Cs[Ag₄Zn₂(SCN)₉]

Caesium tetrasilver dizinc nona­thio­cyanate, Cs[Ag₄Zn₂(SCN)₉], forms a continuous structure, where the Ag atoms and the S atoms of the thio­cyanate groups form chains which run along [101]. These chains are bonded together through the Cs and Zn atoms. It is not possible to distinguish between space groups P1 and P, but, if the latter space group is correct, the structure contains a thio­cyanate group disordered across a centre of inversion. The structure is described in space group P, in which the Cs atom also lies on a centre of inversion.

S1. Comment

Caesium tetrasilver dizinc nonathiocyanate, (I), has been known for a century, but there has been practically no research concerning the compound since those first studies (Wells, 1902, 1922). One reason for this might have been the difficulty of the synthesis of (I). There are a total of four different caesium silver zinc thiocyanates known in the literature, namely Cs[AgZn(SCN)₄]·H₂O, Cs₂[AgZn(SCN)₅], Cs[Ag₃Zn₂(SCN)₈] and (I) (Wells, 1902, 1922; Güneş & Valkonen, 2001), and the synthesis may yield any of these four thiocyanates. Moreover, any of the reactants or several possible combinations of them may crystallize, or, what is worse and is often the case, the yield of the synthesis can be a mixture of different types of crystals. Caesium, silver and zinc all form simple thiocyanates. CsSCN crystallizes in spacegroup Pnma, AgSCN in two polymorphic forms in spacegroups C2/c and Pmnn, and Zn(NCS)₂ in spacegroup P1. Also, Zn(NCS)₂·2H₂O is known in the literature (reference?) and crystallizes in spacegroup P2₁2₁2₁. \sch

Our interest in triple thiocyanates arises from the fact that some of the triple thiocyanates of silver, such as Cs₃Sr[Ag₂(SCN)₇] and Cs₃Ba[Ag₂(SCN)₇], have been found to have a non-centrosymmetric crystal structure (Bohaty & Fröhlich, 1992). Such structures can possess some very interesting optical, electro-optic and electrostrictive properties, which could be utilized, for example, in telecommunications, optical computing, optical information processing, optical-disk data storage, laser remote sensing, laser-driven fusion, colour displays, medical diagnostics and so on. The idea is based on the capability of these materials to convert IR laser radiation efficiently to visible and UV wavelengths, and especially the highly efficient second-harmonic generation of blue-violet light (Wang et al., 2001).

During the optimization of the synthesis of the thiocyanate complexes of silver, zinc and caesium, we managed to obtain some crystals of (I), but, as stated above, the synthesis of these compounds is not so straightforward. The crystals of (I) were obtained in low yield as a co-precipitate during the synthesis and, despite innumerable trials, we have not yet been able to crystallize a pure crop of (I).

The structure of (I) is very interesting, as it cannot be clearly determined whether the space group in which it crystallizes is P1 or P1. In this paper, we have defined the space group to be P1, but we will also discuss the possibility of the space group being P1.

The assignment of the space group is uncertain. The structure refines well in both P1 and P1, giving reasonable molecular geometries in both cases, with a slightly lower goodness of fit in P1 (1.031 versus 1.039). The Flack parameter (Flack, 1983) is 0.48 (6), which is consistent with either P1 or with a P1 crystal containing equal volumes of inversion twins. We have chosen to describe the structure in P1, in which two atoms lie on centres of symmetry, namely the Cs atom, located at (1/2,1/2,1/2), and the C2 atom, located at (1/2,0,1/2). This means that one of the SCN groups is disordered and, locally, atom C2 is slightly displaced from the centre of symmetry toward the N atom, as can be seen from the highly anisotropic atomic displacement ellipsoid shown in Fig. 1.

Because of the disordered thiocyanate group, Cs is ten-coordinated by 2S+8 N atoms or 4S+6 N atoms, each occurring in a quarter of the unit cells, and by 3S+7 N atoms in the remaining half of the unit cells, although if the space group were P1, all the Cs atoms would be coordinated by 3S+7 N atoms. When coordinated by 3S+7 N, the Cs atom is displaced from the centre of symmetry, which is reflected in the large value of U²² for this atom.

Zn and Ag are both tetrahedrally coordinated, Zn being surrounded by four N atoms, Ag2 by four S atoms, and Ag1 by four S atoms or by three S atoms and one N atom, because of the disordered thiocyanate group. The tetrahedra around Ag and Zn are both slightly distorted.

Compound (I) consists of a continuous structure, where the Ag and S atoms form chains (Fig. 1) which run along [101]. These chains are then bonded through N atoms of the thiocyanate groups to Zn atoms, thereby connecting the Ag—S—Ag chains in the ac plane and in the direction of b axis, thus forming a three-dimensional network. The chains in the ac plane are further connected through the disordered thiocyanate group. This group does not bond to Zn but lies between two Ag1 atoms of different chains. The Cs atoms connect the chains in all three dimensions.

S2. Experimental

Compound (I) was synthesized at room temperature by dissolving NH₄SCN (2.05 g; Aldrich Chemical Company Inc.) into deionized water (20.0 g) and then dissolving AgSCN (1.49 g; City Chemical LLC) into that solution. Not all of the AgSCN was dissolved. Without filtering the solution, Zn(NO₃)₂·4H₂O (1.92 g; Merck KGaA) and CsNO₃ (1.75 g; Fluka Chemie AG) were added. The solution was heated with hot tap water for a while and then filtered. Bulbous crystals of (I) were found in the deposit. All of the reagents used were analytical grade.

S3. Refinement

The s.u.s of the cell constants indicate the internal consistency of the measurements themselves i.e. the precision of the measurement, not their accuracy.

Computing details

Data collection: COLLECT (Nonius, 1997-2000); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2000); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

Fig. 1. A view of the Ag—S—Ag chains in (I), connected together through Zn atoms. Displacement ellipsoids are drawn at the 50% probability level and the Cs atom has been omitted for clarity. The heaviest atoms (Ag) are shaded the darkest grey, and the shading is graduated through Zn, S and N, with the lightest atoms (C) being the lightest grey; the exception is atom S2/N2, which is nearly white. Please clarify - atoms N1, N3, N4 and N5 are white, so they are out of order in this atomic weight/shading sequence.

caesium tetrasilver dizinc nonathiocyanate

Crystal data

Cs[Ag4Zn2(SCN)9]	Z = 1
Mr = 1217.85	F(000) = 564
Triclinic, P1	Dx = 2.939 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.5493 (1) Å	Cell parameters from 9151 reflections
b = 8.9297 (2) Å	θ = 1.0–30.0°
c = 10.5701 (2) Å	µ = 6.51 mm^−1
α = 78.045 (1)°	T = 293 K
β = 82.912 (1)°	Botryoidal, colourless
γ = 82.828 (1)°	0.1 × 0.1 × 0.1 mm
V = 688.15 (2) Å^3

Data collection

Nonius KappaCCD area-detector diffractometer	2733 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.04
Horizonally mounted graphite crystal monochromator	θmax = 30.0°, θmin = 2.0°
Detector resolution: 9 pixels mm^-1	h = −10→10
CCD rotation images, thick slices scans	k = −12→12
9429 measured reflections	l = −14→14
4007 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.049	w = 1/[σ^2(Fo^2) + (0.0266P)^2 + 3.677P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.114	(Δ/σ)max < 0.001
S = 1.04	Δρmax = 2.33 e Å^−3
4007 reflections	Δρmin = −2.27 e Å^−3
158 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0034 (4)

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)
Ag1	0.11263 (8)	0.00738 (7)	0.63027 (6)	0.0641 (2)
Ag2	0.29818 (9)	0.04688 (6)	−0.11202 (7)	0.0634 (2)
Cs1	0.5	0.5	0.5	0.0881 (3)
Zn1	0.29349 (9)	0.46434 (8)	0.18914 (6)	0.03385 (18)
S1	0.1081 (2)	−0.21981 (19)	0.47721 (15)	0.0414 (4)
S2	0.4121 (4)	0.1170 (4)	0.5598 (3)	0.0596 (7)	0.5
S3	0.14201 (19)	−0.17662 (17)	0.84704 (14)	0.0365 (3)
S4	−0.1664 (2)	0.67990 (19)	0.19097 (16)	0.0439 (4)
S5	0.3274 (2)	−0.00296 (18)	0.14780 (17)	0.0469 (4)
C1	−0.0376 (8)	−0.3162 (7)	0.5820 (6)	0.0349 (12)
C2	0.5	0.0	0.5	0.074 (4)
C3	0.3339 (8)	−0.2740 (6)	0.8082 (5)	0.0329 (12)
C4	−0.2041 (7)	0.6233 (6)	0.0602 (6)	0.0338 (12)
C5	0.3252 (7)	−0.1900 (7)	0.1661 (6)	0.0335 (12)
N1	0.1387 (7)	0.3846 (6)	0.3448 (5)	0.0442 (12)
N2	0.4121 (4)	0.1170 (4)	0.5598 (3)	0.0596 (7)	0.5
N3	0.5344 (7)	0.3466 (6)	0.2167 (6)	0.0457 (13)
N4	0.2276 (8)	0.4173 (6)	0.0319 (5)	0.0456 (13)
N5	0.3257 (7)	−0.3198 (6)	0.1804 (5)	0.0402 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.0619 (4)	0.0484 (4)	0.0718 (4)	−0.0063 (3)	−0.0183 (3)	0.0190 (3)
Ag2	0.0848 (5)	0.0307 (3)	0.0796 (4)	−0.0063 (3)	−0.0279 (3)	−0.0101 (3)
Cs1	0.0836 (6)	0.1100 (7)	0.0793 (6)	0.0527 (5)	−0.0427 (4)	−0.0547 (5)
Zn1	0.0422 (4)	0.0268 (3)	0.0321 (4)	−0.0070 (3)	−0.0046 (3)	−0.0019 (3)
S1	0.0357 (8)	0.0391 (9)	0.0421 (8)	−0.0002 (6)	0.0049 (6)	0.0012 (7)
S2	0.0555 (17)	0.0480 (17)	0.074 (2)	−0.0114 (13)	0.0003 (14)	−0.0092 (15)
S3	0.0362 (7)	0.0326 (8)	0.0389 (8)	−0.0064 (6)	−0.0007 (6)	−0.0028 (6)
S4	0.0600 (10)	0.0336 (8)	0.0403 (8)	0.0023 (7)	−0.0182 (7)	−0.0085 (6)
S5	0.0610 (10)	0.0256 (8)	0.0545 (10)	−0.0024 (7)	−0.0081 (8)	−0.0084 (7)
C1	0.040 (3)	0.027 (3)	0.035 (3)	0.002 (2)	−0.005 (2)	−0.001 (2)
C2	0.101 (9)	0.075 (9)	0.051 (6)	−0.053 (8)	−0.030 (6)	0.015 (6)
C3	0.041 (3)	0.023 (3)	0.033 (3)	−0.008 (2)	−0.005 (2)	0.001 (2)
C4	0.034 (3)	0.025 (3)	0.040 (3)	−0.004 (2)	−0.005 (2)	−0.002 (2)
C5	0.033 (3)	0.031 (3)	0.036 (3)	−0.003 (2)	−0.002 (2)	−0.007 (2)
N1	0.050 (3)	0.032 (3)	0.042 (3)	−0.004 (2)	−0.005 (2)	0.010 (2)
N2	0.0555 (17)	0.0480 (17)	0.074 (2)	−0.0114 (13)	0.0003 (14)	−0.0092 (15)
N3	0.045 (3)	0.035 (3)	0.054 (3)	0.001 (2)	−0.004 (2)	−0.004 (2)
N4	0.061 (3)	0.035 (3)	0.042 (3)	−0.010 (3)	−0.007 (2)	−0.008 (2)
N5	0.043 (3)	0.029 (3)	0.047 (3)	−0.005 (2)	−0.001 (2)	−0.003 (2)

Geometric parameters (Å, º)

Ag1—S1^i	2.5399 (17)	Zn1—N3	2.006 (5)
Ag1—S2	2.541 (3)	S1—C1	1.649 (6)
Ag1—S3	2.5443 (16)	S1—Ag1^i	2.5399 (17)
Ag1—S1	2.8505 (19)	S1—Cs1^ix	3.6262 (15)
Ag1—Ag2^ii	3.3121 (9)	S2—C2	1.389 (3)
Ag2—S4^iii	2.5286 (17)	S3—C3	1.646 (6)
Ag2—S3^iv	2.5752 (16)	S3—Ag2^ii	2.5752 (16)
Ag2—S5	2.7217 (19)	S4—C4	1.634 (6)
Ag2—S5^v	2.7938 (19)	S4—Ag2^iii	2.5286 (17)
Ag2—Ag1^iv	3.3121 (9)	S4—Cs1^x	4.0494 (18)
Cs1—N2^vi	3.480 (3)	S5—C5	1.643 (6)
Cs1—S2^vi	3.480 (3)	S5—Ag2^v	2.7938 (19)
Cs1—S2	3.480 (3)	C1—N1^i	1.153 (8)
Cs1—N3^vi	3.512 (6)	C2—N2^viii	1.389 (3)
Cs1—N3	3.512 (6)	C2—S2^viii	1.389 (3)
Cs1—S1^vii	3.6262 (15)	C3—N3^viii	1.150 (7)
Cs1—S1^viii	3.6262 (15)	C4—N4^iii	1.147 (8)
Cs1—N1^vi	3.701 (6)	C5—N5	1.138 (7)
Cs1—N1	3.701 (6)	N1—C1^i	1.153 (8)
Cs1—N5^vii	3.748 (5)	N3—C3^viii	1.150 (7)
Cs1—N5^viii	3.748 (5)	N4—C4^iii	1.147 (8)
Zn1—N4	1.931 (5)	N5—Zn1^ix	1.954 (5)
Zn1—N5^vii	1.954 (5)	N5—Cs1^ix	3.748 (5)
Zn1—N1	1.956 (5)
S1^i—Ag1—S2	102.71 (8)	N3^vi—Cs1—N5^vii	128.46 (12)
S1^i—Ag1—S3	139.45 (6)	S1^viii—Cs1—N5^vii	121.83 (8)
S2—Ag1—S3	107.20 (9)	N1^vi—Cs1—N5^vii	128.69 (11)
S1^i—Ag1—S1	100.83 (5)	N2^vi—Cs1—N5^viii	105.84 (10)
S2—Ag1—S1	105.19 (8)	S2^vi—Cs1—N5^viii	105.84 (10)
S3—Ag1—S1	97.10 (5)	S2—Cs1—N5^viii	74.16 (10)
S1^i—Ag1—Ag2^ii	120.51 (5)	N3—Cs1—N5^viii	128.46 (12)
S2—Ag1—Ag2^ii	69.97 (8)	S1^vii—Cs1—N5^viii	121.83 (8)
S1—Ag1—Ag2^ii	138.59 (4)	N1—Cs1—N5^viii	128.69 (11)
S4^iii—Ag2—S3^iv	118.89 (5)	N5^vii—Cs1—N5^viii	180.00 (16)
S4^iii—Ag2—S5	110.14 (5)	N4—Zn1—N5^vii	115.2 (2)
S3^iv—Ag2—S5	107.07 (5)	N4—Zn1—N1	113.5 (2)
S4^iii—Ag2—S5^v	114.33 (6)	N5^vii—Zn1—N1	111.1 (2)
S3^iv—Ag2—S5^v	114.09 (5)	N4—Zn1—N3	105.4 (2)
S5—Ag2—S5^v	87.35 (6)	N5^vii—Zn1—N3	106.0 (2)
S4^iii—Ag2—Ag1^iv	79.09 (4)	N1—Zn1—N3	104.5 (2)
S5—Ag2—Ag1^iv	153.45 (5)	C1—S1—Ag1^i	97.9 (2)
S5^v—Ag2—Ag1^iv	112.11 (4)	C1—S1—Ag1	93.8 (2)
N2^vi—Cs1—S2	180.0000	Ag1^i—S1—Ag1	79.17 (5)
S2^vi—Cs1—S2	180.0000	C1—S1—Cs1^ix	100.2 (2)
N2^vi—Cs1—N3^vi	66.72 (11)	Ag1^i—S1—Cs1^ix	157.51 (6)
S2^vi—Cs1—N3^vi	66.72 (11)	Ag1—S1—Cs1^ix	112.72 (5)
S2—Cs1—N3^vi	113.28 (11)	C2—S2—Ag1	98.66 (15)
N2^vi—Cs1—N3	113.28 (11)	C2—S2—Cs1	127.62 (16)
S2^vi—Cs1—N3	113.28 (11)	Ag1—S2—Cs1	128.24 (11)
S2—Cs1—N3	66.72 (11)	C3—S3—Ag1	98.4 (2)
N3^vi—Cs1—N3	180.0000	C3—S3—Ag2^ii	92.7 (2)
N2^vi—Cs1—S1^vii	64.65 (6)	Ag1—S3—Ag2^ii	80.62 (5)
S2^vi—Cs1—S1^vii	64.65 (6)	C4—S4—Ag2^iii	93.2 (2)
S2—Cs1—S1^vii	115.35 (6)	C4—S4—Cs1^x	110.7 (2)
N3^vi—Cs1—S1^vii	75.05 (9)	Ag2^iii—S4—Cs1^x	106.58 (5)
N3—Cs1—S1^vii	104.95 (9)	C5—S5—Ag2	93.3 (2)
N2^vi—Cs1—S1^viii	115.35 (6)	C5—S5—Ag2^v	88.4 (2)
S2^vi—Cs1—S1^viii	115.35 (6)	Ag2—S5—Ag2^v	92.65 (6)
S2—Cs1—S1^viii	64.65 (6)	N1^i—C1—S1	179.4 (6)
N3^vi—Cs1—S1^viii	104.95 (9)	S2—C2—N2^viii	180.0 (2)
N3—Cs1—S1^viii	75.05 (9)	S2—C2—S2^viii	180.0 (2)
S1^vii—Cs1—S1^viii	180	N3^viii—C3—S3	177.6 (5)
S2—Cs1—N1^vi	120.29 (10)	N4^iii—C4—S4	178.9 (6)
N3—Cs1—N1^vi	128.60 (12)	N5—C5—S5	178.8 (6)
S1^vii—Cs1—N1^vi	113.25 (9)	C1^i—N1—Zn1	163.9 (5)
S1^viii—Cs1—N1^vi	66.75 (9)	C1^i—N1—Cs1	113.3 (4)
N2^vi—Cs1—N1	120.29 (10)	Zn1—N1—Cs1	80.57 (17)
S2^vi—Cs1—N1	120.29 (10)	C3^viii—N3—Zn1	157.4 (5)
N3^vi—Cs1—N1	128.60 (12)	C3^viii—N3—Cs1	117.1 (4)
S1^vii—Cs1—N1	66.75 (9)	Zn1—N3—Cs1	85.09 (18)
S1^viii—Cs1—N1	113.25 (9)	C4^iii—N4—Zn1	172.4 (5)
N1^vi—Cs1—N1	180.00 (15)	C5—N5—Zn1^ix	170.9 (5)
N2^vi—Cs1—N5^vii	74.16 (10)	C5—N5—Cs1^ix	108.5 (4)
S2^vi—Cs1—N5^vii	74.16 (10)	Zn1^ix—N5—Cs1^ix	79.30 (16)
S2—Cs1—N5^vii	105.84 (10)

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