PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
Logo of actaeInternational Union of Crystallographysearchopen accessarticle submissionjournal home pagethis article
 
Acta Crystallogr Sect E Struct Rep Online. 2009 April 1; 65(Pt 4): o885.
Published online 2009 March 28. doi:  10.1107/S1600536809010393
PMCID: PMC2968964

1-Methyl-3,5-bis­[(E)-(3-methyl-2-thienyl)methyl­ene]piperidin-4-one monohydrate

Abstract

In the title mol­ecule, C18H19NOS2·H2O, the piperidine ring adopts an envelope conformation with the methyl substituent in an equatorial position. Each of the olefinic double bonds has an E configuration. The dihedral angle between the two thio­phene rings is 6.04 (14)°. The water mol­ecule forms two donor inter­actions, one with the carbonyl O atom and the other to the hetero N atom. The centrosymmetric {C18H19NOS2·H2O}2 pairs thus formed are linked into a supra­molecular chain via C—H(...)Owater contacts.

Related literature

For piperidine-4-ones as anti­mycobacterial agents, see: Jha & Dimmock (2006 [triangle]). For their cytotoxic properties, see: Das et al. (2007 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-65-0o885-scheme1.jpg

Experimental

Crystal data

  • C18H19NOS2·H2O
  • M r = 347.50
  • Triclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-0o885-efi1.jpg
  • a = 7.5781 (7) Å
  • b = 10.9926 (9) Å
  • c = 11.5304 (10) Å
  • α = 79.531 (2)°
  • β = 83.404 (2)°
  • γ = 71.673 (2)°
  • V = 894.90 (14) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 0.31 mm−1
  • T = 293 K
  • 0.36 × 0.22 × 0.22 mm

Data collection

  • Bruker Kappa APEXII CCD diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker, 2004 [triangle]) T min = 0.901, T max = 0.938
  • 15827 measured reflections
  • 3127 independent reflections
  • 2686 reflections with I > 2σ(I)
  • R int = 0.021

Refinement

  • R[F 2 > 2σ(F 2)] = 0.043
  • wR(F 2) = 0.130
  • S = 1.11
  • 3127 reflections
  • 217 parameters
  • 3 restraints
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.44 e Å−3
  • Δρmin = −0.31 e Å−3

Data collection: APEX2 (Bruker, 2004 [triangle]); cell refinement: SAINT-NT (Bruker, 2004 [triangle]); data reduction: SAINT-NT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: ORTEP-3 (Farrugia, 1997 [triangle]); software used to prepare material for publication: PLATON (Spek, 2009 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809010393/tk2393sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809010393/tk2393Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

The authors are grateful to Dr A. Babu Vargheese, Sophisticated Analytical Instrument Facility (SAIF), IIT-Madras, Chennai, for the X-ray data collection.

supplementary crystallographic information

Comment

1-N-(Arylmaleamoyl)-3,5-bis(phenylmethylene)piperidin-4-ones (Jha & Dimmock, 2006) have been proved as antimycobacterial agents. The cytotoxic properties of 3,5 bis(arylidene)piperidin-4-ones (Das et al., 2007) have also been reported. Due to the above importance, the crystal structure of the title compound (I) has been determined by X-ray diffraction.

The piperidine ring in (I), Fig. 1, adopts an envelope conformation with the methyl substituent in an equatorial position. The sum of the bond angles around N1 [330.9 (2)°] indicates a pyramidal geometry. The N1 atom deviates by -0.645 (3) Å from the least-squares plane passing through atoms C2—C6 . Both olefinic double bonds have an E-configuration. The thiophene rings are co-planar with the adjacent olefinic double bonds and the planar portion of piperidone ring. The dihedral angle between the two thiophene rings is 6.04 (14)°. The molecular conformation is stabilized by weak C—H···O and C—H···S contacts, Table 1. The water molecules forms two O—H donor interactions, one with the carbonyl-O atom and other to the amine-N atom, Table 1. These hydrogen bonds result in the formation of a centrosymmetric {C18H19NOS2.H2O}2 pair, and these are linked into supramolecular chains via C35-H···O contacts, Table 1. Additional stabilisation to the crystal strucutre is afforded by C-H···O and C-H···π contacts, as detailed in Table 1 and illustrated in Fig. 2.

Experimental

To a mixture of N-methylpiperidin-4-one (1.5 ml, 0.01 mol) and 3-methylthiophene-2-aldehyde (2.7 ml, 0.02 mol) in ethanol (95%, 10 ml), sodium hydroxide (20%, 5 ml) was added. The solution was heated on a waterbath for 30 mins. The solid that separated on cooling was filtered and was recrystallized from 95% ethanol in a yield of 2.5 g (80%).

Refinement

The water-H atoms, H1A and H1B, were located in a difference density Fourier map and included in the refinement with the O—H distances restrained to be 0.86±0.01 Å, with the H···H distance restrained to 1.373 Å, and with Uiso(H) = 1.5 times Ueq(O). The remaining H atoms were positioned geometrically and allowed to ride on their parent atoms with C—H = 0.93 - 0.97 Å, and with Uiso(H) = 1.2 - 1.5 times Ueq(C).

Figures

Fig. 1.
The molecular structure of (I), showing the atom-numbering scheme and displacement ellipsoids drawn at the 30% probability level. H atoms are shown as small spheres of arbitrary radius.
Fig. 2.
A view down the b axis of the packing in (I). Dashed lines indicate hydrogen bonds. The H atoms not involved in hydrogen bonding have been omitted for reasons of clarity.

Crystal data

C18H19NOS2·H2OZ = 2
Mr = 347.50F(000) = 368
Triclinic, P1Dx = 1.290 Mg m3
Hall symbol: -P 1Melting point: 423 K
a = 7.5781 (7) ÅMo Kα radiation, λ = 0.71073 Å
b = 10.9926 (9) ÅCell parameters from 9874 reflections
c = 11.5304 (10) Åθ = 2.0–25.0°
α = 79.531 (2)°µ = 0.31 mm1
β = 83.404 (2)°T = 293 K
γ = 71.673 (2)°Prism, colourless
V = 894.90 (14) Å30.36 × 0.22 × 0.22 mm

Data collection

Bruker Kappa APEXII CCD diffractometer3127 independent reflections
Radiation source: fine-focus sealed tube2686 reflections with I > 2σ(I)
graphiteRint = 0.021
Detector resolution: 0 pixels mm-1θmax = 25.0°, θmin = 2.0°
ω and [var phi] scansh = −9→9
Absorption correction: multi-scan (SADABS; Bruker, 2004)k = −13→13
Tmin = 0.901, Tmax = 0.938l = −13→13
15827 measured reflections

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.043Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.130H atoms treated by a mixture of independent and constrained refinement
S = 1.11w = 1/[σ2(Fo2) + (0.0602P)2 + 0.4317P] where P = (Fo2 + 2Fc2)/3
3127 reflections(Δ/σ)max = 0.001
217 parametersΔρmax = 0.44 e Å3
3 restraintsΔρmin = −0.31 e Å3

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles
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 > 2σ(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)

xyzUiso*/Ueq
S310.12090 (9)0.66376 (7)0.92973 (5)0.0616 (2)
S510.60928 (9)0.12751 (6)0.41757 (6)0.0613 (2)
O40.1381 (3)0.60702 (18)0.46923 (16)0.0789 (7)
N10.3386 (3)0.31766 (17)0.73473 (15)0.0491 (6)
C20.3009 (4)0.4473 (2)0.7629 (2)0.0561 (8)
C30.1977 (3)0.5506 (2)0.67020 (19)0.0481 (7)
C40.2189 (3)0.5242 (2)0.54771 (19)0.0517 (7)
C50.3416 (3)0.3973 (2)0.52192 (19)0.0491 (7)
C60.4442 (3)0.3036 (2)0.6214 (2)0.0562 (8)
C110.4415 (4)0.2222 (3)0.8279 (2)0.0644 (9)
C130.0932 (3)0.6700 (2)0.6881 (2)0.0496 (7)
C150.3552 (3)0.3766 (2)0.40958 (19)0.0503 (7)
C320.0478 (3)0.7334 (2)0.7898 (2)0.0508 (7)
C33−0.0590 (3)0.8610 (2)0.7893 (2)0.0580 (8)
C34−0.0799 (4)0.8984 (3)0.9011 (3)0.0717 (10)
C350.0091 (4)0.8029 (3)0.9852 (3)0.0747 (11)
C36−0.1438 (4)0.9519 (3)0.6826 (3)0.0700 (9)
C520.4595 (3)0.2700 (2)0.3507 (2)0.0520 (8)
C530.4559 (3)0.2664 (3)0.2315 (2)0.0564 (8)
C540.5707 (4)0.1487 (3)0.1991 (2)0.0660 (9)
C550.6615 (4)0.0657 (3)0.2886 (3)0.0688 (10)
C560.3477 (4)0.3754 (3)0.1436 (2)0.0733 (10)
O1W0.0177 (4)0.2338 (3)0.7303 (2)0.1048 (11)
H2A0.417930.461990.772000.0673*
H2B0.228270.453490.837750.0673*
H6A0.468570.215720.606100.0675*
H6B0.563080.318110.625160.0675*
H11A0.556530.238810.834940.0966*
H11B0.467320.136700.808580.0966*
H11C0.368290.228280.901530.0966*
H130.039310.721880.620500.0595*
H150.281750.445740.359910.0604*
H34−0.148370.981020.916130.0860*
H350.008910.812271.063750.0897*
H36A−0.059850.935300.614290.1049*
H36B−0.166381.039850.694440.1049*
H36C−0.259320.938600.670700.1049*
H540.582820.129870.122610.0792*
H550.74340−0.016050.281080.0825*
H56A0.260730.440020.184850.1096*
H56B0.281370.342200.097100.1096*
H56C0.432050.413570.092670.1096*
H1A0.099 (5)0.273 (4)0.734 (4)0.1573*
H1B−0.046 (5)0.280 (4)0.672 (3)0.1573*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
S310.0677 (4)0.0680 (4)0.0491 (4)−0.0236 (3)−0.0051 (3)−0.0026 (3)
S510.0647 (4)0.0559 (4)0.0604 (4)−0.0181 (3)−0.0016 (3)−0.0035 (3)
O40.0979 (14)0.0685 (12)0.0485 (10)0.0049 (10)−0.0227 (10)0.0036 (9)
N10.0583 (11)0.0452 (10)0.0402 (9)−0.0132 (8)−0.0086 (8)0.0021 (8)
C20.0684 (15)0.0514 (13)0.0466 (12)−0.0150 (11)−0.0143 (11)−0.0016 (10)
C30.0477 (12)0.0487 (12)0.0466 (12)−0.0157 (10)−0.0068 (9)0.0008 (9)
C40.0536 (13)0.0521 (13)0.0446 (12)−0.0123 (10)−0.0099 (10)0.0025 (10)
C50.0491 (12)0.0531 (12)0.0436 (11)−0.0169 (10)−0.0050 (9)0.0003 (9)
C60.0559 (14)0.0571 (14)0.0469 (12)−0.0084 (11)−0.0046 (10)−0.0002 (10)
C110.0805 (18)0.0536 (14)0.0501 (13)−0.0102 (12)−0.0153 (12)0.0041 (11)
C130.0463 (12)0.0500 (12)0.0493 (12)−0.0143 (10)−0.0070 (9)0.0025 (10)
C150.0509 (12)0.0545 (13)0.0444 (12)−0.0182 (10)−0.0071 (9)0.0021 (10)
C320.0451 (12)0.0544 (13)0.0522 (13)−0.0176 (10)−0.0021 (10)−0.0021 (10)
C330.0458 (12)0.0588 (14)0.0672 (15)−0.0147 (10)0.0035 (11)−0.0106 (12)
C340.0656 (16)0.0710 (17)0.0754 (18)−0.0145 (14)0.0074 (14)−0.0215 (14)
C350.0772 (19)0.093 (2)0.0607 (16)−0.0330 (16)0.0111 (14)−0.0255 (15)
C360.0591 (15)0.0571 (15)0.0807 (18)−0.0026 (12)−0.0072 (13)−0.0027 (13)
C520.0513 (13)0.0602 (14)0.0497 (12)−0.0272 (11)−0.0026 (10)−0.0036 (10)
C530.0563 (14)0.0712 (15)0.0519 (13)−0.0328 (12)−0.0003 (10)−0.0129 (11)
C540.0687 (16)0.0806 (18)0.0608 (15)−0.0361 (14)0.0044 (13)−0.0224 (14)
C550.0650 (16)0.0635 (16)0.0848 (19)−0.0271 (13)0.0106 (14)−0.0246 (14)
C560.0785 (18)0.099 (2)0.0501 (14)−0.0375 (16)−0.0123 (13)−0.0066 (14)
O1W0.114 (2)0.126 (2)0.0823 (15)−0.0674 (16)−0.0458 (14)0.0452 (14)

Geometric parameters (Å, °)

S31—C321.728 (2)C53—C561.506 (4)
S31—C351.698 (3)C53—C541.401 (4)
S51—C521.726 (2)C54—C551.341 (4)
S51—C551.701 (3)C2—H2A0.9700
O4—C41.225 (3)C2—H2B0.9700
O1W—H1A0.86 (4)C6—H6B0.9700
O1W—H1B0.86 (4)C6—H6A0.9700
N1—C111.460 (3)C11—H11C0.9600
N1—C21.452 (3)C11—H11B0.9600
N1—C61.459 (3)C11—H11A0.9600
C2—C31.495 (3)C13—H130.9300
C3—C41.474 (3)C15—H150.9300
C3—C131.342 (3)C34—H340.9300
C4—C51.473 (3)C35—H350.9300
C5—C151.342 (3)C36—H36A0.9600
C5—C61.501 (3)C36—H36C0.9600
C13—C321.426 (3)C36—H36B0.9600
C15—C521.429 (3)C54—H540.9300
C32—C331.381 (3)C55—H550.9300
C33—C341.400 (4)C56—H56C0.9600
C33—C361.502 (4)C56—H56A0.9600
C34—C351.354 (5)C56—H56B0.9600
C52—C531.386 (3)
S31···C23.200 (2)C54···H36Ciii2.9700
S31···C54i3.611 (3)C55···H36Ciii3.0400
S51···C63.208 (2)C56···H152.6900
S51···C13i3.614 (2)H1A···N12.03 (4)
S51···C36ii3.669 (3)H1A···C22.88 (4)
S31···H56Biii3.1200H1A···H35iv2.5000
S31···H2B2.5800H1A···C112.78 (4)
S51···H6A2.5300H1A···C62.87 (4)
O1W···N12.867 (4)H1B···O4iii1.91 (4)
O1W···O4iii2.759 (3)H2A···H11A2.3600
O1W···C35iv3.222 (4)H2A···H6B2.4600
O4···O1Wiii2.759 (3)H2B···C322.9200
O1W···H55v2.5200H2B···H11C2.3800
O1W···H35iv2.3400H2B···S312.5800
O4···H152.2800H6A···S512.5300
O4···H132.2600H6A···H11B2.3400
O4···H6Bi2.7000H6A···C522.9000
O4···H1Biii1.91 (4)H6B···H11A2.4200
N1···O1W2.867 (4)H6B···H2A2.4600
N1···H1A2.03 (4)H6B···O4i2.7000
C2···S313.200 (2)H6B···C4i3.0800
C6···S513.208 (2)H11A···H2A2.3600
C13···S51i3.614 (2)H11A···H6B2.4200
C32···C55i3.525 (4)H11B···H6A2.3400
C32···C56iii3.521 (4)H11C···H2B2.3800
C32···C54i3.543 (4)H11C···C35iv3.1000
C33···C55i3.342 (4)H13···C362.6600
C35···O1Wiv3.222 (4)H13···H36A2.2200
C36···S51vi3.669 (3)H13···O42.2600
C54···C32i3.543 (4)H15···O42.2800
C54···S31i3.611 (3)H15···C562.6900
C55···C32i3.525 (4)H15···H56A2.0600
C55···C33i3.342 (4)H34···H36B2.5300
C56···C32iii3.521 (4)H35···H1Aiv2.5000
C2···H1A2.88 (4)H35···O1Wiv2.3400
C4···H6Bi3.0800H36A···C132.7900
C6···H1A2.87 (4)H36A···H132.2200
C11···H1A2.78 (4)H36B···H342.5300
C13···H36A2.7900H36C···C55iii3.0400
C15···H56A2.6800H36C···C53iii3.0600
C32···H2B2.9200H36C···C54iii2.9700
C32···H56Biii2.9600H55···O1Wv2.5200
C35···H11Civ3.1000H56A···H152.0600
C36···H132.6600H56A···C152.6800
C52···H6A2.9000H56B···S31iii3.1200
C53···H36Ciii3.0600H56B···C32iii2.9600
C32—S31—C3592.06 (14)H2A—C2—H2B108.00
C52—S51—C5591.93 (14)C3—C2—H2A109.00
H1A—O1W—H1B104 (4)N1—C6—H6A109.00
C2—N1—C6111.48 (18)C5—C6—H6A109.00
C2—N1—C11109.72 (19)C5—C6—H6B109.00
C6—N1—C11109.73 (19)N1—C6—H6B109.00
N1—C2—C3112.71 (19)H6A—C6—H6B108.00
C2—C3—C4118.61 (19)N1—C11—H11B109.00
C2—C3—C13125.0 (2)N1—C11—H11C109.00
C4—C3—C13116.3 (2)H11A—C11—H11B109.00
O4—C4—C3120.4 (2)H11A—C11—H11C109.00
O4—C4—C5121.1 (2)H11B—C11—H11C109.00
C3—C4—C5118.50 (19)N1—C11—H11A109.00
C4—C5—C15116.6 (2)C3—C13—H13113.00
C6—C5—C15125.4 (2)C32—C13—H13114.00
C4—C5—C6117.98 (18)C52—C15—H15113.00
N1—C6—C5111.81 (19)C5—C15—H15113.00
C3—C13—C32133.0 (2)C33—C34—H34123.00
C5—C15—C52133.1 (2)C35—C34—H34123.00
S31—C32—C33110.37 (17)C34—C35—H35124.00
C13—C32—C33124.3 (2)S31—C35—H35124.00
S31—C32—C13125.32 (17)C33—C36—H36A109.00
C32—C33—C36125.1 (2)C33—C36—H36C109.00
C34—C33—C36122.7 (2)H36A—C36—H36B109.00
C32—C33—C34112.2 (2)H36A—C36—H36C109.00
C33—C34—C35113.6 (3)H36B—C36—H36C109.00
S31—C35—C34111.7 (3)C33—C36—H36B110.00
S51—C52—C15124.92 (17)C55—C54—H54123.00
S51—C52—C53110.18 (18)C53—C54—H54123.00
C15—C52—C53124.9 (2)S51—C55—H55124.00
C52—C53—C56125.4 (3)C54—C55—H55124.00
C54—C53—C56122.5 (2)C53—C56—H56B109.00
C52—C53—C54112.1 (2)C53—C56—H56C109.00
C53—C54—C55113.8 (2)C53—C56—H56A110.00
S51—C55—C54112.0 (2)H56A—C56—H56C109.00
N1—C2—H2A109.00H56B—C56—H56C109.00
N1—C2—H2B109.00H56A—C56—H56B109.00
C3—C2—H2B109.00
C35—S31—C32—C13179.2 (2)C4—C5—C6—N131.7 (3)
C35—S31—C32—C330.3 (2)C15—C5—C6—N1−150.0 (2)
C32—S31—C35—C34−0.1 (3)C4—C5—C15—C52178.7 (2)
C55—S51—C52—C15179.7 (2)C6—C5—C15—C520.3 (4)
C55—S51—C52—C53−0.7 (2)C3—C13—C32—S31−1.2 (4)
C52—S51—C55—C540.2 (3)C3—C13—C32—C33177.5 (3)
C6—N1—C2—C357.5 (3)C5—C15—C52—S51−0.2 (4)
C11—N1—C2—C3179.2 (2)C5—C15—C52—C53−179.8 (3)
C2—N1—C6—C5−59.9 (3)S31—C32—C33—C34−0.5 (3)
C11—N1—C6—C5178.4 (2)S31—C32—C33—C36179.2 (2)
N1—C2—C3—C4−26.9 (3)C13—C32—C33—C34−179.4 (2)
N1—C2—C3—C13156.9 (2)C13—C32—C33—C360.2 (4)
C2—C3—C4—O4−179.2 (2)C32—C33—C34—C350.4 (4)
C2—C3—C4—C5−0.3 (3)C36—C33—C34—C35−179.2 (3)
C13—C3—C4—O4−2.7 (4)C33—C34—C35—S31−0.2 (4)
C13—C3—C4—C5176.3 (2)S51—C52—C53—C541.1 (3)
C2—C3—C13—C32−0.3 (4)S51—C52—C53—C56−177.2 (2)
C4—C3—C13—C32−176.6 (2)C15—C52—C53—C54−179.3 (2)
O4—C4—C5—C6176.6 (2)C15—C52—C53—C562.4 (4)
O4—C4—C5—C15−1.9 (4)C52—C53—C54—C55−1.0 (4)
C3—C4—C5—C6−2.3 (3)C56—C53—C54—C55177.4 (3)
C3—C4—C5—C15179.2 (2)C53—C54—C55—S510.4 (4)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x+1, y−1, z; (iii) −x, −y+1, −z+1; (iv) −x, −y+1, −z+2; (v) −x+1, −y, −z+1; (vi) x−1, y+1, z.

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
O1W—H1A···N10.86 (4)2.03 (4)2.867 (4)164 (4)
O1W—H1B···O4iii0.86 (4)1.91 (4)2.759 (3)167 (4)
C2—H2B···S310.972.583.200 (2)122
C6—H6A···S510.972.533.208 (2)127
C13—H13···O40.932.262.693 (3)108
C15—H15···O40.932.282.711 (3)108
C35—H35···O1Wiv0.932.343.222 (4)159
C55—H55···O1Wv0.932.523.450 (4)176
C56—H56B···Cg(1)iii0.962.973.763 (3)141
C36—H36C···Cg(2)iii0.962.833.742 (3)159

Symmetry codes: (iii) −x, −y+1, −z+1; (iv) −x, −y+1, −z+2; (v) −x+1, −y, −z+1.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK2393).

References

  • Bruker (2004). APEX2, SAINT-NT and SADABS Bruker AXS Inc., Madison, Wisconsin, USA.
  • Das, U., Alcorn, J., Shrivastav, A., Sharma, R. K., Clercq, E. D., Balzarini, J. & Dimmock, J. R. (2007). Eur. J. Med. Chem 42, 71–80. [PubMed]
  • Farrugia, L. J. (1997). J. Appl. Cryst.30, 565.
  • Jha, A. & Dimmock, J. R. (2006). Pharmazie, 61, 562–563. [PubMed]
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Spek, A. L. (2009). Acta Cryst. D65, 148–155. [PMC free article] [PubMed]

Articles from Acta Crystallographica Section E: Structure Reports Online are provided here courtesy of International Union of Crystallography