4-(4-Chloro­phen­yl)-5-[1-(4-chloro­phenyl)-2-methyl-2-nitro­prop­yl]-1,2,3-selenadiazole

Marx, A.; Saravanan, S.; Muthusubramanian, S.; Manivannan, V.; Rath, N.P.

doi:10.1107/S1600536807067487

4-(4-Chlorophenyl)-5-[1-(4-chlorophenyl)-2-methyl-2-nitropropyl]-1,2,3-selenadiazole

A. Marx, S. Saravanan, S. Muthusubramanian, V. Manivannan and N. P. Rath

In the title compound, C₁₈H₁₅Cl₂N₃O₂Se, the selenadiazole ring makes dihedral angles of 49.87 (3) and 55.70 (3)° with the two benzene rings. The dihedral angle between the two benzene rings is 11.90 (5)°. In the crystal structure, intramolecular C-H

O and C-H

Se interactions and intermolecular C-H

O, C-H

Cl and C-H

N interactions are observed.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807067487/is2267sup1.cif Contains datablocks global, I
	Structure factor file (CIF format) https://doi.org/10.1107/S1600536807067487/is2267Isup2.hkl Contains datablock I

CCDC reference: 677509

checkCIF report

Key indicators

Single-crystal X-ray study
T = 100 K
Mean (C-C) = 0.001 Å
R factor = 0.026
wR factor = 0.064
Data-to-parameter ratio = 39.4

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT154_ALERT_1_C The su's on the Cell Angles are Equal  (x 10000)        100 Deg.
PLAT180_ALERT_3_C Check Cell Rounding: # of Values Ending with 0 =          3
PLAT322_ALERT_2_C Check Hybridisation of  Se1    in Main Residue .          ?
PLAT431_ALERT_2_C Short Inter HL..A Contact  Cl2    ..  N2      ..       3.21 Ang.

Alert level G
PLAT793_ALERT_2_G Check the Absolute Configuration of C9     .....          S

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   3 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

Comment top

Selenium containing compounds like 1,2,3-selenadiazole possess various beneficial activities like antifungal (Kuroda et al., 2001), antibacterial (El-Kashef et al., 1986), antimicrobial (El-Bahaie et al., 1990) and insecticidal (Padmavathi et al., 2002) activities. As naturally occurring nitro compounds exhibit broad antibiotic activity and certain alkyl nitro compounds exhibit antitumor activity, it was decided to synthesize and structurally characterize a set of 1,2,3-selenadiazoles with nitro group in the side chain (Saravanan et al., 2006).

The geometric parameters in the compound, (I) agree with the reported values of similar structure (Mellini & Merlino, 1976a,b; Bertini et al., 1984; Gunasekaran et al., 2007). The C3—C8 benzene ring makes a dihedral angle of 49.87 (3)° with the heterocyclic ring and the C10—C15 benzene ring makes a dihedral angle of 55.70 (3)° with the heterocyclic ring (Fig. 1).

The details of the hydrogen bonding are given in Table 1. The molecular structure is stabilized by weak intramolecular C—H···O and C—H···Se interactions and the crystal packing is stabilized by weak intermolecular C—H···O, C—H···Cl and C—H···N interactions (Fig. 2).

Related literature top

For related literature, see: Bertini et al. (1984); El-Bahaie et al. (1990); El-Kashef et al. (1986); Kuroda et al. (2001); Mellini & Merlino (1976a,b); Padmavathi et al. (2002); Saravanan et al. (2006). A similar compound with a chlorophenyl ring has been reported recently (Gunasekaran et al., 2007).

Experimental top

A solution of 2-[1,3-bis(4-chlorophenyl)-4-methyl-4-nitropentylidene]-1-hydrazine carboxamide (0.005 mol) and powdered selenium dioxide (0.05 mol) in dry THF was gently heated on a water bath for 2 h. The selenium deposited on cooling was removed by filtration, and the filtrate was poured into crushed ice, extracted with chloroform, and purified by column chromatography using silica gel (60–120 mesh) with 97:3 petroleum ether: ethyl acetate as eluent to give 4-(4-chlorophenyl)-5-[1-(4-chlorophenyl)-2-methyl-2- nitropropyl]-1,2,3-selenadiazole. Solvent used for crystallization is ethanol.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 (Bruker, 2004); data reduction: APEX2 (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures top

	Fig. 1. The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms.
	Fig. 2. The packing of (I), viewed down the b axis. Hydrogen bonds are shown as dashed lines. H atoms not involved in hydrogen bonding have been omitted.

4-(4-Chlorophenyl)-5-[1-(4-chlorophenyl)-2-methyl-2-nitropropyl]-1,2,3- selenadiazole top

Crystal data top

C₁₈H₁₅Cl₂N₃O₂Se	Z = 2
M_r = 455.19	F(000) = 456
Triclinic, P1	D_x = 1.592 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.8352 (2) Å	Cell parameters from 8302 reflections
b = 10.9208 (3) Å	θ = 2.7–34.5°
c = 11.5507 (3) Å	µ = 2.28 mm⁻¹
α = 75.381 (1)°	T = 100 K
β = 89.044 (1)°	Rectangular, colourless
γ = 83.331 (1)°	0.33 × 0.18 × 0.17 mm
V = 949.80 (4) Å³

Data collection top

Bruker Kappa-APEXII diffractometer	9335 independent reflections
Radiation source: fine-focus sealed tube	8074 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.028
ω and ϕ scans	θ_max = 36.7°, θ_min = 1.8°
Absorption correction: multi-scan (SADABS; Bruker, 2004)	h = −13→13
T_min = 0.507, T_max = 0.679	k = −18→18
44785 measured reflections	l = −19→19

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.026	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.064	H-atom parameters constrained
S = 1.03	w = 1/[σ²(F_o²) + (0.031P)² + 0.2243P] where P = (F_o² + 2F_c²)/3
9335 reflections	(Δ/σ)_max < 0.001
237 parameters	Δρ_max = 0.57 e Å⁻³
0 restraints	Δρ_min = −0.59 e Å⁻³

Crystal data top

C₁₈H₁₅Cl₂N₃O₂Se	γ = 83.331 (1)°
M_r = 455.19	V = 949.80 (4) Å³
Triclinic, P1	Z = 2
a = 7.8352 (2) Å	Mo Kα radiation
b = 10.9208 (3) Å	µ = 2.28 mm⁻¹
c = 11.5507 (3) Å	T = 100 K
α = 75.381 (1)°	0.33 × 0.18 × 0.17 mm
β = 89.044 (1)°

Data collection top

Bruker Kappa-APEXII diffractometer	9335 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2004)	8074 reflections with I > 2σ(I)
T_min = 0.507, T_max = 0.679	R_int = 0.028
44785 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.026	0 restraints
wR(F²) = 0.064	H-atom parameters constrained
S = 1.03	Δρ_max = 0.57 e Å⁻³
9335 reflections	Δρ_min = −0.59 e Å⁻³
237 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Se1	0.135681 (12)	0.147694 (9)	0.433060 (8)	0.01400 (3)
Cl1	0.22480 (5)	0.30162 (4)	−0.32615 (2)	0.03885 (8)
Cl2	0.23404 (5)	0.83872 (3)	0.28700 (3)	0.03592 (8)
O1	0.76068 (10)	0.34633 (8)	0.28931 (8)	0.02212 (15)
O2	0.67115 (11)	0.31526 (8)	0.12446 (7)	0.02317 (16)
N1	−0.02318 (11)	0.07149 (8)	0.36434 (7)	0.01542 (14)
N2	−0.01345 (10)	0.10161 (8)	0.25070 (7)	0.01371 (13)
N3	0.66526 (11)	0.30096 (8)	0.23302 (8)	0.01522 (14)
C1	0.10681 (11)	0.18154 (8)	0.20053 (8)	0.01114 (14)
C2	0.20509 (11)	0.21946 (8)	0.27992 (8)	0.01124 (14)
C3	0.12393 (12)	0.21352 (9)	0.06915 (8)	0.01239 (14)
C4	0.14006 (15)	0.11629 (10)	0.00999 (9)	0.01870 (18)
H4	0.1326	0.0309	0.0539	0.022*
C5	0.16690 (16)	0.14320 (11)	−0.11262 (9)	0.0233 (2)
H5	0.1771	0.0771	−0.1531	0.028*
C6	0.17854 (15)	0.26821 (12)	−0.17466 (9)	0.0219 (2)
C7	0.15700 (15)	0.36712 (10)	−0.11909 (9)	0.02036 (19)
H7	0.1612	0.4526	−0.1637	0.024*
C8	0.12902 (13)	0.33887 (9)	0.00348 (8)	0.01577 (16)
H8	0.1132	0.4058	0.0429	0.019*
C9	0.35407 (11)	0.29627 (8)	0.24434 (8)	0.01096 (13)
H9	0.3664	0.3057	0.1563	0.013*
C10	0.32202 (12)	0.43177 (9)	0.25869 (8)	0.01282 (14)
C11	0.35859 (14)	0.53150 (9)	0.16337 (9)	0.01794 (17)
H11	0.4016	0.5133	0.0914	0.022*
C12	0.33342 (17)	0.65705 (10)	0.17148 (10)	0.0229 (2)
H12	0.3586	0.7244	0.1059	0.027*
C13	0.27108 (16)	0.68213 (10)	0.27660 (10)	0.0217 (2)
C14	0.23240 (16)	0.58569 (10)	0.37302 (10)	0.0226 (2)
H14	0.1895	0.6045	0.4448	0.027*
C15	0.25739 (15)	0.46091 (10)	0.36297 (9)	0.01862 (18)
H15	0.2299	0.3941	0.4284	0.022*
C16	0.52730 (12)	0.22146 (9)	0.30124 (8)	0.01257 (14)
C17	0.55570 (13)	0.09225 (9)	0.27148 (10)	0.01807 (17)
H17A	0.6722	0.0520	0.2961	0.027*
H17B	0.5412	0.1041	0.1851	0.027*
H17C	0.4719	0.0377	0.3142	0.027*
C18	0.55381 (13)	0.20944 (10)	0.43339 (9)	0.01800 (17)
H18A	0.4704	0.1569	0.4795	0.027*
H18B	0.5375	0.2943	0.4487	0.027*
H18C	0.6706	0.1694	0.4575	0.027*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Se1	0.01575 (4)	0.01765 (5)	0.00888 (4)	−0.00696 (3)	0.00236 (3)	−0.00175 (3)
Cl1	0.0533 (2)	0.0539 (2)	0.01020 (10)	−0.01394 (17)	0.00528 (11)	−0.00641 (12)
Cl2	0.0664 (2)	0.01200 (10)	0.02912 (14)	0.00353 (12)	−0.01822 (14)	−0.00708 (10)
O1	0.0197 (3)	0.0181 (3)	0.0286 (4)	−0.0094 (3)	−0.0035 (3)	−0.0024 (3)
O2	0.0213 (4)	0.0293 (4)	0.0161 (3)	−0.0055 (3)	0.0053 (3)	0.0003 (3)
N1	0.0150 (3)	0.0163 (3)	0.0150 (3)	−0.0058 (3)	0.0021 (3)	−0.0024 (3)
N2	0.0135 (3)	0.0140 (3)	0.0138 (3)	−0.0042 (3)	0.0012 (2)	−0.0027 (3)
N3	0.0130 (3)	0.0131 (3)	0.0177 (3)	−0.0032 (3)	0.0011 (3)	0.0003 (3)
C1	0.0116 (3)	0.0109 (3)	0.0108 (3)	−0.0018 (3)	0.0004 (3)	−0.0022 (3)
C2	0.0123 (3)	0.0116 (3)	0.0095 (3)	−0.0024 (3)	0.0007 (3)	−0.0017 (3)
C3	0.0143 (4)	0.0128 (4)	0.0102 (3)	−0.0031 (3)	−0.0005 (3)	−0.0025 (3)
C4	0.0277 (5)	0.0149 (4)	0.0149 (4)	−0.0051 (4)	−0.0010 (3)	−0.0050 (3)
C5	0.0345 (6)	0.0236 (5)	0.0146 (4)	−0.0046 (4)	0.0005 (4)	−0.0094 (4)
C6	0.0267 (5)	0.0298 (5)	0.0097 (4)	−0.0075 (4)	0.0004 (3)	−0.0042 (3)
C7	0.0276 (5)	0.0191 (4)	0.0130 (4)	−0.0084 (4)	−0.0025 (3)	0.0010 (3)
C8	0.0214 (4)	0.0132 (4)	0.0123 (4)	−0.0033 (3)	−0.0020 (3)	−0.0017 (3)
C9	0.0124 (3)	0.0111 (3)	0.0092 (3)	−0.0030 (3)	0.0004 (3)	−0.0016 (3)
C10	0.0156 (4)	0.0110 (3)	0.0113 (3)	−0.0024 (3)	−0.0012 (3)	−0.0013 (3)
C11	0.0264 (5)	0.0128 (4)	0.0137 (4)	−0.0052 (3)	0.0011 (3)	−0.0006 (3)
C12	0.0365 (6)	0.0120 (4)	0.0186 (4)	−0.0052 (4)	−0.0042 (4)	0.0003 (3)
C13	0.0328 (6)	0.0111 (4)	0.0212 (5)	−0.0001 (4)	−0.0095 (4)	−0.0044 (3)
C14	0.0352 (6)	0.0155 (4)	0.0178 (4)	0.0002 (4)	−0.0016 (4)	−0.0068 (3)
C15	0.0285 (5)	0.0138 (4)	0.0134 (4)	−0.0028 (4)	0.0017 (3)	−0.0031 (3)
C16	0.0122 (3)	0.0118 (3)	0.0133 (3)	−0.0045 (3)	0.0007 (3)	−0.0011 (3)
C17	0.0155 (4)	0.0130 (4)	0.0259 (5)	−0.0022 (3)	−0.0007 (3)	−0.0049 (3)
C18	0.0172 (4)	0.0223 (5)	0.0127 (4)	−0.0040 (3)	−0.0029 (3)	−0.0003 (3)

Geometric parameters (Å, º) top

Se1—C2	1.8455 (9)	C9—C10	1.5220 (13)
Se1—N1	1.8652 (9)	C9—C16	1.5630 (12)
Cl1—C6	1.7360 (10)	C9—H9	1.0000
Cl2—C13	1.7350 (10)	C10—C11	1.3918 (13)
O1—N3	1.2216 (12)	C10—C15	1.3944 (13)
O2—N3	1.2247 (11)	C11—C12	1.3889 (15)
N1—N2	1.2734 (11)	C11—H11	0.9500
N2—C1	1.3795 (12)	C12—C13	1.3802 (16)
N3—C16	1.5451 (12)	C12—H12	0.9500
C1—C2	1.3765 (12)	C13—C14	1.3828 (16)
C1—C3	1.4762 (12)	C14—C15	1.3877 (14)
C2—C9	1.5075 (13)	C14—H14	0.9500
C3—C8	1.3923 (13)	C15—H15	0.9500
C3—C4	1.3938 (13)	C16—C18	1.5144 (13)
C4—C5	1.3895 (15)	C16—C17	1.5259 (13)
C4—H4	0.9500	C17—H17A	0.9800
C5—C6	1.3851 (17)	C17—H17B	0.9800
C5—H5	0.9500	C17—H17C	0.9800
C6—C7	1.3826 (16)	C18—H18A	0.9800
C7—C8	1.3901 (14)	C18—H18B	0.9800
C7—H7	0.9500	C18—H18C	0.9800
C8—H8	0.9500

C2—Se1—N1	87.45 (4)	C11—C10—C15	118.31 (9)
N2—N1—Se1	111.08 (6)	C11—C10—C9	118.61 (8)
N1—N2—C1	117.26 (8)	C15—C10—C9	123.07 (8)
O1—N3—O2	123.86 (9)	C12—C11—C10	121.26 (10)
O1—N3—C16	118.80 (8)	C12—C11—H11	119.4
O2—N3—C16	117.33 (8)	C10—C11—H11	119.4
C2—C1—N2	115.83 (8)	C13—C12—C11	118.80 (10)
C2—C1—C3	126.24 (8)	C13—C12—H12	120.6
N2—C1—C3	117.87 (8)	C11—C12—H12	120.6
C1—C2—C9	124.13 (8)	C12—C13—C14	121.63 (10)
C1—C2—Se1	108.37 (6)	C12—C13—Cl2	119.39 (9)
C9—C2—Se1	127.26 (6)	C14—C13—Cl2	118.95 (9)
C8—C3—C4	119.31 (8)	C13—C14—C15	118.74 (10)
C8—C3—C1	121.17 (8)	C13—C14—H14	120.6
C4—C3—C1	119.50 (8)	C15—C14—H14	120.6
C5—C4—C3	120.54 (10)	C14—C15—C10	121.25 (10)
C5—C4—H4	119.7	C14—C15—H15	119.4
C3—C4—H4	119.7	C10—C15—H15	119.4
C6—C5—C4	118.75 (10)	C18—C16—C17	111.81 (8)
C6—C5—H5	120.6	C18—C16—N3	107.47 (8)
C4—C5—H5	120.6	C17—C16—N3	106.56 (7)
C7—C6—C5	121.93 (9)	C18—C16—C9	116.40 (8)
C7—C6—Cl1	118.93 (9)	C17—C16—C9	110.03 (7)
C5—C6—Cl1	119.13 (9)	N3—C16—C9	103.77 (7)
C6—C7—C8	118.62 (10)	C16—C17—H17A	109.5
C6—C7—H7	120.7	C16—C17—H17B	109.5
C8—C7—H7	120.7	H17A—C17—H17B	109.5
C7—C8—C3	120.74 (9)	C16—C17—H17C	109.5
C7—C8—H8	119.6	H17A—C17—H17C	109.5
C3—C8—H8	119.6	H17B—C17—H17C	109.5
C2—C9—C10	114.26 (7)	C16—C18—H18A	109.5
C2—C9—C16	111.87 (7)	C16—C18—H18B	109.5
C10—C9—C16	114.10 (7)	H18A—C18—H18B	109.5
C2—C9—H9	105.2	C16—C18—H18C	109.5
C10—C9—H9	105.2	H18A—C18—H18C	109.5
C16—C9—H9	105.2	H18B—C18—H18C	109.5

C2—Se1—N1—N2	−0.27 (7)	Se1—C2—C9—C16	56.27 (10)
Se1—N1—N2—C1	−0.06 (10)	C2—C9—C10—C11	−130.65 (9)
N1—N2—C1—C2	0.52 (12)	C16—C9—C10—C11	98.86 (10)
N1—N2—C1—C3	177.82 (8)	C2—C9—C10—C15	49.27 (12)
N2—C1—C2—C9	174.02 (8)	C16—C9—C10—C15	−81.22 (11)
C3—C1—C2—C9	−3.01 (14)	C15—C10—C11—C12	0.63 (16)
N2—C1—C2—Se1	−0.69 (10)	C9—C10—C11—C12	−179.44 (10)
C3—C1—C2—Se1	−177.72 (7)	C10—C11—C12—C13	0.08 (17)
N1—Se1—C2—C1	0.52 (7)	C11—C12—C13—C14	−0.43 (18)
N1—Se1—C2—C9	−173.98 (8)	C11—C12—C13—Cl2	−178.47 (9)
C2—C1—C3—C8	−50.52 (14)	C12—C13—C14—C15	0.03 (18)
N2—C1—C3—C8	132.50 (10)	Cl2—C13—C14—C15	178.09 (9)
C2—C1—C3—C4	127.69 (11)	C13—C14—C15—C10	0.72 (18)
N2—C1—C3—C4	−49.29 (12)	C11—C10—C15—C14	−1.04 (16)
C8—C3—C4—C5	2.21 (16)	C9—C10—C15—C14	179.04 (10)
C1—C3—C4—C5	−176.03 (10)	O1—N3—C16—C18	−4.50 (11)
C3—C4—C5—C6	0.46 (18)	O2—N3—C16—C18	175.98 (8)
C4—C5—C6—C7	−2.80 (19)	O1—N3—C16—C17	−124.49 (9)
C4—C5—C6—Cl1	176.20 (9)	O2—N3—C16—C17	55.98 (10)
C5—C6—C7—C8	2.35 (18)	O1—N3—C16—C9	119.35 (9)
Cl1—C6—C7—C8	−176.64 (9)	O2—N3—C16—C9	−60.17 (10)
C6—C7—C8—C3	0.43 (16)	C2—C9—C16—C18	−74.54 (10)
C4—C3—C8—C7	−2.67 (15)	C10—C9—C16—C18	57.11 (10)
C1—C3—C8—C7	175.54 (9)	C2—C9—C16—C17	53.95 (10)
C1—C2—C9—C10	111.01 (10)	C10—C9—C16—C17	−174.40 (8)
Se1—C2—C9—C10	−75.30 (10)	C2—C9—C16—N3	167.63 (7)
C1—C2—C9—C16	−117.41 (9)	C10—C9—C16—N3	−60.71 (9)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C9—H9···O2	1.00	2.42	2.8271 (12)	104
C15—H15···Se1	0.95	2.86	3.5496 (10)	130
C18—H18A···Se1	0.98	2.70	3.4209 (10)	130
C7—H7···O1ⁱ	0.95	2.44	3.3757 (13)	167
C15—H15···Cl1ⁱⁱ	0.95	2.76	3.5923 (10)	147
C17—H17A···N1ⁱⁱⁱ	0.98	2.57	3.4511 (13)	149
C17—H17A···N2ⁱⁱⁱ	0.98	2.60	3.3919 (13)	138

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

Experimental details

Crystal data
Chemical formula	C₁₈H₁₅Cl₂N₃O₂Se
M_r	455.19
Crystal system, space group	Triclinic, P1
Temperature (K)	100
a, b, c (Å)	7.8352 (2), 10.9208 (3), 11.5507 (3)
α, β, γ (°)	75.381 (1), 89.044 (1), 83.331 (1)
V (Å³)	949.80 (4)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	2.28
Crystal size (mm)	0.33 × 0.18 × 0.17

Data collection
Diffractometer	Bruker Kappa-APEXII diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2004)
T_min, T_max	0.507, 0.679
No. of measured, independent and observed [I > 2σ(I)] reflections	44785, 9335, 8074
R_int	0.028
(sin θ/λ)_max (Å⁻¹)	0.841

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.026, 0.064, 1.03
No. of reflections	9335
No. of parameters	237
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.57, −0.59

Computer programs: APEX2 (Bruker, 2004), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 2003).