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

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 65| Part 11| November 2009| Page o2618
https://doi.org/10.1107/S1600536809038999

1,5-Bis(2,5-di­methyl-1H-pyrrol-1-yl)naphthalene

A. C. Santos,a M. Ramos Silva,b* P. V. Monsanto,c A. Matos Bejab and A. J. F. N. Sobrala

aDepartamento de Qυ'imica, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, P-3004-535 Coimbra, Portugal, bCEMDRX, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, P-3004-516 Coimbra, Portugal, and cForensic Toxicology Service, National Institute of Legal Medicine, Center Branch, P-3000-213 Coimbra, Portugal
*Correspondence e-mail: manuela@pollux.fis.uc.pt

(Received 2 September 2009; accepted 25 September 2009; online 3 October 2009)

In the title compound, C22H22N2, the asymmetric unit contains one half-mol­ecule. A crystallographic inversion centre is located at the mid-point of the bond common to both rings, in the central naphthalene unit. Quantum-mechanical ab initio calculations on the isolated mol­ecule showed that the minimum energy configuration occurs when the naphthalene ring system and the pyrrolyl groups deviate only slightly from perpendicularity. In the crystal, due to the effects of crystal packing, the mol­ecule deviates by approximately 4° from the a priori expected ideal value of 90° [C—C—N—C torsion angle = 86.11 (15)°].

Related literature

For related compounds, see: Andrade et al. (2008[Andrade, S. M., Teixeira, R., Costa, S. M. B. & Sobral, A. J. F. N. (2008). Biophys. Chem. 133, 1-10.]); Ramos Silva et al. (2002[Ramos Silva, M., Matos Beja, A., Paixão, J. A., Sobral, A. J. F. N., Lopes, S. H. & Rocha Gonsalves, A. M. d'A. (2002). Acta Cryst. C58, o572-o574.]); Sobral (2006[Sobral, A. J. F. N. (2006). J. Chem. Educ. 83, 1665-1666.]); Sobral & Rocha Gonsalves (2001a[Sobral, A. J. F. N. & Rocha Gonsalves, A. M. D. (2001a). J. Porph. Phthal. 5, 428-430.],b[Sobral, A. J. F. N. & Rocha Gonsalves, A. M. D. (2001b). J. Porph. Phthal. 5, 861-866.]). For the ab initio calculation method, see: Schmidt et al. (1993[Schmidt, M. W., Baldrige, K. K., Boatz, J. A., Elbert, S. T., Gordon, M. S., Jensen, J. J., Koseki, S., Matsunaga, N., Nguyen, K. A., Sue, S., Windus, T. L., Dupuis, M. & Montgomery, J. A. (1993). J. Comput. Chem. 14, 1347-1363.]).

[Scheme 1]

Experimental

Crystal data

  • C22H22N2

  • Mr = 314.42

  • Monoclinic, P 21 /c

  • a = 8.7562 (3) Å

  • b = 7.2806 (2) Å

  • c = 14.1380 (5) Å

  • β = 101.4721 (16)°

  • V = 883.30 (5) Å3

  • Z = 2

  • Mo Kα radiation

  • μ = 0.07 mm−1

  • T = 293 K

  • 0.30 × 0.30 × 0.02 mm
Data collection

  • Bruker APEXII CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2000[Sheldrick, G. M. (2000). SADABS. University of Göttingen, Germany.]) Tmin = 0.892, Tmax = 0.999

  • 23689 measured reflections

  • 2415 independent reflections

  • 1798 reflections with I > 2σ(I)

  • Rint = 0.028
Refinement

  • R[F2 > 2σ(F2)] = 0.044

  • wR(F2) = 0.160

  • S = 1.11

  • 2415 reflections

  • 111 parameters

  • H-atom parameters constrained

  • Δρmax = 0.19 e Å−3

  • Δρmin = −0.20 e Å−3

Data collection: APEX2 (Bruker, 2003[Bruker (2003). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2003[Bruker (2003). APEX2 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: PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536809038999/pk2188sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536809038999/pk2188Isup2.hkl

checkCIF report


Comment top

Complex pyrroles are important synthons in macromolecular chemistry, environmental chemistry, medical chemistry and nano-technologies based on polymeric organic materials. Following our endeavor in synthesizing new pyrrolic compounds for material chemistry (Andrade et al., 2008; Ramos Silva et al., 2002; Sobral & Rocha Gonsalves 2001a, 2001b; Sobral, 2006), we prepared the title compound, by the Paal-Knorr methodology, using iodine as catalyst. Each molecule contains a crystallographic inversion centre at the mid-point of the bond common to both rings of the naphthalene moiety. All bond lengths and valency angles of the molecule lie within the expected range of values for naphtalene derivatives.

Approximate free rotation of the pyrrolyl group around the formal σ C—N bond is expected. Thus, the conformation observed for such groups in the solid state should be determined by steric rather than electronic effects. We observe in this structure a value of 86.11 (15)° for the C9–C8–N1–C1 dihedral angle, which is close to the a priori expected ideal value of 90° where the steric effects should be at a minimum.

In order to gain some insight into how the crystal packing might affect the molecular geometry we have performed a quantum chemical calculation on the equilibrium geometry of the free molecule. These calculations were performed with the computer program GAMESS (Schmidt et al., 1993). A molecular orbital Roothan Hartree-Fock method was used with an extended 6–31 G(d,p) basis set. Tight conditions for convergence of both the self-consistent field cycles and maximum density and energy gradient variations were imposed (10-6atomic units). The program was run on the Milipeia cluster of UC-LCA (using 16 Opteron cores, 2.2 GHz runing Linux).

The ab-initio calculations reproduce well the observed experimental bond length and angles of the molecule. All angles match the experimental values within 1°. Calculated and experimental bond distances agree within 0.023 Å. The calculated C9–C8–N1–C1 dihedral angle is 91.82°, a value closer to the ideal value of 90° than the experimental value in the solid state.

A check for weak intermolecular interactions in the crystal on the basis of short contacts revealed that a possible C—H···π interaction may exist between atoms C2 and the pyrrole ring [C2—H2···Cg: 3.7791 (16) Å, 159°]

Related literature top

For related compounds, please see: Andrade et al. (2008); Ramos Silva et al. (2002); Sobral (2006); Sobral & Rocha Gonsalves (2001a,b). For the ab initio calculation method, please see: Schmidt et al. (1993).

Experimental top

0.680 g (4.3 mmol) of 1,4-phenylenedimethanamine and 1 ml (8.5 mmol) of hexane-2,5-dione were dissolved in 20 ml of tetrahydrofuran, under nitrogen atmosphere. 0.172 g (0.678 mmol) of iodine was added to the stirred solution at 40°C. The procedure was monitored by TLC. After completion of the reaction (6 h), 20 ml of dichlorometane were added to the mixture. The resulting mixture was washed successively with 5% Na2S2O3 solution (2 ml), NaHCO3 solution (2 ml) and brine (2 ml). The organic layer was then dried with anhydrous sodium sulfate and concentrated. The product was purified by flash chromatography in silica gel 60H FLUKA/dichloromethane and recrystallized in cold dichloromethane, by slow solvent evaporation, to give needle shape crystals 0.473 grams corresponding to 1.5 mmoles (%) = 35; GC/MS (100 µmol/ml in CH2Cl2) m/z = 314; 1H-NMR (0.1 M in CDCl3, 499.428 MHz) σ 1.96 (s, 12H, Methyl), σ 5.34 (s, 4H, pyrrole), σ 7.25 (dd, 2H, Aromatic, J = 0.99, J = 7.49 Hz), 7.48 (dd, 2H, Aromatic, J = 0.99 Hz, J = 6.99 Hz), 7.55 (t, 2H, Aromatic, J = 7.0 Hz); 13C - NMR (0.1 M in CDCl3, 125.692 MHz) σ 12.5 (Methyl), σ 105.6 (Pyrrole), σ 129.8 (Pyrrole), σ 126.7 (Aromatic), σ 132.7 (Aromatic). Melting point: Decomposes at 288 °C.

Refinement top

The methyl H atoms were constrained to an ideal geometry (C—H = 0.96 Å) with Uiso(H)= 1.5Ueq(C), but were allowed to rotate freely about the C—C bonds. All remaining H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with Uiso(H) = 1.2Ueq(parent atom).

Structure description top

Complex pyrroles are important synthons in macromolecular chemistry, environmental chemistry, medical chemistry and nano-technologies based on polymeric organic materials. Following our endeavor in synthesizing new pyrrolic compounds for material chemistry (Andrade et al., 2008; Ramos Silva et al., 2002; Sobral & Rocha Gonsalves 2001a, 2001b; Sobral, 2006), we prepared the title compound, by the Paal-Knorr methodology, using iodine as catalyst. Each molecule contains a crystallographic inversion centre at the mid-point of the bond common to both rings of the naphthalene moiety. All bond lengths and valency angles of the molecule lie within the expected range of values for naphtalene derivatives.

Approximate free rotation of the pyrrolyl group around the formal σ C—N bond is expected. Thus, the conformation observed for such groups in the solid state should be determined by steric rather than electronic effects. We observe in this structure a value of 86.11 (15)° for the C9–C8–N1–C1 dihedral angle, which is close to the a priori expected ideal value of 90° where the steric effects should be at a minimum.

In order to gain some insight into how the crystal packing might affect the molecular geometry we have performed a quantum chemical calculation on the equilibrium geometry of the free molecule. These calculations were performed with the computer program GAMESS (Schmidt et al., 1993). A molecular orbital Roothan Hartree-Fock method was used with an extended 6–31 G(d,p) basis set. Tight conditions for convergence of both the self-consistent field cycles and maximum density and energy gradient variations were imposed (10-6atomic units). The program was run on the Milipeia cluster of UC-LCA (using 16 Opteron cores, 2.2 GHz runing Linux).

The ab-initio calculations reproduce well the observed experimental bond length and angles of the molecule. All angles match the experimental values within 1°. Calculated and experimental bond distances agree within 0.023 Å. The calculated C9–C8–N1–C1 dihedral angle is 91.82°, a value closer to the ideal value of 90° than the experimental value in the solid state.

A check for weak intermolecular interactions in the crystal on the basis of short contacts revealed that a possible C—H···π interaction may exist between atoms C2 and the pyrrole ring [C2—H2···Cg: 3.7791 (16) Å, 159°]

For related compounds, please see: Andrade et al. (2008); Ramos Silva et al. (2002); Sobral (2006); Sobral & Rocha Gonsalves (2001a,b). For the ab initio calculation method, please see: Schmidt et al. (1993).

Computing details top

Data collection: APEX2 (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); 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: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Ellipsoid plot of the title compound. Displacement ellipsoids are drawn at the 50% level. Unlabelled atoms are generated by inversion through the origin.
1,5-Bis(2,5-dimethyl-1H-pyrrol-1-yl)naphthalene top
Crystal data top
C22H22N2F(000) = 336
Mr = 314.42Dx = 1.182 Mg m−3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 8233 reflections
a = 8.7562 (3) Åθ = 2.4–28.6°
b = 7.2806 (2) ŵ = 0.07 mm−1
c = 14.1380 (5) ÅT = 293 K
β = 101.4721 (16)°Plate, brown
V = 883.30 (5) Å30.30 × 0.30 × 0.02 mm
Z = 2
Data collection top
Bruker APEXII CCD area-detector
diffractometer		2415 independent reflections
Radiation source: fine-focus sealed tube1798 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.028
φ and ω scansθmax = 29.5°, θmin = 2.4°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2000)		h = −12→11
Tmin = 0.892, Tmax = 0.999k = −10→9
23689 measured reflectionsl = −18→19
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) = 0.160H-atom parameters constrained
S = 1.11 w = 1/[σ2(Fo2) + (0.0861P)2 + 0.0939P]
where P = (Fo2 + 2Fc2)/3
2415 reflections(Δ/σ)max < 0.001
111 parametersΔρmax = 0.19 e Å−3
0 restraintsΔρmin = −0.20 e Å−3
Crystal data top
C22H22N2V = 883.30 (5) Å3
Mr = 314.42Z = 2
Monoclinic, P21/cMo Kα radiation
a = 8.7562 (3) ŵ = 0.07 mm−1
b = 7.2806 (2) ÅT = 293 K
c = 14.1380 (5) Å0.30 × 0.30 × 0.02 mm
β = 101.4721 (16)°
Data collection top
Bruker APEXII CCD area-detector
diffractometer		2415 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2000)		1798 reflections with I > 2σ(I)
Tmin = 0.892, Tmax = 0.999Rint = 0.028
23689 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0440 restraints
wR(F2) = 0.160H-atom parameters constrained
S = 1.11Δρmax = 0.19 e Å−3
2415 reflectionsΔρmin = −0.20 e Å−3
111 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
N1−0.25783 (11)0.16842 (14)−0.15743 (7)0.0413 (3)
C1−0.37264 (14)0.28237 (17)−0.13576 (10)0.0457 (3)
C2−0.40388 (17)0.41020 (19)−0.20743 (11)0.0581 (4)
H2−0.47650.5046−0.21170.070*
C4−0.21687 (17)0.2256 (2)−0.24234 (10)0.0543 (4)
C3−0.3073 (2)0.3747 (2)−0.27363 (11)0.0644 (5)
H3−0.30540.4416−0.32940.077*
C5−0.4403 (2)0.2558 (2)−0.04885 (14)0.0677 (5)
H5A−0.52350.3419−0.04960.102*
H5B−0.36120.27520.00790.102*
H5C−0.48000.1329−0.04840.102*
C6−0.0984 (3)0.1270 (3)−0.28455 (14)0.0867 (6)
H6A−0.08870.1846−0.34410.130*
H6B−0.12980.0015−0.29660.130*
H6C0.00010.1310−0.24030.130*
C7−0.03746 (12)0.07020 (14)−0.03141 (8)0.0338 (3)
C8−0.18058 (13)0.02723 (15)−0.09515 (8)0.0374 (3)
C9−0.24388 (15)−0.14418 (17)−0.09648 (10)0.0472 (3)
H9−0.3369−0.1703−0.13890.057*
C10−0.16905 (15)−0.28164 (17)−0.03401 (10)0.0478 (3)
H10−0.2135−0.3978−0.03520.057*
C11−0.03195 (14)−0.24638 (15)0.02834 (9)0.0403 (3)
H110.0162−0.33870.06910.048*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0373 (5)0.0397 (5)0.0418 (6)0.0034 (4)−0.0041 (4)0.0032 (4)
C10.0380 (6)0.0377 (6)0.0544 (7)0.0016 (5)−0.0074 (5)−0.0072 (5)
C20.0550 (9)0.0415 (7)0.0643 (9)0.0071 (6)−0.0209 (7)−0.0012 (6)
C40.0542 (8)0.0616 (9)0.0425 (7)0.0017 (6)−0.0016 (6)0.0083 (6)
C30.0725 (10)0.0591 (9)0.0505 (8)−0.0008 (7)−0.0144 (7)0.0161 (7)
C50.0623 (10)0.0612 (9)0.0825 (11)0.0101 (7)0.0214 (8)−0.0053 (8)
C60.0921 (14)0.1113 (16)0.0625 (10)0.0227 (12)0.0292 (10)0.0146 (10)
C70.0322 (6)0.0315 (5)0.0362 (6)0.0009 (4)0.0033 (4)0.0000 (4)
C80.0344 (6)0.0360 (6)0.0390 (6)0.0030 (4)0.0003 (5)0.0012 (4)
C90.0376 (7)0.0421 (6)0.0551 (7)−0.0048 (5)−0.0071 (5)−0.0012 (5)
C100.0444 (7)0.0332 (6)0.0611 (8)−0.0075 (5)−0.0012 (6)0.0011 (5)
C110.0401 (6)0.0316 (5)0.0468 (7)0.0005 (4)0.0026 (5)0.0042 (4)
Geometric parameters (Å, º) top
N1—C41.3835 (17)C6—H6A0.9600
N1—C11.3840 (16)C6—H6B0.9600
N1—C81.4326 (14)C6—H6C0.9600
C1—C21.3628 (19)C7—C11i1.4164 (15)
C1—C51.479 (2)C7—C81.4253 (15)
C2—C31.404 (3)C7—C7i1.426 (2)
C2—H20.9300C8—C91.3642 (17)
C4—C31.365 (2)C9—C101.4075 (18)
C4—C61.481 (2)C9—H90.9300
C3—H30.9300C10—C111.3649 (17)
C5—H5A0.9600C10—H100.9300
C5—H5B0.9600C11—C7i1.4164 (15)
C5—H5C0.9600C11—H110.9300
C4—N1—C1109.68 (11)C4—C6—H6A109.5
C4—N1—C8125.23 (11)C4—C6—H6B109.5
C1—N1—C8124.69 (11)H6A—C6—H6B109.5
C2—C1—N1106.98 (13)C4—C6—H6C109.5
C2—C1—C5130.75 (14)H6A—C6—H6C109.5
N1—C1—C5122.26 (12)H6B—C6—H6C109.5
C1—C2—C3108.15 (13)C11i—C7—C8122.42 (10)
C1—C2—H2125.9C11i—C7—C7i119.26 (12)
C3—C2—H2125.9C8—C7—C7i118.32 (12)
C3—C4—N1106.65 (14)C9—C8—C7120.88 (10)
C3—C4—C6131.51 (15)C9—C8—N1120.47 (10)
N1—C4—C6121.82 (13)C7—C8—N1118.64 (10)
C4—C3—C2108.53 (13)C8—C9—C10120.31 (11)
C4—C3—H3125.7C8—C9—H9119.8
C2—C3—H3125.7C10—C9—H9119.8
C1—C5—H5A109.5C11—C10—C9120.76 (11)
C1—C5—H5B109.5C11—C10—H10119.6
H5A—C5—H5B109.5C9—C10—H10119.6
C1—C5—H5C109.5C10—C11—C7i120.47 (11)
H5A—C5—H5C109.5C10—C11—H11119.8
H5B—C5—H5C109.5C7i—C11—H11119.8
C4—N1—C1—C20.28 (14)C11i—C7—C8—C9179.75 (12)
C8—N1—C1—C2173.32 (11)C7i—C7—C8—C9−0.4 (2)
C4—N1—C1—C5−179.96 (13)C11i—C7—C8—N1−0.83 (18)
C8—N1—C1—C5−6.91 (19)C7i—C7—C8—N1179.03 (12)
N1—C1—C2—C3−0.09 (15)C4—N1—C8—C9−101.92 (16)
C5—C1—C2—C3−179.82 (15)C1—N1—C8—C986.11 (15)
C1—N1—C4—C3−0.36 (16)C4—N1—C8—C778.66 (16)
C8—N1—C4—C3−173.36 (11)C1—N1—C8—C7−93.32 (14)
C1—N1—C4—C6−178.79 (15)C7—C8—C9—C100.5 (2)
C8—N1—C4—C68.2 (2)N1—C8—C9—C10−178.89 (12)
N1—C4—C3—C20.30 (17)C8—C9—C10—C11−0.4 (2)
C6—C4—C3—C2178.52 (17)C9—C10—C11—C7i0.1 (2)
C1—C2—C3—C4−0.14 (17)
Symmetry code: (i) −x, −y, −z.

Experimental details

Crystal data
Chemical formulaC22H22N2
Mr314.42
Crystal system, space groupMonoclinic, P21/c
Temperature (K)293
a, b, c (Å)8.7562 (3), 7.2806 (2), 14.1380 (5)
β (°) 101.4721 (16)
V (Å3)883.30 (5)
Z2
Radiation typeMo Kα
µ (mm−1)0.07
Crystal size (mm)0.30 × 0.30 × 0.02
Data collection
DiffractometerBruker APEXII CCD area-detector
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2000)
Tmin, Tmax0.892, 0.999
No. of measured, independent and
observed [I > 2σ(I)] reflections		23689, 2415, 1798
Rint0.028
(sin θ/λ)max (Å−1)0.692
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.044, 0.160, 1.11
No. of reflections2415
No. of parameters111
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.19, −0.20

Computer programs: APEX2 (Bruker, 2003), SAINT (Bruker, 2003), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009).

 

Acknowledgements

We gratefully acknowledge LCA-UC for a grant of computer time in the Milipeia cluster.

References

First citationAndrade, S. M., Teixeira, R., Costa, S. M. B. & Sobral, A. J. F. N. (2008). Biophys. Chem. 133, 1–10.  Web of Science CrossRef PubMed CAS Google Scholar
 First citationBruker (2003). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
 First citationRamos Silva, M., Matos Beja, A., Paixão, J. A., Sobral, A. J. F. N., Lopes, S. H. & Rocha Gonsalves, A. M. d'A. (2002). Acta Cryst. C58, o572–o574.  Web of Science CSD CrossRef IUCr Journals Google Scholar
 First citationSchmidt, M. W., Baldrige, K. K., Boatz, J. A., Elbert, S. T., Gordon, M. S., Jensen, J. J., Koseki, S., Matsunaga, N., Nguyen, K. A., Sue, S., Windus, T. L., Dupuis, M. & Montgomery, J. A. (1993). J. Comput. Chem. 14, 1347–1363.  Web of Science CrossRef CAS Google Scholar
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ISSN: 2056-9890
Volume 65| Part 11| November 2009| Page o2618
https://doi.org/10.1107/S1600536809038999
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