1,2-Bis[di­(benzo­furan-2-yl)phosphan­yl]ethane

Ahrens, S.; Spannenberg, A.; Beller, M.; Junge, K.

doi:10.1107/S2414314625009162

organic compounds

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ISSN: 2414-3146

Volume 10| Part 10| October 2025| x250916

https://doi.org/10.1107/S2414314625009162

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1,2-Bis[di(benzofuran-2-yl)phosphanyl]ethane

Sebastian Ahrens,^a Anke Spannenberg,^a Matthias Beller ^a and Kathrin Junge ^a ^*

^aLeibniz-Institut für Katalyse e. V., Albert-Einstein-Str. 29a, 18059 Rostock, Germany
^*Correspondence e-mail: [email protected]

Edited by L. Van Meervelt, Katholieke Universiteit Leuven, Belgium (Received 17 October 2025; accepted 20 October 2025; online 24 October 2025)

The title compound, C₃₄H₂₄O₄P₂, consists of an ethylene-bridged diphosphine with benzofuran residues, where the P—C—C—P backbone exhibits an anti-conformation. The asymmetric unit contains one half molecule, which is completed by inversion symmetry.

Keywords: crystal structure; bidentate ligand; benzofuran; phosphine.

CCDC reference: 2496508

Structure description

Bidentate phosphine ligands play a pivotal role in homogeneous catalysis, where their chelation to a metal center enhances complex stability and allows precise control over electronic and steric properties (van Leeuwen et al., 2000 ). Ethylene-bridged diphosphines, such as 1,2-bis(diphenylphosphanyl)ethane (dppe), are among the most widely used ligands owing to their versatile coordination behavior (Clevenger et al., 2020 ). Variations in the substituents on phosphorus strongly influence catalytic activity, selectivity, and metal–ligand interactions. Consequently, structural modification of ethylene-bridged diphosphines remains a key strategy for the design of improved catalysts in transition-metal-mediated transformations. Numerous ethylene-bridged diphosphines have been synthesized, bearing alkyl substituents as well as aryl substituents (Dekker et al., 1992 ).

Recently, our group demonstrated the potential of benzofuran-based phosphines in the Co-catalyzed isomerization of allylamines (Ahrens et al., 2025 ). These studies revealed that benzofurylphosphines represent an alternative structural motif to conventional aryl phosphines, offering distinct electronic and steric properties that can significantly influence catalytic activity. Owing to their unique reactivity, structurally related phosphines have also been successfully applied in the Pd-catalyzed telomerization of butadiene (Souza et al., 2025 ). In our previous work, only monodentate benzofuran phosphines were developed and evaluated in catalytic applications. To expand this ligand family, the corresponding bidentate analogue has now been synthesized. The new diphosphine 1,2-bis[di(benzofuran-2-yl)phosphanyl]ethane was prepared and its crystal structure determined.

The molecular geometry of the title compound reflects the characteristic features of ethylene-bridged diphosphines with the P–C–C–P backbone forming a zigzag chain and exhibiting an anti-conformation (Fig. 1). Each phosphorus atom displays a pyramidal arrangement with two benzofuran substituents and one CH₂ group of the ethylene bridge. The P—C—C—P torsion angle amounts to 180°, bond lengths and angles are in the expected range. The dihedral angle between the benzofuran rings is 84.94 (3)°. The asymmetric unit contains one half-molecule expanded by the symmetry operation −x + 1, −y + 2, −z + 1.

Figure 1
The molecular structure of the title compound with atom labeling and displacement ellipsoids drawn at 50% probability level [symmetry code: (i) −x + 1, −y + 2, −z + 1].

Moreover, the electronic structure of the benzofuryl diphosphine differs significantly from that of dppe. In solution at room temperature, the ³¹P NMR resonance is significantly upfield-shifted (–52.6 ppm compared to −12.6 ppm for dppe), indicating a higher electron density at the phosphorus atoms (Benny et al., 2023 ). The increased shielding can be attributed to the greater π-donor strength and electron delocalization provided by the benzofuryl substituents. Therefore, the ligand shows an increased electron-donating character, altering the electron density and reactivity of its metal complexes relative to dppe.

Synthesis and crystallization

All synthetic procedures were carried out under argon atmosphere using standard Schlenk techniques. The anhydrous and oxygen-free solvents used (tetrahydrofuran, dichloromethane, diethyl ether, and n-pentane) were obtained from an Innovative Technology PS-MD-6 solvent purification system. The purified solvents were stored over 3 Å molecular sieves under argon. The reagents 1,2-bis(dichlorophosphanyl)ethane and benzofuran were obtained from Sigma-Aldrich and Fisher Scientific, respectively, and used as received.

NMR spectra were recorded on a Bruker Avance 300 spectrometer operating at 300 MHz for ¹H, 75 MHz for ¹³C, and 121 MHz for ³¹P. All chemical shifts (δ) are reported in ppm relative to tetramethylsilane (TMS). Solvent references for CD₂Cl₂ are δ = 5.32 ppm for ¹H and 53.84 ppm for ¹³C. ³¹P chemical shifts are reported relative to an external 85% H₃PO₄ standard.

The synthesis of the title compound was carried out following literature procedures for ethylene-bridged diphosphines with minor modifications (Casey et al., 1983 ). Under an argon atmosphere, anhydrous benzofuran (1.181 g, 10.0 mmol, 4 eq.) was charged in a Schlenk flask and dissolved in 20 ml of anhydrous THF. The solution was cooled to 253 K, and n-BuLi (2.5 M, 4.0 ml, 10.0 mmol, 4 eq.) was added dropwise. The reaction mixture was stirred for 2 h. Subsequently, 1,2-bis(dichlorophosphanyl)ethane (580 mg, 2.5 mmol, 1 eq.) was added slowly to the lithiated benzofuran solution. The reaction temperature was maintained at 253 K for 2 h before allowing the reaction mixture to warm to room temperature. After stirring overnight, the solvent was removed in vacuo, yielding a yellow solid. To remove lithium chloride, the yellow solid was dissolved in 60 ml of anhydrous diethyl ether and the resulting suspension was filtered under an inert atmosphere. 1,2-Bis[di(benzofuran-2-yl)phosphanyl]ethane was crystallized from a concentrated dichloromethane solution at 278 K to afford colorless, needle-shaped crystals (894 mg, 1.6 mmol, 64%). Crystals suitable for single-crystal X-ray diffraction were obtained by diffusion of n-pentane into a dichloromethane solution of the phosphine.

¹H NMR (300 MHz, CD₂Cl₂): δ = 7.55 (ddd, J = 7.5, 1.4, 0.7 Hz, 4H), 7.46–7.39 (m, 4H), 7.35–7.18 (m, 8H), 7.13 (q, J = 1.0 Hz, 4H), 2.54 (dd, J = 5.6, 5.0 Hz, 4H).

¹³C NMR (75 MHz, CD₂Cl₂): δ = 158.17, 154.26 (dd, J = 11.0, 8.9 Hz), 128.29 (t, J = 3.2 Hz), 125.68, 123.29, 121.64, 117.50 (t, J = 15.5 Hz), 111.75, 21.43 (dd, J = 6.4, 5.0 Hz).

¹³C-DEPT-135 NMR (75 MHz, CD₂Cl₂): δ = 125.12 (CH, pos.), 122.73 (CH, pos.), 121.08 (CH, pos.), 116.94 (CH, pos.), 111.19 (CH, pos.), 20.77 (CH₂, neg.).

³¹P NMR (122 MHz, CD₂Cl₂): δ = −52.60.

HRMS (ESI): m/z calculated for C₃₄H₂₄O₄P₂: 558.1150 [M+H]⁺, found: 559.1219.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1.

Table 1
Experimental details

Crystal data
Chemical formula	C₃₄H₂₄O₄P₂
M_r	558.47
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	150
a, b, c (Å)	5.6351 (5), 10.5372 (9), 22.7988 (19)
β (°)	93.696 (1)
V (Å³)	1350.9 (2)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	0.20
Crystal size (mm)	0.35 × 0.17 × 0.11

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.93, 0.98
No. of measured, independent and observed [I > 2σ(I)] reflections	23407, 3594, 3145
R_int	0.025
(sin θ/λ)_max (Å⁻¹)	0.682

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.038, 0.102, 1.04
No. of reflections	3594
No. of parameters	181
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.41, −0.28
Computer programs: APEX2 (Bruker, 2014 , SAINT (Bruker, 2013 ), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b ), XP in SHELXTL (Sheldrick, 2008 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2496508

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314625009162/vm4075sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314625009162/vm4075Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314625009162/vm4075Isup3.cml

checkCIF report

Computing details top

1,2-Bis[di(benzofuran-2-yl)phosphanyl]ethane top

Crystal data top

C₃₄H₂₄O₄P₂	F(000) = 580
M_r = 558.47	D_x = 1.373 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.6351 (5) Å	Cell parameters from 9822 reflections
b = 10.5372 (9) Å	θ = 2.6–29.2°
c = 22.7988 (19) Å	µ = 0.20 mm⁻¹
β = 93.696 (1)°	T = 150 K
V = 1350.9 (2) Å³	Needle, colorless
Z = 2	0.35 × 0.17 × 0.11 mm

Data collection top

Bruker APEXII CCD diffractometer	3594 independent reflections
Radiation source: fine-focus sealed tube	3145 reflections with I > 2σ(I)
Detector resolution: 8.3333 pixels mm^-1	R_int = 0.025
φ and ω scans	θ_max = 29.0°, θ_min = 1.8°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −7→7
T_min = 0.93, T_max = 0.98	k = −14→14
23407 measured reflections	l = −31→31

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.038	H-atom parameters constrained
wR(F²) = 0.102	w = 1/[σ²(F_o²) + (0.0496P)² + 0.6701P] where P = (F_o² + 2F_c²)/3
S = 1.04	(Δ/σ)_max = 0.001
3594 reflections	Δρ_max = 0.41 e Å⁻³
181 parameters	Δρ_min = −0.28 e Å⁻³

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

	x	y	z	U_iso*/U_eq
P1	0.71188 (6)	0.84518 (3)	0.46075 (2)	0.02309 (10)
O1	0.49580 (18)	0.91096 (10)	0.35215 (4)	0.0306 (2)
O2	0.66914 (17)	0.61479 (9)	0.40832 (4)	0.0265 (2)
C1	0.4685 (2)	0.92984 (11)	0.49513 (6)	0.0236 (2)
H1A	0.320524	0.923062	0.469453	0.028*
H1B	0.439854	0.889731	0.533297	0.028*
C2	0.6973 (3)	0.92132 (12)	0.38979 (6)	0.0275 (3)
C3	0.8541 (3)	1.00332 (13)	0.36809 (6)	0.0280 (3)
H3	1.005756	1.025137	0.385828	0.034*
C4	0.7503 (3)	1.05138 (13)	0.31355 (6)	0.0273 (3)
C5	0.8159 (3)	1.14240 (15)	0.27287 (7)	0.0362 (3)
H5	0.963404	1.185957	0.277924	0.043*
C6	0.6589 (4)	1.16671 (17)	0.22517 (7)	0.0458 (4)
H6	0.698030	1.229013	0.197263	0.055*
C7	0.4426 (4)	1.1010 (2)	0.21721 (7)	0.0491 (4)
H7	0.339642	1.118676	0.183556	0.059*
C8	0.3754 (3)	1.01094 (17)	0.25715 (8)	0.0422 (4)
H8	0.229594	0.965882	0.251760	0.051*
C9	0.5312 (3)	0.99049 (13)	0.30494 (6)	0.0282 (3)
C10	0.5509 (2)	0.70025 (12)	0.44235 (5)	0.0227 (2)
C11	0.3408 (2)	0.65268 (12)	0.45784 (6)	0.0239 (3)
H11	0.229288	0.693672	0.480968	0.029*
C12	0.3194 (2)	0.52756 (12)	0.43237 (5)	0.0231 (2)
C13	0.1490 (3)	0.43112 (13)	0.43126 (6)	0.0284 (3)
H13	0.008549	0.439902	0.451813	0.034*
C14	0.1906 (3)	0.32213 (13)	0.39931 (7)	0.0326 (3)
H14	0.077800	0.255057	0.398549	0.039*
C15	0.3946 (3)	0.30903 (14)	0.36829 (7)	0.0347 (3)
H15	0.416334	0.233660	0.346410	0.042*
C16	0.5668 (3)	0.40349 (14)	0.36860 (7)	0.0327 (3)
H16	0.705679	0.395315	0.347393	0.039*
C17	0.5236 (2)	0.51025 (12)	0.40171 (6)	0.0245 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
P1	0.02388 (17)	0.01797 (16)	0.02763 (18)	−0.00108 (11)	0.00324 (12)	−0.00143 (11)
O1	0.0314 (5)	0.0278 (5)	0.0333 (5)	−0.0038 (4)	0.0058 (4)	0.0004 (4)
O2	0.0255 (5)	0.0207 (4)	0.0339 (5)	0.0000 (4)	0.0059 (4)	−0.0060 (4)
C1	0.0272 (6)	0.0181 (5)	0.0259 (6)	−0.0009 (5)	0.0047 (5)	−0.0026 (5)
C2	0.0349 (7)	0.0203 (6)	0.0281 (6)	−0.0004 (5)	0.0073 (5)	−0.0034 (5)
C3	0.0339 (7)	0.0230 (6)	0.0273 (6)	−0.0057 (5)	0.0037 (5)	−0.0013 (5)
C4	0.0327 (7)	0.0240 (6)	0.0259 (6)	−0.0005 (5)	0.0072 (5)	−0.0028 (5)
C5	0.0399 (8)	0.0335 (8)	0.0367 (8)	−0.0043 (6)	0.0135 (6)	0.0027 (6)
C6	0.0671 (12)	0.0451 (9)	0.0267 (7)	0.0055 (8)	0.0143 (7)	0.0072 (7)
C7	0.0620 (12)	0.0565 (11)	0.0275 (7)	0.0084 (9)	−0.0089 (7)	−0.0055 (7)
C8	0.0405 (9)	0.0430 (9)	0.0419 (8)	−0.0020 (7)	−0.0059 (7)	−0.0096 (7)
C9	0.0317 (7)	0.0240 (6)	0.0296 (6)	−0.0012 (5)	0.0086 (5)	−0.0043 (5)
C10	0.0263 (6)	0.0172 (5)	0.0247 (6)	0.0020 (4)	0.0028 (5)	−0.0010 (4)
C11	0.0268 (6)	0.0186 (5)	0.0266 (6)	0.0008 (5)	0.0046 (5)	−0.0012 (4)
C12	0.0268 (6)	0.0188 (5)	0.0234 (6)	0.0015 (5)	−0.0017 (5)	0.0010 (4)
C13	0.0296 (7)	0.0239 (6)	0.0315 (7)	−0.0030 (5)	0.0006 (5)	0.0016 (5)
C14	0.0357 (7)	0.0211 (6)	0.0397 (8)	−0.0050 (5)	−0.0074 (6)	−0.0011 (5)
C15	0.0374 (8)	0.0231 (6)	0.0422 (8)	0.0044 (6)	−0.0077 (6)	−0.0110 (6)
C16	0.0299 (7)	0.0284 (7)	0.0396 (8)	0.0051 (5)	0.0003 (6)	−0.0103 (6)
C17	0.0248 (6)	0.0196 (6)	0.0288 (6)	0.0012 (5)	−0.0014 (5)	−0.0017 (5)

Geometric parameters (Å, º) top

P1—C2	1.8028 (14)	C6—H6	0.9500
P1—C10	1.8117 (13)	C7—C8	1.384 (3)
P1—C1	1.8519 (13)	C7—H7	0.9500
O1—C2	1.3829 (18)	C8—C9	1.371 (2)
O1—C9	1.3887 (17)	C8—H8	0.9500
O2—C17	1.3758 (15)	C10—C11	1.3531 (18)
O2—C10	1.3869 (15)	C11—C12	1.4425 (17)
C1—C1ⁱ	1.533 (2)	C11—H11	0.9500
C1—H1A	0.9900	C12—C17	1.3965 (19)
C1—H1B	0.9900	C12—C13	1.3971 (18)
C2—C3	1.3520 (19)	C13—C14	1.388 (2)
C3—C4	1.4321 (19)	C13—H13	0.9500
C3—H3	0.9500	C14—C15	1.394 (2)
C4—C9	1.394 (2)	C14—H14	0.9500
C4—C5	1.400 (2)	C15—C16	1.390 (2)
C5—C6	1.381 (2)	C15—H15	0.9500
C5—H5	0.9500	C16—C17	1.3850 (18)
C6—C7	1.404 (3)	C16—H16	0.9500

C2—P1—C10	100.04 (6)	C9—C8—H8	121.9
C2—P1—C1	99.98 (6)	C7—C8—H8	121.9
C10—P1—C1	97.50 (6)	C8—C9—O1	126.45 (14)
C2—O1—C9	106.27 (11)	C8—C9—C4	123.73 (14)
C17—O2—C10	106.06 (10)	O1—C9—C4	109.80 (12)
C1ⁱ—C1—P1	110.79 (12)	C11—C10—O2	111.43 (11)
C1ⁱ—C1—H1A	109.5	C11—C10—P1	133.26 (10)
P1—C1—H1A	109.5	O2—C10—P1	115.17 (9)
C1ⁱ—C1—H1B	109.5	C10—C11—C12	106.59 (11)
P1—C1—H1B	109.5	C10—C11—H11	126.7
H1A—C1—H1B	108.1	C12—C11—H11	126.7
C3—C2—O1	110.67 (12)	C17—C12—C13	118.91 (12)
C3—C2—P1	128.31 (11)	C17—C12—C11	105.69 (11)
O1—C2—P1	120.64 (10)	C13—C12—C11	135.38 (13)
C2—C3—C4	107.70 (13)	C14—C13—C12	118.18 (14)
C2—C3—H3	126.1	C14—C13—H13	120.9
C4—C3—H3	126.1	C12—C13—H13	120.9
C9—C4—C5	119.42 (14)	C13—C14—C15	121.37 (13)
C9—C4—C3	105.53 (12)	C13—C14—H14	119.3
C5—C4—C3	134.98 (14)	C15—C14—H14	119.3
C6—C5—C4	117.75 (15)	C16—C15—C14	121.64 (13)
C6—C5—H5	121.1	C16—C15—H15	119.2
C4—C5—H5	121.1	C14—C15—H15	119.2
C5—C6—C7	121.14 (16)	C17—C16—C15	115.93 (14)
C5—C6—H6	119.4	C17—C16—H16	122.0
C7—C6—H6	119.4	C15—C16—H16	122.0
C8—C7—C6	121.67 (16)	O2—C17—C16	125.85 (13)
C8—C7—H7	119.2	O2—C17—C12	110.19 (11)
C6—C7—H7	119.2	C16—C17—C12	123.94 (13)
C9—C8—C7	116.23 (16)

C2—P1—C1—C1ⁱ	−66.72 (13)	C3—C4—C9—O1	1.48 (15)
C10—P1—C1—C1ⁱ	−168.36 (12)	C17—O2—C10—C11	0.95 (14)
C9—O1—C2—C3	0.12 (15)	C17—O2—C10—P1	177.25 (9)
C9—O1—C2—P1	173.64 (9)	C2—P1—C10—C11	−113.82 (14)
C10—P1—C2—C3	−150.90 (13)	C1—P1—C10—C11	−12.23 (15)
C1—P1—C2—C3	109.56 (13)	C2—P1—C10—O2	70.91 (10)
C10—P1—C2—O1	36.84 (11)	C1—P1—C10—O2	172.49 (9)
C1—P1—C2—O1	−62.70 (11)	O2—C10—C11—C12	0.06 (15)
O1—C2—C3—C4	0.80 (16)	P1—C10—C11—C12	−175.35 (10)
P1—C2—C3—C4	−172.09 (10)	C10—C11—C12—C17	−1.02 (14)
C2—C3—C4—C9	−1.38 (15)	C10—C11—C12—C13	−179.30 (14)
C2—C3—C4—C5	175.51 (16)	C17—C12—C13—C14	−0.27 (19)
C9—C4—C5—C6	−0.7 (2)	C11—C12—C13—C14	177.84 (14)
C3—C4—C5—C6	−177.27 (16)	C12—C13—C14—C15	−0.9 (2)
C4—C5—C6—C7	−1.0 (2)	C13—C14—C15—C16	0.9 (2)
C5—C6—C7—C8	1.2 (3)	C14—C15—C16—C17	0.3 (2)
C6—C7—C8—C9	0.4 (3)	C10—O2—C17—C16	177.01 (13)
C7—C8—C9—O1	175.93 (14)	C10—O2—C17—C12	−1.61 (14)
C7—C8—C9—C4	−2.2 (2)	C15—C16—C17—O2	179.94 (13)
C2—O1—C9—C8	−179.39 (15)	C15—C16—C17—C12	−1.6 (2)
C2—O1—C9—C4	−1.02 (14)	C13—C12—C17—O2	−179.74 (11)
C5—C4—C9—C8	2.4 (2)	C11—C12—C17—O2	1.64 (14)
C3—C4—C9—C8	179.90 (14)	C13—C12—C17—C16	1.6 (2)
C5—C4—C9—O1	−176.00 (12)	C11—C12—C17—C16	−177.01 (13)

Symmetry code: (i) −x+1, −y+2, −z+1.

References

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