1. Introduction
In the past 10–15 years, intermetallic clathrates have attracted widespread interest, largely due to their demonstrated potential in thermoelectrics development [
1,
2,
3,
4]. Having successfully synthesized Rb
7.3Na
16Ga
20Si
116 and Cs
8Na
16Ga
21Si
115—the first clathrate-II compounds with mixed Ga and Si [
5], as well as the first arsenic-based clathrates of type-I Rb
8Zn
18As
28 and Cs
8Cd
18As
28 [
6], we extended our attention to the
A-Ga-
Pn systems (
A = alkali metal or mixtures of alkali metals,
Pn = pnictogen,
i.e., group 15 element). Our motivation here was the idea to produce gallium-phosphide and/or gallium-arsenide clathrates (in analogy with the well-known III-V semiconductors, which are isoelectronic with Si and Ge), but so far, all synthetic efforts have failed to provide any evidence for the possible existence of such compounds. Instead, these experiments afforded a number of binary, ternary, and even quaternary compounds, some of which are with novel structures.
With this paper we detail the synthesis and the structural characterization of the new quaternary Zintl compounds RbNa
8Ga
3As
6 and RbNa
8Ga
3P
6, which are isoelectronic and isostructural. They crystallize with a novel orthorhombic structure type, featuring a somewhat unusual building block—[Ga
Pn3]
6− trigonal planar units (isosteric with the borate BO
33−, as well as carbonate CO
32− anions), which are cyclically trimerized into [Ga
3Pn6]
9− (isosteric with the metaborate anion B
3O
63−, as well as the 1,3,5-trioxanetrione, a cyclic trimer of carbon dioxide). We note here that while the ternary
A-
Tr-
Pn (
Tr = triel
i.e., group 13 element) phase diagrams have already been extensively explored, and many
A-
Tr-
Pn compounds have been reported [
7,
8,
9,
10,
11,
12], very little is known about the corresponding
A'-A''-
Tr-
Pn systems, where
A' and A'' are two different alkali metals. The newly identified RbNa
8Ga
3As
6 and RbNa
8Ga
3P
6 (formally
A3TrPn2) underscore the utility of mixtures of chemically and spatially dissimilar cations for the discovery of new compounds with novel structures. On this note, we point out that the prevailing motifs in the structures of most ternary
A-
Tr-
Pn compounds are [
TrPn4]
9− tetrahedra, either isolated or condensed in different fashions to form diverse polyanionic structures, e.g.,
and
chains in Na
3AlAs
2 [
7] and K
3Al
2As
3 [
8], respectively;
and
layers in K
2Al
2Sb
3 [
9] and K
3Ga
3As
4 [
10], respectively; and 3-D framework in Na
9In
3Bi
6 structure [
11]. Planar [Ga
3As
6]
9−, [Ga
3Sb
6]
9− and [Ga
3Bi
6]
9− units, analogous to the ones described herein are known only for K
20(Ga
3As
6)
2As
0.66 and K
20(Ga
3Sb
6)
2Sb
0.66 [
12]; and K
20(Ga
3Bi
6)
2Bi
0.66 [
11].
Reported as well is the new compound Na
10NbGaAs
6, which is isoelectronic and isostructural to K
10NbInAs
6 [
13]. This phase was identified as an inadvertent product from the unwanted reaction of the reaction vessel (niobium) with elemental arsenic; its structure comprises NbAs
4 and GaAs
4 tetrahedra, edge-shared into [NbGaAs
6]
10− dimers, which are isosteric with diborane molecule, B
2H
6.
2. Results and Discussion
RbNa
8Ga
3As
6 and RbNa
8Ga
3P
6 both crystallize with the orthorhombic space group
Pnma (No. 62, Pearson symbol
oP72). The structure contains 18 independent sites in the asymmetric unit—one Rb, eight Na, three Ga, and six pnictogen atoms—all located at special position 4
c. The structure can be viewed as being built from [Ga
3Pn6]
9− polyanions with alkali metal cations counterbalancing the charges and filling the space among them (
Figure 1). The triangularly-shaped [Ga
3Pn6]
9− motif could be considered as a cyclic trimer of the [Ga
Pn3]
6− trigonal planar units, which form a 6-membered ring by sharing two of the
Pn atoms from each [Ga
Pn3]
6−. Therefore, all three Ga atoms are 3-bonded, while the three
Pn atoms on the 6-membered ring are 2-bonded and the three
Pn atoms attaching to the ring are 1-bonded. The distances between Ga and the
Pn atoms are all within the normal ranges for covalently bound Ga–As and Ga–P. For example, the Ga–As distances range from 2.335 to 2.422 Å; the Ga–P distances range from 2.245 to 2.337 Å (
Table 1). These values compare very well with the sums of the corresponding covalent radii (
rGa = 1.246 Å;
rAs = 1.210 Å;
rP = 1.10 Å) [
14], as well as with the Ga–
Pn distances found in compounds with Ga in similar 3-fold coordination environment of As or P (
Table 2), e.g.,
dGa–As = 2.367 ÷ 2.426 Å in Rb
2GaAs
2 [
15],
dGa–As = 2.367 ÷ 2.442 Å in K
20(Ga
3As
6)
2As
0.66 [
12], and
dGa–P = 2.226 ÷ 2.392 Å in Rb
3GaP
2 [
16]. In general, the distances between Ga and the 2-bonded
Pn are just about 0.08 Å longer than those between Ga and the 1-bonded
Pn atom, which indicates that there is no appreciable
π-bonding in the 6-membered ring. Hence, the formula RbNa
8Ga
3Pn6 represents a salt-like, electron-balanced Zintl phase [
17]. According to the valence rules, the charges could be assigned as Rb
+(Na
+)
8(Ga
3+)
3(
Pn3–)
6 based on oxidation states and counting the Ga and the
Pn atoms as tri-valent species; alternatively, based on formal charges, the formula can be broken down to Rb
+(Na
+)
8(3
b-Ga
0)
3(2
b-
Pn1–)
3(1
b-
Pn2–)
3, where 2-bonded and 1-bonded
Pn atoms carry different negative charges, consistent with the Zintl formalism.
Figure 1.
Crystal structure of RbNa8Ga3Pn6 (Pn = P, As).The different elements are color-coded as follows: Ga—green; Pn—orange; Rb—purple; and Na-grey. The covalent Ga–Pn bonds are emphasized as yellow-green cylinders.
Figure 1.
Crystal structure of RbNa8Ga3Pn6 (Pn = P, As).The different elements are color-coded as follows: Ga—green; Pn—orange; Rb—purple; and Na-grey. The covalent Ga–Pn bonds are emphasized as yellow-green cylinders.
Three-coordinated Ga (or a triel element in general) is much less common within the
A-
Tr-
Pn compounds than the four-coordinated tetrahedral geometry, which appears to be the prevailing building block among such solids. Examples of borate-like (or carbonate-like) [
TrPn3]
6− units exist and can be exemplified by [InAs
3]
6− seen in the K
6InAs
3 structure [
18]; [Ga
2P
4]
6− found in the Rb
3GaP
2 structure [
16] can be cited as an example of 4-membered rings formed via condensation of two [GaP
3]
6− units into [Ga
2P
4]
6− dimers (isosteric with 1,3-Dioxetanedione). Higher oligomers, such as the cyclic trimers [Ga
3Pn6]
9− that present 6-membered rings are known in the K
20(Ga
3Pn6)
2Pn0.66 structures [
12] and in the structures of the title compounds. Since the [
TrPn3]
6− unit is a planar structural motif, it is not common for it to form structures in higher dimension. A search of the ICSD database only reveals
the chain found in the K
2GaP
2 type structure [
19]. In this bonding arrangement, 5-memered rings are generated by sharing one common
Pn and forming one
Pn–
Pn bond between every two [Ga
Pn3]
6– units—these 5-membered rings are further connected to form an infinite chain using the third
Pn atom as a linker (
Figure 2).
Table 1.
Important interatomic distances (Å) in RbNa8Ga3Pn6 (Pn = As, P).
Table 1.
Important interatomic distances (Å) in RbNa8Ga3Pn6 (Pn = As, P).
| | RbNa8Ga3As6 | RbNa8Ga3P6 | | | | RbNa8Ga3As6 | RbNa8Ga3P6 |
---|
Ga1– | Pn1 | 2.335(1) | 2.245(2) | | Na3– | Pn2 | 3.015(3) | 2.935(3) |
| Pn2 | 2.388(1) | 2.303(2) | | | Pn3 (×2) | 3.235(2) | 3.158(2) |
| Pn3 | 2.400(1) | 2.312(2) | | | Pn5 (×2) | 3.270(2) | 3.213(2) |
Ga2– | Pn4 | 2.351(1) | 2.259(2) | | | Ga3 (×2) | 3.270(2) | 3.216(2) |
| Pn2 | 2.383(1) | 2.300(2) | | Na4– | Ga2 (×2) | 3.336(2) | 3.260(2) |
| Pn6 | 2.391(1) | 2.309(2) | | | Ga3 (×2) | 3.346(2) | 3.257(2) |
Ga3– | Pn5 | 2.351(1) | 2.259(2) | | | Ga1 (×2) | 3.364(2) | 3.282(2) |
| Pn3 | 2.418(1) | 2.329(2) | | | Pn3 (×2) | 3.375(2) | 3.265(2) |
| Pn6 | 2.422(1) | 2.337(2) | | | Pn6 (×2) | 3.416(2) | 3.314(2) |
Pn1– | Ga1 | 2.335(1) | 2.245(2) | | | Pn2 (×2) | 3.500(2) | 3.401(2) |
Pn2– | Ga1 | 2.388(1) | 2.303(2) | | Na5– | Pn3 | 2.967(3) | 2.892(3) |
| Ga2 | 2.383(1) | 2.300(2) | | | Pn2 (×2) | 3.190(2) | 3.116(2) |
Pn3– | Ga1 | 2.400(1) | 2.312(2) | | | Pn4 (×2) | 3.338(2) | 3.278(2) |
| Ga3 | 2.418(1) | 2.329(2) | | | Ga2 (×2) | 3.296(2) | 3.244(2) |
Pn4– | Ga2 | 2.351(1) | 2.259(2) | | Na6– | Pn4 | 2.970(3) | 2.882(3) |
Pn5– | Ga3 | 2.351(1) | 2.259(2) | | | Pn1 (×2) | 3.211(2) | 3.126(2) |
Pn6– | Ga2 | 2.391(1) | 2.309(2) | | | Pn3 (×2) | 3.386(2) | 3.328(2) |
| Ga3 | 2.422(1) | 2.337(2) | | | Ga1 (×2) | 3.240(2) | 3.181(2) |
Rb– | Pn1 (×2) | 3.5491(9) | 3.487(1) | | Na7– | Pn5 | 3.019(3) | 2.933(3) |
| Pn6 (×2) | 3.5929(9) | 3.523(1) | | | Pn1 (×2) | 3.209(2) | 3.134(2) |
| Pn5 (×2) | 3.6975(9) | 3.623(1) | | | Pn2 (×2) | 3.343(2) | 3.280(2) |
| Ga3 (×2) | 3.735(1) | 3.6707(8) | | | Ga1 (×2) | 3.284(2) | 3.227(2) |
Na1– | Pn5 (×2) | 2.992(2) | 2.931(2) | | Na8– | Pn4 | 2.967(3) | 2.874(3) |
| Pn1 | 3.018(3) | 2.965(3) | | | Pn4 (×2) | 3.239(2) | 3.176(2) |
| Pn5 | 3.117(3) | 3.051(3) | | | Pn6 (×2) | 3.330(2) | 3.250(2) |
Na2– | Pn4 (×2) | 2.967(2) | 2.909(2) | | | Ga2 (×2) | 3.245(2) | 3.183(2) |
| Pn1 | 2.970(3) | 2.911(3) | | | | | |
| Pn6 | 3.069(3) | 3.008(3) | | | | | |
Table 2.
Selected angles (°) in RbNa8Ga3Pn6 (Pn = As, P).
Table 2.
Selected angles (°) in RbNa8Ga3Pn6 (Pn = As, P).
| | RbNa8Ga3As6 | RbNa8Ga3P6 | | | | RbNa8Ga3As6 | RbNa8Ga3P6 |
---|
Pn1-Ga1-Pn2 | 115.89(4) | 116.42(7) | | Pn5-Ga3-Pn3 | 113.79(4) | 114.48(7) |
Pn1-Ga1-Pn3 | 119.19(4) | 119.78(7) | | Pn5-Ga3-Pn6 | 124.65(4) | 125.05(7) |
Pn2-Ga1-Pn3 | 124.92(4) | 123.81(7) | | Pn3-Ga3-Pn6 | 121.56(4) | 120.47(7) |
Pn4-Ga2-Pn2 | 114.31(4) | 114.77(7) | | Ga2-
Pn2-Ga1 | 113.01(4) | 114.04(8) |
Pn4-Ga2-Pn6 | 117.77(4) | 118.39(7) | | Ga1-
Pn3-Ga3 | 117.57(4) | 118.85(8) |
Pn2-Ga2-Pn6 | 127.93(4) | 126.84(7) | | Ga2-
Pn6-Ga3 | 115.01(4) | 115.98(7) |
Figure 2.
Diverse structural motifs based on the [TrPn3]6− unit (Tr = triel, Pn = pnictogen).
Figure 2.
Diverse structural motifs based on the [TrPn3]6− unit (Tr = triel, Pn = pnictogen).
As we already mentioned, there are nine crystallographically different cations in the RbNa
8Ga
3Pn6 structure and they have subtly different coordination environments. The large Rb cation is coordinated to six pnictogen atoms that form trigonal prism, with Rb–
Pn distances falling in the range from 3.549 to 3.698 Å for Rb–As, and from 3.487 to 3.623 Å for Rb–P (
Table 1). Two Ga atoms are found at a little longer distance, enlarging the Rb first coordination sphere to the shape of a quadrilateral prism (
Figure 3). Three different local environments could be found for Na: Na1 and Na2 are found in a tetrahedral surrounding of four pnictogen atoms; square pyramids formed by five next-nearest pnictogen atoms are observed for Na3, Na5, Na6, Na7, and Na8—notice that the bases of the square-pyramids are capped by two Ga atoms, enlarging the coordination number to 7; and a hexagonal prism for Na4, where each hexagonal base is formed by three Ga and three
Pn atoms. The Na–
Pn distances fall into a very wide range due to the different coordination numbers (CN) for Na, with the shortest Na–
Pn distance noted for 4-coordinated Na, and the longest Na–
Pn distance found for the 12-coordinated Na (
Table 1).
Figure 3.
Cation coordination in RbNa8Ga3Pn6. The polyhedron around Rb is shown in purple (a); Na1 and Na2 in light blue (b); Na3, Na5, Na6, Na7, and Na8 in dark blue (c); and Na4 in olive (d). See text for details.
Figure 3.
Cation coordination in RbNa8Ga3Pn6. The polyhedron around Rb is shown in purple (a); Na1 and Na2 in light blue (b); Na3, Na5, Na6, Na7, and Na8 in dark blue (c); and Na4 in olive (d). See text for details.
Figure 4.
Side-by-side comparison of the cation packing in the crystal structures of K20(Ga3As6)2As0.66 and RbNa8Ga3As6, where the trigonal prisms formed by the cations are emphasized. Different shades represent the different heights in the projected directions. The corresponding elements are color-coded as follows: Ga—green;Pn—orange; K—light blue; Rb—purple; and Na—grey. The covalent Ga–As bonds and the unit cells are outlined too.
Figure 4.
Side-by-side comparison of the cation packing in the crystal structures of K20(Ga3As6)2As0.66 and RbNa8Ga3As6, where the trigonal prisms formed by the cations are emphasized. Different shades represent the different heights in the projected directions. The corresponding elements are color-coded as follows: Ga—green;Pn—orange; K—light blue; Rb—purple; and Na—grey. The covalent Ga–As bonds and the unit cells are outlined too.
As already noted, the [Ga
3Pn6]
9− 6-membered motif is not without a precedent, having been reported for some time already in K
20(Ga
3Pn6)
2Pn0.66 (defect Ho
6Ni
20P
13 structure type, Pearson symbol
hP39) [
11,
12]. However, in the latter hexagonal structure, in addition to the [Ga
3Pn6]
9− polyanions, there are isolated
Pn3− anions (note the partial occupancy of this site). Apparently, a single cation like K
+ cannot pack well enough with the [Ga
3Pn6]
9− polyanions, requiring some subtle rearrangements to accommodate the counterbalancing
Pn3− anions. Following the notion of describing the structure from the standpoint of cation packing, in analogy with what has already been presented for K
20(Ga
3Pn6)
2Pn0.66 [
12], one can see that the cation arrangements in both cases are actually very similar. From
Figure 4, it can be seen that in both structures, apart from the partially occupied
Pn atoms in the K
20(Ga
3Pn6)
2Pn0.66 structure, which reside in large hexagonal channels, all Ga and
Pn atoms are at the centers of trigonal prisms formed by the cations. Nine such trigonal prisms are conjoined, forming a much larger prism that encloses the entire [Ga
3Pn6]
9− unit. The difference is that in K
20(Ga
3Pn6)
2Pn0.66, these larger trigonal prisms can be noted as discrete components, while in RbNa
8Ga
3Pn6 (=Rb
2Na
16(Ga
3Pn6)
2,
i.e., two cations less per formula) they further connect with each other along the
a axis by sharing Rb atoms (
Figure 4). It seems that the much bigger Rb brings the necessary distortion to the larger trigonal prisms, which leads to a slightly different packing of the cations compared with K
20(Ga
3Pn6)
2Pn0.66.
Na
10NbGaAs
6 crystallizes with the monoclinic space group
P2
1/
n (No. 14, Pearson symbol
mP36), and is found to be isoelectronic and isostructural to the Zintl compound K
10NbInAs
6 [
13]. The structure is composed of isolated dimers of edge-shared tetrahedra (NbAs
4 or GaAs
4), which are isosteric with diborane, B
2H
6. These dimeric units are separated by the alkali metal cations (
Figure 5). Note that there is only one tetrahedral site in the structure, which is co-occupied by Ga and Nb in equal amounts. In the earlier paper on K
10NbInAs
6, a diamagnetic response from the magnetic susceptibility of the compound can be inferred, suggesting the Nb to be assigned as Nb
5+ (
i.e.,
d0 closed-shell species) [
13]. This argument allows for the structure to be rationalized readily as (K
+)
10Nb
5+In
3+(As
3–)
6. Clearly, the same approach will be applicable to Na
10NbGaAs
6 (e.g., (Na
+)
10Nb
5+Ga
3+(As
3–)
6), which means that it can be classified as a Zintl compound with a transition metal [
13,
20].
Figure 5.
(a)Crystal structure of Na10NbGaAs6, viewed along the a axis; (b) representation of [(As)2Nb(μ-As)2Ga(As)2]10– with thermal ellipsoids, drawn at the 95% probability. The atoms at the centers of the tetrahedra of As atoms are statistically distributed Nb and Ga. The corresponding elements are color-coded as follows: Ga/Nb—light blue; As—orange; and Na—grey.
Figure 5.
(a)Crystal structure of Na10NbGaAs6, viewed along the a axis; (b) representation of [(As)2Nb(μ-As)2Ga(As)2]10– with thermal ellipsoids, drawn at the 95% probability. The atoms at the centers of the tetrahedra of As atoms are statistically distributed Nb and Ga. The corresponding elements are color-coded as follows: Ga/Nb—light blue; As—orange; and Na—grey.
Table 3.
Selected interatomic distances (Å) and angles (°) in Na10NbGaAs6.
Table 3.
Selected interatomic distances (Å) and angles (°) in Na10NbGaAs6.
Nb/Ga– | As3 | 2.4855(6) | As3-Nb/Ga-As2 | 114.20(2) |
| As2 | 2.4959(6) | As3-Nb/Ga-As1 | 108.68(2) |
| As1 | 2.5274(6) | As2-Nb/Ga-As1 | 113.79(2) |
| As1 | 2.5645(6) | As3-Nb/Ga-As1 | 111.17(2) |
| | | As2-Nb/Ga-As1 | 106.78(2) |
| | | As1-Nb/Ga-As1 | 101.49(2) |
The Nb/Ga–;As distances fall in the range of 2.4855(6) to 2.5645(6) Å, and all of the As-Nb/Ga-As angles are close to the ideal tetrahedral angle 109°28' (
Table 3). An examination of the structures of some compounds with ordered GaAs
4 and NbAs
4 tetrahedra reveals similar lengths for the Ga–As and Nb–As bonds. For example, the Ga–As bonds range from 2.444 to 2.556 Å in K
3Ga
3As
4 [
9], and from 2.435 to 2.599 Å in Na
2Ga
2As
3 [
21], respectively. The Nb–As distances, as reported for K
38Nb
7As
24 [
22] fall in the range of 2.444–2.571 Å; very similar values for
dNb-As are seen in Cs
9Nb
2As
6 (2.464–2.592 Å) [
22]. Since the established ranges for the Nb–As and Ga–As distances are similar, refinements of the thermal ellipsoids in Na
10NbGaAs
6 do not show any abnormal behavior—in fact they are virtually spherical. This is not the case for K
10NbInAs
6, where the significant difference between the lengths of the Nb–As and In–As bonds gives rise to characteristic features in their thermal ellipsoids—the thermal ellipsoids of the bridging As atoms are elongated tangentially to the central square (Nb/In-As-Nb/In-As). This observation has been considered as a key evidence of these dimers being heteroatomic [(As)
2Nb(
µ-As)
2In(As)
2] species, and not an equimolar mixture of [(As)
2Nb(
µ-As)
2Nb(As)
2] and [(As)
2In(
µ-As)
2In(As)
2] dimers [
13].
3. Experimental Section
All the manipulations involving alkali metals were performed either inside an argon-filled glove box or under vacuum. The starting materials were elemental Rb, Na, Ga, As, and P, either from Alfa Aesar or Aldrich with the stated purity higher than 99.9%. Crystals of RbNa
8Ga
3As
6 were first identified from a reaction starting with Na/Rb/Ga/As with a molar ratio of 16/8/80/56, which was originally attempted for type II clathrate Na
16Rb
8Ga
80As
56. The elements with a total mass of ca. 500 mg were loaded into a niobium ampoule, which was subsequently arc-welded under high purity Ar and then jacketed in a fused silica tube under vacuum. The reaction mixture was heated up to 550 °C, and equilibrated for one week before it was slowly cooled to room temperature. This experiment resulted in black, small crystals of RbNa
8Ga
3As
6, which were found to be extremely air-sensitive and had to be handled with great care. After the composition was established, the reaction was repeated with the correct stoichiometry. However, besides RbNa
8Ga
3As
6, Na
10NbGaAs
6, which formed from a side reaction with the Nb container, was also identified. This observation indicated that Nb containers were not well suited for such reactions; more expensive Ta or Mo tubes should be considered. RbNa
8Ga
3P
6 could be synthesized from the same setup as well as the same heat treatment, with the coexistence of another known Zintl compound, Na
6GaP
3 [
23].
The crystal structures of the title compounds were established using single-crystal X-ray diffraction with a Bruker SMART CCD-based diffractometer (monochromated Mo Kα
1 radiation). Crystals with suitable dimensions (<100 µm) were mounted on glass fiber with Paratone-N oil, and then quickly transferred to the goniometer of the diffractometer. A cold nitrogen stream (200(2) K) was used to keep the crystals at low temperature as well as to protect them from being oxidized. Full spheres of data were collected in four batch runs with a frame width of 0.4° for ω and θ. Integration of the intensity data was done with the SAINT program [
24], and semi-empirical absorption correction based on equivalents was applied with the SADABS code [
25]. The structures were solved by direct method and refined to convergence by full matrix least squares on
F2 using the SHELXTL package [
26]. The unit cell axes and the atomic coordinates of RbNa
8Ga
3Pn6 were standardized with the aid of the Structure TIDY [
27] in the last refinement cycles.
The structure refinements for Na10NbGaAs6 required some specific attention. In this structure, the tetrahedrally coordinated site was originally assigned as Ga, which is a common coordination environment for it. However, the thermal displacement parameter in this situation was unreasonably small. Based on the discussion on K10NbInAs6 structure, the model that this site was co-occupied by Ga and Nb was considered, where Nb was from the reaction vessel. Such refinement lead to nearly half and half occupancy of Ga and Nb, i.e., 49% Ga and 51% Nb. Thus, the ratio was fixed at 1:1 in the final refinement cycle, which resulted in R1 values as low as 0.0263 and reasonable thermal ellipsoids.
Selected crystal data and refinement parameters are given in
Table 4; important bond distances and angles are listed in
Table 1,
Table 2,
Table 3. CIFs have also been deposited with the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany, (fax: (49) 7247-808-666; Email:
[email protected])—depository numbers CSD-423946 for RbNa
8Ga
3As
6, CSD-423947 for RbNa
8Ga
3P
6, and CSD-423948 for Na
10NbGaAs
6.
Table 4.
Selected crystal data and structure refinement parameters for RbNa8Ga3Pn6 (Pn = As, P) and Na10NbGaAs6.
Table 4.
Selected crystal data and structure refinement parameters for RbNa8Ga3Pn6 (Pn = As, P) and Na10NbGaAs6.
Empirical formula | RbNa8Ga3As6 | RbNa8Ga3P6 | Na10NbGaAs6 |
Formula weight | 928.07 | 664.37 | 842.05 |
Space group,
Z | Pnma (No. 62), 4 | Pnma (No. 62), 4 | P21/n (No. 14), 2 |
Temperature | 200(2) K |
Wavelength | Mo
Kα, 0.71073 Å |
Cell parameters | a (Å) | 22.843(6) | 22.276(3) | 8.3243(7) |
| b (Å) | 4.7892(12) | 4.6947(6) | 7.5173(6) |
| c (Å) | 16.861(4) | 16.356(2) | 13.546(2) |
| β(°) | | | 90.908(1)° |
| V (Å3) | 1844.6(8) | 1710.4(4) | 847.58(12) |
Calculated density (g/cm3) | 3.342 | 2.580 | 3.299 |
Absorption coefficient (cm−1) | 178.14 | 82.52 | 141.13 |
Crystal size (mm3) | 0.070 × 0.030 × 0.025 | 0.050 × 0.030 × 0.030 | 0.060 × 0.055 × 0.035 |
Reflections collected/independent | 24813/2575 | 22860/2382 | 10644/1948 |
Rint | 0.0888 | 0.0954 | 0.0528 |
Goodness-of-fit on
F2 | 1.031 | 1.104 | 1.006 |
R1 (I > 2σI)a | 0.0326 | 0.0410 | 0.0263 |
w
R2 (I > 2σI)a | 0.0521 | 0.0625 | 0.0464 |
Largest diff. peak/hole (e–/Å3) | 1.164/−0.928 | 0.802/−0.880 | 0.751/−0.578 |
Weight coefficient,
A/Ba | 0.0163/0 | 0.0109/1.1965 | 0.0176/0 |