2-Bromo-1,3-diisopropyl-4,5-dimethyl-1H-imidazol-3-ium dicyanidoargentate

Mallah, E.; Sweidan, K.; Abu-Salem, Q.; Abu Dayyih, W.; Steimann, M.

doi:10.1107/S1600536811051828

metal-organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 68| Part 1| January 2012| Page m17

doi:10.1107/S1600536811051828

Open

access

2-Bromo-1,3-diisopropyl-4,5-dimethyl-1H-imidazol-3-ium dicyanidoargentate

Eyad Mallah,^a ^* Kamal Sweidan,^b Qutaiba Abu-Salem,^c Wael Abu Dayyih ^a and Manfred Steimann ^d

^aFaculty of Pharmacy and Medical Sciences, Petra University, PO Box 961343, Amman 11196, Jordan, ^bDepartment of Chemistry, Faculty of Science, The University of Jordan, Amman, Jordan, ^cDepartment of Chemistry, Faculty of Science, University of Al al-Bayt, Al-Mafraq, Jordan, and ^dInstitut für Anorganische Chemie der Universität Tübingen, Auf der Morgenstelle 18, D-72076 Tübingen, Germany
^*Correspondence e-mail: eyad782002@yahoo.com

(Received 5 August 2011; accepted 1 December 2011; online 7 December 2011)

The title structure, (C₁₁H₂₀BrN₂)[Ag(CN)₂)], is built up from an approximately C_2v-symmetric imidazolium cation and a nearly linear dicyanidoargentate anion [N—Ag—N = 176.6 (9)° and Ag—C—N = 178.8 (9) and 177.2 (11)°]. These two constituents are linked by a remarkably short interaction between the Br atom of the imidazolium cation [C—Br = 1.85 (3) Å] and one N atom of the cyanidoargentate anion [Br⋯N = 2.96 (2) Å], which is much less than the sum of the van der Waals radii (3.40 Å). The crystal studied was twinned by merohedry.

Related literature

For similar structures, see: Mallah et al. (2009 , 2011 ); Kuhn et al. (2009 ); Potocenak & Chomic (2006 ); Mascal et al. (1996 ). For the synthesis of the starting material, see: Kuhn et al. (2004 ).

Experimental

Crystal data

(C₁₁H₂₀BrN₂)[Ag(CN)₂)]
M_r = 420.11
Orthorhombic, P 2₁ 2₁ 2₁
a = 6.6986 (15) Å
b = 10.6222 (14) Å
c = 23.989 (4) Å
V = 1706.9 (5) Å³
Z = 4
Mo Kα radiation
μ = 3.52 mm⁻¹
T = 291 K
0.40 × 0.20 × 0.20 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
Absorption correction: refined from ΔF (DIFABS; Walker & Stuart, 1983 ) T_min = 0.41, T_max = 1.00
4327 measured reflections
3475 independent reflections
1781 reflections with I > 2σ(I)
R_int = 0.052
3 standard reflections every 300 reflections intensity decay: 1.5%

Refinement

R[F² > 2σ(F²)] = 0.052
wR(F²) = 0.082
S = 0.98
3475 reflections
180 parameters
H-atom parameters constrained
Δρ_max = 0.33 e Å⁻³
Δρ_min = −0.46 e Å⁻³

Data collection: CAD-4 Software; cell refinement: CELDIM (Enraf–Nonius, 1989 ); data reduction: HELENA/PLATON (Spek, 2009 ); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811051828/qk2020sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811051828/qk2020Isup2.hkl

checkCIF report

Comment top

N-heterocyclic carbenes can form stable coordination compounds with main group elements by using their strongly basic character. Kuhn et al. (2004) showed that weak interionic halogen contacts between 2-haloimidazolium cations and halogen containing counter anions do exist in the solid state. Results of related investigations were reported by Kuhn et al. (2009), Mallah et al. (2009), and Potocenak & Chomic (2006). The reaction of 2-bromo-1,3-diisopropyl-4,5-dimethylimidazolium bromide with silver cyanide gives the title compound as stable crystalline solid in a good yield. The structure contains an approximately C_2v imidazolium cation (Fig. 1), similar to the crystal structure of the 2-chloroimidazolium analogue (Mallah et al., 2011), where the C—Cl bond (1.677 (5) Å) is shorter than the C—Br bond of the title compound (1.848 (6) Å). The title structure contains a cation-anion pair (Fig. 1) with a short N(12)(x-1,y,z)···Br(1) interaction of 2.96 (2) Å, by ca. 0.4 Å shorther than the sum of the van der Waals radii. Mascal et al. (1996) found for a s-triazine–dibromine cocrystal a N···Br contact distance as short as 2.515 Å.

Related literature top

For similar structures, see: Mallah et al. (2009, 2011); Kuhn et al. (2009); Potocenak & Chomic (2006); Mascal et al. (1996). For the synthesis of the starting material, see: Kuhn et al. (2004).

Experimental top

The title compound was prepared by addition of silver cyanide (1.3 g, 9.7 mmol) to a solution of 2-bromo-1,3-diisopropyl-4,5-dimethylimidazoliumbromide, see: Kuhn et al. (2004), (1.1 g, 3.2 mmol) in 30 ml of acetonitrile. The mixture was stirred for 48 hr at room temperature, then the solvent was removed in vacuo and 20 ml of dichloromethane was added. The resulting solution was filtered off and solvent was removed in vacuo. Yield after recrystallisation from dichloromethane/diethyl ether 0.98 g (73 %), as colorless crystals.

Computing details top

Data collection: CAD-4 Software (Enraf–Nonius, 1989); cell refinement: CELDIM (Enraf–Nonius, 1989); data reduction: HELENA/PLATON (Spek, 2009),; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

Fig. 1. The molecular structure the cation-anion pair of the title compound showing 20% probability displacement ellipsoids for non-H atoms. The symmetry transformation for the depicted dicyanoargentate anion is x-1, y, z.

2-Bromo-1,3-diisopropyl-4,5-dimethyl-1H-imidazol-3-ium dicyanidoargentate top

Crystal data top

(C₁₁H₂₀BrN₂)[Ag(CN)₂)]	F(000) = 832
M_r = 420.11	D_x = 1.635 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 25 reflections
a = 6.6986 (15) Å	θ = 6.7–13.0°
b = 10.6222 (14) Å	µ = 3.52 mm⁻¹
c = 23.989 (4) Å	T = 291 K
V = 1706.9 (5) Å³	Block, colourless
Z = 4	0.40 × 0.20 × 0.20 mm

Data collection top

Enraf–Nonius CAD-4 diffractometer	1781 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.052
Graphite monochromator	θ_max = 26.4°, θ_min = 3.2°
ω scans	h = −8→8
Absorption correction: part of the refinement model (ΔF) (DIFABS; Walker & Stuart, 1983)	k = −1→13
T_min = 0.40, T_max = 1.00	l = −1→29
4327 measured reflections	3 standard reflections every 300 reflections
3475 independent reflections	intensity decay: 1.5%

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.052	H-atom parameters constrained
wR(F²) = 0.082	w = 1/[σ²(F_o²) + (0.0199P)²] where P = (F_o² + 2F_c²)/3
S = 0.98	(Δ/σ)_max = 0.001
3475 reflections	Δρ_max = 0.33 e Å⁻³
180 parameters	Δρ_min = −0.46 e Å⁻³
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00128 (16)

Crystal data top

(C₁₁H₂₀BrN₂)[Ag(CN)₂)]	V = 1706.9 (5) Å³
M_r = 420.11	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 6.6986 (15) Å	µ = 3.52 mm⁻¹
b = 10.6222 (14) Å	T = 291 K
c = 23.989 (4) Å	0.40 × 0.20 × 0.20 mm

Data collection top

Enraf–Nonius CAD-4 diffractometer	1781 reflections with I > 2σ(I)
Absorption correction: part of the refinement model (ΔF) (DIFABS; Walker & Stuart, 1983)	R_int = 0.052
T_min = 0.40, T_max = 1.00	3 standard reflections every 300 reflections
4327 measured reflections	intensity decay: 1.5%
3475 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.052	0 restraints
wR(F²) = 0.082	H-atom parameters constrained
S = 0.98	Δρ_max = 0.33 e Å⁻³
3475 reflections	Δρ_min = −0.46 e Å⁻³
180 parameters

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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

	x	y	z	U_iso*/U_eq
Ag1	0.71941 (9)	0.98742 (7)	0.12744 (3)	0.0718 (2)
C1	0.6144 (9)	0.5300 (5)	0.1252 (3)	0.0411 (16)
N2	0.7155 (9)	0.5116 (6)	0.0780 (2)	0.0417 (16)
C3	0.8807 (12)	0.4401 (6)	0.0898 (3)	0.045 (2)
C4	0.8812 (11)	0.4187 (7)	0.1450 (3)	0.048 (2)
N5	0.7109 (9)	0.4757 (6)	0.1669 (2)	0.0470 (16)
C11	0.5572 (13)	1.1454 (10)	0.1123 (4)	0.072 (3)
C12	0.8919 (14)	0.8303 (9)	0.1400 (4)	0.073 (3)
C21	0.6467 (13)	0.5572 (8)	0.0225 (3)	0.059 (2)
H21	0.5233	0.6041	0.0296	0.071*
C22	0.7867 (15)	0.6484 (9)	−0.0028 (3)	0.092 (3)
H22A	0.8289	0.7079	0.0249	0.138*
H22B	0.7212	0.6921	−0.0327	0.138*
H22C	0.9010	0.6044	−0.0171	0.138*
C23	0.5874 (13)	0.4462 (9)	−0.0143 (3)	0.087 (3)
H23A	0.7051	0.4020	−0.0260	0.131*
H23B	0.5170	0.4766	−0.0465	0.131*
H23C	0.5027	0.3902	0.0063	0.131*
C31	1.0326 (11)	0.3991 (9)	0.0475 (3)	0.076 (3)
H31A	1.1349	0.3508	0.0656	0.115*
H31B	1.0910	0.4719	0.0303	0.115*
H31C	0.9689	0.3484	0.0196	0.115*
C41	1.0252 (11)	0.3428 (9)	0.1781 (3)	0.085 (3)
H41A	1.1237	0.3072	0.1537	0.128*
H41B	0.9553	0.2763	0.1969	0.128*
H41C	1.0896	0.3957	0.2051	0.128*
C51	0.6523 (12)	0.4807 (8)	0.2263 (3)	0.056 (2)
H51	0.5282	0.5296	0.2266	0.067*
C52	0.5934 (14)	0.3535 (9)	0.2481 (3)	0.089 (3)
H52A	0.5176	0.3096	0.2202	0.133*
H52B	0.5138	0.3635	0.2811	0.133*
H52C	0.7112	0.3060	0.2569	0.133*
C53	0.7912 (14)	0.5544 (8)	0.2608 (3)	0.086 (3)
H53A	0.9073	0.5047	0.2688	0.129*
H53B	0.7267	0.5776	0.2950	0.129*
H53C	0.8301	0.6290	0.2410	0.129*
N11	0.4683 (10)	1.2343 (8)	0.1047 (3)	0.076 (2)
N12	0.9891 (11)	0.7474 (8)	0.1450 (4)	0.090 (3)
Br1	0.37724 (11)	0.61731 (7)	0.13261 (3)	0.0596 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ag1	0.0664 (4)	0.0772 (5)	0.0718 (4)	0.0139 (4)	0.0084 (4)	0.0021 (5)
C1	0.040 (4)	0.032 (4)	0.051 (4)	−0.001 (3)	0.002 (5)	−0.007 (5)
N2	0.040 (3)	0.053 (4)	0.033 (3)	0.010 (4)	−0.003 (3)	−0.001 (4)
C3	0.050 (5)	0.043 (5)	0.042 (5)	0.008 (4)	−0.005 (4)	−0.004 (4)
C4	0.037 (4)	0.052 (5)	0.054 (5)	0.003 (4)	−0.007 (4)	0.010 (4)
N5	0.046 (3)	0.053 (4)	0.042 (3)	0.003 (4)	−0.001 (3)	0.009 (4)
C11	0.070 (7)	0.077 (8)	0.069 (7)	0.017 (5)	0.009 (5)	−0.001 (6)
C12	0.077 (6)	0.069 (7)	0.072 (7)	−0.005 (5)	0.015 (6)	−0.009 (6)
C21	0.057 (5)	0.070 (6)	0.050 (5)	0.016 (5)	−0.005 (4)	0.010 (5)
C22	0.106 (8)	0.100 (9)	0.070 (6)	−0.029 (7)	−0.004 (6)	0.030 (6)
C23	0.081 (6)	0.108 (9)	0.073 (6)	0.010 (6)	−0.026 (6)	−0.013 (6)
C31	0.061 (5)	0.104 (8)	0.063 (5)	0.024 (6)	0.003 (4)	−0.011 (6)
C41	0.072 (6)	0.112 (9)	0.072 (6)	0.031 (6)	−0.012 (5)	0.023 (6)
C51	0.063 (6)	0.062 (6)	0.042 (4)	0.007 (6)	0.003 (4)	0.006 (5)
C52	0.104 (8)	0.100 (9)	0.061 (6)	−0.016 (7)	0.022 (6)	0.010 (6)
C53	0.112 (8)	0.094 (8)	0.052 (5)	−0.028 (7)	−0.008 (5)	−0.013 (5)
N11	0.069 (5)	0.079 (6)	0.079 (5)	0.009 (5)	0.001 (4)	−0.006 (5)
N12	0.082 (6)	0.071 (6)	0.117 (8)	0.005 (5)	0.002 (5)	−0.001 (6)
Br1	0.0552 (5)	0.0610 (5)	0.0624 (5)	0.0161 (4)	0.0033 (5)	−0.0025 (6)

Geometric parameters (Å, º) top

Ag1—C11	2.032 (10)	C22—H22C	0.9600
Ag1—C12	2.053 (10)	C23—H23A	0.9600
C1—N5	1.325 (7)	C23—H23B	0.9600
C1—N2	1.332 (7)	C23—H23C	0.9600
C1—Br1	1.848 (6)	C31—H31A	0.9600
N2—C3	1.371 (8)	C31—H31B	0.9600
N2—C21	1.490 (8)	C31—H31C	0.9600
C3—C4	1.344 (8)	C41—H41A	0.9600
C3—C31	1.501 (10)	C41—H41B	0.9600
C4—N5	1.394 (8)	C41—H41C	0.9600
C4—C41	1.486 (9)	C51—C53	1.471 (11)
N5—C51	1.478 (8)	C51—C52	1.502 (11)
C11—N11	1.131 (10)	C51—H51	0.9800
C12—N12	1.102 (10)	C52—H52A	0.9600
C21—C22	1.479 (10)	C52—H52B	0.9600
C21—C23	1.526 (10)	C52—H52C	0.9600
C21—H21	0.9800	C53—H53A	0.9600
C22—H22A	0.9600	C53—H53B	0.9600
C22—H22B	0.9600	C53—H53C	0.9600

C11—Ag1—C12	177.5 (4)	C21—C23—H23C	109.5
N5—C1—N2	109.2 (5)	H23A—C23—H23C	109.5
N5—C1—Br1	124.4 (6)	H23B—C23—H23C	109.5
N2—C1—Br1	126.4 (6)	C3—C31—H31A	109.5
C1—N2—C3	108.5 (5)	C3—C31—H31B	109.5
C1—N2—C21	123.6 (6)	H31A—C31—H31B	109.5
C3—N2—C21	127.9 (6)	C3—C31—H31C	109.5
C4—C3—N2	107.4 (7)	H31A—C31—H31C	109.5
C4—C3—C31	127.9 (8)	H31B—C31—H31C	109.5
N2—C3—C31	124.6 (6)	C4—C41—H41A	109.5
C3—C4—N5	107.2 (7)	C4—C41—H41B	109.5
C3—C4—C41	128.3 (8)	H41A—C41—H41B	109.5
N5—C4—C41	124.4 (6)	C4—C41—H41C	109.5
C1—N5—C4	107.7 (5)	H41A—C41—H41C	109.5
C1—N5—C51	125.7 (6)	H41B—C41—H41C	109.5
C4—N5—C51	126.6 (6)	C53—C51—N5	113.2 (7)
N11—C11—Ag1	178.8 (9)	C53—C51—C52	116.7 (7)
N12—C12—Ag1	177.2 (11)	N5—C51—C52	111.9 (7)
C22—C21—N2	112.6 (7)	C53—C51—H51	104.5
C22—C21—C23	115.7 (7)	N5—C51—H51	104.5
N2—C21—C23	110.3 (6)	C52—C51—H51	104.5
C22—C21—H21	105.8	C51—C52—H52A	109.5
N2—C21—H21	105.8	C51—C52—H52B	109.5
C23—C21—H21	105.8	H52A—C52—H52B	109.5
C21—C22—H22A	109.5	C51—C52—H52C	109.5
C21—C22—H22B	109.5	H52A—C52—H52C	109.5
H22A—C22—H22B	109.5	H52B—C52—H52C	109.5
C21—C22—H22C	109.5	C51—C53—H53A	109.5
H22A—C22—H22C	109.5	C51—C53—H53B	109.5
H22B—C22—H22C	109.5	H53A—C53—H53B	109.5
C21—C23—H23A	109.5	C51—C53—H53C	109.5
C21—C23—H23B	109.5	H53A—C53—H53C	109.5
H23A—C23—H23B	109.5	H53B—C53—H53C	109.5

N5—C1—N2—C3	1.5 (7)	Br1—C1—N5—C51	−3.3 (10)
Br1—C1—N2—C3	−178.6 (5)	C3—C4—N5—C1	−0.5 (8)
N5—C1—N2—C21	178.3 (6)	C41—C4—N5—C1	−177.2 (7)
Br1—C1—N2—C21	−1.8 (9)	C3—C4—N5—C51	−177.7 (7)
C1—N2—C3—C4	−1.8 (8)	C41—C4—N5—C51	5.7 (12)
C21—N2—C3—C4	−178.5 (7)	C12—Ag1—C11—N11	−100 (52)
C1—N2—C3—C31	180.0 (7)	C11—Ag1—C12—N12	−5 (30)
C21—N2—C3—C31	3.3 (12)	C1—N2—C21—C22	118.1 (8)
N2—C3—C4—N5	1.4 (8)	C3—N2—C21—C22	−65.7 (10)
C31—C3—C4—N5	179.5 (7)	C1—N2—C21—C23	−111.1 (8)
N2—C3—C4—C41	177.9 (7)	C3—N2—C21—C23	65.2 (10)
C31—C3—C4—C41	−4.0 (14)	C1—N5—C51—C53	−111.4 (8)
N2—C1—N5—C4	−0.6 (8)	C4—N5—C51—C53	65.2 (11)
Br1—C1—N5—C4	179.5 (5)	C1—N5—C51—C52	114.3 (9)
N2—C1—N5—C51	176.6 (7)	C4—N5—C51—C52	−69.0 (10)

Experimental details

Crystal data
Chemical formula	(C₁₁H₂₀BrN₂)[Ag(CN)₂)]
M_r	420.11
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	291
a, b, c (Å)	6.6986 (15), 10.6222 (14), 23.989 (4)
V (Å³)	1706.9 (5)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	3.52
Crystal size (mm)	0.40 × 0.20 × 0.20

Data collection
Diffractometer	Enraf–Nonius CAD-4 diffractometer
Absorption correction	Part of the refinement model (ΔF) (DIFABS; Walker & Stuart, 1983)
T_min, T_max	0.40, 1.00
No. of measured, independent and observed [I > 2σ(I)] reflections	4327, 3475, 1781
R_int	0.052
(sin θ/λ)_max (Å⁻¹)	0.625

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.052, 0.082, 0.98
No. of reflections	3475
No. of parameters	180
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.33, −0.46

Computer programs: CAD-4 Software (Enraf–Nonius, 1989), CELDIM (Enraf–Nonius, 1989), HELENA/PLATON (Spek, 2009),, SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Acknowledgements

The authors are grateful to the Deutsche Forschungsgemeinschaft, the Higher Council for Science and Technology of Jordan and Petra University for financial support. We also thank Dr Cäcilia Maichle-Mössmer for helpful discussions.

References

Enraf–Nonius (1989). CAD-4 Software and CELDIM. Enraf–Nonius, Delft, The Netherlands. Google Scholar
Kuhn, N., Abu-Rayyan, A., Eichele, K., Schwarz, S. & Steimann, M. (2004). Inorg. Chim. Acta, 357, 1799–1804. Web of Science CSD CrossRef CAS Google Scholar
Kuhn, N., Mallah, E., Maichle-Mössmer, C. & Steimann, M. (2009). Z. Naturforsch. Teil B, 64, 835–839. CAS Google Scholar
Mallah, E., Abu-Salem, Q., Sweidan, K., Kuhn, N., Maichle-Mössmer, C., Steimann, M., Ströbele, M. & Walker, M. (2011). Z. Naturforsch. Teil B, 66, 545–548. CrossRef CAS Google Scholar
Mallah, E., Kuhn, N., Maichle-Mössmer, C., Steimann, M., Ströbele, M. & Zeller, K. P. (2009). Z. Naturforsch. Teil B, 64, 1176–1182. CAS Google Scholar
Mascal, M., Richardson, J. L., Blake, A. J. & Li, W.-S. (1996). Tetrahedron Lett. 37, 3505–3506. CSD CrossRef CAS Web of Science Google Scholar
Potocenak, I. & Chomic, J. (2006). Transition Met. Chem. 31, 504–515. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
Walker, N. & Stuart, D. (1983). Acta Cryst. A39, 158–166. CrossRef CAS Web of Science IUCr Journals Google Scholar