organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890

2-(4-Methyl-2-phenyl­piperazin-4-ium-1-yl)pyridine-3-carboxyl­ate dihydrate

aCollege of Chemical and Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, People's Republic of China, bDepartment of Chemical and Environmental Engineering, Hebei Chemical and Pharmaceutical College, Shijiazhuang 050026, People's Republic of China, and cSchool of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China
*Correspondence e-mail: liaj@yeah.net

(Received 11 January 2008; accepted 21 April 2008; online 7 June 2008)

The title compound, C17H19N3O2·2H2O, is particularly useful in the preparation of mirtaza­pine, which is the active agent in a new class of anti­depressants. It crystallized as a zwitterion with two mol­ecules of water in the asymmetric unit. The crystal structure is dominated by a system of hydrogen bonds involving the positively charged N atom and both water mol­ecules.

Related literature

For details of the synthesis see: Eiichi et al. (2002a[Eiichi, I. & Kanami, Y. (2002a). US patent 6 376 668.],b[Eiichi, I. & Kanami, Y. (2002b). US patent 6 437 120.]); Metzger et al. (2004[Metzger, L.. & Wizel, S. (2004). US patent 6 774 230.]). For related literature, see: Singer et al. (2004[Singer, C., Liberman, A. & Finkelstein, N. (2004). US patent 20 040 176 591.]).

[Scheme 1]

Experimental

Crystal data
  • C17H19N3O2·2H2O

  • Mr = 333.38

  • Monoclinic, P 21 /n

  • a = 12.730 (7) Å

  • b = 8.157 (4) Å

  • c = 16.814 (9) Å

  • β = 94.031 (10)°

  • V = 1741.6 (16) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.09 mm−1

  • T = 294 (2) K

  • 0.24 × 0.20 × 0.18 mm

Data collection
  • Bruker SMART CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Bruker, 2002[Bruker (2002). SADABS, SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.978, Tmax = 0.984

  • 9611 measured reflections

  • 3550 independent reflections

  • 2039 reflections with I > 2σ(I)

  • Rint = 0.051

Refinement
  • R[F2 > 2σ(F2)] = 0.043

  • wR(F2) = 0.117

  • S = 1.00

  • 3550 reflections

  • 218 parameters

  • 7 restraints

  • H-atom parameters constrained

  • Δρmax = 0.18 e Å−3

  • Δρmin = −0.20 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N3—H3A⋯O1i 0.91 1.77 2.681 (2) 178
O3—H3C⋯O4ii 0.87 1.92 2.781 (3) 179
O4—H4A⋯O2iii 0.85 1.94 2.761 (2) 162
O3—H3B⋯O1 0.87 2.21 3.038 (3) 161
O4—H4B⋯N1 0.85 2.23 3.037 (3) 159
Symmetry codes: (i) [-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]; (ii) [-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]; (iii) x, y+1, z.

Data collection: SMART (Bruker, 2002[Bruker (2002). SADABS, SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2002[Bruker (2002). SADABS, SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; 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: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

The title compound, C17H19N3O2.2H2O, is particularly useful in the preparation of mirtazapine which is the active agent in a new class of antidepressants. It crystallized as a zwitterion with two molecues of water in the asymmetric unit (Fig 1). The central piperazine ring has a normal chair conformation. In the molecule, the dihedral angle is 81.20 between plane 1(C7 C8 C9 C10) and plane 2(C11 C12 C13 C14 C15 C16), the dihedral angle is 68.40 between plane 2(C11 C12 C13 C14 C15 C16) and plane 3(N1 C2 C3 C4 C5 C6)and the the dihedral angle is 36.90 between plane 1 and plane 3. Packing is dominated by a system of hydrogen bonds involving the positively charged nitrogen and both water molecules (Table 1, Fig. 2)

Related literature top

For details of the synthesis see: Eiichi et al. (2002a,b); Metzger et al. (2004). For related literature, see: Singer et al. (2004).

Experimental top

To 162 g of 1-butanol were added 2-(4-methyl-2-phenylpiperazine-1-yl)pyridine-3-carbonitrile(54 g, 0.2 mol) and 60.93 g of potassium hydroxide. The mixture was heated to 125 - 135 centigrade degree. (Eiichi, et al., 2002a; Eiichi, et al., 2002b; Metzger, et al., 2004) After 7 h, the reaction mixture was cooled and the butanol removed from the mixture by vacuum distilation after which fresh water and toluene were added and the two phases were separated. The water solution was neutralized with hydrochloric acid to pH=6.5–7. The water was evaporated and toluene was added. The inorganic salt were filtered and toluene solution was evaporated to dryness. Yield:52 g(90%). (Singer et al., 2004) Colourless crystals suitable for X-ray analysis were obtained by slow evaporation of an methanol-toluene solution at room temperature over 30 days.

Refinement top

All H atoms were positioned geometrically and refined as riding, with C—H = 0.93–0.98 Å and N—H=0.949 Å Uiso(H) = 1.2 Ueq(C).

Computing details top

Data collection: SMART (Bruker, 2002); cell refinement: SMART (Bruker, 2002); data reduction: SAINT (Bruker, 2002); 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
[Figure 1] Fig. 1. The molecular structure of the title compound, drawn with 30% probability ellipsoids.
[Figure 2] Fig. 2. The crystal structure of (I), viewed along a axis
2-(4-Methyl-2-phenylpiperazin-4-ium-1-yl)pyridine-3-carboxylate dihydrate top
Crystal data top
C17H19N3O2·2H2OF(000) = 712
Mr = 333.38Dx = 1.271 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
a = 12.730 (7) ÅCell parameters from 1949 reflections
b = 8.157 (4) Åθ = 3.0–22.9°
c = 16.814 (9) ŵ = 0.09 mm1
β = 94.031 (10)°T = 294 K
V = 1741.6 (16) Å3Block, colorless
Z = 40.24 × 0.20 × 0.18 mm
Data collection top
Bruker SMART CCD area-detector
diffractometer
3550 independent reflections
Radiation source: fine-focus sealed tube2039 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.051
ϕ and ω scansθmax = 26.5°, θmin = 1.9°
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
h = 1415
Tmin = 0.978, Tmax = 0.984k = 109
9611 measured reflectionsl = 2118
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)] = 0.044Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.117H-atom parameters constrained
S = 1.00 w = 1/[σ2(Fo2) + (0.0459P)2 + 0.2854P]
where P = (Fo2 + 2Fc2)/3
3550 reflections(Δ/σ)max = 0.001
218 parametersΔρmax = 0.18 e Å3
7 restraintsΔρmin = 0.20 e Å3
Crystal data top
C17H19N3O2·2H2OV = 1741.6 (16) Å3
Mr = 333.38Z = 4
Monoclinic, P21/nMo Kα radiation
a = 12.730 (7) ŵ = 0.09 mm1
b = 8.157 (4) ÅT = 294 K
c = 16.814 (9) Å0.24 × 0.20 × 0.18 mm
β = 94.031 (10)°
Data collection top
Bruker SMART CCD area-detector
diffractometer
3550 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
2039 reflections with I > 2σ(I)
Tmin = 0.978, Tmax = 0.984Rint = 0.051
9611 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0447 restraints
wR(F2) = 0.117H-atom parameters constrained
S = 1.00Δρmax = 0.18 e Å3
3550 reflectionsΔρmin = 0.20 e Å3
218 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
O10.23746 (11)0.07865 (17)0.91677 (8)0.0468 (4)
O20.09369 (12)0.19110 (17)0.85735 (9)0.0523 (4)
N10.01524 (12)0.33067 (19)0.81432 (9)0.0336 (4)
N20.09094 (11)0.12896 (18)0.73567 (8)0.0276 (4)
N30.18394 (12)0.11644 (19)0.58307 (8)0.0317 (4)
H3A0.21100.22030.58470.038*
C10.14487 (17)0.0721 (2)0.88370 (10)0.0326 (5)
C20.09270 (14)0.0949 (2)0.88117 (10)0.0284 (4)
C30.06312 (16)0.1573 (2)0.95305 (11)0.0377 (5)
H30.08160.10151.00020.045*
C40.00669 (17)0.3009 (3)0.95524 (12)0.0433 (5)
H40.01560.34111.00300.052*
C50.01572 (17)0.3828 (3)0.88490 (12)0.0412 (5)
H50.05430.47950.88600.049*
C60.06542 (14)0.1873 (2)0.81196 (10)0.0276 (4)
C70.20574 (14)0.1119 (2)0.72897 (10)0.0322 (5)
H7A0.23620.05150.77460.039*
H7B0.23770.21980.72960.039*
C80.23032 (16)0.0240 (2)0.65354 (10)0.0345 (5)
H8A0.30600.01550.65090.041*
H8B0.20130.08600.65350.041*
C90.06793 (15)0.1316 (2)0.58939 (10)0.0333 (5)
H9A0.03670.02310.58800.040*
H9B0.03750.19240.54390.040*
C100.04152 (14)0.2186 (2)0.66603 (10)0.0278 (4)
H100.07020.33000.66580.033*
C110.07784 (15)0.2284 (2)0.66480 (10)0.0302 (5)
C120.12829 (16)0.3603 (3)0.62727 (11)0.0396 (5)
H120.08870.44090.60420.048*
C130.23716 (18)0.3743 (3)0.62352 (13)0.0502 (6)
H130.26990.46380.59810.060*
C140.29645 (18)0.2561 (3)0.65735 (13)0.0530 (6)
H140.36930.26600.65560.064*
C150.24739 (17)0.1225 (3)0.69391 (13)0.0530 (6)
H150.28750.04180.71640.064*
C160.13856 (16)0.1075 (3)0.69733 (11)0.0419 (5)
H160.10620.01620.72150.050*
C170.20966 (18)0.0401 (3)0.50601 (11)0.0486 (6)
H17A0.18180.06930.50280.073*
H17B0.28470.03640.50330.073*
H17C0.17900.10400.46240.073*
O30.40776 (15)0.1829 (2)0.92970 (9)0.0746 (5)
H3B0.36150.10800.93850.112*
H3C0.43100.17360.88270.112*
O40.01683 (14)0.6489 (2)0.72071 (9)0.0695 (5)
H4A0.03910.71720.75630.104*
H4B0.00950.55000.73530.104*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0447 (10)0.0401 (9)0.0542 (9)0.0108 (7)0.0058 (7)0.0023 (7)
O20.0587 (11)0.0337 (9)0.0632 (10)0.0008 (8)0.0061 (8)0.0103 (8)
N10.0378 (10)0.0320 (10)0.0306 (9)0.0057 (8)0.0001 (7)0.0031 (7)
N20.0271 (9)0.0327 (9)0.0230 (8)0.0018 (7)0.0017 (6)0.0002 (7)
N30.0354 (10)0.0322 (9)0.0282 (8)0.0069 (7)0.0073 (7)0.0036 (7)
C10.0419 (13)0.0324 (12)0.0242 (10)0.0035 (10)0.0065 (9)0.0006 (9)
C20.0286 (11)0.0301 (11)0.0264 (10)0.0013 (8)0.0006 (8)0.0015 (8)
C30.0480 (13)0.0394 (12)0.0258 (10)0.0048 (10)0.0033 (9)0.0010 (9)
C40.0550 (15)0.0448 (13)0.0307 (11)0.0100 (11)0.0075 (10)0.0093 (10)
C50.0489 (14)0.0374 (12)0.0373 (12)0.0131 (10)0.0026 (10)0.0088 (10)
C60.0261 (10)0.0290 (11)0.0275 (10)0.0016 (9)0.0000 (8)0.0032 (8)
C70.0297 (11)0.0376 (12)0.0294 (10)0.0010 (9)0.0037 (8)0.0016 (9)
C80.0356 (12)0.0325 (11)0.0359 (11)0.0026 (9)0.0066 (9)0.0000 (9)
C90.0321 (11)0.0389 (12)0.0288 (10)0.0060 (9)0.0027 (8)0.0013 (9)
C100.0297 (11)0.0288 (10)0.0248 (10)0.0026 (8)0.0009 (8)0.0010 (8)
C110.0313 (12)0.0376 (12)0.0215 (9)0.0016 (9)0.0004 (8)0.0035 (9)
C120.0370 (13)0.0410 (12)0.0401 (12)0.0013 (10)0.0026 (9)0.0009 (10)
C130.0420 (14)0.0486 (14)0.0579 (14)0.0055 (11)0.0114 (11)0.0019 (12)
C140.0327 (13)0.0750 (18)0.0506 (14)0.0020 (13)0.0014 (11)0.0101 (13)
C150.0366 (14)0.0773 (18)0.0455 (13)0.0175 (13)0.0051 (10)0.0070 (13)
C160.0383 (13)0.0498 (14)0.0373 (12)0.0060 (11)0.0002 (9)0.0063 (10)
C170.0517 (14)0.0610 (15)0.0350 (12)0.0073 (12)0.0166 (10)0.0150 (11)
O30.1035 (15)0.0632 (12)0.0586 (10)0.0064 (11)0.0167 (9)0.0125 (9)
O40.0919 (14)0.0659 (11)0.0516 (10)0.0169 (10)0.0098 (9)0.0118 (9)
Geometric parameters (Å, º) top
O1—C11.269 (2)C9—C101.529 (2)
O2—C11.234 (2)C9—H9A0.9700
N1—C61.335 (2)C9—H9B0.9700
N1—C51.346 (2)C10—C111.520 (3)
N2—C61.427 (2)C10—H100.9800
N2—C71.480 (2)C11—C121.382 (3)
N2—C101.482 (2)C11—C161.389 (3)
N3—C81.491 (2)C12—C131.388 (3)
N3—C91.493 (2)C12—H120.9300
N3—C171.495 (2)C13—C141.373 (3)
N3—H3A0.9140C13—H130.9300
C1—C21.514 (3)C14—C151.379 (3)
C2—C31.388 (2)C14—H140.9300
C2—C61.409 (2)C15—C161.388 (3)
C3—C41.376 (3)C15—H150.9300
C3—H30.9300C16—H160.9300
C4—C51.371 (3)C17—H17A0.9600
C4—H40.9300C17—H17B0.9600
C5—H50.9300C17—H17C0.9600
C7—C81.509 (2)O3—H3B0.8682
C7—H7A0.9700O3—H3C0.8664
C7—H7B0.9700O4—H4A0.8512
C8—H8A0.9700O4—H4B0.8504
C8—H8B0.9700
C6—N1—C5118.28 (16)H8A—C8—H8B108.2
C6—N2—C7112.85 (13)N3—C9—C10112.07 (14)
C6—N2—C10115.78 (14)N3—C9—H9A109.2
C7—N2—C10110.66 (13)C10—C9—H9A109.2
C8—N3—C9108.89 (14)N3—C9—H9B109.2
C8—N3—C17112.30 (16)C10—C9—H9B109.2
C9—N3—C17111.98 (14)H9A—C9—H9B107.9
C8—N3—H3A108.5N2—C10—C11113.90 (14)
C9—N3—H3A107.1N2—C10—C9109.32 (15)
C17—N3—H3A107.9C11—C10—C9106.98 (14)
O2—C1—O1125.09 (19)N2—C10—H10108.8
O2—C1—C2118.56 (18)C11—C10—H10108.8
O1—C1—C2116.26 (18)C9—C10—H10108.8
C3—C2—C6117.18 (17)C12—C11—C16118.62 (19)
C3—C2—C1116.78 (16)C12—C11—C10118.64 (17)
C6—C2—C1125.90 (16)C16—C11—C10122.70 (18)
C4—C3—C2120.64 (18)C11—C12—C13121.0 (2)
C4—C3—H3119.7C11—C12—H12119.5
C2—C3—H3119.7C13—C12—H12119.5
C5—C4—C3118.00 (18)C14—C13—C12120.0 (2)
C5—C4—H4121.0C14—C13—H13120.0
C3—C4—H4121.0C12—C13—H13120.0
N1—C5—C4123.40 (19)C13—C14—C15119.7 (2)
N1—C5—H5118.3C13—C14—H14120.2
C4—C5—H5118.3C15—C14—H14120.2
N1—C6—C2122.34 (16)C14—C15—C16120.5 (2)
N1—C6—N2117.30 (15)C14—C15—H15119.8
C2—C6—N2120.36 (16)C16—C15—H15119.8
N2—C7—C8111.90 (14)C15—C16—C11120.2 (2)
N2—C7—H7A109.2C15—C16—H16119.9
C8—C7—H7A109.2C11—C16—H16119.9
N2—C7—H7B109.2N3—C17—H17A109.5
C8—C7—H7B109.2N3—C17—H17B109.5
H7A—C7—H7B107.9H17A—C17—H17B109.5
N3—C8—C7109.50 (16)N3—C17—H17C109.5
N3—C8—H8A109.8H17A—C17—H17C109.5
C7—C8—H8A109.8H17B—C17—H17C109.5
N3—C8—H8B109.8H3B—O3—H3C111.9
C7—C8—H8B109.8H4A—O4—H4B117.0
O2—C1—C2—C3106.1 (2)C17—N3—C8—C7177.34 (15)
O1—C1—C2—C370.7 (2)N2—C7—C8—N359.1 (2)
O2—C1—C2—C669.5 (3)C8—N3—C9—C1058.5 (2)
O1—C1—C2—C6113.8 (2)C17—N3—C9—C10176.74 (16)
C6—C2—C3—C42.0 (3)C6—N2—C10—C1155.0 (2)
C1—C2—C3—C4174.01 (19)C7—N2—C10—C11175.00 (15)
C2—C3—C4—C52.4 (3)C6—N2—C10—C9174.59 (14)
C6—N1—C5—C43.7 (3)C7—N2—C10—C955.40 (18)
C3—C4—C5—N10.5 (3)N3—C9—C10—N257.03 (19)
C5—N1—C6—C24.1 (3)N3—C9—C10—C11179.19 (15)
C5—N1—C6—N2175.71 (16)N2—C10—C11—C12151.89 (16)
C3—C2—C6—N11.4 (3)C9—C10—C11—C1287.2 (2)
C1—C2—C6—N1176.95 (18)N2—C10—C11—C1630.5 (2)
C3—C2—C6—N2178.48 (16)C9—C10—C11—C1690.4 (2)
C1—C2—C6—N22.9 (3)C16—C11—C12—C131.4 (3)
C7—N2—C6—N1117.95 (18)C10—C11—C12—C13179.18 (17)
C10—N2—C6—N111.0 (2)C11—C12—C13—C140.0 (3)
C7—N2—C6—C262.2 (2)C12—C13—C14—C151.0 (3)
C10—N2—C6—C2168.87 (15)C13—C14—C15—C160.6 (3)
C6—N2—C7—C8170.43 (15)C14—C15—C16—C110.8 (3)
C10—N2—C7—C858.0 (2)C12—C11—C16—C151.8 (3)
C9—N3—C8—C758.05 (19)C10—C11—C16—C15179.48 (18)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H3A···O1i0.911.772.681 (2)178
O3—H3C···O4ii0.871.922.781 (3)179
O4—H4A···O2iii0.851.942.761 (2)162
O3—H3B···O10.872.213.038 (3)161
O4—H4B···N10.852.233.037 (3)159
Symmetry codes: (i) x+1/2, y+1/2, z+3/2; (ii) x+1/2, y1/2, z+3/2; (iii) x, y+1, z.

Experimental details

Crystal data
Chemical formulaC17H19N3O2·2H2O
Mr333.38
Crystal system, space groupMonoclinic, P21/n
Temperature (K)294
a, b, c (Å)12.730 (7), 8.157 (4), 16.814 (9)
β (°) 94.031 (10)
V3)1741.6 (16)
Z4
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.24 × 0.20 × 0.18
Data collection
DiffractometerBruker SMART CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2002)
Tmin, Tmax0.978, 0.984
No. of measured, independent and
observed [I > 2σ(I)] reflections
9611, 3550, 2039
Rint0.051
(sin θ/λ)max1)0.627
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.044, 0.117, 1.00
No. of reflections3550
No. of parameters218
No. of restraints7
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.18, 0.20

Computer programs: SMART (Bruker, 2002), SAINT (Bruker, 2002), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H3A···O1i0.911.772.681 (2)177.5
O3—H3C···O4ii0.871.922.781 (3)178.9
O4—H4A···O2iii0.851.942.761 (2)161.7
O3—H3B···O10.872.213.038 (3)160.7
O4—H4B···N10.852.233.037 (3)159.3
Symmetry codes: (i) x+1/2, y+1/2, z+3/2; (ii) x+1/2, y1/2, z+3/2; (iii) x, y+1, z.
 

References

First citationBruker (2002). SADABS, SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
First citationEiichi, I. & Kanami, Y. (2002a). US patent 6 376 668.  Google Scholar
First citationEiichi, I. & Kanami, Y. (2002b). US patent 6 437 120.  Google Scholar
First citationMetzger, L.. & Wizel, S. (2004). US patent 6 774 230.  Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationSinger, C., Liberman, A. & Finkelstein, N. (2004). US patent 20 040 176 591.  Google Scholar

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