1161 (8) 0.1026 (9) 0.0317 (7) 0.4237 (7) 0.1690 (7) 0.2672 (8) 0.4340 (7) 0.1732 (7) 0.2997 (11) 0.5648 (7) 0.8127 (7) 0.7127 (9) 0.5759 (7) 0.8178 (7) 0.7091 (7)
0.0789 (2) 0.07703 (18) 0.5759 (2) 0.5767 (2) 0.6256 (2) 0.6248 (2) 0.1250 (2) 0.1226 (2) 0.4429 (2) 0.9013 (4) 0.9157 (4) 0.3062 (4) 0.3040 (4) 0.9467 (4) 0.4172 (4) 0.4017 (4) 0.7780 (4) 0.7801 (4) 0.2560 (2) 0.2500 (4) 0.5942 (9) 0.5984 (11) 0.8784 (10) 0.8613 (11) 0.2776 (10) 0.2894 (9) 0.7708 (8) 0.7719 (10) 0.4200 (9) 0.4156 (8) 0.9185 (9) 0.9167 (9) 0.1155 (8) 0.5965 (7) 0.3405 (8) 0.8184 (7) 0.5460 (9) 0.5608 (8) 0.6457 (10) 0.5251 (8) 0.5375 (9) 0.7433 (8) 0.8531 (8) 0.8479 (9) 0.9469 (8) 0.9051 (10) 0.9561 (13) 0.7012 (9) 0.1939 (7) 0.2545 (7) 0.4046 (8) 0.2107 (11) 0.2615 (10) 0.3970 (10) 0.6841 (9) 0.7411 (9) 0.9074 (9) 0.6763 (10) 0.7505 (7) 0.9069 (7)
0.0175(4) 0.0174(4) 0.0185(4) 0.0213(4) 0.0162(4) 0.0166(4) 0.0221(4) 0.0198(4) 0.0208(4) 0.0202(8) 0.0190(8) 0.0098(6) 0.0193(8) 0.0130(6) 0.0251(6) 0.0328(7) 0.0228(6) 0.0370(8) 0.0236(5) 0.0453(8) 0.0188(13) 0.0324(17) 0.0307(16) 0.0291(16) 0.0201(13) 0.0174(12) 0.0145(11) 0.0206(14) 0.0135(11) 0.0128(11) 0.0171(12) 0.0171(12) 0.0130(10) 0.0025(7) 0.0117(10) 0.0054(8) 0.040(2) 0.0306(17) 0.072(3) 0.0353(18) 0.0383(18) 0.047(2) 0.042(2) 0.048(2) 0.0371(18) 0.065(3) 0.092(3) 0.057(2) 0.0298(16) 0.0327(16) 0.045(2) 0.068(3) 0.071(3) 0.092(3) 0.0359(19) 0.0412(19) 0.057(2) 0.0405(19) 0.0332(17) 0.0333(16)
C
Occ. (
