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Tris(2-pyridyl)­phosphine oxide, (I), C15H12N3OP, is isomorphous with tris(2-pyridyl)­phosphine. Because of a combination of C—H...O and C—H...N interactions, the crystal packing is denser in the title compound than in the related compounds tri­phenyl­phosphine oxide and tris(2-pyridyl)­phosphine.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270104003956/ga1045sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270104003956/ga1045Isup2.hkl
Contains datablock I

CCDC reference: 237938

Comment top

Tris(2-pyridyl)phosphine oxide has been used as a ligand in the coordination chemistry of transition metals and a number of complexes have been characterized by X-ray crystallography [Cambridge Structural Database (Allen, 2002) refcodes XAMNUU (Anderson et al., 2000), QATYUF and QATZAM (Casares et al., 2001), VOPREX (Keene et al., 1991), and MAWYOY (Espinet et al., 2000)]. The solid-state structure of the free tris(2-pyridyl)phosphine oxide (I) is, however, still outstanding and crystallographic data are presented in this paper.

Compound (I) is isomorphous with the parent compound tris(2-pyridyl)phosphine (TP; GEKTIZ; Keene et al., 1988), with the O atom replacing the lone pair in the phosphine [a = 9.162 (1) Å, b = 9.163 (1) Å, c = 16.071 (2) Å and β = 100.92 (1)°; space group P21/c]. With the exception of the O atom, the coordinates of the two structures are related by (1 − x, y, 1/2 − x). The molecular geometry of (I) (Fig. 1) is pyramidal, with a propeller-type arrangement of the three pyridyl rings, and shows considerable deviation from C3v symmetry. One of the N atoms points to the same side as the O atom, while the remaining two N atoms point in the opposite direction. The P—C bond distances (Table 1) are comparable to those in TP [mean 1.828 (3) Å] but slightly longer than those in triphenylphosphine oxide (TPO) (mean 1.800 Å; Brock et al., 1985). An opposite trend is observed for the P=O bond, which is slightly shorter in (I) [1.479 (1) Å] than in triphenylphosphine oxide [1.491 (2) and 1.494 (2) Å; Brock et al., 1985].

No classical (strong) hydrogen bonding occurs in the structure of (I). Molecules are bound together by weak C—H···O and C—H···N interactions (Table 2 and Fig. 2). The same C—H···N interaction exists in TP, the intermolecular C···N distances being 3.341 and 3.353 (2) Å in TP and (I), respectively.

Three modifications of TPO, viz. one orthorhombic (Form I) and two monoclinic (Forms II and III), have been described in the literature (Brock et al., 1985; Spek, 1987; Thomas & Hamor, 1993; Table 3). Unique to Form II is a pair of molecules connected by C—H···O interactions, forming a ring described by the graph set motif R22(12) (Etter, 1990; Bernstein et al., 1995). Extending the C—H···O network produces a chain of rings (Bernstein et al., 1995) running slomg the a axis (in P21/c, e.g. TPEPHO06; Brock et al., 1995). A similar chain of R22(12) C—H···O rings runs along the b axis in (I). In the structure of (I), the additional C—H···N interaction seems to reinforce the R22(12) C—H···O ring, leading to C—H···O contacts that are significantly shorter than those found in Form II of TPO. Intermolecular C···O distances in TPO are in the range 3.488–3.586 Å (TPEHO10 and TPEPHO11; Falvello et al., 2002), while they are considerably shorter in (I) [3.202 (2) and 3.313 (2) Å; Table 2].

The three polymorphs of TPO have calculated densities in the range 1.215–1.285 Mg m−3, considerably lower than that of (I) (1.422 Mg m−3). Molecular volumes range from 380.3 Å3 (at 295 K) in Form III (Spek, 1987) to 365.9 Å3 (at 153 K; Brock et al., 1985) in Form I and 365.3 Å3 (at 153 K; Brock et al., 1985) in Form II. The molecular volume tfound in (I) [328.35 (5) Å3] is considerably smaller, possibly as a consequence of the reduced number of H atoms (three per molecule) and/or the more efficient packing in (I) as a result of there being additional C—H···N contacts (Fig. 2) that are not found in the carbon analogue.

The cell volume and calculated crystal density in TP are 1325 (2) Å3 and 1.330 Mg m−3 (at 283–303 K). The fact that TPO and TP have almost identical molecular volumes indicates that there is little cost in inserting the extra O atom into the TP structure. Thus it seems logical that the extra C—H···O interactions in (I) promote more efficient packing. Since (I) and TP are isomorphous and the crystal packing of (I) is directed by weak interactions, it is likely that the structure of TP is also dominated by weak interactions. It is therefore possible that in place of the C—H···O interactions, the TP structure has interactions between the equivalent C/H groups and the phosphine lone pair. The two closest C···P (D···A) distances in the two structures are 4.319 and 4.249 Å for TP, and 4.443 and 4.374 Å for (I). Although rarely mentioned in the literature, such interactions have been described previously (Desiraju and Steiner, 1999). However, since these C···P distances in TP are somewhat longer than examples cited in the above reference (3.19–3.83 Å) the interaction must be considered very weak, certainly when compared with the C—H···O interaction in (I). Note that this C—H···P interaction is not unreasonable given that a C···O distance of 4.0 Å is regarded as a reasonable upper limit for a C—H···O interaction (Desiraju, 1991; Desiraju, 1996; Taylor & Kennard, 1982).

Experimental top

Tris(2-pyridyl)phosphine oxide was obtained as a by-product during the attempted synthesis of phenyl tris(2-pyridyl)phosphonium bromide from tris(2-pyridyl)phosphine and bromobenzene under reflux conditions. Crystals suitable for X-ray analysis were obtained by dissolving the crude product in methanol and cooling it to 213 K.

Refinement top

H atoms were positioned geometrically and allowed to ride on their parent atoms, with C—H bond lengths of 0.95 Å and Uiso values equal to 1.2Ueq of the parent atom.

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1999); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Bruker, 1999); program(s) used to refine structure: SHELXTL; molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. A view of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radius.
[Figure 2] Fig. 2. Intermolecular close contacts in (I). [Symmetry codes: (a) 2 − x, 1/2 + y, 1/2 − z; (b) 2 − x, y − 1/2, 1/2 − z.]
(I) top
Crystal data top
C15H12N3OPF(000) = 584
Mr = 281.25Dx = 1.422 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 1007 reflections
a = 9.0807 (9) Åθ = 2.3–28.2°
b = 9.1550 (9) ŵ = 0.21 mm1
c = 16.0629 (16) ÅT = 173 K
β = 100.409 (2)°Prism, light brown
V = 1313.4 (2) Å30.24 × 0.20 × 0.17 mm
Z = 4
Data collection top
Bruker SMART 1K CCD area-detector
diffractometer
2589 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.026
Graphite monochromatorθmax = 28.3°, θmin = 2.3°
ϕ and ω scansh = 1112
8966 measured reflectionsk = 912
3251 independent reflectionsl = 2121
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)] = 0.036Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.096H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.0454P)2 + 0.563P]
where P = (Fo2 + 2Fc2)/3
3251 reflections(Δ/σ)max = 0.001
181 parametersΔρmax = 0.41 e Å3
0 restraintsΔρmin = 0.36 e Å3
Crystal data top
C15H12N3OPV = 1313.4 (2) Å3
Mr = 281.25Z = 4
Monoclinic, P21/cMo Kα radiation
a = 9.0807 (9) ŵ = 0.21 mm1
b = 9.1550 (9) ÅT = 173 K
c = 16.0629 (16) Å0.24 × 0.20 × 0.17 mm
β = 100.409 (2)°
Data collection top
Bruker SMART 1K CCD area-detector
diffractometer
2589 reflections with I > 2σ(I)
8966 measured reflectionsRint = 0.026
3251 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0360 restraints
wR(F2) = 0.096H-atom parameters constrained
S = 1.02Δρmax = 0.41 e Å3
3251 reflectionsΔρmin = 0.36 e Å3
181 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
xyzUiso*/Ueq
P0.86663 (4)0.29096 (4)0.11854 (2)0.01960 (11)
O1.02875 (12)0.29006 (13)0.15391 (7)0.0285 (3)
C110.82427 (17)0.19197 (16)0.01882 (9)0.0217 (3)
N120.69184 (15)0.12300 (16)0.00009 (8)0.0286 (3)
C130.66551 (19)0.0480 (2)0.07296 (10)0.0327 (4)
H130.57280.00220.08740.039*
C140.7654 (2)0.03949 (19)0.12839 (10)0.0311 (4)
H140.74140.01500.17940.037*
C150.8996 (2)0.1112 (2)0.10839 (11)0.0364 (4)
H150.97000.10770.14550.044*
C160.9309 (2)0.1892 (2)0.03311 (11)0.0329 (4)
H161.02330.23940.01750.039*
C210.78892 (16)0.47360 (16)0.09830 (9)0.0201 (3)
N220.82838 (14)0.56238 (14)0.16552 (8)0.0220 (3)
C230.78126 (17)0.70115 (17)0.15693 (10)0.0247 (3)
H230.80950.76580.20330.030*
C240.69341 (18)0.75533 (18)0.08376 (11)0.0288 (4)
H240.66220.85450.08050.035*
C250.65196 (19)0.66228 (19)0.01564 (11)0.0312 (4)
H250.59070.69610.03500.037*
C260.70164 (18)0.51843 (18)0.02264 (10)0.0269 (3)
H260.67640.45230.02330.032*
C310.75141 (16)0.20849 (16)0.18732 (9)0.0189 (3)
N320.61072 (14)0.26016 (14)0.18119 (8)0.0227 (3)
C330.52699 (17)0.19927 (17)0.23244 (10)0.0252 (3)
H330.42790.23470.22980.030*
C340.57598 (18)0.08765 (17)0.28908 (10)0.0259 (3)
H340.51130.04730.32340.031*
C350.72075 (18)0.03610 (17)0.29466 (10)0.0248 (3)
H350.75760.04020.33290.030*
C360.81123 (16)0.09871 (16)0.24287 (9)0.0220 (3)
H360.91160.06700.24550.026*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
P0.02009 (19)0.0208 (2)0.01789 (18)0.00168 (14)0.00331 (13)0.00064 (14)
O0.0223 (6)0.0320 (6)0.0303 (6)0.0016 (5)0.0023 (4)0.0006 (5)
C110.0250 (7)0.0202 (7)0.0201 (7)0.0004 (6)0.0049 (6)0.0004 (5)
N120.0272 (7)0.0335 (8)0.0257 (7)0.0044 (6)0.0063 (5)0.0078 (6)
C130.0320 (9)0.0348 (9)0.0306 (9)0.0059 (7)0.0037 (7)0.0096 (7)
C140.0430 (10)0.0291 (9)0.0210 (8)0.0010 (7)0.0055 (7)0.0053 (6)
C150.0430 (10)0.0407 (10)0.0302 (9)0.0058 (8)0.0197 (8)0.0071 (7)
C160.0320 (9)0.0374 (10)0.0318 (9)0.0099 (7)0.0129 (7)0.0078 (7)
C210.0201 (7)0.0210 (7)0.0193 (7)0.0025 (5)0.0035 (5)0.0015 (5)
N220.0220 (6)0.0239 (7)0.0201 (6)0.0026 (5)0.0038 (5)0.0018 (5)
C230.0244 (7)0.0234 (8)0.0278 (8)0.0038 (6)0.0084 (6)0.0041 (6)
C240.0269 (8)0.0236 (8)0.0369 (9)0.0025 (6)0.0089 (7)0.0053 (7)
C250.0306 (9)0.0331 (9)0.0278 (8)0.0014 (7)0.0008 (7)0.0085 (7)
C260.0296 (8)0.0288 (8)0.0206 (7)0.0025 (7)0.0001 (6)0.0002 (6)
C310.0206 (7)0.0190 (7)0.0168 (7)0.0011 (5)0.0028 (5)0.0029 (5)
N320.0219 (6)0.0228 (6)0.0235 (6)0.0018 (5)0.0045 (5)0.0013 (5)
C330.0226 (7)0.0267 (8)0.0272 (8)0.0025 (6)0.0070 (6)0.0001 (6)
C340.0288 (8)0.0252 (8)0.0253 (8)0.0027 (6)0.0092 (6)0.0012 (6)
C350.0311 (8)0.0208 (7)0.0219 (7)0.0025 (6)0.0034 (6)0.0024 (6)
C360.0215 (7)0.0224 (7)0.0213 (7)0.0018 (6)0.0021 (6)0.0016 (6)
Geometric parameters (Å, º) top
P—O1.4792 (11)C23—C241.387 (2)
P—C311.8173 (15)C23—H230.9500
P—C111.8200 (15)C24—C251.384 (2)
P—C211.8211 (15)C24—H240.9500
C11—N121.343 (2)C25—C261.390 (2)
C11—C161.388 (2)C25—H250.9500
N12—C131.343 (2)C26—H260.9500
C13—C141.383 (2)C31—N321.3492 (18)
C13—H130.9500C31—C361.388 (2)
C14—C151.371 (2)N32—C331.3389 (19)
C14—H140.9500C33—C341.387 (2)
C15—C161.389 (2)C33—H330.9500
C15—H150.9500C34—C351.384 (2)
C16—H160.9500C34—H340.9500
C21—N221.3473 (19)C35—C361.394 (2)
C21—C261.388 (2)C35—H350.9500
N22—C231.340 (2)C36—H360.9500
O—P—C31113.99 (7)N22—C23—H23118.3
O—P—C11111.88 (7)C24—C23—H23118.3
C31—P—C11105.95 (7)C25—C24—C23118.83 (15)
O—P—C21113.60 (7)C25—C24—H24120.6
C31—P—C21104.06 (7)C23—C24—H24120.6
C11—P—C21106.65 (7)C24—C25—C26118.76 (15)
N12—C11—C16123.39 (14)C24—C25—H25120.6
N12—C11—P118.00 (11)C26—C25—H25120.6
C16—C11—P118.60 (12)C21—C26—C25118.47 (15)
C13—N12—C11116.54 (14)C21—C26—H26120.8
N12—C13—C14123.87 (16)C25—C26—H26120.8
N12—C13—H13118.1N32—C31—C36123.80 (13)
C14—C13—H13118.1N32—C31—P116.84 (11)
C15—C14—C13118.74 (15)C36—C31—P119.36 (11)
C15—C14—H14120.6C33—N32—C31116.40 (13)
C13—C14—H14120.6N32—C33—C34124.03 (14)
C14—C15—C16118.95 (16)N32—C33—H33118.0
C14—C15—H15120.5C34—C33—H33118.0
C16—C15—H15120.5C35—C34—C33118.81 (14)
C11—C16—C15118.51 (16)C35—C34—H34120.6
C11—C16—H16120.7C33—C34—H34120.6
C15—C16—H16120.7C34—C35—C36118.46 (14)
N22—C21—C26123.41 (14)C34—C35—H35120.8
N22—C21—P111.87 (10)C36—C35—H35120.8
C26—C21—P124.72 (12)C31—C36—C35118.50 (13)
C23—N22—C21117.12 (13)C31—C36—H36120.8
N22—C23—C24123.39 (15)C35—C36—H36120.8
O—P—C11—N12148.29 (12)P—C21—N22—C23178.00 (10)
C31—P—C11—N1223.51 (14)C21—N22—C23—C241.1 (2)
C21—P—C11—N1286.93 (13)N22—C23—C24—C250.2 (2)
O—P—C11—C1630.52 (15)C23—C24—C25—C260.9 (2)
C31—P—C11—C16155.30 (13)N22—C21—C26—C250.1 (2)
C21—P—C11—C1694.26 (14)P—C21—C26—C25178.89 (12)
C16—C11—N12—C130.3 (2)C24—C25—C26—C211.0 (2)
P—C11—N12—C13178.41 (12)O—P—C31—N32150.58 (11)
C11—N12—C13—C140.4 (3)C11—P—C31—N3285.96 (12)
N12—C13—C14—C150.1 (3)C21—P—C31—N3226.30 (13)
C13—C14—C15—C160.3 (3)O—P—C31—C3628.91 (14)
N12—C11—C16—C150.0 (3)C11—P—C31—C3694.55 (12)
P—C11—C16—C15178.77 (14)C21—P—C31—C36153.18 (11)
C14—C15—C16—C110.4 (3)C36—C31—N32—C330.2 (2)
O—P—C21—N2249.20 (12)P—C31—N32—C33179.65 (11)
C31—P—C21—N2275.33 (11)C31—N32—C33—C340.8 (2)
C11—P—C21—N22172.92 (10)N32—C33—C34—C351.0 (2)
O—P—C21—C26129.72 (13)C33—C34—C35—C360.1 (2)
C31—P—C21—C26105.75 (14)N32—C31—C36—C351.0 (2)
C11—P—C21—C266.00 (15)P—C31—C36—C35179.54 (11)
C26—C21—N22—C230.9 (2)C34—C35—C36—C310.8 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C23—H23···Oi0.952.503.313 (2)144
C35—H35···Oii0.952.463.202 (2)134
C36—H36···N22ii0.952.533.353 (2)145
Symmetry codes: (i) x+2, y+1/2, z+1/2; (ii) x+2, y1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaC15H12N3OP
Mr281.25
Crystal system, space groupMonoclinic, P21/c
Temperature (K)173
a, b, c (Å)9.0807 (9), 9.1550 (9), 16.0629 (16)
β (°) 100.409 (2)
V3)1313.4 (2)
Z4
Radiation typeMo Kα
µ (mm1)0.21
Crystal size (mm)0.24 × 0.20 × 0.17
Data collection
DiffractometerBruker SMART 1K CCD area-detector
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
8966, 3251, 2589
Rint0.026
(sin θ/λ)max1)0.667
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.036, 0.096, 1.02
No. of reflections3251
No. of parameters181
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.41, 0.36

Computer programs: SMART (Bruker, 1998), SAINT-Plus (Bruker, 1999), SAINT-Plus, SHELXTL (Bruker, 1999), SHELXTL, PLATON (Spek, 2003).

Selected geometric parameters (Å, º) top
P—O1.4792 (11)P—C111.8200 (15)
P—C311.8173 (15)P—C211.8211 (15)
O—P—C31113.99 (7)O—P—C21113.60 (7)
O—P—C11111.88 (7)C31—P—C21104.06 (7)
C31—P—C11105.95 (7)C11—P—C21106.65 (7)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C23—H23···Oi0.952.503.313 (2)144
C35—H35···Oii0.952.463.202 (2)134
C36—H36···N22ii0.952.533.353 (2)145
Symmetry codes: (i) x+2, y+1/2, z+1/2; (ii) x+2, y1/2, z+1/2.
Cell parameters for the various forms of triphenyl phosphine oxide top
FormSGa/Åb/Åc/ÅβV/Å3T/K
IaPbca28.898 (3)9.094 (2)11.138 (2)-2929.0153
IIaP21/c10.952 (2)8.687 (2)16.221 (6)108.78 (2)1461.1153
IIIbP21/c15.066 (1)9.037 (2)11.296 (3)98.47 (1)1521.2295
aBrock et al. (1985); bSpek (1987);
 

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