supplementary materials


kj2223 scheme

Acta Cryst. (2013). E69, o689    [ doi:10.1107/S1600536813008647 ]

2-[3-(Pyridin-1-ium-2-yl)-1H-pyrazol-1-yl]-6-[3-(pyridin-2-yl)-1H-pyrazol-1-yl]pyridinium sulfate methanol monosolvate

L. Huang and M. Shu

Abstract top

The title solvated salt, C21H17N72+·SO42-·CH3OH, was obtained when we attempted to prepare the complex of ferrous sulfate and 2,6-bis[3-(pyridin-2-yl)-1H-pyrazol-1-yl]pyridine in methanol. The dihedral angles between adjacent pyridine and pyrazole rings range from 3.8 (1) to 13.4 (1)°. An intramolecular N-H...N hydrogen bond occurs. In the crystal, N-H...O and O-H...N hydrogen bonds between solvent methanol molecules and the cations generate zigzag chains along [110].

Comment top

Helicates can be obtained by the self assembly of oligopyridine ligands with transition metal ions (Constable, 1992). 2,6':2',6":2",6'":2'",6""-Quinquepyridine reacts with AgI ions to give a mononuclear single-stranded helical complex (Constable et al. 1988). MnII single-stranded helicates bridged by Cl- (Fu, Li et al. 1996) and AgI dinuclear double-stranded helicates (Fu, Sun et al. 1996) were obtained from the quinquepyridine when methyl groups were introduced at the 6 and 6"" positions. The presence of alkyl groups bound to the 4 and 4' positions of quaterpyridine leads to the complete formation of the head-to-head conformer over the head-to-tail conformer (Constable et al. 1997). This encouraged us to investigate the coordination chemistry of transition metal ions with a new ligand containing a N5 donor set. In this work, 2,6-di[3-(2-pyridyl)-1H-pyrazol-1-yl]-pyridine (Jameson & Goldsby, 1990) was used to react with ferrous sulfate in methanol, and the title compoud was obtained as yellow crystals.

In the structure, dihedral angles between the pyrazole and the pyridine rings (the rings are defined by the nitrogen atoms) are as follows: N1/N2N3 = 3.8 (1), N2N3/N4 = 4.3 (1), N4/N5N6 = 13.4 (1), N5N6/N7 =4.3 (1) °. Intramolecular N—H···N hydrogen bond and intermolecular N—H···O, and O—H···N hydrogen bonds were observed in the crystal. The intermolecular N—H···O and O—H···N hydrogen bonds between solvent methanol molecules and the organic molecules generate zigzag hydrogen bond chains running in the [110] direction.

Related literature top

For general background to the chemistry of oligapyridine ligands, see: Constable et al. (1988, 1992, 1997); Fu, Li et al. (1996); Fu, Sun et al. (1996). For the synthesis of the ligand, see: Jameson & Goldsby (1990).

Experimental top

2,6-Di[3-(2-pyridyl)-1H-pyrazol-1-yl]-pyridine was prepared using methods described in the literature (Jameson & Goldsby, 1990). A solution of 2-(1H-pyrazol-3-yl)-pyridine (11.76 g, 81 mmol) in 100 ml of anhydrous 2-methoxyethyl ether was stirred with potassium (6.0 g, 153 mmol) at 70 ° C under argon until the metal dissolved. To this solution was aadded 2,6-dibromopyridine (5.90 g, 24.8 mmol) in one portion. The mixture was stirred at 110 ° C for 4 days. The crude product was washed with hot water twice, and recrystallized from dichloromethane-hexane, 2,6-di[3- (2-pyridyl)-1H-pyrazol-1-yl]-pyridine was obtained as light yellow powder (yield 60%).

2,6-Di[3-(2-pyridyl)-1H-pyrazol-1-yl]-pyridine (18.3 mg, 0.05 mmol) and FeSO4.4H2O (14 mg, 0.05 mmol) were mixed in methanol (3 ml) in a vial, the vial was covered and heated to 60 ° C for 48 h. After cooling, the title compound was obtained as yellow crystals suitable for X-ray structure analysis.

Refinement top

H atoms bonded to O atoms were located in a difference map. Other H atoms were positioned geometrically and refined using a riding model with N—H = 0.86 (aromatic), C—H = 0.93 (aromatic) and C—H = 0.96 (CH3). All H atoms were refined with Uiso(H) = 1.2 times (1.5 for methyl groups) Ueq(C). The four oxygen atoms in sulfate anion are disordered over two positions. The site occupancy factors of these disordered oxygen atoms were refined by free variable to 0.782 (10) for O1, O2, O3 and O4, and 0.218 (10) for O1', O2', O3'and O4', respectively, with distances restraints of S—O = 1.44 (1) Å and angles restraints of O—S—O = 109.5°. Only the major component O atoms were refined with anisotropic displacement parameters.

Computing details top

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); 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: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title complex with atom labels and 30% probability displacement ellipsoids for non-H atoms.
[Figure 2] Fig. 2. The chain formed by the lintermolecular N—H···O, and O—H···N hydrogen bonds (dashed lines) in the crystal. H atoms not involved in hydrogen bonding have been omitted for clarity.
2-[3-(Pyridin-1-ium-2-yl)-1H-pyrazol-1-yl]-6-[3-(pyridin-2-yl)-1H-pyrazol-1-yl]pyridinium sulfate methanol monosolvate top
Crystal data top
C21H17N72+·SO42·CH4OZ = 2
Mr = 495.52F(000) = 516
Triclinic, P1Dx = 1.439 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 9.2575 (5) ÅCell parameters from 2589 reflections
b = 12.1707 (7) Åθ = 3.3–29.3°
c = 12.1991 (7) ŵ = 0.19 mm1
α = 112.786 (6)°T = 293 K
β = 100.997 (5)°Block, yellow
γ = 106.363 (5)°0.26 × 0.23 × 0.20 mm
V = 1143.90 (11) Å3
Data collection top
Bruker APEX CCD area-detector
diffractometer
4192 independent reflections
Radiation source: fine-focus sealed tube2629 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.027
Detector resolution: 10.3592 pixels mm-1θmax = 25.4°, θmin = 3.3°
phi and ω scansh = 1111
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
k = 1214
Tmin = 0.952, Tmax = 0.963l = 1414
7326 measured reflections
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)] = 0.053Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.163H atoms treated by a mixture of independent and constrained refinement
S = 1.01 w = 1/[σ2(Fo2) + (0.092P)2 + 0.0074P]
where P = (Fo2 + 2Fc2)/3
4192 reflections(Δ/σ)max < 0.001
334 parametersΔρmax = 0.28 e Å3
21 restraintsΔρmin = 0.39 e Å3
Crystal data top
C21H17N72+·SO42·CH4Oγ = 106.363 (5)°
Mr = 495.52V = 1143.90 (11) Å3
Triclinic, P1Z = 2
a = 9.2575 (5) ÅMo Kα radiation
b = 12.1707 (7) ŵ = 0.19 mm1
c = 12.1991 (7) ÅT = 293 K
α = 112.786 (6)°0.26 × 0.23 × 0.20 mm
β = 100.997 (5)°
Data collection top
Bruker APEX CCD area-detector
diffractometer
4192 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
2629 reflections with I > 2σ(I)
Tmin = 0.952, Tmax = 0.963Rint = 0.027
7326 measured reflectionsθmax = 25.4°
Refinement top
R[F2 > 2σ(F2)] = 0.053H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.163Δρmax = 0.28 e Å3
S = 1.01Δρmin = 0.39 e Å3
4192 reflectionsAbsolute structure: ?
334 parametersFlack parameter: ?
21 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*/UeqOcc. (<1)
S10.08891 (9)0.24309 (9)0.39262 (8)0.0688 (3)
O10.0316 (7)0.2731 (8)0.3422 (6)0.143 (2)0.782 (10)
O20.1501 (6)0.1801 (6)0.2961 (4)0.123 (2)0.782 (10)
O30.0335 (7)0.1588 (5)0.4409 (6)0.146 (2)0.782 (10)
O40.2181 (6)0.3518 (4)0.4819 (6)0.145 (3)0.782 (10)
O1'0.034 (3)0.262 (3)0.320 (3)0.177 (7)*0.218 (10)
O2'0.033 (3)0.1150 (12)0.373 (2)0.177 (7)*0.218 (10)
O3'0.127 (3)0.3358 (19)0.5232 (11)0.177 (7)*0.218 (10)
O4'0.231 (2)0.281 (3)0.366 (3)0.177 (7)*0.218 (10)
O50.0119 (3)0.2807 (3)0.8003 (2)0.0970 (9)
H50.042 (5)0.344 (3)0.875 (2)0.146*
N10.2107 (3)0.4485 (2)1.0422 (2)0.0633 (7)
N20.4816 (3)0.7105 (2)1.01850 (19)0.0505 (6)
N30.4380 (3)0.7522 (2)0.9335 (2)0.0510 (6)
N40.4932 (3)0.8909 (2)0.84709 (19)0.0498 (6)
H4A0.39470.85120.79840.060*
N50.5238 (3)1.0240 (2)0.7534 (2)0.0501 (6)
N60.6192 (3)1.1068 (2)0.7231 (2)0.0510 (6)
N70.7420 (3)1.2708 (2)0.6334 (2)0.0594 (6)
H70.79901.26190.69130.071*
C10.2076 (4)0.3868 (3)1.1128 (3)0.0732 (9)
H10.11240.31951.09300.088*
C20.3357 (4)0.4170 (3)1.2119 (3)0.0681 (9)
H20.32740.37221.25870.082*
C30.4761 (4)0.5147 (3)1.2404 (3)0.0653 (9)
H30.56600.53611.30620.078*
C40.4840 (3)0.5811 (3)1.1715 (2)0.0552 (7)
H40.57890.64821.19020.066*
C50.3484 (3)0.5469 (3)1.0735 (2)0.0481 (7)
C60.3476 (3)0.6161 (3)0.9981 (2)0.0506 (7)
C70.2185 (3)0.5979 (3)0.9010 (3)0.0622 (8)
H7A0.11340.53830.87000.075*
C80.2800 (4)0.6859 (3)0.8621 (3)0.0611 (8)
H80.22470.69840.79880.073*
C90.5506 (3)0.8563 (3)0.9304 (2)0.0477 (6)
C100.7073 (3)0.9165 (3)1.0114 (3)0.0572 (7)
H100.74300.88941.06900.069*
C110.8084 (4)1.0183 (3)1.0032 (3)0.0636 (8)
H110.91471.06141.05600.076*
C120.7519 (3)1.0566 (3)0.9164 (3)0.0581 (7)
H120.81821.12470.90900.070*
C130.5926 (3)0.9889 (3)0.8413 (2)0.0477 (6)
C140.3652 (3)0.9869 (3)0.6920 (3)0.0565 (7)
H140.27900.93080.69820.068*
C150.3582 (3)1.0485 (3)0.6199 (3)0.0584 (7)
H150.26691.04310.56690.070*
C160.5178 (3)1.1216 (3)0.6422 (2)0.0507 (7)
C170.5826 (3)1.2052 (3)0.5893 (2)0.0515 (7)
C180.4928 (4)1.2218 (3)0.4983 (3)0.0623 (8)
H180.38221.17750.46580.075*
C190.5648 (5)1.3030 (4)0.4550 (3)0.0745 (10)
H190.50281.31450.39410.089*
C200.7278 (5)1.3675 (3)0.5008 (3)0.0786 (10)
H200.77731.42230.47110.094*
C210.8167 (4)1.3495 (3)0.5917 (3)0.0729 (9)
H210.92761.39170.62380.087*
C220.0440 (5)0.1814 (5)0.7471 (4)0.1141 (14)
H22A0.04330.16810.66410.171*
H22B0.02460.10240.74170.171*
H22C0.15110.20660.79970.171*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0483 (5)0.0784 (6)0.0764 (6)0.0165 (4)0.0085 (4)0.0448 (5)
O10.090 (3)0.216 (6)0.144 (4)0.085 (3)0.009 (3)0.102 (4)
O20.119 (4)0.146 (5)0.108 (3)0.061 (4)0.046 (3)0.053 (3)
O30.193 (5)0.137 (4)0.151 (5)0.051 (4)0.087 (4)0.105 (4)
O40.112 (3)0.080 (3)0.146 (4)0.014 (2)0.060 (3)0.025 (3)
O50.0841 (17)0.0708 (18)0.0880 (18)0.0114 (15)0.0245 (14)0.0295 (15)
N10.0612 (16)0.0629 (17)0.0612 (15)0.0157 (14)0.0120 (13)0.0350 (14)
N20.0603 (15)0.0498 (14)0.0427 (12)0.0229 (13)0.0153 (11)0.0231 (11)
N30.0574 (14)0.0456 (14)0.0464 (12)0.0191 (12)0.0135 (11)0.0208 (11)
N40.0498 (13)0.0459 (14)0.0433 (12)0.0162 (12)0.0099 (10)0.0156 (11)
N50.0551 (14)0.0462 (14)0.0478 (13)0.0199 (12)0.0161 (11)0.0217 (12)
N60.0549 (13)0.0464 (14)0.0482 (13)0.0182 (12)0.0130 (11)0.0220 (11)
N70.0757 (18)0.0522 (15)0.0476 (13)0.0229 (14)0.0098 (12)0.0276 (12)
C10.075 (2)0.071 (2)0.079 (2)0.0189 (18)0.0226 (18)0.048 (2)
C20.079 (2)0.078 (2)0.0627 (19)0.035 (2)0.0237 (18)0.0445 (19)
C30.082 (2)0.076 (2)0.0429 (16)0.044 (2)0.0162 (16)0.0251 (17)
C40.0577 (17)0.0513 (18)0.0465 (15)0.0196 (15)0.0112 (14)0.0177 (14)
C50.0535 (16)0.0457 (17)0.0437 (14)0.0205 (14)0.0167 (13)0.0187 (13)
C60.0558 (17)0.0440 (16)0.0458 (15)0.0196 (14)0.0134 (13)0.0170 (13)
C70.0514 (17)0.0538 (19)0.0665 (18)0.0087 (15)0.0031 (15)0.0301 (16)
C80.0600 (19)0.0566 (19)0.0597 (18)0.0196 (16)0.0044 (15)0.0303 (16)
C90.0535 (16)0.0453 (16)0.0424 (14)0.0215 (14)0.0165 (13)0.0173 (13)
C100.0591 (18)0.063 (2)0.0544 (17)0.0257 (16)0.0172 (15)0.0314 (16)
C110.0526 (17)0.073 (2)0.0581 (18)0.0192 (17)0.0113 (14)0.0305 (17)
C120.0539 (17)0.0571 (19)0.0592 (17)0.0154 (15)0.0172 (15)0.0287 (16)
C130.0545 (16)0.0451 (17)0.0427 (14)0.0208 (14)0.0166 (13)0.0188 (13)
C140.0522 (17)0.0539 (18)0.0522 (16)0.0184 (15)0.0122 (14)0.0185 (15)
C150.0560 (18)0.0578 (19)0.0530 (16)0.0247 (16)0.0103 (14)0.0202 (15)
C160.0635 (18)0.0450 (17)0.0409 (14)0.0263 (15)0.0137 (13)0.0160 (13)
C170.0630 (19)0.0444 (16)0.0431 (15)0.0258 (15)0.0129 (14)0.0157 (13)
C180.076 (2)0.068 (2)0.0525 (16)0.0421 (18)0.0160 (15)0.0295 (17)
C190.108 (3)0.080 (2)0.0595 (19)0.057 (2)0.028 (2)0.0413 (19)
C200.119 (3)0.068 (2)0.066 (2)0.042 (2)0.036 (2)0.041 (2)
C210.085 (2)0.060 (2)0.0634 (19)0.0145 (19)0.0183 (18)0.0320 (18)
C220.105 (3)0.122 (4)0.106 (3)0.047 (3)0.019 (3)0.051 (3)
Geometric parameters (Å, º) top
S1—O41.365 (3)C3—H30.9300
S1—O11.378 (3)C4—C51.387 (4)
S1—O31.396 (3)C4—H40.9300
S1—O2'1.400 (9)C5—C61.469 (4)
S1—O4'1.403 (9)C6—C71.411 (4)
S1—O1'1.432 (9)C7—C81.359 (4)
S1—O21.448 (4)C7—H7A0.9300
S1—O3'1.451 (9)C8—H80.9300
O5—C221.422 (5)C9—C101.382 (4)
O5—H50.863 (11)C10—C111.378 (4)
N1—C11.342 (4)C10—H100.9300
N1—C51.344 (3)C11—C121.385 (4)
N2—C61.334 (3)C11—H110.9300
N2—N31.363 (3)C12—C131.381 (4)
N3—C81.362 (4)C12—H120.9300
N3—C91.415 (3)C14—C151.362 (4)
N4—C91.321 (3)C14—H140.9300
N4—C131.321 (3)C15—C161.402 (4)
N4—H4A0.8600C15—H150.9300
N5—N61.357 (3)C16—C171.458 (4)
N5—C141.366 (3)C17—C181.372 (4)
N5—C131.410 (3)C18—C191.366 (5)
N6—C161.329 (3)C18—H180.9300
N7—C211.339 (4)C19—C201.370 (5)
N7—C171.343 (4)C19—H190.9300
N7—H70.8600C20—C211.377 (4)
C1—C21.367 (4)C20—H200.9300
C1—H10.9300C21—H210.9300
C2—C31.364 (4)C22—H22A0.9600
C2—H20.9300C22—H22B0.9600
C3—C41.372 (4)C22—H22C0.9600
O4—S1—O1111.7 (4)N1—C5—C6116.3 (2)
O4—S1—O3111.2 (3)C4—C5—C6121.8 (3)
O1—S1—O3111.2 (4)N2—C6—C7111.2 (2)
O4—S1—O2'132.2 (10)N2—C6—C5120.1 (2)
O1—S1—O2'112.3 (12)C7—C6—C5128.6 (3)
O3—S1—O2'33.1 (10)C8—C7—C6105.5 (3)
O4—S1—O4'60.1 (10)C8—C7—H7A127.2
O1—S1—O4'116.2 (10)C6—C7—H7A127.2
O3—S1—O4'131.3 (9)C7—C8—N3106.9 (2)
O2'—S1—O4'113.6 (11)C7—C8—H8126.6
O4—S1—O1'116.8 (13)N3—C8—H8126.6
O1—S1—O1'9.8 (16)N4—C9—C10124.0 (3)
O3—S1—O1'114.6 (14)N4—C9—N3114.9 (2)
O2'—S1—O1'109.6 (12)C10—C9—N3121.0 (2)
O4'—S1—O1'110.6 (13)C11—C10—C9117.2 (3)
O4—S1—O2104.5 (3)C11—C10—H10121.4
O1—S1—O2110.1 (3)C9—C10—H10121.4
O3—S1—O2107.8 (3)C10—C11—C12120.2 (3)
O2'—S1—O277.0 (10)C10—C11—H11119.9
O4'—S1—O245.5 (11)C12—C11—H11119.9
O1'—S1—O2100.4 (13)C13—C12—C11116.9 (3)
O4—S1—O3'44.6 (9)C13—C12—H12121.5
O1—S1—O3'96.3 (11)C11—C12—H12121.5
O3—S1—O3'79.9 (9)N4—C13—C12124.2 (2)
O2'—S1—O3'112.3 (11)N4—C13—N5115.0 (2)
O4'—S1—O3'104.6 (11)C12—C13—N5120.7 (3)
O1'—S1—O3'105.8 (12)C15—C14—N5106.4 (3)
O2—S1—O3'146.4 (10)C15—C14—H14126.8
C22—O5—H5120 (3)N5—C14—H14126.8
C1—N1—C5117.1 (3)C14—C15—C16105.5 (2)
C6—N2—N3104.5 (2)C14—C15—H15127.2
C8—N3—N2111.9 (2)C16—C15—H15127.2
C8—N3—C9127.6 (2)N6—C16—C15111.6 (2)
N2—N3—C9120.4 (2)N6—C16—C17118.6 (3)
C9—N4—C13117.5 (2)C15—C16—C17129.8 (2)
C9—N4—H4A121.3N7—C17—C18117.8 (3)
C13—N4—H4A121.3N7—C17—C16117.4 (2)
N6—N5—C14112.0 (2)C18—C17—C16124.8 (3)
N6—N5—C13119.9 (2)C19—C18—C17120.4 (3)
C14—N5—C13128.1 (2)C19—C18—H18119.8
C16—N6—N5104.4 (2)C17—C18—H18119.8
C21—N7—C17123.3 (3)C18—C19—C20120.4 (3)
C21—N7—H7118.3C18—C19—H19119.8
C17—N7—H7118.3C20—C19—H19119.8
N1—C1—C2124.0 (3)C19—C20—C21118.7 (3)
N1—C1—H1118.0C19—C20—H20120.7
C2—C1—H1118.0C21—C20—H20120.7
C3—C2—C1118.3 (3)N7—C21—C20119.4 (3)
C3—C2—H2120.9N7—C21—H21120.3
C1—C2—H2120.9C20—C21—H21120.3
C2—C3—C4119.6 (3)O5—C22—H22A109.5
C2—C3—H3120.2O5—C22—H22B109.5
C4—C3—H3120.2H22A—C22—H22B109.5
C3—C4—C5119.0 (3)O5—C22—H22C109.5
C3—C4—H4120.5H22A—C22—H22C109.5
C5—C4—H4120.5H22B—C22—H22C109.5
N1—C5—C4121.9 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N7—H7···N60.86 (1)2.35 (1)2.713 (10)106 (1)
O5—H5···N10.86 (3)1.97 (3)2.79 (3)159 (4)
N7—H7···O5i0.86 (1)1.88 (1)2.690 (10)156 (1)
Symmetry code: (i) x+1, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N7—H7···N60.86 (1)2.35 (1)2.713 (10)106 (1)
O5—H5···N10.86 (3)1.97 (3)2.786 (30)159 (4)
N7—H7···O5i0.86 (1)1.88 (1)2.690 (10)156 (1)
Symmetry code: (i) x+1, y+1, z.
Acknowledgements top

The authors acknowledge financial support by the Natural Science Foundation of China (grant No. 21271129).

references
References top

Bruker (2000). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.

Constable, E. C. (1992). Tetrahedron, 48, 10013–10059.

Constable, E. C., Drew, M. G. B., Forsyth, G. & Ward, M. D. (1988). J. Chem. Soc. Chem. Commun. pp. 1450–1451.

Constable, E. C., Heitzler, F., Neuburger, M. & Zehnder, M. (1997). J. Am. Chem. Soc. 119, 5606–5617.

Fu, Y., Li, Q., Zhou, Z., Wang, D., Wak, T. C. W., Hu, H. & Tang, W. (1996). Chem. Commun. pp. 1549–1550.

Fu, Y., Sun, J., Li, Q., Chen, Y., Dai, W., Wang, D., Mak, T. C. W., Tang, W. & Hu, H. (1996). J. Chem. Soc. Dalton Trans. pp. 2309–2313.

Jameson, D. L. & Goldsby, K. A. (1990). J. Org. Chem., 55, 4992–4994.

Sheldrick, G. M. (2003). SADABS. University of Göttingen, Germany.

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

Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925.