4-[Tris(1H-pyrazol-1-yl)meth­yl]phenol

Chen, X.-Y.; Yang, X.; Holliday, B.J.

doi:10.1107/S1600536811043042

organic compounds

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ISSN: 2056-9890

Volume 67| Part 11| November 2011| Page o3045

doi:10.1107/S1600536811043042

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4-[Tris(1H-pyrazol-1-yl)methyl]phenol

Xiao-Yan Chen,^a Xiaoping Yang ^a and Bradley J. Holliday ^a ^*

^aDepartment of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station, A5300, Austin, TX 78712, USA
^*Correspondence e-mail: bholliday@cm.utexas.edu

(Received 9 August 2011; accepted 17 October 2011; online 29 October 2011)

The title compound, C₁₆H₁₄N₆O, was prepared by the condensation of 4-(trifluoromethyl)phenol and sodium pyrazol-1-ide in a yield of 58%. The dihedral angles formed by the planes of the pyrazole rings are 50.7 (2), 71.2 (3) and 95.8 (2)°. The molecules are associated into dimers by pairs of intermolecular O—H⋯N hydrogen bonds involving the hydroxy groups and pyrazole N atoms. In addition, π–π stacking between the phenol rings of these inversion-related dimers is observed, with a ring centroid-to-centroid distance of 3.9247 (10) Å.

Related literature

For the preparation and coordination chemistry of tris(pyrazolyl)borates and tris(pyrazolyl)methanes, see: Trofimenko (1966 , 1970 , 1999 ); Pettinari & Pettinari (2005 ); Reger et al. (2000 ). For the chemistry of tris(pyrazolyl)methane derivatives, see: Humphrey et al. (1999 ). For similar structures, see: Liddle & Gardinier (2007 ).

Experimental

Crystal data

C₁₆H₁₄N₆O
M_r = 306.33
Triclinic, $[P \overline 1]$
a = 8.5065 (17) Å
b = 8.6829 (17) Å
c = 10.815 (2) Å
α = 96.97 (3)°
β = 91.51 (2)°
γ = 109.40 (3)°
V = 746.0 (3) Å³
Z = 2
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 153 K
0.30 × 0.28 × 0.20 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: Gaussian (XPREP in SHELXTL; Sheldrick, 2008 ) T_min = 0.973, T_max = 0.983
4225 measured reflections
2609 independent reflections
1975 reflections with I > 2σ(I)
R_int = 0.025

Refinement

R[F² > 2σ(F²)] = 0.043
wR(F²) = 0.099
S = 1.07
2609 reflections
209 parameters
H-atom parameters constrained
Δρ_max = 0.18 e Å⁻³
Δρ_min = −0.27 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1A⋯N4ⁱ	0.82	2.02	2.836 (2)	173
Symmetry code: (i) -x+2, -y+2, -z.

Data collection: COLLECT (Nonius, 1998 ); cell refinement: SCALEPACK (Otwinowski & Minor, 1997 ); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999 ); program(s) used to refine structure: XL in SHELXTL/PC (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997 ) and POV-RAY (Persistence of Vision Team, 2004 ); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811043042/pk2340sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811043042/pk2340Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536811043042/pk2340Isup3.cml

checkCIF report

Comment top

Since seminal reports on tris(pyrazolyl)borates and tris(pyrazolyl)methanes (Trofimenko, 1966, 1970), variations on these ligands have been widely studied. Currently, there are great research efforts to study ligands of this type that are functionalized at the back boron or methine positions. The synthesis and coordination chemistry of aryltris(pyrazolyl)borates have also been well investigated, which has allowed significant advances in iron(II) spin-crossover chemistry. However, the chemistry of analogous tris(pyrazolyl)methane derivatives is almost unknown. Herein, we demonstrate the preparation of a new tris(pyrazolyl)methane derivative, 4-[tris(1H-pyrazol-1-yl)methyl]phenol, using a one-pot synthesis method with 4-(trifluoromethyl)phenol and freshly prepared sodium pyrazol-1-ide to give the desired product in good yield.

The solid state structure of 4-[tris(1H-pyrazol-1-yl)methyl]phenol can be seen in Fig. 1. There are two molecules in the unit cell. The molecules are associated into dimers by pairs of intermolecular O—H···N hydrogen bonds involving the hydroxyl groups and pyrazole N atoms. In addition, π–π stacking between the phenol rings of these inversion-related (-x + 2, -y + 2, -z) dimers is observed with a ring centroid-to-centroid distance of 3.9247 (10) Å.

Related literature top

For the preparation and coordination chemistry of tris(pyrazolyl)borates and tris(pyrazolyl)methanes, see: Trofimenko (1966, 1970, 1999); Pettinari & Pettinari (2005); Reger et al. (2000). For the chemistry of tris(pyrazolyl)methane derivatives, see: Humphrey et al. (1999). For similar structures, see: Liddle & Gardinier (2007).

Experimental top

The title compound was prepared by refluxing 4-(trifluoromethyl)phenol (0.162 g, 1.0 mmol) and freshly prepared sodium pyrazol-1-ide (0.361 g, 4.0 mmol) in tetrahydrofuran (20 ml) for 12 h under a nitrogen atomsphere. The desired product was purified by column chromatography on silica gel using CH₂Cl₂ as the eluent with a yield of 58%. Single crystals suitable for X-ray diffraction were obtained via slow evaporation from a methanol solution.

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: XL in SHELXTL/PC (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and POV-RAY (Persistence of Vision Team, 2004); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and WinGX (Farrugia, 1999).

Figures top

	Fig. 1. Ellipsoid plot of C₁₆H₁₄N₆O showing selected atoms at 30% probability level.
	Fig. 2. A packing diagram of C₁₆H₁₄N₆O.

4-[Tris(1H-pyrazol-1-yl)methyl]phenol top

Crystal data top

C₁₆H₁₄N₆O	Z = 2
M_r = 306.33	F(000) = 320
Triclinic, P1	D_x = 1.364 Mg m⁻³
Hall symbol: -P 1	Melting point: 443 K
a = 8.5065 (17) Å	Mo Kα radiation, λ = 0.71073 Å
b = 8.6829 (17) Å	Cell parameters from 2208 reflections
c = 10.815 (2) Å	θ = 2.9–27.5°
α = 96.97 (3)°	µ = 0.09 mm⁻¹
β = 91.51 (2)°	T = 153 K
γ = 109.40 (3)°	Block, colourless
V = 746.0 (3) Å³	0.30 × 0.28 × 0.20 mm

Data collection top

Nonius KappaCCD diffractometer	2609 independent reflections
Radiation source: fine-focus sealed tube	1975 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.025
ω scans	θ_max = 25.0°, θ_min = 2.9°
Absorption correction: gaussian (XPREP in SHELXTL; Sheldrick, 2008)	h = −10→10
T_min = 0.973, T_max = 0.983	k = −10→10
4225 measured reflections	l = −12→11

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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.099	H-atom parameters constrained
S = 1.07	w = 1/[σ²(F_o²) + (0.038P)² + 0.1787P] where P = (F_o² + 2F_c²)/3
2609 reflections	(Δ/σ)_max < 0.001
209 parameters	Δρ_max = 0.18 e Å⁻³
0 restraints	Δρ_min = −0.27 e Å⁻³

Crystal data top

C₁₆H₁₄N₆O	γ = 109.40 (3)°
M_r = 306.33	V = 746.0 (3) Å³
Triclinic, P1	Z = 2
a = 8.5065 (17) Å	Mo Kα radiation
b = 8.6829 (17) Å	µ = 0.09 mm⁻¹
c = 10.815 (2) Å	T = 153 K
α = 96.97 (3)°	0.30 × 0.28 × 0.20 mm
β = 91.51 (2)°

Data collection top

Nonius KappaCCD diffractometer	2609 independent reflections
Absorption correction: gaussian (XPREP in SHELXTL; Sheldrick, 2008)	1975 reflections with I > 2σ(I)
T_min = 0.973, T_max = 0.983	R_int = 0.025
4225 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.043	0 restraints
wR(F²) = 0.099	H-atom parameters constrained
S = 1.07	Δρ_max = 0.18 e Å⁻³
2609 reflections	Δρ_min = −0.27 e Å⁻³
209 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

	x	y	z	U_iso*/U_eq
O1	1.00800 (16)	1.32161 (15)	0.03852 (13)	0.0266 (3)
H1A	0.9790	1.2970	−0.0362	0.054 (8)*
N1	0.74972 (17)	0.78542 (18)	0.40566 (13)	0.0180 (4)
N2	0.69159 (19)	0.65739 (19)	0.47332 (15)	0.0244 (4)
N3	0.98104 (17)	0.72693 (18)	0.31464 (14)	0.0181 (4)
N4	1.08607 (18)	0.73336 (19)	0.22092 (15)	0.0237 (4)
N5	0.70790 (17)	0.60541 (17)	0.21695 (14)	0.0173 (4)
N6	0.54566 (18)	0.59411 (18)	0.19620 (14)	0.0216 (4)
C1	0.9528 (2)	1.1846 (2)	0.09625 (17)	0.0197 (4)
C2	0.8251 (2)	1.0424 (2)	0.04486 (17)	0.0213 (4)
H2A	0.7695	1.0394	−0.0311	0.026*
C3	0.7802 (2)	0.9051 (2)	0.10623 (16)	0.0191 (4)
H3A	0.6944	0.8103	0.0711	0.023*
C4	0.8613 (2)	0.9069 (2)	0.21937 (16)	0.0165 (4)
C5	0.9873 (2)	1.0523 (2)	0.27129 (17)	0.0206 (4)
H5A	1.0427	1.0560	0.3475	0.025*
C6	1.0305 (2)	1.1896 (2)	0.21160 (17)	0.0213 (4)
H6A	1.1121	1.2863	0.2487	0.026*
C7	0.8240 (2)	0.7575 (2)	0.28833 (16)	0.0173 (4)
C8	0.6124 (2)	0.7133 (2)	0.56240 (18)	0.0250 (5)
H8A	0.5599	0.6528	0.6241	0.030*
C9	0.6169 (2)	0.8729 (2)	0.55301 (18)	0.0263 (5)
H9A	0.5710	0.9371	0.6055	0.032*
C10	0.7026 (2)	0.9154 (2)	0.45071 (17)	0.0208 (4)
H10A	0.7246	1.0141	0.4180	0.025*
C11	1.2086 (2)	0.6894 (2)	0.2675 (2)	0.0268 (5)
H11A	1.2999	0.6832	0.2244	0.032*
C12	1.1831 (2)	0.6538 (2)	0.3889 (2)	0.0281 (5)
H12A	1.2517	0.6210	0.4405	0.034*
C13	1.0367 (2)	0.6771 (2)	0.41634 (18)	0.0225 (5)
H13A	0.9846	0.6617	0.4906	0.027*
C14	0.4724 (2)	0.4422 (2)	0.13858 (17)	0.0220 (4)
H14A	0.3599	0.3985	0.1111	0.026*
C15	0.5835 (2)	0.3552 (2)	0.12394 (19)	0.0284 (5)
H15A	0.5602	0.2468	0.0870	0.034*
C16	0.7341 (2)	0.4636 (2)	0.17562 (18)	0.0238 (5)
H16A	0.8347	0.4434	0.1811	0.029*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0374 (8)	0.0219 (8)	0.0236 (9)	0.0116 (6)	0.0085 (6)	0.0092 (6)
N1	0.0197 (8)	0.0170 (8)	0.0171 (8)	0.0049 (7)	0.0029 (7)	0.0049 (7)
N2	0.0284 (9)	0.0226 (9)	0.0218 (9)	0.0056 (7)	0.0055 (7)	0.0093 (7)
N3	0.0155 (8)	0.0185 (9)	0.0209 (9)	0.0065 (6)	0.0013 (7)	0.0034 (7)
N4	0.0187 (8)	0.0256 (9)	0.0297 (10)	0.0101 (7)	0.0072 (7)	0.0066 (8)
N5	0.0149 (8)	0.0167 (9)	0.0207 (9)	0.0063 (6)	0.0007 (6)	0.0017 (7)
N6	0.0152 (8)	0.0231 (9)	0.0255 (9)	0.0057 (7)	0.0005 (7)	0.0023 (7)
C1	0.0231 (10)	0.0180 (11)	0.0234 (11)	0.0126 (8)	0.0098 (8)	0.0056 (8)
C2	0.0241 (10)	0.0261 (11)	0.0178 (10)	0.0133 (9)	0.0009 (8)	0.0044 (9)
C3	0.0184 (10)	0.0202 (11)	0.0183 (10)	0.0067 (8)	0.0003 (8)	0.0001 (8)
C4	0.0156 (9)	0.0167 (10)	0.0189 (10)	0.0077 (8)	0.0041 (8)	0.0025 (8)
C5	0.0181 (10)	0.0235 (11)	0.0199 (11)	0.0070 (8)	−0.0014 (8)	0.0020 (8)
C6	0.0210 (10)	0.0167 (10)	0.0235 (11)	0.0032 (8)	0.0030 (8)	0.0011 (8)
C7	0.0145 (9)	0.0186 (10)	0.0188 (10)	0.0061 (8)	0.0008 (8)	0.0017 (8)
C8	0.0210 (10)	0.0329 (12)	0.0185 (11)	0.0049 (9)	0.0037 (8)	0.0048 (9)
C9	0.0228 (11)	0.0321 (12)	0.0248 (11)	0.0120 (9)	0.0039 (9)	−0.0010 (9)
C10	0.0206 (10)	0.0201 (10)	0.0241 (11)	0.0106 (8)	−0.0002 (8)	0.0013 (8)
C11	0.0181 (10)	0.0227 (11)	0.0415 (14)	0.0090 (9)	0.0027 (9)	0.0056 (10)
C12	0.0228 (11)	0.0230 (11)	0.0400 (14)	0.0101 (9)	−0.0097 (9)	0.0057 (10)
C13	0.0255 (11)	0.0191 (11)	0.0223 (11)	0.0066 (8)	−0.0046 (8)	0.0046 (8)
C14	0.0190 (10)	0.0220 (11)	0.0199 (11)	0.0005 (8)	0.0004 (8)	0.0023 (8)
C15	0.0305 (12)	0.0193 (11)	0.0309 (12)	0.0053 (9)	0.0004 (9)	−0.0042 (9)
C16	0.0253 (11)	0.0198 (11)	0.0297 (12)	0.0128 (9)	0.0023 (9)	0.0012 (9)

Geometric parameters (Å, º) top

O1—C1	1.360 (2)	C4—C5	1.399 (3)
O1—H1A	0.8200	C4—C7	1.521 (3)
N1—C10	1.360 (2)	C5—C6	1.371 (3)
N1—N2	1.366 (2)	C5—H5A	0.9300
N1—C7	1.462 (2)	C6—H6A	0.9300
N2—C8	1.325 (2)	C8—C9	1.390 (3)
N3—C13	1.358 (2)	C8—H8A	0.9300
N3—N4	1.363 (2)	C9—C10	1.362 (3)
N3—C7	1.473 (2)	C9—H9A	0.9300
N4—C11	1.330 (2)	C10—H10A	0.9300
N5—C16	1.349 (2)	C11—C12	1.391 (3)
N5—N6	1.361 (2)	C11—H11A	0.9300
N5—C7	1.470 (2)	C12—C13	1.361 (3)
N6—C14	1.323 (2)	C12—H12A	0.9300
C1—C6	1.385 (3)	C13—H13A	0.9300
C1—C2	1.387 (3)	C14—C15	1.393 (3)
C2—C3	1.382 (3)	C14—H14A	0.9300
C2—H2A	0.9300	C15—C16	1.369 (3)
C3—C4	1.385 (2)	C15—H15A	0.9300
C3—H3A	0.9300	C16—H16A	0.9300

C1—O1—H1A	109.5	N1—C7—N3	109.47 (14)
C10—N1—N2	111.56 (15)	N5—C7—N3	107.01 (14)
C10—N1—C7	128.86 (15)	N1—C7—C4	110.73 (14)
N2—N1—C7	118.61 (14)	N5—C7—C4	113.65 (14)
C8—N2—N1	104.13 (15)	N3—C7—C4	108.88 (14)
C13—N3—N4	111.24 (14)	N2—C8—C9	112.15 (18)
C13—N3—C7	130.58 (16)	N2—C8—H8A	123.9
N4—N3—C7	117.89 (14)	C9—C8—H8A	123.9
C11—N4—N3	104.65 (15)	C10—C9—C8	105.46 (18)
C16—N5—N6	112.33 (15)	C10—C9—H9A	127.3
C16—N5—C7	129.11 (15)	C8—C9—H9A	127.3
N6—N5—C7	118.30 (14)	N1—C10—C9	106.65 (17)
C14—N6—N5	103.95 (14)	N1—C10—H10A	126.7
O1—C1—C6	117.37 (17)	C9—C10—H10A	126.7
O1—C1—C2	123.26 (17)	N4—C11—C12	111.55 (17)
C6—C1—C2	119.36 (17)	N4—C11—H11A	124.2
C3—C2—C1	120.19 (17)	C12—C11—H11A	124.2
C3—C2—H2A	119.9	C13—C12—C11	105.54 (17)
C1—C2—H2A	119.9	C13—C12—H12A	127.2
C2—C3—C4	120.83 (17)	C11—C12—H12A	127.2
C2—C3—H3A	119.6	N3—C13—C12	107.00 (18)
C4—C3—H3A	119.6	N3—C13—H13A	126.5
C3—C4—C5	118.31 (17)	C12—C13—H13A	126.5
C3—C4—C7	123.42 (16)	N6—C14—C15	112.14 (17)
C5—C4—C7	118.25 (16)	N6—C14—H14A	123.9
C6—C5—C4	121.01 (17)	C15—C14—H14A	123.9
C6—C5—H5A	119.5	C16—C15—C14	105.15 (17)
C4—C5—H5A	119.5	C16—C15—H15A	127.4
C5—C6—C1	120.22 (17)	C14—C15—H15A	127.4
C5—C6—H6A	119.9	N5—C16—C15	106.41 (17)
C1—C6—H6A	119.9	N5—C16—H16A	126.8
N1—C7—N5	106.98 (14)	C15—C16—H16A	126.8

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···N4ⁱ	0.82	2.02	2.836 (2)	173

Symmetry code: (i) −x+2, −y+2, −z.

Experimental details

Crystal data
Chemical formula	C₁₆H₁₄N₆O
M_r	306.33
Crystal system, space group	Triclinic, P1
Temperature (K)	153
a, b, c (Å)	8.5065 (17), 8.6829 (17), 10.815 (2)
α, β, γ (°)	96.97 (3), 91.51 (2), 109.40 (3)
V (Å³)	746.0 (3)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.09
Crystal size (mm)	0.30 × 0.28 × 0.20

Data collection
Diffractometer	Nonius KappaCCD diffractometer
Absorption correction	Gaussian (XPREP in SHELXTL; Sheldrick, 2008)
T_min, T_max	0.973, 0.983
No. of measured, independent and observed [I > 2σ(I)] reflections	4225, 2609, 1975
R_int	0.025
(sin θ/λ)_max (Å⁻¹)	0.595

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.043, 0.099, 1.07
No. of reflections	2609
No. of parameters	209
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.18, −0.27

Computer programs: COLLECT (Nonius, 1998), SCALEPACK (Otwinowski & Minor, 1997), DENZO-SMN (Otwinowski & Minor, 1997), SIR97 (Altomare et al., 1999), XL in SHELXTL/PC (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997) and POV-RAY (Persistence of Vision Team, 2004), SHELXL97 (Sheldrick, 2008) and WinGX (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···N4ⁱ	0.82	2.02	2.836 (2)	172.9

Symmetry code: (i) −x+2, −y+2, −z.

Acknowledgements

The authors gratefully acknowledge the Robert A. Welch Foundation (grant No. F-1631), the National Science Foundation (grant Nos. CHE-0741973 and CHE-0847763), the Advanced Research Program of the Texas Higher Education Coordinating Board (grant No. 01916-090-2010) and the University of Texas at Austin for financial support of this research.

References

Altomare, A., Burla, M. C., Camalli, M., Cascarano, G. L., Giacovazzo, C., Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J. Appl. Cryst. 32, 115–119. Web of Science CrossRef CAS IUCr Journals Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Humphrey, E. R., Mann, K. L. V., Reeves, Z. R., Behrendt, A., Jeffery, J. C., Maher, J. P., McCleverty, J. A. & Ward, M. D. (1999). New J. Chem. 23, 417–423. Web of Science CSD CrossRef CAS Google Scholar
Liddle, B. & Gardinier, J. R. (2007). J. Org. Chem. 72, 9794–9797. Web of Science CSD CrossRef PubMed CAS Google Scholar
Nonius (1998). COLLECT. Nonius BV, Delft, The Netherlands. Google Scholar
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press. Google Scholar
Persistence of Vision Team (2004). POV-RAY. Persistence of Vision Raytracer Pty. Ltd, Victoria, Australia. http://www.povray.org/ Google Scholar
Pettinari, C. & Pettinari, R. (2005). Coord. Chem. Rev. 249, 525–543. CAS Google Scholar
Reger, D. L., Grattan, T. C., Brown, K. J., Little, C. A., Lamba, J. J. S., Rheingold, A. L. & Sommer, R. D. (2000). J. Organomet. Chem. 607, 120–128. Web of Science CrossRef CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Trofimenko, S. (1966). J. Am. Chem. Soc. 88, 1842–1844. CrossRef CAS Web of Science Google Scholar
Trofimenko, S. (1970). J. Am. Chem. Soc. 92, 5118–5126. CrossRef CAS Web of Science Google Scholar
Trofimenko, S. (1999). Scorpionates: The Coordination Chemistry of Polypyrazolylborate Ligands. London: Imperial College Press. Google Scholar