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

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ISSN: 2414-3146

4-Cyano-3,5-bis­­(phen­yl)pyrazole

aDepartment of Chemistry, Jacksonville University, Jacksonville, FL 32211, USA
*Correspondence e-mail: pzhao@ju.edu

Edited by P. C. Healy, Griffith University, Australia (Received 30 August 2017; accepted 1 September 2017; online 8 September 2017)

There are two independent mol­ecules in the asymmetric unit of the title compound, C16H11N3. The mol­ecules are linked by pairs of N—H⋯N hydrogen bonds, forming inversion dimers with an R22 (6) ring motif.

3D view (loading...)
[Scheme 3D1]
Chemical scheme
[Scheme 1]

Structure description

The title compound, representing a symmetrically phenyl substituted 4-cyano pyrazole, was prepared as a precursor for the preparation of scorpionate ligands (Trofimenko, 1999[Trofimenko, S. (1999). Scorpionates: The Coordination Chemistry of Polypyrazolylborate Ligands. Imperial College Press, London.]). There are two mol­ecules in the asymmetric unit. The C—C≡N fragments deviate only slightly from linearity with a bonding angle of 179.4 (2)° (N1—C1—C2) and 178.9 (2)° (N1′—C1′—C2′) (Fig. 1[link]). The dihedral angles between one pyrazole ring (N2/N3/C2–C4) and the mean planes of the two phenyl rings are 21.26° (C5–C10) and 24.31° (C11–C16) in one mol­ecule of the asymmetric unit. In the other mol­ecule, the dihedral angles between the pyrazole ring (N2′/N3′/C2′–C4′) and the mean planes of the two phenyl rings are 19.72° (C5′–C10′) and 34.39° (C11′–C16′).

[Figure 1]
Figure 1
A view of the asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are shown as spheres of arbitrary radii.

In the crystal, mol­ecules are linked by pairs of N—H⋯N hydrogen bonds, forming inversion dimers with an R22 (6) ring motif (Fig. 2[link] and Table 1[link]). There are no other significant inter­molecular inter­actions present.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N2—H2⋯N3i 0.88 2.13 2.812 (2) 133
N2′—H2′⋯N3′ii 0.88 2.13 2.793 (2) 131
Symmetry codes: (i) -x+1, -y+1, -z+1; (ii) -x+2, -y+1, -z+1.
[Figure 2]
Figure 2
A view along the b axis of the crystal packing of the title compound. The N—H⋯N hydrogen bonds (Table 1[link]) are shown as dashed lines.

Synthesis and crystallization

Toluene was dried over sodium and benzo­phenone. All other solvents and reagents were used as received from Alfa Aesar or Fisher Scientific without further purification. The synthesis of 4-cyano-3,5-bis­phenyl pyrazole has been reported (Som, 2013[Som, B. (2013). MS Thesis, East Tennessee State University.]). The procedure was modified in this work to recrystallize the final product. 0.69 g (17.24 mmol, 60% dispersion in mineral oil) of sodium hydride was added to 100 ml dry toluene. To this solution was added 2.50 g of benzoyl­aceto­nitrile (17.24 mmol), resulting in the immediate appearance of bubbles. The mixture was stirred for 18 h before benzoyl chloride (2.43 g, 17.24 mmol) was added. The reaction mixture was stirred overnight followed by three extractions using 100 ml of 0.2 M NaOH solution each time. The aqueous layers were combined and acidified with HCl/H2O (50/50) solution to pH ∼1. A white precipitate appeared immediately and was extracted with three 100 ml portions of ethyl acetate. Removal of the solvent under reduced pressure yielded 2.55 g (10.24 mmol, yield 59.40%) of crude product, which was recrystallized from ethanol to give 2-cyano-1,3-diphenyl-1,3-propane­dione (1.38 g, 5.54 mmol, 32.15%). This diketone compound (1.38 g, 5.54 mmol) was then reacted with hydrazine monohydrate (0.28 g, 5.54 mmol) in 100 ml of methanol and stirred overnight. The solvent was removed under reduced pressure to yield the crude product of 4-cyano-3,5-bis­phenyl pyrazole as a pale-yellow solid, which was recrystallized from ethanol (1.01 g, 4.65 mmol, 27.00%). Infrared spectroscopy showed characteristic peaks at 3177 cm−1 and 2227 cm−1 for N—H and C≡N stretches respectively. The 1H NMR (chloro­form-d) showed chemical shifts at 8.06 (d, 4H), 7.64 (t, 4H), and 7.54 p.p.m. (t, 2H).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link].

Table 2
Experimental details

Crystal data
Chemical formula C16H11N3
Mr 245.28
Crystal system, space group Triclinic, P[\overline{1}]
Temperature (K) 100
a, b, c (Å) 9.6036 (7), 10.4998 (6), 13.4359 (7)
α, β, γ (°) 104.899 (2), 106.704 (2), 90.647 (2)
V3) 1248.70 (13)
Z 4
Radiation type Mo Kα
μ (mm−1) 0.08
Crystal size (mm) 0.25 × 0.24 × 0.16
 
Data collection
Diffractometer Bruker X8 APEX II
Absorption correction Multi-scan (SADABS; Bruker, 2016[Bruker (2016). APEX3, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.])
Tmin, Tmax 0.235, 0.260
No. of measured, independent and observed [I > 2σ(I)] reflections 25032, 5069, 3178
Rint 0.050
(sin θ/λ)max−1) 0.625
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.047, 0.122, 1.02
No. of reflections 5069
No. of parameters 343
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 0.30, −0.29
Computer programs: APEX3 (Bruker, 2016[Bruker (2016). APEX3, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]), SAINT (Bruker, 2016[Bruker (2016). APEX3, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXL (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. A71, 3-8.]), OLEX2 (Dolomanov et al., 2009[Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339-341.]).

Structural data


Computing details top

Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to refine structure: SHELXL (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

4-Cyano-3,5-bis(phenyl)pyrazole top
Crystal data top
C16H11N3Z = 4
Mr = 245.28F(000) = 512
Triclinic, P1Dx = 1.305 Mg m3
a = 9.6036 (7) ÅMo Kα radiation, λ = 0.71073 Å
b = 10.4998 (6) ÅCell parameters from 2987 reflections
c = 13.4359 (7) Åθ = 2.9–26.3°
α = 104.899 (2)°µ = 0.08 mm1
β = 106.704 (2)°T = 100 K
γ = 90.647 (2)°Block, colourless
V = 1248.70 (13) Å30.25 × 0.24 × 0.16 mm
Data collection top
Bruker X8 APEX II
diffractometer
5069 independent reflections
Radiation source: sealed tube, fine-focus3178 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.050
Detector resolution: 7.9 pixels mm-1θmax = 26.4°, θmin = 2.3°
ω and φ scansh = 1211
Absorption correction: multi-scan
(SADABS; Bruker, 2016)
k = 1113
Tmin = 0.235, Tmax = 0.260l = 1612
25032 measured reflections
Refinement top
Refinement on F2Primary atom site location: dual
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.047Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.122H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.0555P)2 + 0.1764P]
where P = (Fo2 + 2Fc2)/3
5069 reflections(Δ/σ)max < 0.001
343 parametersΔρmax = 0.30 e Å3
0 restraintsΔρmin = 0.29 e Å3
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
N10.02188 (18)0.73573 (16)0.25572 (13)0.0251 (4)
N20.37446 (17)0.51162 (15)0.39966 (12)0.0186 (4)
H20.4335140.4484920.3938340.022*
N30.38722 (16)0.60550 (15)0.49310 (12)0.0179 (4)
C10.0762 (2)0.69081 (18)0.30236 (15)0.0176 (4)
C20.1967 (2)0.63420 (17)0.36031 (14)0.0162 (4)
C30.2628 (2)0.52451 (17)0.31689 (14)0.0155 (4)
C40.27925 (19)0.68260 (17)0.47057 (14)0.0154 (4)
C50.2349 (2)0.43615 (18)0.20816 (14)0.0164 (4)
C60.3463 (2)0.36427 (19)0.17986 (15)0.0213 (5)
H60.4401960.3747460.2311650.026*
C70.3211 (2)0.2782 (2)0.07803 (16)0.0254 (5)
H70.3973750.2295880.0600130.031*
C80.1852 (2)0.2628 (2)0.00262 (16)0.0265 (5)
H80.1679090.2035690.0672000.032*
C90.0740 (2)0.3338 (2)0.02888 (15)0.0252 (5)
H90.0191240.3240020.0232970.030*
C100.0983 (2)0.41922 (19)0.13107 (14)0.0211 (5)
H100.0211780.4666780.1487550.025*
C110.2659 (2)0.79827 (17)0.55498 (14)0.0161 (4)
C120.1333 (2)0.85396 (18)0.55028 (15)0.0181 (4)
H120.0486720.8163210.4915530.022*
C130.1247 (2)0.96388 (18)0.63099 (15)0.0204 (4)
H130.0341331.0007610.6274230.024*
C140.2476 (2)1.02033 (19)0.71690 (15)0.0221 (5)
H140.2414231.0958910.7718240.026*
C150.3795 (2)0.96562 (19)0.72200 (15)0.0217 (5)
H150.4638001.0040180.7807110.026*
C160.3891 (2)0.85577 (18)0.64240 (14)0.0184 (4)
H160.4798640.8189350.6469430.022*
N1'0.46981 (18)0.72545 (15)0.25682 (12)0.0225 (4)
N2'0.87772 (17)0.59563 (15)0.49062 (12)0.0192 (4)
H2'0.9406730.6018740.5542830.023*
N3'0.87116 (17)0.50046 (15)0.39906 (12)0.0192 (4)
C1'0.5726 (2)0.68557 (17)0.30272 (14)0.0163 (4)
C2'0.69826 (19)0.63418 (17)0.35991 (14)0.0155 (4)
C3'0.7753 (2)0.67868 (17)0.47078 (14)0.0156 (4)
C4'0.7634 (2)0.52153 (17)0.31792 (14)0.0154 (4)
C5'0.7632 (2)0.79276 (18)0.55686 (14)0.0168 (4)
C6'0.8279 (2)0.79538 (19)0.66520 (15)0.0206 (5)
H6'0.8746860.7211590.6823100.025*
C7'0.8244 (2)0.90496 (19)0.74751 (16)0.0245 (5)
H7'0.8688090.9057140.8206470.029*
C8'0.7563 (2)1.01351 (19)0.72334 (16)0.0238 (5)
H8'0.7542131.0889010.7797990.029*
C9'0.6910 (2)1.01187 (19)0.61653 (15)0.0206 (4)
H9'0.6433331.0859920.6000590.025*
C10'0.6948 (2)0.90301 (18)0.53375 (15)0.0181 (4)
H10'0.6505890.9032320.4608160.022*
C11'0.73338 (19)0.43430 (18)0.20814 (14)0.0164 (4)
C12'0.6884 (2)0.48498 (19)0.11845 (14)0.0189 (4)
H12'0.6743830.5762730.1281530.023*
C13'0.6642 (2)0.4018 (2)0.01540 (15)0.0230 (5)
H13'0.6340180.4365590.0453430.028*
C14'0.6837 (2)0.2686 (2)0.00036 (15)0.0242 (5)
H14'0.6658210.2118880.0704940.029*
C15'0.7295 (2)0.2180 (2)0.08919 (16)0.0254 (5)
H15'0.7437720.1267080.0789760.030*
C16'0.7545 (2)0.29997 (18)0.19248 (15)0.0207 (4)
H16'0.7860210.2648490.2529230.025*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0250 (10)0.0233 (9)0.0222 (9)0.0065 (8)0.0012 (8)0.0043 (8)
N20.0189 (9)0.0168 (9)0.0200 (9)0.0067 (7)0.0053 (7)0.0051 (7)
N30.0183 (9)0.0166 (9)0.0187 (9)0.0044 (7)0.0059 (7)0.0042 (7)
C10.0193 (11)0.0155 (10)0.0166 (10)0.0027 (9)0.0050 (9)0.0020 (8)
C20.0159 (10)0.0156 (10)0.0180 (10)0.0015 (8)0.0048 (8)0.0066 (8)
C30.0132 (10)0.0169 (10)0.0170 (10)0.0016 (8)0.0028 (8)0.0075 (8)
C40.0135 (10)0.0153 (10)0.0182 (10)0.0012 (8)0.0037 (8)0.0074 (8)
C50.0179 (10)0.0169 (10)0.0159 (10)0.0016 (8)0.0057 (8)0.0066 (8)
C60.0194 (11)0.0243 (11)0.0217 (11)0.0035 (9)0.0072 (9)0.0079 (9)
C70.0291 (12)0.0269 (12)0.0234 (11)0.0085 (10)0.0133 (10)0.0058 (9)
C80.0326 (13)0.0278 (12)0.0177 (11)0.0028 (10)0.0084 (10)0.0028 (9)
C90.0240 (12)0.0313 (12)0.0171 (11)0.0037 (9)0.0023 (9)0.0054 (9)
C100.0203 (11)0.0234 (11)0.0202 (11)0.0047 (9)0.0061 (9)0.0065 (9)
C110.0193 (11)0.0150 (10)0.0161 (10)0.0030 (8)0.0062 (8)0.0069 (8)
C120.0197 (11)0.0181 (10)0.0168 (10)0.0016 (8)0.0053 (8)0.0055 (8)
C130.0205 (11)0.0210 (11)0.0244 (11)0.0062 (9)0.0110 (9)0.0094 (9)
C140.0291 (12)0.0179 (10)0.0204 (11)0.0025 (9)0.0118 (9)0.0026 (9)
C150.0223 (11)0.0215 (11)0.0192 (11)0.0011 (9)0.0043 (9)0.0041 (9)
C160.0182 (11)0.0186 (10)0.0198 (10)0.0036 (8)0.0054 (9)0.0077 (9)
N1'0.0234 (10)0.0217 (9)0.0192 (9)0.0034 (8)0.0023 (8)0.0043 (7)
N2'0.0192 (9)0.0195 (9)0.0161 (9)0.0021 (7)0.0005 (7)0.0052 (7)
N3'0.0202 (9)0.0202 (9)0.0149 (9)0.0000 (7)0.0022 (7)0.0046 (7)
C1'0.0190 (11)0.0151 (10)0.0145 (10)0.0002 (8)0.0052 (8)0.0035 (8)
C2'0.0136 (10)0.0167 (10)0.0156 (10)0.0007 (8)0.0028 (8)0.0057 (8)
C3'0.0149 (10)0.0150 (10)0.0183 (10)0.0028 (8)0.0046 (8)0.0072 (8)
C4'0.0146 (10)0.0161 (10)0.0166 (10)0.0002 (8)0.0045 (8)0.0065 (8)
C5'0.0152 (10)0.0178 (10)0.0180 (10)0.0004 (8)0.0061 (8)0.0047 (8)
C6'0.0212 (11)0.0222 (11)0.0201 (11)0.0010 (9)0.0056 (9)0.0093 (9)
C7'0.0274 (12)0.0279 (12)0.0171 (10)0.0013 (9)0.0059 (9)0.0054 (9)
C8'0.0255 (12)0.0213 (11)0.0239 (11)0.0027 (9)0.0125 (9)0.0006 (9)
C9'0.0194 (11)0.0180 (10)0.0264 (11)0.0030 (8)0.0091 (9)0.0072 (9)
C10'0.0173 (10)0.0196 (10)0.0183 (10)0.0023 (8)0.0061 (8)0.0061 (9)
C11'0.0116 (10)0.0200 (10)0.0170 (10)0.0021 (8)0.0041 (8)0.0040 (8)
C12'0.0178 (11)0.0202 (10)0.0180 (10)0.0038 (8)0.0036 (8)0.0056 (9)
C13'0.0209 (11)0.0308 (12)0.0182 (10)0.0054 (9)0.0057 (9)0.0085 (9)
C14'0.0236 (12)0.0272 (12)0.0191 (11)0.0039 (9)0.0071 (9)0.0006 (9)
C15'0.0292 (12)0.0205 (11)0.0266 (12)0.0056 (9)0.0104 (10)0.0046 (9)
C16'0.0226 (11)0.0228 (11)0.0175 (10)0.0024 (9)0.0056 (9)0.0072 (9)
Geometric parameters (Å, º) top
N1—C11.151 (2)N1'—C1'1.150 (2)
N2—H20.8800N2'—H2'0.8800
N2—N31.355 (2)N2'—N3'1.356 (2)
N2—C31.342 (2)N2'—C3'1.337 (2)
N3—C41.337 (2)N3'—C4'1.338 (2)
C1—C21.426 (3)C1'—C2'1.426 (3)
C2—C31.398 (2)C2'—C3'1.409 (2)
C2—C41.418 (2)C2'—C4'1.409 (2)
C3—C51.463 (3)C3'—C5'1.468 (3)
C4—C111.468 (3)C4'—C11'1.467 (3)
C5—C61.401 (3)C5'—C6'1.402 (2)
C5—C101.394 (3)C5'—C10'1.398 (2)
C6—H60.9500C6'—H6'0.9500
C6—C71.384 (3)C6'—C7'1.384 (3)
C7—H70.9500C7'—H7'0.9500
C7—C81.381 (3)C7'—C8'1.385 (3)
C8—H80.9500C8'—H8'0.9500
C8—C91.385 (3)C8'—C9'1.387 (3)
C9—H90.9500C9'—H9'0.9500
C9—C101.386 (3)C9'—C10'1.384 (3)
C10—H100.9500C10'—H10'0.9500
C11—C121.400 (3)C11'—C12'1.399 (2)
C11—C161.401 (3)C11'—C16'1.397 (3)
C12—H120.9500C12'—H12'0.9500
C12—C131.387 (3)C12'—C13'1.386 (3)
C13—H130.9500C13'—H13'0.9500
C13—C141.387 (3)C13'—C14'1.384 (3)
C14—H140.9500C14'—H14'0.9500
C14—C151.388 (3)C14'—C15'1.389 (3)
C15—H150.9500C15'—H15'0.9500
C15—C161.381 (3)C15'—C16'1.383 (3)
C16—H160.9500C16'—H16'0.9500
N3—N2—H2123.4N3'—N2'—H2'124.7
C3—N2—H2123.4C3'—N2'—H2'124.7
C3—N2—N3113.27 (15)C3'—N2'—N3'110.59 (15)
C4—N3—N2106.08 (14)C4'—N3'—N2'108.59 (15)
N1—C1—C2179.40 (19)N1'—C1'—C2'178.85 (18)
C3—C2—C1126.21 (16)C3'—C2'—C1'127.30 (17)
C3—C2—C4106.48 (15)C4'—C2'—C1'126.42 (16)
C4—C2—C1127.18 (17)C4'—C2'—C3'106.12 (15)
N2—C3—C2105.10 (16)N2'—C3'—C2'106.76 (16)
N2—C3—C5121.48 (17)N2'—C3'—C5'120.83 (16)
C2—C3—C5133.38 (17)C2'—C3'—C5'132.37 (16)
N3—C4—C2109.06 (16)N3'—C4'—C2'107.95 (16)
N3—C4—C11119.72 (16)N3'—C4'—C11'120.35 (17)
C2—C4—C11131.19 (16)C2'—C4'—C11'131.69 (16)
C6—C5—C3119.99 (17)C6'—C5'—C3'119.77 (16)
C10—C5—C3121.67 (17)C10'—C5'—C3'121.56 (16)
C10—C5—C6118.34 (17)C10'—C5'—C6'118.58 (17)
C5—C6—H6119.6C5'—C6'—H6'119.7
C7—C6—C5120.81 (18)C7'—C6'—C5'120.69 (17)
C7—C6—H6119.6C7'—C6'—H6'119.7
C6—C7—H7120.0C6'—C7'—H7'120.0
C8—C7—C6120.07 (19)C6'—C7'—C8'120.06 (18)
C8—C7—H7120.0C8'—C7'—H7'120.0
C7—C8—H8120.0C7'—C8'—H8'120.1
C7—C8—C9119.94 (19)C7'—C8'—C9'119.83 (18)
C9—C8—H8120.0C9'—C8'—H8'120.1
C8—C9—H9119.9C8'—C9'—H9'119.8
C8—C9—C10120.19 (19)C10'—C9'—C8'120.47 (18)
C10—C9—H9119.9C10'—C9'—H9'119.8
C5—C10—H10119.7C5'—C10'—H10'119.8
C9—C10—C5120.66 (19)C9'—C10'—C5'120.36 (17)
C9—C10—H10119.7C9'—C10'—H10'119.8
C12—C11—C4121.76 (17)C12'—C11'—C4'120.66 (16)
C12—C11—C16118.72 (17)C16'—C11'—C4'120.00 (15)
C16—C11—C4119.52 (17)C16'—C11'—C12'119.30 (17)
C11—C12—H12119.9C11'—C12'—H12'120.0
C13—C12—C11120.28 (18)C13'—C12'—C11'119.92 (17)
C13—C12—H12119.9C13'—C12'—H12'120.0
C12—C13—H13119.8C12'—C13'—H13'119.8
C12—C13—C14120.48 (18)C14'—C13'—C12'120.49 (17)
C14—C13—H13119.8C14'—C13'—H13'119.8
C13—C14—H14120.2C13'—C14'—H14'120.1
C13—C14—C15119.52 (19)C13'—C14'—C15'119.80 (18)
C15—C14—H14120.2C15'—C14'—H14'120.1
C14—C15—H15119.7C14'—C15'—H15'119.9
C16—C15—C14120.51 (19)C16'—C15'—C14'120.29 (18)
C16—C15—H15119.7C16'—C15'—H15'119.9
C11—C16—H16119.8C11'—C16'—H16'119.9
C15—C16—C11120.49 (18)C15'—C16'—C11'120.18 (17)
C15—C16—H16119.8C15'—C16'—H16'119.9
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H2···N3i0.882.132.812 (2)133
N2—H2···N3ii0.882.132.793 (2)131
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+2, y+1, z+1.
 

Acknowledgements

The authors thank Dr Curtis Moore, Director of the X-ray Crystallography Facility at University of California, San Diego, for providing the single-crystal X-ray diffraction data, and the Department of Chemistry at Jacksonville University for supporting the research.

References

First citationBruker (2016). APEX3, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
First citationDolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationSheldrick, G. M. (2015). Acta Cryst. A71, 3–8.  Web of Science CrossRef IUCr Journals Google Scholar
First citationSom, B. (2013). MS Thesis, East Tennessee State University.  Google Scholar
First citationTrofimenko, S. (1999). Scorpionates: The Coordination Chemistry of Polypyrazolylborate Ligands. Imperial College Press, London.  Google Scholar

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