A new thio­phosphate, Rb_0.38Ag_0.5Nb₂PS₁₀

The structure of the new pentanary thio­phosphate rubidium silver diniobium tris(disulfide) tetrathio­phosphate, Rb_0.38Ag_0.5Nb₂PS₁₀, is made up of one-dimensional [Nb₂PS] chains along the [001] direction. These chains are separated from one another by Ag⁺ and disordered Rb⁺ ions. The Nb₂PS chain is built up from bicapped trigonal prismatic Nb₂S₁₂ units which lie about inversion centres and tetrahedral PS₄ groups. The Nb₂S₁₂ units are linked together to form linear Nb₂S₉ chains by sharing S—S prism edges. Short [2.898 (1) and 2.908 (1) Å] and long [3.724 (1) Å] Nb...Nb distances alternate along the chains, and S and S²⁻ anionic species co-exist in the structure. The Ag⁺ cation lies on an inversion centre and has distorted octahedral coordination described as a [2+4]-bonding interaction.

S1. Comment

Due to their low-dimensional structures and interesting anisotropic properties (Rouxel, 1986), group 5 transition metal thiophosphates form an interesting class of compounds. In particular, these low-dimensional compounds have potential applications as cathode materials for high energy density secondary batteries (Evain et al., 1987). The preparation of alkali metal thiophosphates is crucial to understanding the nature of the intercalation and to analysing their electronic structure.

Since the report of the first niobium thiophosphates containing alkali metals (Do & Yun, 1996), we have used metal halides as reactive fluxes to find new thiophosphates. This technique exploits metal halides as both flux and reactant. The resultant products usually include various monovalent cations.

The structure of Rb_0.38Ag_0.5Nb₂PS₁₀ is similar to that of the previously reported compounds KNb₂PS₁₀ (Do & Yun, 1996), RbNb₂PS₁₀ (Kim & Yun, 2002), and AgNb₂PS₁₀ and NaNb₂PS₁₀ (Goh et al., 2002). It is also closely related to the other group 5 metal thiophosphates, V₂PS₁₀ (Brec, Ouvrard et al., 1983), Nb₄P₂S₂₁ (Brec, Evain et al., 1983) and Nb₂PS₁₀ (Brec, Grenouilleau et al., 1983). It consists of one-dimensional _∞¹[Nb₂PS₁₀⁻] chains along the [001] direction (Fig. 1), separated by Rb⁺ and Ag⁺ ions. Each chain is made up of typical bicapped biprismatic [Nb₂S₁₂] units and tetrahedral [PS₄] groups.

Both Nb1 and Nb2 atoms are surrounded by eight S atoms in a bicapped trigonal prismatic fashion. Two adjacent prisms share a rectangular face to form the [Nb₂S₁₂] unit (Fig. 2). This [Nb₂S₁₂] unit differs from those found in ANb₂PS₁₀ (A = K or Rb) in the arrangement of the (S—S)²⁻ ligands. While the ligands occupy the same sites, an inversion symmetry is found in the title compound, whereas a twofold rotation symmetry is found in ANb₂PS₁₀.

The [Nb₂S₁₂] units are bound to each other to form infinite _∞¹[Nb₂S₉] chains by sharing S—S prism edges. One of the S atoms at the prism edge and two other capping S atoms are bound to the P atom, and an additional S atom (S10) is attached to the P atom to complete the PS₄ tetrahedral coordination. The average P—S distance in the PS₄ unit [2.046 (3) Å] is in good agreement with P—S distances found in other related phases. Atom S10 is the only terminal atom in the compound, and this fact accounts for the short P—S10 distance [2.007 (2) Å] and the large anisotropic displacement parameter of atom S10 (Do & Yun, 1996).

Along the chain, the Nb atoms associate in pairs, with Nb···Nb interactions in an alternating sequence of short and long distances. The Nb2···Nb2 distance [2.898 (1) Å] is in good agreement with typical Nb⁴⁺—Nb⁴⁺ bonding distances (2.86–2.89 Å; Angenault et al., 2000). However, the separation between Nb1 atoms is longer [2.908 (1) Å] and implies that Nb1 could be more oxidized than Nb2. A similar Nb···Nb separation [2.961 (1) Å] has been observed for the cation-deficient phase AuNb₄P₂S₂₀ (Kim et al., 2003). The long Nb1···Nb2 distance [3.724 (1) Å] shows that there is no significant intermetallic bonding interaction, and such an arrangement is consistent with the highly resistive nature of the compound. The classical charge balance of the compound should be represented by [Rb⁺]_0.38[Ag⁺]_0.5[Nb^4.06+]₂[P⁵⁺][S₂²⁻]₃[S²⁻]₄. Assuming that the two Nb atoms are not equivalent, oxidation states of 4.12 and 4 can be assigned to Nb1 and Nb2, respectively.

The coordination around the Ag atom can be described as a [2 + 4] bonding interaction. Four S atoms are bound to the Ag atoms in the plane [Ag—S6 3.048 (2) and Ag—S9 3.234 (2) Å], whereas two trans S atoms are coordinated to the Ag atom [Ag—S10 2.471 (2) Å]. These values are comparable with the sums of the ionic radii of each element (2.51 Å for coordination number 2 and 2.99 Å for coordination number 6; Shannon, 1976). According to theory, a tetragonal contraction would be favoured for the d¹⁰ configuration (Burdett and Eisenstein, 1992) and this prediction is compatible with our results.

S2. Experimental

The compound Rb_0.38Ag_0.5Nb₂PS₁₀ was prepared by the reaction of elemental Nb, P and S with the use of the reactive halide flux technique. Stoichiometric amounts of Nb powder (CERAC, 99.8%), P powder (CERAC, 99.5%) and S powder (Aldrich, 99.999%) were mixed in quartz tubes with the addition of a eutectic mixture of RbI/AgI. The mass ratio of reactants and flux was 1:3. The tubes were evacuated (10⁻² Torr; 1 Torr = 133.322 Pa), sealed and heated gradually to 1073 K, where they were kept for 72 h. The tubes were then cooled to room temperature at the rate of 5 K h⁻¹. The excess halide fluxes were removed with distilled water and dark-red needle-shaped crystals of the title compound were obtained. The crystals are stable in air and water. Qualitative analysis of the crystals with an EDAX-equipped AMRAY 1200 C scanning electron microscope indicated the presence of Rb, Ag, Nb, P and S. No other element was detected.

S3. Refinement

Once all atoms had been located, the occupancies of the Rb and Ag sites were allowed to vary throughout the remainder of the refinement. The occupancy factors for Rb and Ag were refined to 0.372 (3) and 0.483 (2), respectively. Consequently, a full occupancy was assigned for the Ag site and the Rb site was refined to 0.375 (3). Because no evidence was found for ordering of the Rb site, a statistically disordered structure was assumed.

Computing details

Data collection: MXC3 Software (MacScience Corporation, 1994); cell refinement: MXC3 Software; data reduction: MXC3 Software; program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Please provide missing information; software used to prepare material for publication: Please provide missing information.

Figures

	Fig. 1. A view of Rb0.38Ag0.5Nb2PS10. Displacement ellipsoids are drawn at the 70% probability level. [Symmetry code: (vi) x, 1 + y, z.]
	Fig. 2. A perspective view of the [Nb2S12] unit with inversion symmetry. Small filled circles denote Nb atoms and large open circles denote S atoms. Nb—S bonds have been omitted for clarity, except for those involving capping S atoms. [Symmetry code: (iv) 1 − x, 2 − y, −z.]

rubidium silver diniobium tris(disulfide) tetrathiophosphate

Crystal data

Rb0.38Ag0.5Nb2PS10	Z = 2
Mr = 623.56	F(000) = 588.8
Triclinic, P1	Dx = 3.275 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.7107 Å
a = 7.011 (2) Å	Cell parameters from 24 reflections
b = 7.196 (2) Å	θ = 10.0–15.0°
c = 12.907 (3) Å	µ = 5.73 mm^−1
α = 89.51 (3)°	T = 293 K
β = 76.24 (2)°	Needle, dark red
γ = 89.39 (2)°	0.40 × 0.03 × 0.03 mm
V = 632.4 (3) Å^3

Data collection

MacScience MXC3 diffractometer	Rint = 0.018
ω/2θ scans	θmax = 27.5°, θmin = 1.6°
Absorption correction: analytical (de Meulenaer & Tompa, 1965)	h = −9→8
Tmin = 0.822, Tmax = 0.844	k = −9→9
2797 measured reflections	l = −16→0
2666 independent reflections	2 standard reflections every 100 reflections
2233 reflections with I > 2σ(I)	intensity decay: 0.5%

Refinement

Refinement on F^2	134 parameters
Least-squares matrix: full	0 restraints
R[F^2 > 2σ(F^2)] = 0.037	w = 1/[σ^2(Fo^2) + (0.0199P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.067	(Δ/σ)max < 0.001
S = 1.04	Δρmax = 0.82 e Å^−3
2666 reflections	Δρmin = −1.03 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Rb	−0.0544 (3)	0.5002 (3)	0.5586 (2)	0.0402 (8)	0.375 (3)
Ag	1.0000	0.5000	0.0000	0.0347 (2)
Nb1	0.49589 (8)	0.93137 (8)	0.10676 (4)	0.00803 (12)
Nb2	0.49685 (8)	0.93155 (8)	0.39517 (4)	0.00881 (13)
P	0.7111 (2)	0.6092 (2)	0.22446 (12)	0.0111 (3)
S1	0.7630 (2)	0.8943 (2)	0.21626 (12)	0.0101 (3)
S2	0.2395 (2)	0.8880 (2)	0.28389 (12)	0.0117 (3)
S3	0.2178 (2)	1.0877 (2)	0.52166 (12)	0.0129 (3)
S4	0.3680 (2)	1.1456 (2)	0.26670 (12)	0.0112 (3)
S5	0.2143 (2)	1.0836 (2)	0.05000 (12)	0.0114 (3)
S6	0.2816 (2)	0.8231 (2)	−0.00983 (12)	0.0118 (3)
S7	0.2749 (2)	0.8263 (2)	0.56869 (12)	0.0136 (3)
S8	0.5503 (2)	0.5760 (2)	0.37779 (12)	0.0146 (3)
S9	0.5440 (2)	0.5765 (2)	0.11582 (13)	0.0136 (3)
S10	0.9571 (3)	0.4536 (2)	0.19405 (13)	0.0181 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Rb	0.0357 (14)	0.0189 (11)	0.0761 (18)	−0.0029 (9)	−0.0333 (12)	−0.0002 (11)
Ag	0.0494 (6)	0.0344 (5)	0.0141 (4)	−0.0065 (4)	0.0051 (4)	−0.0020 (4)
Nb1	0.0083 (3)	0.0095 (3)	0.0064 (3)	0.0012 (2)	−0.0021 (2)	0.0000 (2)
Nb2	0.0090 (3)	0.0123 (3)	0.0054 (3)	0.0019 (2)	−0.0023 (2)	−0.0002 (2)
P	0.0141 (8)	0.0117 (8)	0.0070 (7)	0.0040 (6)	−0.0015 (6)	−0.0004 (6)
S1	0.0106 (7)	0.0139 (8)	0.0059 (7)	0.0014 (6)	−0.0022 (6)	0.0004 (6)
S2	0.0113 (8)	0.0160 (8)	0.0081 (7)	0.0000 (6)	−0.0029 (6)	−0.0002 (6)
S3	0.0111 (8)	0.0187 (8)	0.0091 (7)	0.0035 (6)	−0.0030 (6)	−0.0022 (6)
S4	0.0135 (8)	0.0125 (7)	0.0083 (7)	0.0033 (6)	−0.0041 (6)	−0.0015 (6)
S5	0.0115 (8)	0.0150 (8)	0.0078 (7)	0.0032 (6)	−0.0026 (6)	0.0000 (6)
S6	0.0138 (8)	0.0126 (8)	0.0101 (7)	−0.0019 (6)	−0.0048 (6)	0.0020 (6)
S7	0.0134 (8)	0.0186 (8)	0.0082 (7)	−0.0017 (6)	−0.0011 (6)	0.0003 (6)
S8	0.0208 (9)	0.0130 (8)	0.0084 (7)	0.0039 (7)	−0.0005 (6)	0.0001 (6)
S9	0.0193 (8)	0.0106 (8)	0.0120 (7)	0.0005 (6)	−0.0060 (6)	−0.0005 (6)
S10	0.0214 (9)	0.0184 (8)	0.0127 (8)	0.0109 (7)	−0.0012 (7)	−0.0005 (7)

Geometric parameters (Å, º)

Rb—Rb^i	1.524 (5)	Nb1—S4	2.5663 (17)
Rb—S8^i	3.426 (3)	Nb1—S2	2.5689 (18)
Rb—S7	3.334 (3)	Nb1—S9	2.5779 (18)
Rb—S3^ii	3.409 (3)	Nb1—S1	2.6112 (17)
Rb—S7^i	3.459 (3)	Nb2—S3^x	2.4875 (17)
Rb—S10^iii	3.439 (3)	Nb2—S3	2.4942 (18)
Rb—S2^i	3.514 (3)	Nb2—S7^x	2.4988 (18)
Rb—S3^iv	3.486 (3)	Nb2—S7	2.5197 (18)
Rb—S4^ii	3.746 (3)	Nb2—S4	2.5646 (17)
Rb—S8^iii	3.847 (3)	Nb2—S2	2.5824 (17)
Ag—S10	2.4707 (18)	Nb2—S8	2.5861 (18)
Ag—S10^v	2.4707 (18)	Nb2—S1	2.6147 (18)
Ag—S6^vi	3.0484 (17)	Nb1—Nb1^ix	2.9075 (13)
Ag—S6^vii	3.0484 (17)	Nb2—Nb2^x	2.8981 (13)
Ag—S9	3.2343 (19)	P—S10	2.007 (2)
Ag—S9^v	3.2343 (19)	P—S8	2.045 (2)
Ag—S5^viii	3.4618 (18)	P—S9	2.046 (2)
Ag—S5^ix	3.4618 (18)	P—S1	2.084 (2)
Nb1—S6^ix	2.4926 (18)	S2—S4	2.056 (2)
Nb1—S6	2.5000 (17)	S5—S6	2.041 (2)
Nb1—S5	2.5027 (17)	S3—S7	2.037 (2)
Nb1—S5^ix	2.5055 (18)
S10—Ag—S10^v	180.00 (8)	S7^x—Nb2—S2	139.56 (6)
S10—Ag—S6^vi	93.56 (6)	S7—Nb2—S2	95.10 (6)
S10^v—Ag—S6^vi	86.44 (6)	S4—Nb2—S2	47.09 (5)
S10—Ag—S6^vii	86.44 (6)	S3^x—Nb2—S8	83.09 (6)
S10^v—Ag—S6^vii	93.56 (6)	S3—Nb2—S8	125.06 (6)
S6^vi—Ag—S6^vii	180.0	S7^x—Nb2—S8	128.91 (6)
S10—Ag—S9	71.56 (5)	S7—Nb2—S8	80.04 (6)
S10^v—Ag—S9	108.44 (5)	S4—Nb2—S8	126.48 (6)
S6^vi—Ag—S9	116.90 (5)	S2—Nb2—S8	85.74 (6)
S6^vii—Ag—S9	63.10 (5)	S3^x—Nb2—S1	84.16 (5)
S10—Ag—S9^v	108.44 (5)	S3—Nb2—S1	155.23 (6)
S10^v—Ag—S9^v	71.56 (5)	S7^x—Nb2—S1	83.29 (6)
S6^vi—Ag—S9^v	63.10 (5)	S7—Nb2—S1	156.11 (6)
S6^vii—Ag—S9^v	116.90 (5)	S4—Nb2—S1	77.11 (5)
S9—Ag—S9^v	180.0	S2—Nb2—S1	86.64 (5)
S6^ix—Nb1—S6	108.77 (5)	S8—Nb2—S1	76.33 (6)
S6^ix—Nb1—S5	89.57 (6)	S3^x—Nb2—Nb2^x	54.53 (4)
S6—Nb1—S5	48.16 (5)	S3—Nb2—Nb2^x	54.32 (4)
S6^ix—Nb1—S5^ix	48.21 (6)	S7^x—Nb2—Nb2^x	55.07 (4)
S6—Nb1—S5^ix	89.35 (6)	S7—Nb2—Nb2^x	54.39 (4)
S5—Nb1—S5^ix	109.02 (5)	S4—Nb2—Nb2^x	118.93 (5)
S6^ix—Nb1—S4	91.81 (6)	S2—Nb2—Nb2^x	137.18 (5)
S6—Nb1—S4	122.29 (6)	S8—Nb2—Nb2^x	113.02 (5)
S5—Nb1—S4	80.13 (5)	S1—Nb2—Nb2^x	133.96 (5)
S5^ix—Nb1—S4	137.37 (6)	S3^x—Nb2—Rb^i	122.01 (5)
S6^ix—Nb1—S2	139.01 (6)	S3—Nb2—Rb^i	79.06 (6)
S6—Nb1—S2	95.92 (6)	S7^x—Nb2—Rb^i	161.89 (5)
S5—Nb1—S2	83.03 (6)	S7—Nb2—Rb^i	52.61 (5)
S5^ix—Nb1—S2	167.16 (6)	S4—Nb2—Rb^i	99.51 (5)
S4—Nb1—S2	47.21 (5)	S2—Nb2—Rb^i	53.87 (5)
S6^ix—Nb1—S9	130.77 (6)	S8—Nb2—Rb^i	51.93 (5)
S6—Nb1—S9	79.14 (6)	S1—Nb2—Rb^i	112.52 (6)
S5—Nb1—S9	123.80 (6)	Nb2^x—Nb2—Rb^i	106.95 (5)
S5^ix—Nb1—S9	84.60 (6)	S10—P—S8	112.11 (10)
S4—Nb1—S9	125.81 (6)	S10—P—S9	113.66 (10)
S2—Nb1—S9	84.91 (6)	S8—P—S9	112.02 (10)
S6^ix—Nb1—S1	83.79 (6)	S10—P—S1	113.66 (10)
S6—Nb1—S1	155.19 (6)	S8—P—S1	102.21 (9)
S5—Nb1—S1	156.07 (6)	S9—P—S1	102.25 (9)
S5^ix—Nb1—S1	83.40 (5)	P—S1—Nb1	88.68 (7)
S4—Nb1—S1	77.14 (5)	P—S1—Nb2	88.68 (7)
S2—Nb1—S1	86.99 (5)	Nb1—S1—Nb2	90.90 (5)
S9—Nb1—S1	76.59 (6)	P—S1—Ag	51.81 (6)
S6^ix—Nb1—Nb1^ix	54.50 (4)	Nb1—S1—Ag	85.40 (5)
S6—Nb1—Nb1^ix	54.27 (4)	Nb2—S1—Ag	140.32 (6)
S5—Nb1—Nb1^ix	54.56 (4)	S4—S2—Nb1	66.33 (7)
S5^ix—Nb1—Nb1^ix	54.47 (4)	S4—S2—Nb2	66.00 (6)
S4—Nb1—Nb1^ix	119.11 (5)	Nb1—S2—Nb2	92.59 (6)
S2—Nb1—Nb1^ix	137.37 (5)	S7—S3—Nb2^x	66.18 (7)
S9—Nb1—Nb1^ix	113.44 (5)	S7—S3—Nb2	66.69 (7)
S1—Nb1—Nb1^ix	133.45 (5)	Nb2^x—S3—Nb2	71.15 (5)
S6^ix—Nb1—Ag	88.92 (4)	S2—S4—Nb2	66.91 (6)
S6—Nb1—Ag	97.53 (4)	S2—S4—Nb1	66.46 (6)
S5—Nb1—Ag	142.57 (4)	Nb2—S4—Nb1	93.07 (6)
S5^ix—Nb1—Ag	47.07 (4)	S6—S5—Nb1	65.85 (6)
S4—Nb1—Ag	137.30 (4)	S6—S5—Nb1^ix	65.57 (7)
S2—Nb1—Ag	120.39 (4)	Nb1—S5—Nb1^ix	70.98 (5)
S9—Nb1—Ag	42.18 (4)	S6—S5—Ag^xii	142.27 (8)
S1—Nb1—Ag	60.50 (4)	Nb1—S5—Ag^xii	145.99 (6)
Nb1^ix—Nb1—Ag	95.54 (3)	Nb1^ix—S5—Ag^xii	100.93 (6)
S6^ix—Nb1—Ag^xi	133.39 (4)	S6—S5—Ag^xi	32.12 (5)
S6—Nb1—Ag^xi	25.19 (4)	Nb1—S5—Ag^xi	87.47 (5)
S5—Nb1—Ag^xi	63.30 (4)	Nb1^ix—S5—Ag^xi	94.49 (5)
S5^ix—Nb1—Ag^xi	103.26 (5)	Ag^xii—S5—Ag^xi	126.49 (4)
S4—Nb1—Ag^xi	117.30 (4)	S5—S6—Nb1^ix	66.23 (7)
S2—Nb1—Ag^xi	77.80 (4)	S5—S6—Nb1	65.99 (6)
S9—Nb1—Ag^xi	60.51 (4)	Nb1^ix—S6—Nb1	71.23 (5)
S1—Nb1—Ag^xi	135.29 (4)	S5—S6—Ag^xi	127.03 (8)
Nb1^ix—Nb1—Ag^xi	79.10 (3)	Nb1^ix—S6—Ag^xi	152.84 (6)
Ag—Nb1—Ag^xi	91.69 (2)	Nb1—S6—Ag^xi	134.39 (6)
S3^x—Nb2—S3	108.85 (5)	S3—S7—Nb2^x	65.60 (7)
S3^x—Nb2—S7^x	48.21 (6)	S3—S7—Nb2	65.38 (7)
S3—Nb2—S7^x	89.95 (6)	Nb2^x—S7—Nb2	70.55 (5)
S3^x—Nb2—S7	89.63 (6)	P—S8—Nb2	90.33 (8)
S3—Nb2—S7	47.93 (6)	P—S9—Nb1	90.44 (8)
S7^x—Nb2—S7	109.45 (5)	P—S9—Ag	70.95 (7)
S3^x—Nb2—S4	138.40 (6)	Nb1—S9—Ag	105.46 (6)
S3—Nb2—S4	79.42 (6)	P—S9—Ag^xi	157.25 (8)
S7^x—Nb2—S4	92.47 (6)	Nb1—S9—Ag^xi	89.25 (5)
S7—Nb2—S4	120.91 (6)	Ag—S9—Ag^xi	130.81 (5)
S3^x—Nb2—S2	166.94 (6)	P—S10—Ag	91.12 (8)
S3—Nb2—S2	83.15 (6)

Symmetry codes: (i) −x, −y+1, −z+1; (ii) −x, −y+2, −z+1; (iii) −x+1, −y+1, −z+1; (iv) x, y−1, z; (v) −x+2, −y+1, −z; (vi) x+1, y, z; (vii) −x+1, −y+1, −z; (viii) x+1, y−1, z; (ix) −x+1, −y+2, −z; (x) −x+1, −y+2, −z+1; (xi) x−1, y, z; (xii) x−1, y+1, z.