Buy article online - an online subscription or single-article purchase is required to access this article.
Download citation
Download citation
link to html
The title compound, CaCs2[Ag2(SCN)6]·2H2O, forms a continuous structure where the Ag atoms form chains with S atoms in the c-axis direction. The chains are bonded together through Cs and Ca atoms. The crystal water of the structure is bonded to the Ca atoms, which lie on centers of symmetry.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101017413/br1348sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270101017413/br1348Isup2.hkl
Contains datablock I

Comment top

The title compound has been known since the beginning of the last century (Wells, 1902; Wells, 1922). At that time, most studies were synthetic and analytical. Since those days, many crystal structures of thiocyanates have been solved. The crystal structure of the title compound has not been reported before. Calcium, caesium and silver all form simple thiocyanates. CsSCN crystallizes in space group Pnma and AgSCN in two polymorphic forms in space groups Pmnn and C2/c. The crystal structure of Ca(SCN)2·2H2O is not available in the literature because while crystallizing it forms powder instead of large single crystals, and until recently it has not usually been possible to determine the crystal structure of a powder sample. However, a quite recently published crystal structure determination of Ca(SCN)2·4H2O (Held & Bohaty, 2001) is now available in the literature.

The main reason why we are so interested in thiocyanates like the title compound is that some of the thiocyanates of silver have very interesting optical, electro-optic and electrostrictive properties (Bohaty & Fröhlich, 1992), which are interrelated with non-centrosymmetric crystal structure. Earlier, we have reported the crystal structures of KAg(SCN)2 (Valkonen & Güneş, 2001) and Cs2[AgZn(SCN)5] (Güneş & Valkonen, 2001) of which the Cs2[AgZn(SCN)5] has a non-centrosymmetric crystal structure. We presume that an odd number of thiocyanate groups could lead to a noncentrosymmetric crystal structure as there are also other thiocyanate complexes of silver such as Cs3Sr[Ag2(SCN)7] and Cs3Ba[Ag2(SCN)7] (Bohaty & Fröhlich, 1992), which have been found to have the same property. We look forward to synthesizing more of these compounds in the future as it might turn out that they will indeed have non-centrosymmetric crystal structures and as a consequence some chemically useful optical, electro-optic and electrostrictive properties.

In the present compound caesium is nine coordinated, with four S, four N and one O atom around it. Ag is tetrahedrally four coordinated being surrounded by four S atoms. The tetrahedron around Ag is slightly distorted (see the tables). Ca is octahedrally six coordinated with two O and four N atoms around it. The octahedron around Ca is nearly regular (see the tables). The average S—C distance of the thiocyanate group is 1.65 Å and the average C—N distance about 1.15 Å. The angles of the thiocyanate groups (at C) are all close to 180°.

The title compound consists of a continuous structure where the Ag atoms form chains (Fig. 1) in the direction of the c axis, bonded together through the S2 atoms of the bridging thiocyanate groups which bond through N to calcium atoms thereby connecting the Ag—S—Ag chains in the direction of the b axis. There are also two terminal thiocyanate groups attached through S to every silver of the Ag—S—Ag chains. One of the terminal thiocyanate groups of every other Ag of the chain is bonded through N to Ca atoms thereby also connecting the Ag—S—Ag chains. The bonding of the Ag—S—Ag chains is presented in Fig 1. The Cs atoms connect the Ag—S—Ag chains both in the direction of b axis and in the direction of the a axis. The crystal water of the structure is bonded to the Ca atoms. The water molecules are located in the capping positions of the coordination octahedron around calcium.

Experimental top

Silver thiocyanate was delivered by the Aldrich Chemical Company Inc. Calcium thiocyanate dihydrate and caesium thiocyanate were synthesized in the research laboratory.

CaCs2[Ag2(SCN)6]·2H2O was synthesized at room temperature by dissolving 1.45 g Ca(SCN)2·2H2O into 1.00 ml deionized water and 2.63 g CsSCN into 2.00 ml deionized water. The Ca(SCN)2·2H2O solution was added to CsSCN solution and 2.28 g AgSCN was dissolved into that solution. The dissolution of AgSCN was accelerated by heating the solution on a water bath. The final solution was filtered with a dense sinter glass (No: 4) while still hot. The filtered solution was allowed to cool and evaporate at room temperature. Within two days colorless crystals of CaCs2[Ag2(SCN)6]·2H2O were formed.

Calcium thiocyanate dihydrate was synthesized at room temperature by suspending 60.00 g Ca(OH)2 into 150 ml deionized water and 102.53 g NH4SCN into 65.0 ml deionized water. The solutions were mixed and the mixture was heated under magnetic stirring until the smell of ammonia was not sensed anymore (about 2 h). The solution was filtered while still hot. The filtered solution was evaporated to dryness in 350–360 K using a vacuum pump on a water bath. Ca(SCN)2·2H2O was stored in a desiccator due to its hygroscopicity.

Caesium thiocyanate was synthesized by dissolving 6.98 g NH4SCN into 20.0 ml deionized water and 15.0 g C s2CO3 into 55.0 ml deionized water. The solutions were mixed at room temperature and the mixture was heated under magnetic stirring until the smell of ammonia was not sensed anymore (about 2.5 h). The residue was evaporated close to dryness at room temperature. CsSCN was dried using a vacuum pump and was stored in an desiccator due to its hygroscopicity.

Calcium hydroxide was delivered by the Merck KGaA and ammonium thiocyanate and caesium carbonate by the Aldrich Chemical Company Inc.

Refinement top

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. During the crystal structure determination absorption correction for the measured intensities was calculated but not applied. The absorption correction was found to have no significant effect on the refinement results.

Computing details top

Data collection: Collect (Nonius, 1997–2000); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND 2.1d (Brandenburg, 2000); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. The Ag—S—Ag chains connected together through Ca atoms. The Cs atom is omitted from the figure for clarity. The displacement ellipsoids are represented in 50% probability.
dicaesium calcium disilver thiocyanate dihydrate top
Crystal data top
CaCs2[Ag2(SCN)6].2(H2O)F(000) = 836
Mr = 906.15Dx = 2.592 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 7.8696 (1) ÅCell parameters from 5696 reflections
b = 19.0910 (2) Åθ = 1.0–28.3°
c = 7.7411 (1) ŵ = 5.55 mm1
β = 93.338 (1)°T = 293 K
V = 1161.04 (2) Å3Prism, colorless
Z = 20.1 × 0.1 × 0.1 mm
Data collection top
Nonius KappaCCD
diffractometer
2588 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.024
Horizonally mounted graphite crystal monochromatorθmax = 28.3°, θmin = 2.1°
Detector resolution: 9 pixels mm-1h = 1010
CCD scansk = 2525
11177 measured reflectionsl = 1010
2881 independent reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033All H-atom parameters refined
wR(F2) = 0.059 w = 1/[σ2(Fo2) + 3.4217P]
where P = (Fo2 + 2Fc2)/3
S = 1.12(Δ/σ)max = 0.001
2881 reflectionsΔρmax = 1.86 e Å3
124 parametersΔρmin = 1.41 e Å3
0 restraintsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.00268 (16)
Crystal data top
CaCs2[Ag2(SCN)6].2(H2O)V = 1161.04 (2) Å3
Mr = 906.15Z = 2
Monoclinic, P21/cMo Kα radiation
a = 7.8696 (1) ŵ = 5.55 mm1
b = 19.0910 (2) ÅT = 293 K
c = 7.7411 (1) Å0.1 × 0.1 × 0.1 mm
β = 93.338 (1)°
Data collection top
Nonius KappaCCD
diffractometer
2588 reflections with I > 2σ(I)
11177 measured reflectionsRint = 0.024
2881 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0330 restraints
wR(F2) = 0.059All H-atom parameters refined
S = 1.12Δρmax = 1.86 e Å3
2881 reflectionsΔρmin = 1.41 e Å3
124 parameters
Special details top

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.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Cs0.24537 (4)0.382640 (15)0.47667 (4)0.05609 (11)
Ag0.72580 (5)0.283818 (17)0.51759 (5)0.05416 (12)
Ca0.00000.50000.00000.0419 (3)
S10.69567 (15)0.41671 (5)0.53277 (14)0.0459 (3)
S20.94462 (14)0.25482 (5)0.29024 (13)0.0431 (2)
S30.46489 (15)0.21714 (6)0.59864 (15)0.0491 (3)
C10.8123 (5)0.44028 (19)0.3743 (5)0.0391 (8)
C20.9913 (5)0.1751 (2)0.3620 (5)0.0405 (9)
C30.4706 (5)0.1525 (2)0.4570 (5)0.0417 (9)
N10.8973 (6)0.4591 (2)0.2690 (6)0.0672 (12)
N21.0237 (5)0.1192 (2)0.4068 (6)0.0620 (11)
N30.4720 (6)0.1056 (2)0.3633 (6)0.0623 (11)
O0.2849 (5)0.4839 (2)0.1070 (5)0.0572 (9)
H10.336 (9)0.461 (4)0.044 (9)0.09 (2)*
H20.335 (8)0.515 (3)0.122 (8)0.07 (2)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cs0.05030 (17)0.04272 (16)0.0739 (2)0.00388 (12)0.00835 (13)0.00223 (13)
Ag0.0530 (2)0.03568 (17)0.0745 (3)0.00441 (14)0.01010 (17)0.00121 (16)
Ca0.0456 (6)0.0324 (5)0.0492 (7)0.0003 (5)0.0156 (5)0.0114 (5)
S10.0604 (6)0.0301 (5)0.0496 (6)0.0031 (4)0.0237 (5)0.0016 (4)
S20.0601 (6)0.0352 (5)0.0337 (5)0.0037 (4)0.0016 (4)0.0008 (4)
S30.0552 (6)0.0408 (5)0.0526 (6)0.0079 (5)0.0142 (5)0.0019 (5)
C10.043 (2)0.0300 (18)0.045 (2)0.0024 (16)0.0068 (17)0.0067 (16)
C20.040 (2)0.041 (2)0.040 (2)0.0005 (17)0.0014 (16)0.0068 (17)
C30.040 (2)0.039 (2)0.047 (2)0.0067 (17)0.0124 (17)0.0068 (18)
N10.072 (3)0.064 (3)0.068 (3)0.001 (2)0.029 (2)0.023 (2)
N20.064 (3)0.039 (2)0.082 (3)0.0062 (18)0.002 (2)0.003 (2)
N30.069 (3)0.052 (2)0.068 (3)0.009 (2)0.025 (2)0.011 (2)
O0.052 (2)0.050 (2)0.070 (2)0.0027 (17)0.0101 (17)0.0203 (18)
Geometric parameters (Å, º) top
Cs—N3i3.401 (5)Ca—H22.76 (6)
Cs—N1ii3.421 (5)S1—C11.637 (4)
Cs—O3.483 (4)S1—Csiii3.8599 (10)
Cs—S13.6042 (12)S2—C21.655 (4)
Cs—C1iii3.609 (4)S2—Agix2.7461 (11)
Cs—C1ii3.625 (4)S2—Csx3.6389 (11)
Cs—S2ii3.6389 (11)S3—C31.653 (4)
Cs—S33.6970 (12)S3—Csi3.9706 (11)
Cs—N1iii3.811 (5)C1—N11.142 (5)
Cs—C2iv3.848 (4)C1—Csiii3.609 (4)
Cs—N2iv3.848 (5)C1—Csx3.625 (4)
Cs—S1iii3.8599 (10)C2—N21.146 (5)
Ag—S32.5259 (11)C2—Csxi3.848 (4)
Ag—S12.5513 (10)C3—N31.153 (5)
Ag—S22.5927 (11)N1—Cax2.407 (4)
Ag—S2i2.7461 (11)N1—Csx3.421 (5)
Ca—Ov2.365 (4)N1—Csiii3.811 (5)
Ca—O2.365 (4)N2—Caxii2.397 (4)
Ca—N2vi2.397 (4)N2—Csxi3.848 (5)
Ca—N2vii2.397 (4)N3—Csix3.401 (5)
Ca—N1viii2.407 (4)O—H10.78 (7)
Ca—N1ii2.407 (4)O—H20.71 (6)
Ca—H12.75 (7)
N3i—Cs—N1ii138.57 (10)N2vi—Ca—N1viii89.35 (15)
N3i—Cs—O128.26 (10)N2vii—Ca—N1viii90.65 (15)
N1ii—Cs—S1137.24 (7)Ov—Ca—N1ii89.19 (15)
O—Cs—S182.21 (6)O—Ca—N1ii90.81 (15)
N3i—Cs—S2ii133.54 (7)N2vi—Ca—N1ii90.65 (15)
N1ii—Cs—S2ii67.38 (8)N2vii—Ca—N1ii89.35 (15)
O—Cs—S2ii97.67 (7)N1viii—Ca—N1ii180
S1—Cs—S2ii141.35 (2)C1—S1—Ag100.44 (14)
N3i—Cs—S367.56 (7)C1—S1—Cs123.32 (15)
N1ii—Cs—S3146.52 (8)Ag—S1—Cs84.74 (3)
O—Cs—S3128.43 (7)C1—S1—Csiii68.88 (13)
S1—Cs—S371.45 (2)Ag—S1—Csiii167.00 (4)
S2ii—Cs—S379.14 (2)Cs—S1—Csiii107.17 (3)
N3i—Cs—N1iii69.41 (10)C2—S2—Ag96.42 (15)
N1ii—Cs—N1iii69.66 (13)C2—S2—Agix97.35 (14)
O—Cs—N1iii91.58 (9)Ag—S2—Agix99.64 (4)
S1—Cs—N1iii96.43 (7)C2—S2—Csx110.94 (14)
S2ii—Cs—N1iii122.15 (7)Ag—S2—Csx91.72 (3)
S3—Cs—N1iii133.86 (7)Agix—S2—Csx148.13 (4)
N1ii—Cs—N2iv91.12 (9)C3—S3—Ag99.06 (14)
O—Cs—N2iv141.52 (9)C3—S3—Cs119.92 (15)
S1—Cs—N2iv112.92 (7)Ag—S3—Cs83.13 (3)
S2ii—Cs—N2iv91.15 (6)C3—S3—Csi99.24 (13)
S3—Cs—N2iv90.00 (6)Ag—S3—Csi145.06 (4)
N3i—Cs—S1iii83.90 (7)Cs—S3—Csi112.42 (3)
N1ii—Cs—S1iii70.21 (8)N1—C1—S1176.6 (4)
S1—Cs—S1iii72.83 (3)N2—C2—S2178.0 (4)
S2ii—Cs—S1iii137.23 (3)N3—C3—S3177.2 (4)
S3—Cs—S1iii142.95 (3)C1—N1—Cax163.6 (4)
N2iv—Cs—S1iii94.95 (6)C1—N1—Csx91.0 (3)
S3—Ag—S1114.24 (4)Cax—N1—Csx104.19 (14)
S3—Ag—S2129.99 (4)C1—N1—Csiii71.2 (3)
S1—Ag—S2108.10 (3)Cax—N1—Csiii108.29 (13)
S3—Ag—S2i98.98 (4)Csx—N1—Csiii110.34 (13)
S1—Ag—S2i106.71 (4)C2—N2—Caxii162.7 (4)
S2—Ag—S2i93.03 (3)C2—N2—Csxi81.4 (3)
Ov—Ca—O180Caxii—N2—Csxi107.41 (13)
Ov—Ca—N2vi83.87 (14)C3—N3—Csix118.6 (4)
O—Ca—N2vi96.13 (14)Ca—O—Cs103.39 (12)
Ov—Ca—N2vii96.13 (14)Ca—O—H1111 (5)
O—Ca—N2vii83.87 (14)Cs—O—H1106 (5)
N2vi—Ca—N2vii180Ca—O—H2117 (5)
Ov—Ca—N1viii90.81 (15)Cs—O—H2113 (5)
O—Ca—N1viii89.19 (15)H1—O—H2106 (7)
Symmetry codes: (i) x, y+1/2, z+1/2; (ii) x1, y, z; (iii) x+1, y+1, z+1; (iv) x1, y+1/2, z+1/2; (v) x, y+1, z; (vi) x+1, y+1/2, z+1/2; (vii) x1, y+1/2, z1/2; (viii) x+1, y+1, z; (ix) x, y+1/2, z1/2; (x) x+1, y, z; (xi) x+1, y+1/2, z1/2; (xii) x+1, y1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaCaCs2[Ag2(SCN)6].2(H2O)
Mr906.15
Crystal system, space groupMonoclinic, P21/c
Temperature (K)293
a, b, c (Å)7.8696 (1), 19.0910 (2), 7.7411 (1)
β (°) 93.338 (1)
V3)1161.04 (2)
Z2
Radiation typeMo Kα
µ (mm1)5.55
Crystal size (mm)0.1 × 0.1 × 0.1
Data collection
DiffractometerNonius KappaCCD
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
11177, 2881, 2588
Rint0.024
(sin θ/λ)max1)0.667
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.033, 0.059, 1.12
No. of reflections2881
No. of parameters124
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)1.86, 1.41

Computer programs: Collect (Nonius, 1997–2000), HKL SCALEPACK (Otwinowski & Minor 1997), HKL DENZO and SCALEPACK (Otwinowski & Minor 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), DIAMOND 2.1d (Brandenburg, 2000), WinGX (Farrugia, 1999).

Selected geometric parameters (Å, º) top
Cs—N3i3.401 (5)Ag—S32.5259 (11)
Cs—N1ii3.421 (5)Ag—S12.5513 (10)
Cs—O3.483 (4)Ag—S22.5927 (11)
Cs—S13.6042 (12)Ag—S2i2.7461 (11)
Cs—S2ii3.6389 (11)Ca—O2.365 (4)
Cs—S33.6970 (12)Ca—N2v2.397 (4)
Cs—N1iii3.811 (5)Ca—N1vi2.407 (4)
Cs—N2iv3.848 (5)O—H10.78 (7)
Cs—S1iii3.8599 (10)O—H20.71 (6)
S3—Ag—S1114.24 (4)N2v—Ca—N2viii180
S3—Ag—S2129.99 (4)Ovii—Ca—N1vi90.81 (15)
S1—Ag—S2108.10 (3)O—Ca—N1vi89.19 (15)
S3—Ag—S2i98.98 (4)N2v—Ca—N1vi89.35 (15)
S1—Ag—S2i106.71 (4)N2viii—Ca—N1vi90.65 (15)
S2—Ag—S2i93.03 (3)Ovii—Ca—N1ii89.19 (15)
Ovii—Ca—O180O—Ca—N1ii90.81 (15)
Ovii—Ca—N2v83.87 (14)N2v—Ca—N1ii90.65 (15)
O—Ca—N2v96.13 (14)N2viii—Ca—N1ii89.35 (15)
Ovii—Ca—N2viii96.13 (14)N1vi—Ca—N1ii180
O—Ca—N2viii83.87 (14)H1—O—H2106 (7)
Symmetry codes: (i) x, y+1/2, z+1/2; (ii) x1, y, z; (iii) x+1, y+1, z+1; (iv) x1, y+1/2, z+1/2; (v) x+1, y+1/2, z+1/2; (vi) x+1, y+1, z; (vii) x, y+1, z; (viii) x1, y+1/2, z1/2.
 

Subscribe to Acta Crystallographica Section C: Structural Chemistry

The full text of this article is available to subscribers to the journal.

If you have already registered and are using a computer listed in your registration details, please email support@iucr.org for assistance.

Buy online

You may purchase this article in PDF and/or HTML formats. For purchasers in the European Community who do not have a VAT number, VAT will be added at the local rate. Payments to the IUCr are handled by WorldPay, who will accept payment by credit card in several currencies. To purchase the article, please complete the form below (fields marked * are required), and then click on `Continue'.
E-mail address* 
Repeat e-mail address* 
(for error checking) 

Format*   PDF (US $40)
   HTML (US $40)
   PDF+HTML (US $50)
In order for VAT to be shown for your country javascript needs to be enabled.

VAT number 
(non-UK EC countries only) 
Country* 
 

Terms and conditions of use
Contact us

Follow Acta Cryst. C
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds