supplementary materials


is5277 scheme

Acta Cryst. (2013). E69, o1100    [ doi:10.1107/S1600536813015365 ]

(-)-Norfluorocurarine ethanol monosolvate

S. M. Adizov, J. Ashurov, Z. Karimov, P. K. Yuldashev and B. Tashkhodjaev

Abstract top

The title compound, C19H20N2O·C2H5OH, is an ethanol solvate of an indol alkaloid which was extracted from the plant Vinca erecta. The fused piperidine ring adopts an approximate boat conformation and the pyrrolidine ring an envelope conformation with one of the methylene C atoms at the flap. An intramolecular N-H...O hydrogen bond forms an S6 ring motif. In the crystal, norfulorocurarine and ethanol molecules are linked into a chain along the c-axis direction through N-H...O and O-H...N hydrogen bonds.

Comment top

Because of possessing high biological activity, plants containing norfluorocurarine class alkaloids have been widely used in traditional medicine. A number of plants as Vinca major L. and Vinca herbacea Waldst. et Kit. are examples which are used as a healing agent in traditional medicine (Lavrenova et al., 1997). Norfluorocurarine for the first time was extracted from the root of Vinca erecta and called vincanine (Yunusov & Yuldashev, 1952). Later the alkaloid was extraxted from the upper parts of the same plant (Yunusov & Yuldashev, 1957).

Earlier unsolvated crystal form of (-)-norfluorocurarine was obtained from acetone and stereochemistry studied by Tashkhodjaev et al. (2011). When we used ethanol as a solvent, XRD experiments showed the solvated structure in the molar ratio 1:1. Crystals which were obtained in acetone and in ethanol showed the same absolute configuration of alkaloid molecule. But the crystal packing and intermolecular bonds are quite different.

In the molecule, the carbonyl group is oriented to N1—H group. The torsion angle of C2C16—C17O1 atoms is -11.7 (5)°. Therefore, the carbonyl group and N1—H group form an intramolecular hydrogen bond N1—H···O1 C17 (Table 1). In the crystal, the hydroxyl group of solvated ethanol molecules forms intermolecular hydrogen bonds with norfluorocurarine N1 and N4 atoms (Table 1). The hydrogen bonds links the norfluorocurarine and ethanol molecules along the c axis.

Related literature top

For the biological activity of plants containing norfluorocurarine class alkaloids, see: Lavrenova & Lavrenov (1997). For the isolation of norfluorocurarine from the plant Vinca erecta, see: Yunusov & Yuldashev (1952, 1957). For the physical properties and crystal structures of several norfluorocurarine solvates, see: Tashkhodjaev et al. (2011).

Experimental top

The title compound was isolated from the chloroform fraction of the plant Vinca erecta by a known method (Yunusov et al., 1957). Norflurocurarine was dissolved in ethanol and evaporated in room temperature and obtained suitable for X-ray crystals. Since the crystal was unstable in air, we covered it with epoxide glue.

Refinement top

The H atoms bonded to N1 and O2 were located in a difference Fourier map and refined isotropically. The H atoms bonded to C atoms were placed geometrically (with C—H distances of 0.98 Å for CH, 0.97 Å for CH2, 0.96 Å for CH3 and 0.93 Å for Car) and included in the refinement in a riding motion approximation with Uiso(H) = 1.2Ueq(C) [Uiso(H) = 1.5Ueq(C) for methyl H atoms].

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXS97 (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, showing the atomic numbering scheme and displacement ellipsoids drawn at the 30% probability level.
(-)-Norfluorocurarine ethanol monosolvate top
Crystal data top
C19H20N2O·C2H6OF(000) = 728
Mr = 338.44Dx = 1.208 Mg m3
Orthorhombic, P212121Cu Kα radiation, λ = 1.54184 Å
Hall symbol: P 2ac 2abCell parameters from 1783 reflections
a = 7.0138 (5) Åθ = 3.8–75.7°
b = 16.090 (1) ŵ = 0.62 mm1
c = 16.490 (2) ÅT = 293 K
V = 1860.9 (3) Å3Prysmatic, orange
Z = 40.60 × 0.30 × 0.20 mm
Data collection top
Oxford Xcalibur, Ruby
diffractometer
3178 independent reflections
Radiation source: fine-focus sealed tube2393 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.027
Detector resolution: 10.2576 pixels mm-1θmax = 70.0°, θmin = 3.8°
ω–scanh = 87
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2009)
k = 1917
Tmin = 0.801, Tmax = 0.884l = 1820
5608 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.051H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.142 w = 1/[σ2(Fo2) + (0.0858P)2]
where P = (Fo2 + 2Fc2)/3
S = 0.99(Δ/σ)max < 0.001
3178 reflectionsΔρmax = 0.33 e Å3
237 parametersΔρmin = 0.19 e Å3
0 restraintsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0029 (5)
Crystal data top
C19H20N2O·C2H6OV = 1860.9 (3) Å3
Mr = 338.44Z = 4
Orthorhombic, P212121Cu Kα radiation
a = 7.0138 (5) ŵ = 0.62 mm1
b = 16.090 (1) ÅT = 293 K
c = 16.490 (2) Å0.60 × 0.30 × 0.20 mm
Data collection top
Oxford Xcalibur, Ruby
diffractometer
3178 independent reflections
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2009)
2393 reflections with I > 2σ(I)
Tmin = 0.801, Tmax = 0.884Rint = 0.027
5608 measured reflectionsθmax = 70.0°
Refinement top
R[F2 > 2σ(F2)] = 0.051H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.142Δρmax = 0.33 e Å3
S = 0.99Δρmin = 0.19 e Å3
3178 reflectionsAbsolute structure: ?
237 parametersAbsolute structure parameter: ?
0 restraintsRogers parameter: ?
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
O10.3603 (4)0.42899 (18)0.25960 (15)0.0803 (8)
N10.3795 (4)0.54279 (16)0.38661 (17)0.0502 (6)
C20.2579 (4)0.48488 (18)0.41767 (17)0.0449 (6)
C30.1580 (4)0.44089 (18)0.56238 (18)0.0480 (7)
H3A0.23810.44950.61030.058*
N40.0460 (3)0.44531 (15)0.58692 (15)0.0497 (6)
C50.1003 (4)0.53164 (17)0.57301 (18)0.0502 (7)
H5A0.05570.56670.61690.060*
H5B0.23780.53680.56900.060*
C60.0061 (4)0.55619 (17)0.49369 (18)0.0458 (7)
H6A0.00520.61610.48900.055*
H6B0.07690.53500.44750.055*
C70.1943 (4)0.51410 (16)0.50026 (16)0.0415 (6)
C80.3434 (4)0.57872 (15)0.51991 (17)0.0429 (6)
C90.3820 (4)0.62291 (17)0.58936 (18)0.0483 (7)
H9A0.31780.61140.63740.058*
C100.5188 (5)0.68503 (18)0.5862 (2)0.0548 (8)
H10A0.54900.71440.63300.066*
C110.6111 (4)0.70392 (17)0.5142 (2)0.0545 (8)
H11A0.70140.74630.51340.065*
C120.5718 (4)0.66105 (18)0.4433 (2)0.0519 (8)
H12A0.63230.67400.39480.062*
C130.4380 (4)0.59779 (17)0.44827 (19)0.0451 (6)
C140.2033 (5)0.35663 (17)0.5262 (2)0.0561 (8)
H14A0.15690.31290.56150.067*
H14B0.34010.35020.52030.067*
C150.1066 (5)0.35033 (17)0.4430 (2)0.0542 (8)
H15A0.12390.29370.42240.065*
C160.2053 (4)0.41012 (19)0.3855 (2)0.0507 (7)
C170.2757 (5)0.3843 (2)0.3081 (2)0.0644 (9)
H17A0.25570.32930.29320.077*
C180.2094 (6)0.3305 (2)0.3113 (2)0.0717 (10)
H18A0.30630.29090.29700.108*
H18B0.08620.30490.30640.108*
H18C0.21670.37740.27550.108*
C190.2388 (5)0.35864 (19)0.3968 (2)0.0591 (8)
H19A0.36320.37250.41100.071*
C200.1099 (5)0.36621 (16)0.4544 (2)0.0519 (7)
C210.1658 (4)0.3855 (2)0.5405 (2)0.0578 (8)
H21A0.29510.40690.53980.069*
H21B0.16820.33360.57030.069*
O20.6272 (5)0.5922 (2)0.2494 (2)0.0966 (10)
C220.8184 (10)0.5554 (3)0.2572 (3)0.122 (2)
H22A0.83170.53000.31020.146*
H22B0.83520.51250.21650.146*
C230.9609 (10)0.6183 (5)0.2469 (4)0.142 (2)
H23A1.08520.59350.24980.213*
H23B0.94820.65910.28900.213*
H23C0.94490.64450.19510.213*
H10.428 (5)0.544 (2)0.338 (2)0.073 (12)*
H20.599 (8)0.585 (3)0.193 (3)0.125 (19)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0735 (16)0.1134 (19)0.0539 (16)0.0183 (17)0.0078 (14)0.0189 (14)
N10.0464 (13)0.0663 (14)0.0377 (15)0.0053 (12)0.0064 (12)0.0009 (11)
C20.0343 (13)0.0568 (14)0.0435 (17)0.0022 (13)0.0031 (12)0.0060 (12)
C30.0483 (15)0.0554 (15)0.0403 (17)0.0032 (13)0.0033 (13)0.0104 (12)
N40.0471 (13)0.0575 (13)0.0446 (15)0.0064 (11)0.0011 (11)0.0065 (11)
C50.0431 (15)0.0573 (16)0.0503 (19)0.0014 (13)0.0048 (13)0.0017 (13)
C60.0386 (13)0.0491 (14)0.0496 (19)0.0003 (12)0.0025 (13)0.0056 (13)
C70.0421 (14)0.0448 (12)0.0374 (16)0.0035 (11)0.0002 (12)0.0046 (11)
C80.0391 (14)0.0467 (14)0.0429 (16)0.0034 (12)0.0034 (12)0.0068 (11)
C90.0463 (15)0.0536 (15)0.0452 (17)0.0026 (14)0.0017 (14)0.0012 (12)
C100.0530 (18)0.0528 (16)0.059 (2)0.0033 (14)0.0081 (16)0.0091 (15)
C110.0400 (15)0.0482 (14)0.075 (2)0.0026 (13)0.0006 (16)0.0034 (14)
C120.0408 (15)0.0559 (16)0.059 (2)0.0014 (13)0.0056 (15)0.0046 (14)
C130.0402 (13)0.0517 (14)0.0433 (17)0.0034 (12)0.0011 (13)0.0033 (12)
C140.0549 (18)0.0500 (15)0.063 (2)0.0010 (14)0.0056 (16)0.0103 (14)
C150.0532 (17)0.0443 (13)0.065 (2)0.0029 (13)0.0015 (17)0.0026 (13)
C160.0426 (14)0.0571 (16)0.0523 (18)0.0017 (13)0.0007 (14)0.0054 (14)
C170.0554 (18)0.074 (2)0.063 (2)0.0033 (18)0.0025 (18)0.0231 (17)
C180.067 (2)0.074 (2)0.074 (3)0.0043 (19)0.007 (2)0.0130 (18)
C190.0529 (18)0.0570 (16)0.067 (2)0.0049 (15)0.0005 (17)0.0034 (15)
C200.0522 (17)0.0448 (14)0.059 (2)0.0074 (13)0.0003 (16)0.0029 (13)
C210.0508 (17)0.0622 (17)0.061 (2)0.0128 (14)0.0042 (16)0.0074 (15)
O20.0799 (19)0.159 (3)0.0515 (18)0.028 (2)0.0055 (16)0.0156 (18)
C220.194 (6)0.102 (3)0.068 (3)0.011 (4)0.040 (4)0.007 (3)
C230.128 (5)0.167 (6)0.132 (5)0.044 (4)0.007 (4)0.002 (5)
Geometric parameters (Å, º) top
O1—C171.228 (4)C12—C131.387 (4)
N1—C21.363 (4)C12—H12A0.9300
N1—C131.409 (4)C14—C151.533 (5)
N1—H10.87 (4)C14—H14A0.9700
C2—C161.365 (4)C14—H14B0.9700
C2—C71.508 (4)C15—C161.518 (4)
C3—N41.489 (4)C15—C201.551 (5)
C3—C141.515 (4)C15—H15A0.9800
C3—C71.582 (3)C16—C171.431 (5)
C3—H3A0.9800C17—H17A0.9300
N4—C51.459 (4)C18—C191.496 (5)
N4—C211.489 (4)C18—H18A0.9600
C5—C61.518 (4)C18—H18B0.9600
C5—H5A0.9700C18—H18C0.9600
C5—H5B0.9700C19—C201.317 (5)
C6—C71.564 (4)C19—H19A0.9300
C6—H6A0.9700C20—C211.505 (5)
C6—H6B0.9700C21—H21A0.9700
C7—C81.509 (4)C21—H21B0.9700
C8—C91.375 (4)O2—C221.471 (7)
C8—C131.389 (4)O2—H20.95 (5)
C9—C101.387 (4)C22—C231.433 (8)
C9—H9A0.9300C22—H22A0.9700
C10—C111.386 (4)C22—H22B0.9700
C10—H10A0.9300C23—H23A0.9600
C11—C121.384 (4)C23—H23B0.9600
C11—H11A0.9300C23—H23C0.9600
C2—N1—C13109.9 (3)C8—C13—N1109.6 (2)
C2—N1—H1128 (2)C3—C14—C15108.6 (2)
C13—N1—H1122 (2)C3—C14—H14A110.0
N1—C2—C16128.7 (3)C15—C14—H14A110.0
N1—C2—C7108.1 (2)C3—C14—H14B110.0
C16—C2—C7123.0 (3)C15—C14—H14B110.0
N4—C3—C14110.6 (2)H14A—C14—H14B108.4
N4—C3—C7107.2 (2)C16—C15—C14108.3 (3)
C14—C3—C7112.2 (2)C16—C15—C20114.7 (2)
N4—C3—H3A109.0C14—C15—C20108.3 (3)
C14—C3—H3A109.0C16—C15—H15A108.4
C7—C3—H3A109.0C14—C15—H15A108.4
C5—N4—C3104.7 (2)C20—C15—H15A108.4
C5—N4—C21112.8 (2)C2—C16—C17120.6 (3)
C3—N4—C21111.8 (2)C2—C16—C15116.1 (3)
N4—C5—C6105.6 (2)C17—C16—C15122.1 (3)
N4—C5—H5A110.6O1—C17—C16125.3 (3)
C6—C5—H5A110.6O1—C17—H17A117.3
N4—C5—H5B110.6C16—C17—H17A117.3
C6—C5—H5B110.6C19—C18—H18A109.5
H5A—C5—H5B108.7C19—C18—H18B109.5
C5—C6—C7102.6 (2)H18A—C18—H18B109.5
C5—C6—H6A111.2C19—C18—H18C109.5
C7—C6—H6A111.2H18A—C18—H18C109.5
C5—C6—H6B111.2H18B—C18—H18C109.5
C7—C6—H6B111.2C20—C19—C18127.8 (3)
H6A—C6—H6B109.2C20—C19—H19A116.1
C2—C7—C8101.8 (2)C18—C19—H19A116.1
C2—C7—C6109.8 (2)C19—C20—C21121.4 (3)
C8—C7—C6109.8 (2)C19—C20—C15124.7 (3)
C2—C7—C3113.6 (2)C21—C20—C15113.7 (3)
C8—C7—C3119.0 (2)N4—C21—C20118.1 (2)
C6—C7—C3102.9 (2)N4—C21—H21A107.8
C9—C8—C13120.0 (3)C20—C21—H21A107.8
C9—C8—C7132.2 (3)N4—C21—H21B107.8
C13—C8—C7107.5 (2)C20—C21—H21B107.8
C8—C9—C10118.5 (3)H21A—C21—H21B107.1
C8—C9—H9A120.7C22—O2—H2103 (3)
C10—C9—H9A120.7C23—C22—O2110.0 (5)
C11—C10—C9120.9 (3)C23—C22—H22A109.7
C11—C10—H10A119.5O2—C22—H22A109.7
C9—C10—H10A119.5C23—C22—H22B109.7
C12—C11—C10121.3 (3)O2—C22—H22B109.7
C12—C11—H11A119.3H22A—C22—H22B108.2
C10—C11—H11A119.3C22—C23—H23A109.5
C11—C12—C13116.8 (3)C22—C23—H23B109.5
C11—C12—H12A121.6H23A—C23—H23B109.5
C13—C12—H12A121.6C22—C23—H23C109.5
C12—C13—C8122.4 (3)H23A—C23—H23C109.5
C12—C13—N1128.0 (3)H23B—C23—H23C109.5
C13—N1—C2—C16162.4 (3)C10—C11—C12—C130.9 (4)
C13—N1—C2—C713.9 (3)C11—C12—C13—C81.4 (4)
C14—C3—N4—C5146.6 (2)C11—C12—C13—N1176.8 (3)
C7—C3—N4—C524.0 (3)C9—C8—C13—C120.4 (4)
C14—C3—N4—C2124.2 (3)C7—C8—C13—C12173.6 (2)
C7—C3—N4—C2198.4 (3)C9—C8—C13—N1178.1 (2)
C3—N4—C5—C640.5 (3)C7—C8—C13—N17.9 (3)
C21—N4—C5—C681.3 (3)C2—N1—C13—C12174.5 (3)
N4—C5—C6—C740.3 (3)C2—N1—C13—C83.9 (3)
N1—C2—C7—C817.6 (3)N4—C3—C14—C1570.8 (3)
C16—C2—C7—C8159.0 (3)C7—C3—C14—C1548.7 (3)
N1—C2—C7—C698.7 (3)C3—C14—C15—C1668.8 (3)
C16—C2—C7—C684.7 (3)C3—C14—C15—C2056.2 (3)
N1—C2—C7—C3146.8 (2)N1—C2—C16—C171.8 (5)
C16—C2—C7—C329.8 (4)C7—C2—C16—C17177.7 (3)
C5—C6—C7—C2145.0 (2)N1—C2—C16—C15165.5 (3)
C5—C6—C7—C8104.0 (2)C7—C2—C16—C1510.3 (4)
C5—C6—C7—C323.7 (3)C14—C15—C16—C238.9 (4)
N4—C3—C7—C2119.1 (3)C20—C15—C16—C282.2 (3)
C14—C3—C7—C22.4 (3)C14—C15—C16—C17128.2 (3)
N4—C3—C7—C8121.1 (3)C20—C15—C16—C17110.7 (3)
C14—C3—C7—C8117.4 (3)C2—C16—C17—O111.7 (5)
N4—C3—C7—C60.6 (3)C15—C16—C17—O1178.3 (3)
C14—C3—C7—C6120.9 (3)C18—C19—C20—C21172.5 (3)
C2—C7—C8—C9171.9 (3)C18—C19—C20—C152.8 (5)
C6—C7—C8—C971.9 (4)C16—C15—C20—C1964.9 (4)
C3—C7—C8—C946.2 (4)C14—C15—C20—C19173.9 (3)
C2—C7—C8—C1315.1 (3)C16—C15—C20—C21119.4 (3)
C6—C7—C8—C13101.1 (3)C14—C15—C20—C211.7 (3)
C3—C7—C8—C13140.8 (3)C5—N4—C21—C2085.3 (3)
C13—C8—C9—C101.2 (4)C3—N4—C21—C2032.3 (4)
C7—C8—C9—C10173.5 (3)C19—C20—C21—N4139.5 (3)
C8—C9—C10—C111.8 (4)C15—C20—C21—N444.7 (4)
C9—C10—C11—C120.7 (5)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O10.87 (3)2.31 (3)2.785 (4)115 (3)
N1—H1···O20.87 (3)2.17 (3)2.961 (4)152 (3)
O2—H2···N4i0.96 (5)1.85 (5)2.805 (4)172 (5)
Symmetry code: (i) x+1/2, y+1, z1/2.

Experimental details

Crystal data
Chemical formulaC19H20N2O·C2H6O
Mr338.44
Crystal system, space groupOrthorhombic, P212121
Temperature (K)293
a, b, c (Å)7.0138 (5), 16.090 (1), 16.490 (2)
V3)1860.9 (3)
Z4
Radiation typeCu Kα
µ (mm1)0.62
Crystal size (mm)0.60 × 0.30 × 0.20
Data collection
DiffractometerOxford Xcalibur, Ruby
diffractometer
Absorption correctionMulti-scan
(CrysAlis PRO; Oxford Diffraction, 2009)
Tmin, Tmax0.801, 0.884
No. of measured, independent and
observed [I > 2σ(I)] reflections
5608, 3178, 2393
Rint0.027
(sin θ/λ)max1)0.609
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.051, 0.142, 0.99
No. of reflections3178
No. of parameters237
No. of restraints0
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.33, 0.19

Computer programs: CrysAlis PRO (Oxford Diffraction, 2009), SHELXS97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O10.87 (3)2.31 (3)2.785 (4)115 (3)
N1—H1···O20.87 (3)2.17 (3)2.961 (4)152 (3)
O2—H2···N4i0.96 (5)1.85 (5)2.805 (4)172 (5)
Symmetry code: (i) x+1/2, y+1, z1/2.
Acknowledgements top

We thank the Academy of Sciences of the Republic of Uzbekistan for supporting this study (grant No. FA-F7-T185)

references
References top

Lavrenova, G. V. & Lavrenov, V. K. (1997). Entsiklopedia lekarstvennykh rastenii, Vol. 1. Ukraine: Donnechina.

Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Tashkhodjaev, B., Turgunov, K. K., Yuldashev, P. Kh. & Mirzaeva, M. M. (2011). Chem. Nat. Compd. 47, 531–535.

Yunusov, S. Yu. & Yuldashev, P. Kh. (1952). Dokl. Akad. Nauk Uzbekiskoi SSR, 12, 24–27.

Yunusov, S. Yu. & Yuldashev, P. Kh. (1957). Zh. Obshch. Khim. 27, 2015–2018.