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COMMUNICATIONS
ISSN: 2056-9890

Ethane-1,2-diaminium bis­­(4-carb­­oxy-2-propyl-1H-imidazole-5-carb­­oxy­ate) monohydrate

aInstitute of Environmental and Municipal Engineering, North China University of Water Conservancy and Electric Power, Zhengzhou 450011, People's Republic of China, and bHenan Museum, Zhengzhou 450001, People's Republic of China
*Correspondence e-mail: hbsymaning@163.com

(Received 14 May 2012; accepted 28 June 2012; online 4 July 2012)

In the title hydrated molecular salt, C2H10N22+·2C8H9N2O4·H2O, an intra­molecular O—H⋯O hydrogen bond occurs in the anion, forming an S(7) ring. The –CO2 and –CO2H groups make dihedral angles of 3.2 (2) and 2.0 (3)°, respectively, with the five-membered ring. In the crystal, N—H⋯O, N—H⋯N and O—H⋯O hydrogen bonds lead to the formation of a three-dimensional supra­molecular architecture. The methyl group in the anion is disordered over two sets of sites in a 0.716 (9):0.284 (9) ratio. The ethylenediamine cation is generated by symmetry and the water molecule lies on a twofold axis.

Related literature

For background to studies of supra­molecular structures of co-crystals containing organic acids and organic bases resulting from hydrogen bonding, see: Wang & Wei (2005[Wang, Z.-L. & Wei, L.-H. (2005). Acta Cryst. E61, o3129-o3130.]).

[Scheme 1]

Experimental

Crystal data
  • C2H10N22+·2C8H9N2O4·H2O

  • Mr = 474.48

  • Monoclinic, C 2/c

  • a = 15.234 (4) Å

  • b = 16.859 (4) Å

  • c = 9.699 (3) Å

  • β = 112.991 (5)°

  • V = 2293.1 (10) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.11 mm−1

  • T = 296 K

  • 0.36 × 0.28 × 0.16 mm

Data collection
  • Bruker SMART CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2001[Sheldrick, G. M. (2001). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.961, Tmax = 0.983

  • 5444 measured reflections

  • 2011 independent reflections

  • 1500 reflections with I > 2σ(I)

  • Rint = 0.032

Refinement
  • R[F2 > 2σ(F2)] = 0.060

  • wR(F2) = 0.182

  • S = 1.05

  • 2011 reflections

  • 169 parameters

  • 34 restraints

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.30 e Å−3

  • Δρmin = −0.45 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N2—H2A⋯O4i 0.86 1.92 2.759 (3) 166
N3—H3A⋯N1 0.89 2.03 2.921 (3) 176
N3—H3A⋯O1 0.89 2.54 2.964 (3) 110
N3—H3B⋯O1ii 0.89 1.94 2.792 (3) 160
N3—H3C⋯O1Wiii 0.89 2.08 2.917 (3) 157
O2—H2⋯O3 0.82 1.64 2.457 (3) 177
O1W—H1W⋯O3 0.85 (1) 1.96 (1) 2.795 (2) 169 (4)
Symmetry codes: (i) [-x+1, y, -z+{\script{1\over 2}}]; (ii) [-x, y, -z-{\script{1\over 2}}]; (iii) [-x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z].

Data collection: SMART (Bruker, 2001[Bruker (2001). SAINT-Plus and SMART. Bruker AXS, Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT-Plus (Bruker, 2001[Bruker (2001). SAINT-Plus and SMART. Bruker AXS, Inc., Madison, Wisconsin, USA.]); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]); software used to prepare material for publication: PLATON.

Supporting information


Comment top

Currently, many groups are studying the supramolecular structures of co-crystals containing organic acids and organic bases resulting from hydrogen bonding (Wang & Wei, 2005).

The asymmetric unit of the title complex, (I), is composed of two 2-propyl-1H-imidazole-4-carboxylic acid-5-carboxyate anions, one diprotonated ethylenediaminium cation and one water molecule in general positions (Fig. 1). The C–O bond distances range from 1.221 (3)to 1.289 (3) Å, in which the C1–O1 [1.223 (3) Å], C4–O4 [1.221 (3) Å] and C4–O3 [1.266 (3) Å] are typical for C=O double bonds, whereas the C1–O2 bond length of 1.289 (3) Å indicates a C–O single bond. The elongation of the C4=O3 double bond is affected by the intra-molecular O2—H2···O3 hydrogen bonding interaction. Thus, the 5-carboxyl group of 2-propyl-1H-imidazole-4,5-dicarboxy acid is deprotonated, which must be balanced in charge terms by the presence of half of the diprotonated ethylenediamine. Furthermore, the acidic environment is propitious to the protonation of ethylenediamine.

In the crystal structure, intra-molecular hydrogen bonds are present, with O2–H2 acting as a hydrogen bond donor, and O3 atom as a hydrogen bond acceptor, thereby constructing S(7) rings. In addition, the diprotonated ethylenediaminium cations and 2-propyl-1H-imidazole-4-carboxylic acid-5-carboxyate anions together with water molecules are further linked into a three-dimensional supramolecular framework by multiple N—H···O, N—H···N and O—H···O hydrogen bonds (Fig. 2 and Table 1).

Related literature top

For background to studies of supramolecular structures of co-crystals containing organic acids and organic bases resulting from hydrogen bonding, see: Wang & Wei (2005).

Experimental top

All reagents were commercially available and of analytical grade. The mixture of DyCl3.6H2O (0.189 g, 0.50 mmol), 2-propyl-1H-imidazole-4,5-dicarboxylic acid (0.197 g, 1.00 mmol), and ethylenediamine (1 ml) was dissolved in 50 ml H2O, and the mixture was stirred and heated to reflux at 80°C for two hours. The resulting solution was filtered, the filtrate was adjusted to pH = 7.5 using 4 M HCl solution, then was placed inside a programmable electric furnace at 130 °C for five days. After cooling the autoclave to room temperature, colorless block crystals of (I) were obtained.

Refinement top

H atoms were treated as riding, with C—H distances of 0.96 Å for methyl, 0.97 Å for methylene, N—H distances in the range of 0.96–0.89 Å and O—H distances of 0.82 Å for hydroxy group and 0.84 Å for water, and were refined as riding with Uiso(H)=1.2Ueq(Cmethylene, O2 and N) and Uiso(H)=1.5Ueq(O1W and (Cmethyl)).

Structure description top

Currently, many groups are studying the supramolecular structures of co-crystals containing organic acids and organic bases resulting from hydrogen bonding (Wang & Wei, 2005).

The asymmetric unit of the title complex, (I), is composed of two 2-propyl-1H-imidazole-4-carboxylic acid-5-carboxyate anions, one diprotonated ethylenediaminium cation and one water molecule in general positions (Fig. 1). The C–O bond distances range from 1.221 (3)to 1.289 (3) Å, in which the C1–O1 [1.223 (3) Å], C4–O4 [1.221 (3) Å] and C4–O3 [1.266 (3) Å] are typical for C=O double bonds, whereas the C1–O2 bond length of 1.289 (3) Å indicates a C–O single bond. The elongation of the C4=O3 double bond is affected by the intra-molecular O2—H2···O3 hydrogen bonding interaction. Thus, the 5-carboxyl group of 2-propyl-1H-imidazole-4,5-dicarboxy acid is deprotonated, which must be balanced in charge terms by the presence of half of the diprotonated ethylenediamine. Furthermore, the acidic environment is propitious to the protonation of ethylenediamine.

In the crystal structure, intra-molecular hydrogen bonds are present, with O2–H2 acting as a hydrogen bond donor, and O3 atom as a hydrogen bond acceptor, thereby constructing S(7) rings. In addition, the diprotonated ethylenediaminium cations and 2-propyl-1H-imidazole-4-carboxylic acid-5-carboxyate anions together with water molecules are further linked into a three-dimensional supramolecular framework by multiple N—H···O, N—H···N and O—H···O hydrogen bonds (Fig. 2 and Table 1).

For background to studies of supramolecular structures of co-crystals containing organic acids and organic bases resulting from hydrogen bonding, see: Wang & Wei (2005).

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT-Plus (Bruker, 2001); data reduction: SAINT-Plus (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), with displacement ellipsoids for the non-hydrogen atoms drawn at the 50% probability level.
[Figure 2] Fig. 2. Three-dimensional structure of (I), with H-bonds indicated by dashed lines. Displacement ellipsoids for the non-hydrogen atoms are drawn at the 50% probability level.
Ethane-1,2-diaminium bis(4-carboxy-2-propyl-1H-imidazole-5-carboxyate) monohydrate top
Crystal data top
C2H10N22+·2C8H9N2O4·H2OF(000) = 1008
Mr = 474.48Dx = 1.374 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 356 reflections
a = 15.234 (4) Åθ = 2.5–14.8°
b = 16.859 (4) ŵ = 0.11 mm1
c = 9.699 (3) ÅT = 296 K
β = 112.991 (5)°Block, colorless
V = 2293.1 (10) Å30.36 × 0.28 × 0.16 mm
Z = 4
Data collection top
Bruker SMART CCD area-detector
diffractometer
2011 independent reflections
Radiation source: fine-focus sealed tube1500 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.032
phi and ω scansθmax = 25.0°, θmin = 1.9°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)
h = 1817
Tmin = 0.961, Tmax = 0.983k = 1920
5444 measured reflectionsl = 118
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.060Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.182H atoms treated by a mixture of independent and constrained refinement
S = 1.05 w = 1/[σ2(Fo2) + (0.1098P)2 + 0.4118P]
where P = (Fo2 + 2Fc2)/3
2011 reflections(Δ/σ)max < 0.001
169 parametersΔρmax = 0.30 e Å3
34 restraintsΔρmin = 0.45 e Å3
Crystal data top
C2H10N22+·2C8H9N2O4·H2OV = 2293.1 (10) Å3
Mr = 474.48Z = 4
Monoclinic, C2/cMo Kα radiation
a = 15.234 (4) ŵ = 0.11 mm1
b = 16.859 (4) ÅT = 296 K
c = 9.699 (3) Å0.36 × 0.28 × 0.16 mm
β = 112.991 (5)°
Data collection top
Bruker SMART CCD area-detector
diffractometer
2011 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)
1500 reflections with I > 2σ(I)
Tmin = 0.961, Tmax = 0.983Rint = 0.032
5444 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.06034 restraints
wR(F2) = 0.182H atoms treated by a mixture of independent and constrained refinement
S = 1.05Δρmax = 0.30 e Å3
2011 reflectionsΔρmin = 0.45 e Å3
169 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*/UeqOcc. (<1)
N10.21377 (15)0.37000 (13)0.0929 (2)0.0456 (6)
N20.35960 (14)0.32244 (13)0.1911 (2)0.0433 (6)
H2A0.41250.30570.25780.052*
N30.00885 (15)0.38982 (11)0.0087 (2)0.0402 (5)
H3A0.07120.38590.03130.048*
H3B0.02290.38080.08870.048*
H3C0.00830.35420.06130.048*
O10.10537 (13)0.39974 (12)0.2035 (2)0.0555 (6)
O20.21678 (14)0.35742 (13)0.2760 (2)0.0566 (6)
H20.27140.34040.23720.068*
O30.37886 (14)0.30257 (13)0.1635 (2)0.0578 (6)
O40.48440 (12)0.27422 (11)0.0614 (2)0.0509 (5)
O1W0.50000.20888 (16)0.25000.0544 (7)
H1W0.460 (2)0.2394 (18)0.236 (4)0.082*
C10.18526 (18)0.37268 (15)0.1732 (3)0.0420 (6)
C20.24741 (17)0.35651 (13)0.0175 (3)0.0381 (6)
C30.33827 (17)0.32705 (13)0.0420 (3)0.0383 (6)
C40.40669 (18)0.29940 (14)0.0224 (3)0.0427 (6)
C50.28372 (19)0.34863 (17)0.2174 (3)0.0483 (7)
C60.2826 (3)0.3534 (2)0.3692 (4)0.0794 (11)
H6A0.22210.33240.36380.095*
H6B0.33210.31850.43430.095*
C70.2958 (4)0.4296 (3)0.4395 (5)0.1099 (14)
H7A0.25000.46710.37430.132*0.716 (9)
H7B0.28630.42610.53250.132*0.716 (9)
H7C0.23450.44510.43990.132*0.284 (9)
H7D0.30650.46420.36760.132*0.284 (9)
C80.3826 (5)0.4534 (3)0.4659 (8)0.095 (2)0.716 (9)
H8A0.39690.44360.37940.142*0.716 (9)
H8B0.42680.42480.55000.142*0.716 (9)
H8C0.38790.50910.48770.142*0.716 (9)
C8'0.3712 (10)0.4585 (7)0.5926 (14)0.074 (4)0.284 (9)
H8'A0.40970.49940.57560.111*0.284 (9)
H8'B0.41100.41470.64350.111*0.284 (9)
H8'C0.33930.47910.65290.111*0.284 (9)
C90.0132 (2)0.46962 (15)0.0454 (3)0.0439 (6)
H9A0.02190.47980.15130.053*
H9B0.08070.47350.02450.053*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0374 (12)0.0566 (13)0.0414 (12)0.0062 (10)0.0139 (10)0.0008 (10)
N20.0337 (11)0.0519 (12)0.0387 (12)0.0060 (9)0.0081 (9)0.0002 (9)
N30.0384 (12)0.0418 (12)0.0415 (12)0.0015 (9)0.0168 (9)0.0007 (8)
O10.0392 (11)0.0788 (13)0.0444 (11)0.0144 (9)0.0120 (8)0.0084 (9)
O20.0443 (11)0.0833 (14)0.0414 (11)0.0144 (10)0.0160 (9)0.0085 (9)
O30.0480 (11)0.0825 (15)0.0470 (12)0.0123 (10)0.0230 (9)0.0021 (9)
O40.0334 (10)0.0600 (11)0.0520 (12)0.0067 (8)0.0088 (8)0.0088 (8)
O1W0.0606 (19)0.0557 (17)0.0575 (17)0.0000.0347 (15)0.000
C10.0373 (14)0.0487 (14)0.0387 (14)0.0001 (11)0.0134 (11)0.0057 (10)
C20.0347 (13)0.0398 (13)0.0390 (14)0.0000 (10)0.0135 (11)0.0001 (10)
C30.0362 (13)0.0375 (12)0.0401 (13)0.0014 (10)0.0137 (11)0.0004 (10)
C40.0388 (15)0.0417 (13)0.0482 (16)0.0007 (11)0.0176 (12)0.0028 (11)
C50.0401 (14)0.0608 (16)0.0419 (15)0.0049 (12)0.0138 (12)0.0007 (12)
C60.070 (2)0.121 (3)0.0458 (18)0.025 (2)0.0207 (16)0.0054 (18)
C70.118 (3)0.114 (3)0.086 (3)0.023 (3)0.027 (3)0.003 (2)
C80.130 (4)0.069 (3)0.109 (5)0.012 (3)0.073 (4)0.005 (3)
C8'0.108 (9)0.052 (6)0.061 (7)0.002 (6)0.030 (6)0.002 (5)
C90.0491 (15)0.0442 (14)0.0442 (14)0.0007 (11)0.0245 (12)0.0034 (10)
Geometric parameters (Å, º) top
N1—C51.311 (3)C6—C71.433 (6)
N1—C21.375 (3)C6—H6A0.9700
N2—C51.351 (3)C6—H6B0.9700
N2—C31.355 (3)C7—C81.309 (7)
N2—H2A0.8600C7—C8'1.558 (13)
N3—C91.464 (3)C7—H7A0.9700
N3—H3A0.8900C7—H7B0.9700
N3—H3B0.8900C7—H7C0.9699
N3—H3C0.8900C7—H7D0.9698
O1—C11.223 (3)C8—H7D1.1934
O2—C11.289 (3)C8—H8A0.9600
O2—H20.8200C8—H8B0.9600
O3—C41.266 (3)C8—H8C0.9600
O4—C41.221 (3)C8'—H8'A0.9600
O1W—H1W0.849 (10)C8'—H8'B0.9600
C1—C21.461 (4)C8'—H8'C0.9600
C2—C31.368 (3)C9—C9i1.505 (5)
C3—C41.484 (4)C9—H9A0.9700
C5—C61.481 (4)C9—H9B0.9700
C5—N1—C2104.8 (2)C6—C7—H7A110.1
C5—N2—C3108.4 (2)C8'—C7—H7A119.5
C5—N2—H2A125.8C8—C7—H7B110.1
C3—N2—H2A125.8C6—C7—H7B110.1
C9—N3—H3A109.5C8'—C7—H7B57.0
C9—N3—H3B109.5H7A—C7—H7B108.4
H3A—N3—H3B109.5C8—C7—H7C144.9
C9—N3—H3C109.5C6—C7—H7C106.7
H3A—N3—H3C109.5C8'—C7—H7C105.3
H3B—N3—H3C109.5H7A—C7—H7C51.7
C1—O2—H2109.5H7B—C7—H7C61.3
O1—C1—O2121.7 (2)C8—C7—H7D61.0
O1—C1—C2120.0 (2)C6—C7—H7D103.2
O2—C1—C2118.4 (2)C8'—C7—H7D103.3
C3—C2—N1110.8 (2)H7A—C7—H7D54.6
C3—C2—C1130.1 (2)H7B—C7—H7D146.5
N1—C2—C1119.1 (2)H7C—C7—H7D105.9
N2—C3—C2104.6 (2)C7—C8—H7D45.3
N2—C3—C4121.1 (2)C7—C8—H8A109.5
C2—C3—C4134.3 (2)H7D—C8—H8A79.0
O4—C4—O3124.2 (2)C7—C8—H8B109.5
O4—C4—C3119.2 (2)H7D—C8—H8B153.6
O3—C4—C3116.6 (2)C7—C8—H8C109.5
N1—C5—N2111.3 (2)H7D—C8—H8C89.9
N1—C5—C6125.5 (3)C7—C8'—H8'A109.5
N2—C5—C6123.2 (3)C7—C8'—H8'B109.5
C7—C6—C5117.9 (4)H8'A—C8'—H8'B109.5
C7—C6—H6A107.8C7—C8'—H8'C109.5
C5—C6—H6A107.8H8'A—C8'—H8'C109.5
C7—C6—H6B107.8H8'B—C8'—H8'C109.5
C5—C6—H6B107.8N3—C9—C9i110.1 (2)
H6A—C6—H6B107.2N3—C9—H9A109.6
C8—C7—C6108.1 (5)C9i—C9—H9A109.6
C8—C7—C8'53.5 (6)N3—C9—H9B109.6
C6—C7—C8'130.3 (6)C9i—C9—H9B109.6
C8—C7—H7A110.1H9A—C9—H9B108.2
Symmetry code: (i) x, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H2A···O4ii0.861.922.759 (3)166
N3—H3A···N10.892.032.921 (3)176
N3—H3A···O10.892.542.964 (3)110
N3—H3B···O1iii0.891.942.792 (3)160
N3—H3C···O1Wiv0.892.082.917 (3)157
O2—H2···O30.821.642.457 (3)177
O1W—H1W···O30.85 (1)1.96 (1)2.795 (2)169 (4)
Symmetry codes: (ii) x+1, y, z+1/2; (iii) x, y, z1/2; (iv) x+1/2, y+1/2, z.

Experimental details

Crystal data
Chemical formulaC2H10N22+·2C8H9N2O4·H2O
Mr474.48
Crystal system, space groupMonoclinic, C2/c
Temperature (K)296
a, b, c (Å)15.234 (4), 16.859 (4), 9.699 (3)
β (°) 112.991 (5)
V3)2293.1 (10)
Z4
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.36 × 0.28 × 0.16
Data collection
DiffractometerBruker SMART CCD area-detector
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2001)
Tmin, Tmax0.961, 0.983
No. of measured, independent and
observed [I > 2σ(I)] reflections
5444, 2011, 1500
Rint0.032
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.060, 0.182, 1.05
No. of reflections2011
No. of parameters169
No. of restraints34
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.30, 0.45

Computer programs: SMART (Bruker, 2001), SAINT-Plus (Bruker, 2001), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H2A···O4i0.861.922.759 (3)166.2
N3—H3A···N10.892.032.921 (3)175.7
N3—H3A···O10.892.542.964 (3)110.2
N3—H3B···O1ii0.891.942.792 (3)159.6
N3—H3C···O1Wiii0.892.082.917 (3)156.8
O2—H2···O30.821.642.457 (3)177.4
O1W—H1W···O30.849 (10)1.957 (13)2.795 (2)169 (4)
Symmetry codes: (i) x+1, y, z+1/2; (ii) x, y, z1/2; (iii) x+1/2, y+1/2, z.
 

Acknowledgements

This work was supported financially by the North China University of Water Conservancy and Electric Power, China.

References

First citationBruker (2001). SAINT-Plus and SMART. Bruker AXS, Inc., Madison, Wisconsin, USA.  Google Scholar
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First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationSpek, A. L. (2009). Acta Cryst. D65, 148–155.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationWang, Z.-L. & Wei, L.-H. (2005). Acta Cryst. E61, o3129–o3130.  Web of Science CSD CrossRef IUCr Journals Google Scholar

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