Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S2053229615003009/fn3187sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S2053229615003009/fn3187Isup2.hkl | |
Chemical Markup Language (CML) file https://doi.org/10.1107/S2053229615003009/fn3187Isup3.cml |
CCDC reference: 1048929
Trioctylphosphine oxide (TOPO) is a widely used chemical compound in nanocrystal synthesis, for the removal of heavy metals, and removal of toxins in waste water (Praveen & Loh, 2013). TOPO is often used as a ligand stabilizer for colloids in traditional thermal decomposition synthetic techniques (Manna et al., 2000; Murray et al., 1993; Rockenberger et al., 1998; Talapin et al., 2001). The white crystalline material is also used as a phosphorus source, as the compound decomposes in high-temperature (> 573 K) reactions for colloidal synthesis (Zhang et al., 2011) and has been characterized by nuclear magnetic resonance (Hens et al., 2005; Hilliard et al., 2012; Kriz et al., 2009; Liu et al., 2007). In this report, we provide additional spectroscopic data for TOPO beyond the single-crystal diffraction results.
Trioctylphosphine oxide (90%) was purchased from Sigma–Aldrich and acetone (99.5% reagent grade) was purchased from Fisher Scientific. TOPO (0.5 g) was dissolved in acetone (5 ml) in a 25 ml scintillation vial, which was left uncapped for ambient evaporation at 293 K for 12 h. Single crystals were collected and loaded onto a Kapton capillary tube for measurement.
Crystal data, data collection and structure refinement details are summarised in Table 1. H atoms were refined using a riding model, in which standard C—H bond distances were applied, and the H-atom positions were adjusted during refinement. Isotropic displacement parameters of methylene H atoms were assigned as 33% larger than the attached C atom, while methyl H atoms had displacement parameters 50% larger. In addition, the methyl torsion angle (for rotation about the C—Me bond) was optimized by the refinement program.
Trioctylphosphine oxide (0.05 g) was mixed with potassium bromide and pressed to form a pellet for FT–IR analysis, which was carried out using a Nicolet spectrometer and averaged for 16 scans in a nitrogen atmosphere to reduce molecular vibrations from ambient environment. Raman spectroscopy was performed using a B&W Tek iRaman spectrometer with a 532 nm excitation source. Modeling of the X-ray scattering patterns were done using an in-house code (Gordon et al., 2015) calculating the Debye Equation (Equation 1). In computing the X-ray scattering intensities for the 2 to 8 nm crystallite sizes of trioctylphosphine oxide, the parameters fi and fj are the atomic scattering factors tabulated from Cromer–Mann coefficients, q is the wave vector in Å-1, rij is the pairwise distance in Å (Brown et al., 2004; Debye, 1915; Hovestreydt, 1983). The bulk crystal simulation was performed using CrystalDiffract (CrystalMaker, 2015).
<fi>I = Σi,j fifj (sin(qrij))/(qrij)</fi> (1)
Slow evaporation resulted in a mixture of single crystals, of which the highest-quality single crystals were collected. The molecular structure of TOPO is shown in Fig. 1 (Johnson, 1976). The unit cell is drawn more compactly in Fig. 2, where the phosphonyl group within each molecular unit is oriented such that the polar functional groups are 180° from each other. Each O atom is 3.94 Å from the P atom on the nearest neighboring molecular unit. The two-dimensional projection of the unit cell onto the (010) plane depicts the alternating directions of the dipole from the P═O bonds. The flexible hydrocarbon chains are aligned parallel to neighboring octyl chains, which allows for compact packing of the molecular units.
In processes that require careful removal of excess TOPO from solution, such as post-synthesis nanocrystal purification, total X-ray scattering provides high-resolution and rapid acquisition of data to track TOPO impurities that will crystallize with varying grain sizes. The X-ray scattering for the 77-atom unit cell was calculated as a function of crystallite size for comparison with the total X-ray scattering data obtained with a synchrotron light source (λ = 0.2114 Å).
The simulations in Fig. 3(a) track the peak width broadening as the crystal size decreased from an infinite crystal to a few unit cells. The decrease in the inverse of full-width half-maximum of the Gaussian fits is linearly correlated with the crystal size (Fig. 3b) and matches well with the collected scattering data. The slope of the fit for crystal diameter as a function of the inverse of full-width half maximum was calculated to be 1.101±0.323 for the dominant (114) set of planes, which corresponds with the κλ/cos(θ) in which κ is the shape factor of value 0.9, λ is the X-ray wavelength of value 0.2114 Å, and θ is the peak center of value 1.40 Å-1. Spectroscopy from FT–IR shows the –CH2 stretching modes in the three alkyl chains at 2850 and 2919 cm-1. The characteristic P═O and P—C stretching modes were observed at 1146 and 1465 cm-1, respectively.
The complementary Raman spectroscopic data, which has previously been unreported, confirms the phosphonyl stretching mode in a trialkylphosphonyl environment results in a much weaker peak at 1145 cm-1 than the dominant methylene stretching modes at 2847 and 2882 cm-1 (Fig. 5).
Data collection: APEX2 (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).
C24H51OP | Z = 4 |
Mr = 386.62 | F(000) = 872 |
Monoclinic, P21/c | Dx = 0.984 Mg m−3 |
a = 15.0889 (4) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 5.2252 (1) Å | µ = 0.12 mm−1 |
c = 33.5535 (9) Å | T = 100 K |
β = 99.449 (1)° | Prism, colorless |
V = 2609.55 (11) Å3 | 0.38 × 0.24 × 0.07 mm |
Bruker APEXII diffractometer | 5926 independent reflections |
Radiation source: sealed tube | 5115 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.026 |
phi and ω scans | θmax = 27.5°, θmin = 1.7° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2007) | h = −9→19 |
Tmin = 0.709, Tmax = 0.746 | k = −6→6 |
43246 measured reflections | l = −43→43 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.039 | H-atom parameters constrained |
wR(F2) = 0.103 | w = 1/[σ2(Fo2) + (0.0421P)2 + 1.0549P] where P = (Fo2 + 2Fc2)/3 |
S = 1.10 | (Δ/σ)max = 0.001 |
5926 reflections | Δρmax = 0.41 e Å−3 |
239 parameters | Δρmin = −0.35 e Å−3 |
0 restraints |
C24H51OP | V = 2609.55 (11) Å3 |
Mr = 386.62 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 15.0889 (4) Å | µ = 0.12 mm−1 |
b = 5.2252 (1) Å | T = 100 K |
c = 33.5535 (9) Å | 0.38 × 0.24 × 0.07 mm |
β = 99.449 (1)° |
Bruker APEXII diffractometer | 5926 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2007) | 5115 reflections with I > 2σ(I) |
Tmin = 0.709, Tmax = 0.746 | Rint = 0.026 |
43246 measured reflections |
R[F2 > 2σ(F2)] = 0.039 | 0 restraints |
wR(F2) = 0.103 | H-atom parameters constrained |
S = 1.10 | Δρmax = 0.41 e Å−3 |
5926 reflections | Δρmin = −0.35 e Å−3 |
239 parameters |
x | y | z | Uiso*/Ueq | ||
P1 | 0.964925 (19) | 0.28059 (5) | 0.807347 (8) | 0.01219 (8) | |
O1 | 0.97088 (6) | 0.55665 (15) | 0.79639 (2) | 0.01736 (18) | |
C1 | 1.06979 (7) | 0.1118 (2) | 0.80961 (3) | 0.0139 (2) | |
H1a | 1.0611 | −0.0667 | 0.8159 | 0.018* | |
H1b | 1.0888 | 0.1193 | 0.7834 | 0.018* | |
C2 | 1.14331 (8) | 0.2257 (2) | 0.84150 (3) | 0.0168 (2) | |
H2a | 1.1504 | 0.4052 | 0.8354 | 0.022* | |
H2b | 1.1240 | 0.2160 | 0.8676 | 0.022* | |
C3 | 1.23423 (8) | 0.0937 (2) | 0.84433 (3) | 0.0167 (2) | |
H3a | 1.2273 | −0.0874 | 0.8493 | 0.022* | |
H3b | 1.2558 | 0.1115 | 0.8188 | 0.022* | |
C4 | 1.30304 (8) | 0.2070 (2) | 0.87799 (4) | 0.0199 (2) | |
H4a | 1.3125 | 0.3851 | 0.8717 | 0.026* | |
H4b | 1.2782 | 0.2030 | 0.9029 | 0.026* | |
C5 | 1.39368 (8) | 0.0723 (3) | 0.88518 (4) | 0.0248 (3) | |
H5a | 1.3848 | −0.1063 | 0.8914 | 0.033* | |
H5b | 1.4197 | 0.0791 | 0.8606 | 0.033* | |
C6 | 1.45903 (9) | 0.1911 (3) | 0.91950 (5) | 0.0340 (3) | |
H6a | 1.4687 | 0.3686 | 0.9129 | 0.045* | |
H6b | 1.4319 | 0.1890 | 0.9438 | 0.045* | |
C7 | 1.54930 (11) | 0.0577 (4) | 0.92834 (6) | 0.0550 (5) | |
H7a | 1.5770 | 0.0601 | 0.9042 | 0.073* | |
H7b | 1.5401 | −0.1197 | 0.9351 | 0.073* | |
C8 | 1.61270 (15) | 0.1832 (6) | 0.96298 (9) | 0.0929 (10) | |
H8a | 1.6269 | 0.3534 | 0.9553 | 0.139* | |
H8b | 1.6669 | 0.0845 | 0.9689 | 0.139* | |
H8c | 1.5842 | 0.1905 | 0.9865 | 0.139* | |
C9 | 0.93336 (8) | 0.2526 (2) | 0.85700 (3) | 0.0147 (2) | |
H9a | 0.9750 | 0.3552 | 0.8756 | 0.020* | |
H9b | 0.8743 | 0.3285 | 0.8558 | 0.020* | |
C10 | 0.93063 (8) | −0.0148 (2) | 0.87519 (3) | 0.0159 (2) | |
H10a | 0.8877 | −0.1195 | 0.8576 | 0.021* | |
H10b | 0.9893 | −0.0941 | 0.8770 | 0.021* | |
C11 | 0.90403 (8) | −0.0038 (2) | 0.91718 (3) | 0.0179 (2) | |
H11a | 0.9469 | 0.1032 | 0.9344 | 0.024* | |
H11b | 0.8456 | 0.0773 | 0.9150 | 0.024* | |
C12 | 0.89991 (8) | −0.2624 (2) | 0.93744 (3) | 0.0163 (2) | |
H12a | 0.9581 | −0.3450 | 0.9395 | 0.022* | |
H12b | 0.8563 | −0.3693 | 0.9206 | 0.022* | |
C13 | 0.87432 (9) | −0.2429 (2) | 0.97944 (3) | 0.0198 (3) | |
H13a | 0.9205 | −0.1471 | 0.9967 | 0.026* | |
H13b | 0.8187 | −0.1474 | 0.9775 | 0.026* | |
C14 | 0.86248 (8) | −0.5003 (2) | 0.99905 (3) | 0.0176 (2) | |
H14a | 0.9182 | −0.5959 | 1.0012 | 0.023* | |
H14b | 0.8163 | −0.5967 | 0.9818 | 0.023* | |
C15 | 0.83663 (10) | −0.4757 (2) | 1.04085 (4) | 0.0264 (3) | |
H15a | 0.8837 | −0.3832 | 1.0582 | 0.035* | |
H15b | 0.7820 | −0.3755 | 1.0388 | 0.035* | |
C16 | 0.82193 (11) | −0.7311 (3) | 1.06044 (4) | 0.0302 (3) | |
H16a | 0.7737 | −0.8211 | 1.0441 | 0.045* | |
H16b | 0.8070 | −0.7022 | 1.0868 | 0.045* | |
H16c | 0.8759 | −0.8313 | 1.0628 | 0.045* | |
C17 | 0.88283 (7) | 0.1070 (2) | 0.77284 (3) | 0.0141 (2) | |
H17a | 0.9013 | 0.1036 | 0.7465 | 0.019* | |
H17b | 0.8807 | −0.0683 | 0.7821 | 0.019* | |
C18 | 0.78867 (8) | 0.2239 (2) | 0.76869 (3) | 0.0171 (2) | |
H18a | 0.7684 | 0.2158 | 0.7946 | 0.023* | |
H18b | 0.7917 | 0.4028 | 0.7613 | 0.023* | |
C19 | 0.72044 (8) | 0.0881 (2) | 0.73714 (3) | 0.0178 (2) | |
H19a | 0.7417 | 0.0921 | 0.7114 | 0.024* | |
H19b | 0.7164 | −0.0898 | 0.7449 | 0.024* | |
C20 | 0.62707 (8) | 0.2075 (2) | 0.73202 (4) | 0.0196 (2) | |
H20a | 0.6053 | 0.1997 | 0.7576 | 0.026* | |
H20b | 0.6315 | 0.3866 | 0.7249 | 0.026* | |
C21 | 0.55913 (8) | 0.0772 (2) | 0.69986 (4) | 0.0210 (3) | |
H21a | 0.5533 | −0.1005 | 0.7074 | 0.028* | |
H21b | 0.5817 | 0.0802 | 0.6744 | 0.028* | |
C22 | 0.46664 (8) | 0.2019 (3) | 0.69385 (4) | 0.0225 (3) | |
H22a | 0.4435 | 0.1958 | 0.7191 | 0.030* | |
H22b | 0.4726 | 0.3805 | 0.6869 | 0.030* | |
C23 | 0.39931 (9) | 0.0748 (3) | 0.66114 (4) | 0.0294 (3) | |
H23a | 0.3920 | −0.1027 | 0.6684 | 0.039* | |
H23b | 0.4228 | 0.0776 | 0.6359 | 0.039* | |
C24 | 0.30764 (9) | 0.2059 (3) | 0.65488 (5) | 0.0385 (4) | |
H24a | 0.2837 | 0.2022 | 0.6797 | 0.058* | |
H24b | 0.2675 | 0.1176 | 0.6342 | 0.058* | |
H24c | 0.3141 | 0.3803 | 0.6468 | 0.058* |
U11 | U22 | U33 | U12 | U13 | U23 | |
P1 | 0.01648 (14) | 0.00943 (14) | 0.01102 (14) | 0.00030 (11) | 0.00335 (10) | 0.00056 (10) |
O1 | 0.0257 (4) | 0.0109 (4) | 0.0163 (4) | 0.0000 (3) | 0.0058 (3) | 0.0012 (3) |
C1 | 0.0173 (5) | 0.0121 (5) | 0.0126 (5) | 0.0005 (4) | 0.0034 (4) | −0.0004 (4) |
C2 | 0.0170 (5) | 0.0167 (6) | 0.0169 (5) | −0.0007 (4) | 0.0033 (4) | −0.0026 (4) |
C3 | 0.0188 (6) | 0.0167 (6) | 0.0151 (5) | 0.0004 (4) | 0.0044 (4) | −0.0001 (4) |
C4 | 0.0170 (6) | 0.0221 (6) | 0.0206 (6) | −0.0002 (5) | 0.0034 (4) | −0.0023 (5) |
C5 | 0.0191 (6) | 0.0262 (7) | 0.0285 (7) | 0.0026 (5) | 0.0022 (5) | −0.0007 (5) |
C6 | 0.0203 (6) | 0.0389 (8) | 0.0398 (8) | 0.0019 (6) | −0.0037 (6) | −0.0038 (7) |
C7 | 0.0250 (8) | 0.0568 (12) | 0.0756 (13) | 0.0091 (8) | −0.0143 (8) | −0.0050 (10) |
C8 | 0.0389 (11) | 0.100 (2) | 0.121 (2) | 0.0108 (12) | −0.0427 (13) | −0.0212 (17) |
C9 | 0.0186 (5) | 0.0132 (5) | 0.0128 (5) | 0.0013 (4) | 0.0042 (4) | −0.0002 (4) |
C10 | 0.0209 (6) | 0.0147 (5) | 0.0130 (5) | 0.0001 (4) | 0.0050 (4) | 0.0005 (4) |
C11 | 0.0247 (6) | 0.0166 (6) | 0.0134 (5) | 0.0010 (5) | 0.0065 (4) | 0.0014 (4) |
C12 | 0.0208 (6) | 0.0158 (6) | 0.0131 (5) | 0.0003 (4) | 0.0049 (4) | 0.0009 (4) |
C13 | 0.0295 (6) | 0.0159 (6) | 0.0157 (5) | 0.0013 (5) | 0.0088 (5) | 0.0019 (4) |
C14 | 0.0230 (6) | 0.0164 (6) | 0.0143 (5) | −0.0007 (5) | 0.0059 (4) | 0.0008 (4) |
C15 | 0.0447 (8) | 0.0195 (6) | 0.0187 (6) | 0.0017 (6) | 0.0158 (6) | 0.0021 (5) |
C16 | 0.0481 (9) | 0.0243 (7) | 0.0215 (6) | −0.0031 (6) | 0.0157 (6) | 0.0049 (5) |
C17 | 0.0173 (5) | 0.0124 (5) | 0.0125 (5) | 0.0011 (4) | 0.0027 (4) | −0.0004 (4) |
C18 | 0.0179 (5) | 0.0161 (6) | 0.0173 (5) | 0.0019 (4) | 0.0029 (4) | −0.0023 (4) |
C19 | 0.0188 (6) | 0.0176 (6) | 0.0166 (5) | 0.0016 (5) | 0.0021 (4) | −0.0012 (4) |
C20 | 0.0181 (6) | 0.0207 (6) | 0.0198 (6) | 0.0009 (5) | 0.0029 (4) | −0.0018 (5) |
C21 | 0.0195 (6) | 0.0229 (6) | 0.0199 (6) | 0.0011 (5) | 0.0011 (5) | −0.0013 (5) |
C22 | 0.0186 (6) | 0.0250 (6) | 0.0236 (6) | 0.0001 (5) | 0.0024 (5) | 0.0007 (5) |
C23 | 0.0219 (6) | 0.0379 (8) | 0.0266 (7) | −0.0015 (6) | −0.0014 (5) | 0.0006 (6) |
C24 | 0.0207 (7) | 0.0525 (10) | 0.0397 (8) | −0.0011 (7) | −0.0034 (6) | 0.0061 (7) |
P1—O1 | 1.4949 (8) | C11—C12 | 1.5184 (16) |
P1—C17 | 1.7962 (11) | C12—C13 | 1.5246 (15) |
P1—C1 | 1.8023 (11) | C13—C14 | 1.5207 (16) |
P1—C9 | 1.8123 (11) | C14—C15 | 1.5217 (16) |
C1—C2 | 1.5300 (15) | C15—C16 | 1.5196 (18) |
C2—C3 | 1.5246 (16) | C17—C18 | 1.5316 (15) |
C3—C4 | 1.5229 (16) | C18—C19 | 1.5251 (16) |
C4—C5 | 1.5217 (17) | C19—C20 | 1.5247 (16) |
C5—C6 | 1.5202 (18) | C20—C21 | 1.5217 (16) |
C6—C7 | 1.516 (2) | C21—C22 | 1.5232 (17) |
C7—C8 | 1.527 (3) | C22—C23 | 1.5201 (18) |
C9—C10 | 1.5283 (15) | C23—C24 | 1.527 (2) |
C10—C11 | 1.5281 (15) | ||
O1—P1—C17 | 113.05 (5) | C11—C10—C9 | 111.23 (9) |
O1—P1—C1 | 113.26 (5) | C12—C11—C10 | 114.54 (10) |
C17—P1—C1 | 106.72 (5) | C11—C12—C13 | 112.92 (9) |
O1—P1—C9 | 109.84 (5) | C14—C13—C12 | 113.99 (10) |
C17—P1—C9 | 107.12 (5) | C13—C14—C15 | 112.97 (10) |
C1—P1—C9 | 106.46 (5) | C16—C15—C14 | 113.71 (11) |
C2—C1—P1 | 111.70 (8) | C18—C17—P1 | 112.87 (8) |
C3—C2—C1 | 114.16 (9) | C19—C18—C17 | 112.84 (9) |
C4—C3—C2 | 111.54 (9) | C20—C19—C18 | 113.19 (10) |
C5—C4—C3 | 115.04 (10) | C21—C20—C19 | 113.53 (10) |
C6—C5—C4 | 112.68 (11) | C20—C21—C22 | 113.48 (10) |
C7—C6—C5 | 114.25 (14) | C23—C22—C21 | 113.46 (11) |
C6—C7—C8 | 112.46 (17) | C22—C23—C24 | 112.74 (12) |
C10—C9—P1 | 117.98 (8) |
Experimental details
Crystal data | |
Chemical formula | C24H51OP |
Mr | 386.62 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 100 |
a, b, c (Å) | 15.0889 (4), 5.2252 (1), 33.5535 (9) |
β (°) | 99.449 (1) |
V (Å3) | 2609.55 (11) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.12 |
Crystal size (mm) | 0.38 × 0.24 × 0.07 |
Data collection | |
Diffractometer | Bruker APEXII diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2007) |
Tmin, Tmax | 0.709, 0.746 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 43246, 5926, 5115 |
Rint | 0.026 |
(sin θ/λ)max (Å−1) | 0.651 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.039, 0.103, 1.10 |
No. of reflections | 5926 |
No. of parameters | 239 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.41, −0.35 |
Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEPII (Johnson, 1976).