Tri­phenyl­methanol–tri­phenylphos­phine oxide (1/1)

In the crystalline 1:1 molecular complex of tri­phenyl­methanol (TPMeOH) and tri­phenyl­phosphine oxide (TPPO), C₁₉H₁₆O·C₁₈H₁₅OP, molecular dimers are formed which are linked by O—H...O=P hydrogen bonds. The dimers are aligned by sixfold phenyl embraces to form columns. The structure is disordered with half a dimer per asymmetric crystal unit, i.e. with only one molecular site which is half-occupied by both TPMeOH and TPPO.

S1. Comment

In recent years, there has been considerable interest in multiple phenyl interactions of –XPh₃ groups and XPh₄⁺ cations (Dance & Scudder, 1996). The most characteristic of these interactions is the `sixfold phenyl embrace' (6PE) that involves six concerted edge-to-face phenyl-phenyl interactions. Typically, 6PEs are formed between chemically equivalent groups, such as M-PPh₃ or PPh₄⁺, and frequently, the groups are even equivalent crystallographically. 6PEs can also be formed between unequal XPh₃ groups; an example has been described in some detail for –SiPh₃···Ph₃P═ (Steiner et al., 1997). 6PEs frequently aggregate in molecular columns which form hexagonal or quasi-hexagonal supramolecular arrays (Scudder & Dance, 1998; Steiner, 1998). Relative frequencies of 6PE formation in crystals have been determined for –XPh₃ groups with all tetrahedral central atoms X (Steiner, 2000).

The typical 6PE found in crystal structures has not been made on purpose, but appeared unexpectedly. To see if it can also be controlled in the experiment, it was planned to make a particular kind of 6PE in a new crystal structure. Because there is little literature on 6PEs between unequal XPh₃ groups, the aim was to create a 6PE of the kind XPh₃···Ph₃Y with X ≠ Y. A promising system would be a molecular complex of triphenylmethanol (TPMeOH) and triphenylphosphine oxide (TPPO). The idea is that in a complex of these compounds, there would be dimer formation by O—H···O═P hydrogen bonding, (I). Such a dimer carries unequal XPh₃ groups at its ends, and can readily aggregate in columns linked by 6PEs, –CPh₃···Ph₃P═. With this aim in mind, complex (I) was prepared from methanolic solution. \sch

In the crystal structure of (I) (space group P2₁/c), only one triphenyl molecule per asymmetric unit is found, as shown in Figure 1. The refined molecule represents neither pure TPMeOH nor TPPO, but rather an overlay of the two. The central atom cannot be refined well as C or P, but refines nicely with site occupation 1/2 C + 1/2 P. The average X—C(Ph) bond length is 1.690 (4) Å, which is close to the average of P—C(Ph) in TPPO (1.803 Å; average over three modifications, Brock et al., 1985; Spek, 1987), and C—C(Ph) in TPMeOH (1.514 Å; Ferguson et al., 1992). The H(O) atom shown in Figure 1 has been found in difference Fourier calculations, is in proper covalent geometry [O—H = 0.82 (6) Å, X—O—H = 104 (4)°, staggered conformation with C11—X—O—H = 167 (5)^o], has a refined occupancy of 0.49 (7) and a displacement parameter of U_eq = 0.05 (3) Ų. All this indicates that the molecular site in crystalline (I) is equally populated by TPMeOH and TPPO molecules. The phenyl rings form a propeller, with dihedral angles between the phenyl least-squares planes and the O—X—C1n planes of 28.4 (2), 44.1 (2) and 48.8 (2)° for rings 1, 2 and 3, respectively.

In the crystal lattice, the O-atoms form intermolecular contacts across a centre of symmetry with an O···O distance of 2.824 (5) Å. The H atom is in almost ideal hydrogen bonding geometry, with H···O = 2.04 (6) Å [for O—H = 0.82 (6) Å] and an O—H···O angle of 161 (6)°. Because there can be no such interaction between two molecules of the same kind, be it TPPO or TPMeOH [for the latter case, there would be a H···H contact of 1.3 (1) Å], this means that in each molecular pair in the lattice, one molecule is TPMeOH and one is TPPO. The two molecules are linked by the expected C—O—H···O═P hydrogen bond.

The TPMeOH-TPPO dimers are arranged in columns as shown in Figure 2 (only one of the two possible orientations per dimer is shown). The dimers are linked by 6PEs of close to ideal geometry, with an X···X distance between the central atoms of 6.751 (3) Å, and an O—X···O angle of 177.6 (1)°. In the ideal 6PE, this angle ('collinearity'; Dance & Scudder, 1995) would be 180°. It should be noted that similar to the hydrogen bond, also the 6PE is formed across a symmetry centre. Between neighboring columns, there are lateral phenyl-phenyl interactions which need not be shown here.

The disorder within the columns deserves a closer look. The molecules TPMeOH and TPPO have dissimilar polar groups, but their triphenyl moieties are almost identical in size and shape. In consequence, the outer surface of dimer (I) is close to centrosymmetric, and it is not really surprising that (I) can crystallize on a center of symmetry. In the molecular columns formed, the dimers are incorporated in two different ways, Ph₃C—OH···O═PPh₃ and Ph₃P═O···HO-CPh₃. It would be of interest to know whether the dimer orientation is completely at random, or if there are locally ordered sequences; unfortunately, this cannot be answered from data of the present kind. In any case, there are three kinds of 6PEs in the disordered columns, depending on the mutual orientation of neighboring dimers: –CPh₃···Ph₃P═, –CPh₃···Ph₃C–, and ═PPh₃···Ph₃P═. The mere fact of disorder indicates that formation of a 6PE involving a, say, ═PPh₃ group is not very specific for discriminating a –CPh₃ from a ═PPh₃ group. In the complex of triphenylsilylacetylene with TPPO, peculiarly, there are 3.5 symmetry-independent dimers, forming two ordered and two disordered columns (Steiner et al., 1997). In the related complex 4-(triphenylmethyl)phenol-TPPO (Jetti et al., 1999), molecular columns assembled by O—H···O hydrogen bonds and 6PEs are formed too, but no disorder is observed. This important difference compared to (I) is most probably due to the lack of pseudo-centrosymmetry of that adduct.

S2. Experimental

Crystals were obtained by slow evaporation of a methanolic solution of 1:1 triphenylmethanol (Aldrich) and triphenylphosphine oxide (Lancester).

S3. Refinement

H atoms bonded to C were treated in the default riding model with isotropic displacement parameters allowed to vary. The hydroxyl H atom was located in difference Fourier calculations, and refined isotropically with a free occupation factor, leading to realistic values [occupied = 0.49 (7), U_eq = 0.05 (3) Ų].

Computing details

Program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Molecular structure of (I), showing 30% probability displacement ellipsoids.
	Fig. 2. Molecular column in (I), organized by O—H···O hydrogen bonds and sixfold phenyl embraces.

Triphenylmethanol - triphenylphosphinoxide

Crystal data

C19H16O·C18H15OP	F(000) = 568
Mr = 538.59	Dx = 1.239 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.483 (2) Å	Cell parameters from 25 reflections
b = 15.994 (3) Å	θ = 15.0–16.9°
c = 10.988 (2) Å	µ = 0.13 mm^−1
β = 104.50 (3)°	T = 293 K
V = 1443.3 (5) Å^3	Plate, colourless
Z = 2	0.5 × 0.3 × 0.05 mm

Data collection

Rigaku AFC-5 diffractometer	Rint = 0.033
Radiation source: fine-focus sealed tube	θmax = 27.5°, θmin = 2.3°
Graphite monochromator	h = −2→10
ω–scans	k = −20→20
7018 measured reflections	l = −14→13
3306 independent reflections	3 standard reflections every 200 reflections
2195 reflections with I > 2σ(I)	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.069	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.160	H atoms treated by a mixture of independent and constrained refinement
S = 1.19	w = 1/[σ^2(Fo^2) + (0.0326P)^2 + 0.8066P] where P = (Fo^2 + 2Fc^2)/3
3306 reflections	(Δ/σ)max < 0.001
201 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.20 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
P	0.06213 (13)	−0.03935 (7)	0.21381 (11)	0.0438 (3)	0.50
C1	0.06213 (13)	−0.03935 (7)	0.21381 (11)	0.0438 (3)	0.50
O	0.0896 (3)	−0.05192 (14)	0.0968 (2)	0.0585 (6)
H100	0.041 (7)	−0.014 (4)	0.054 (5)	0.05 (3)*	0.49 (7)
C11	0.1161 (3)	−0.12423 (17)	0.3073 (2)	0.0434 (6)
C21	0.0448 (4)	−0.14780 (19)	0.4029 (3)	0.0532 (7)
H21	−0.0363	−0.1146	0.4210	0.074 (11)*
C31	0.0931 (4)	−0.2201 (2)	0.4715 (3)	0.0640 (9)
H31	0.0455	−0.2349	0.5360	0.084 (11)*
C41	0.2113 (4)	−0.2697 (2)	0.4441 (3)	0.0671 (9)
H41	0.2422	−0.3191	0.4883	0.072 (10)*
C51	0.2838 (4)	−0.2463 (2)	0.3510 (3)	0.0671 (9)
H51	0.3651	−0.2795	0.3331	0.069 (10)*
C61	0.2374 (4)	−0.17403 (19)	0.2839 (3)	0.0559 (7)
H61	0.2888	−0.1586	0.2218	0.047 (8)*
C12	−0.1380 (3)	−0.02597 (17)	0.2089 (3)	0.0461 (6)
C22	−0.2449 (4)	−0.0804 (2)	0.1308 (3)	0.0681 (9)
H22	−0.2045	−0.1218	0.0875	0.069 (10)*
C32	−0.4089 (5)	−0.0738 (3)	0.1170 (4)	0.0891 (13)
H32	−0.4790	−0.1107	0.0643	0.126 (17)*
C42	−0.4712 (4)	−0.0136 (3)	0.1799 (5)	0.0892 (14)
H42	−0.5831	−0.0093	0.1694	0.108 (14)*
C52	−0.3682 (5)	0.0405 (3)	0.2585 (4)	0.0787 (11)
H52	−0.4099	0.0812	0.3021	0.084 (12)*
C62	−0.2012 (4)	0.0340 (2)	0.2726 (3)	0.0587 (8)
H62	−0.1314	0.0708	0.3258	0.050 (8)*
C13	0.1614 (3)	0.04257 (18)	0.2924 (3)	0.0481 (7)
C23	0.1548 (4)	0.1162 (2)	0.2264 (3)	0.0720 (10)
H23	0.0927	0.1188	0.1437	0.062 (9)*
C33	0.2383 (5)	0.1859 (2)	0.2805 (4)	0.0880 (12)
H33	0.2311	0.2355	0.2353	0.102 (13)*
C43	0.3328 (5)	0.1819 (2)	0.4020 (4)	0.0809 (11)
H43	0.3903	0.2288	0.4389	0.094 (12)*
C53	0.3421 (4)	0.1093 (2)	0.4681 (4)	0.0727 (10)
H53	0.4066	0.1067	0.5501	0.091 (12)*
C63	0.2564 (4)	0.0398 (2)	0.4142 (3)	0.0581 (8)
H63	0.2627	−0.0094	0.4604	0.059 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P	0.0401 (6)	0.0410 (6)	0.0451 (6)	0.0023 (5)	0.0013 (5)	0.0012 (5)
C1	0.0401 (6)	0.0410 (6)	0.0451 (6)	0.0023 (5)	0.0013 (5)	0.0012 (5)
O	0.0593 (13)	0.0551 (13)	0.0561 (13)	0.0095 (11)	0.0050 (10)	−0.0006 (11)
C11	0.0438 (14)	0.0475 (15)	0.0336 (13)	−0.0059 (12)	−0.0003 (11)	−0.0025 (11)
C21	0.0544 (17)	0.0570 (17)	0.0452 (16)	0.0011 (15)	0.0066 (13)	0.0093 (13)
C31	0.068 (2)	0.067 (2)	0.0515 (17)	−0.0042 (17)	0.0047 (16)	0.0221 (16)
C41	0.074 (2)	0.0487 (18)	0.063 (2)	−0.0010 (17)	−0.0109 (18)	0.0108 (16)
C51	0.070 (2)	0.0572 (19)	0.065 (2)	0.0131 (17)	−0.0008 (17)	−0.0020 (17)
C61	0.0586 (18)	0.0591 (18)	0.0478 (17)	−0.0003 (15)	0.0091 (14)	−0.0021 (14)
C12	0.0474 (15)	0.0459 (15)	0.0470 (15)	0.0037 (12)	0.0154 (12)	0.0083 (12)
C22	0.0557 (19)	0.067 (2)	0.080 (2)	−0.0083 (17)	0.0134 (17)	−0.0099 (19)
C32	0.056 (2)	0.087 (3)	0.114 (3)	−0.013 (2)	0.002 (2)	0.011 (3)
C42	0.0445 (19)	0.102 (3)	0.121 (4)	0.007 (2)	0.020 (2)	0.048 (3)
C52	0.070 (2)	0.081 (3)	0.097 (3)	0.031 (2)	0.044 (2)	0.026 (2)
C62	0.0568 (18)	0.0615 (19)	0.0594 (18)	0.0083 (16)	0.0175 (15)	0.0061 (16)
C13	0.0436 (14)	0.0525 (16)	0.0451 (14)	0.0103 (13)	0.0052 (12)	−0.0004 (13)
C23	0.077 (2)	0.060 (2)	0.064 (2)	0.0097 (18)	−0.0114 (18)	0.0054 (17)
C33	0.096 (3)	0.056 (2)	0.097 (3)	0.003 (2)	−0.003 (2)	0.015 (2)
C43	0.076 (2)	0.062 (2)	0.091 (3)	−0.0059 (19)	−0.006 (2)	−0.011 (2)
C53	0.070 (2)	0.068 (2)	0.067 (2)	−0.0015 (18)	−0.0066 (18)	−0.0081 (19)
C63	0.0604 (18)	0.0600 (19)	0.0479 (16)	0.0027 (15)	0.0021 (14)	−0.0030 (15)

Geometric parameters (Å, º)

P—O	1.378 (2)	C22—H22	0.9300
P—C13	1.675 (3)	C32—C42	1.366 (6)
P—C11	1.695 (3)	C32—H32	0.9300
P—C12	1.699 (3)	C42—C52	1.370 (6)
P—H100	1.76 (6)	C42—H42	0.9300
O—H100	0.82 (6)	C52—C62	1.390 (4)
C11—C61	1.376 (4)	C52—H52	0.9300
C11—C21	1.388 (4)	C62—H62	0.9300
C21—C31	1.386 (4)	C13—C23	1.377 (4)
C21—H21	0.9300	C13—C63	1.379 (4)
C31—C41	1.370 (5)	C23—C33	1.374 (5)
C31—H31	0.9300	C23—H23	0.9300
C41—C51	1.371 (5)	C33—C43	1.375 (5)
C41—H41	0.9300	C33—H33	0.9300
C51—C61	1.374 (4)	C43—C53	1.362 (5)
C51—H51	0.9300	C43—H43	0.9300
C61—H61	0.9300	C53—C63	1.379 (4)
C12—C62	1.373 (4)	C53—H53	0.9300
C12—C22	1.388 (4)	C63—H63	0.9300
C22—C32	1.365 (5)
O—P—C13	114.50 (16)	C32—C22—H22	119.7
O—P—C11	111.45 (15)	C12—C22—H22	119.7
C13—P—C11	106.82 (14)	C22—C32—C42	120.7 (4)
O—P—C12	112.97 (15)	C22—C32—H32	119.6
C13—P—C12	106.68 (15)	C42—C32—H32	119.6
C11—P—C12	103.65 (14)	C32—C42—C52	119.8 (3)
O—P—H100	27 (2)	C32—C42—H42	120.1
C13—P—H100	104 (2)	C52—C42—H42	120.1
C11—P—H100	137 (2)	C42—C52—C62	119.6 (4)
C12—P—H100	95 (2)	C42—C52—H52	120.2
P—O—H100	104 (4)	C62—C52—H52	120.2
C61—C11—C21	118.2 (3)	C12—C62—C52	120.8 (3)
C61—C11—P	116.8 (2)	C12—C62—H62	119.6
C21—C11—P	125.0 (2)	C52—C62—H62	119.6
C31—C21—C11	120.9 (3)	C23—C13—C63	118.4 (3)
C31—C21—H21	119.6	C23—C13—P	116.6 (2)
C11—C21—H21	119.6	C63—C13—P	124.8 (2)
C41—C31—C21	119.8 (3)	C33—C23—C13	121.2 (3)
C41—C31—H31	120.1	C33—C23—H23	119.4
C21—C31—H31	120.1	C13—C23—H23	119.4
C31—C41—C51	119.7 (3)	C23—C33—C43	119.7 (4)
C31—C41—H41	120.2	C23—C33—H33	120.2
C51—C41—H41	120.2	C43—C33—H33	120.2
C41—C51—C61	120.6 (3)	C53—C43—C33	120.0 (4)
C41—C51—H51	119.7	C53—C43—H43	120.0
C61—C51—H51	119.7	C33—C43—H43	120.0
C51—C61—C11	120.9 (3)	C43—C53—C63	120.3 (3)
C51—C61—H61	119.6	C43—C53—H53	119.8
C11—C61—H61	119.6	C63—C53—H53	119.8
C62—C12—C22	118.4 (3)	C53—C63—C13	120.5 (3)
C62—C12—P	125.9 (2)	C53—C63—H63	119.7
C22—C12—P	115.7 (2)	C13—C63—H63	119.7
C32—C22—C12	120.6 (4)
O—P—C11—C61	28.0 (3)	P—C12—C22—C32	−178.2 (3)
C13—P—C11—C61	−97.8 (2)	C12—C22—C32—C42	−0.1 (6)
C12—P—C11—C61	149.8 (2)	C22—C32—C42—C52	−0.5 (6)
O—P—C11—C21	−150.5 (2)	C32—C42—C52—C62	0.6 (6)
C13—P—C11—C21	83.7 (3)	C22—C12—C62—C52	−0.5 (4)
C12—P—C11—C21	−28.8 (3)	P—C12—C62—C52	178.1 (2)
C61—C11—C21—C31	−0.9 (4)	C42—C52—C62—C12	−0.1 (5)
P—C11—C21—C31	177.6 (2)	O—P—C13—C23	46.6 (3)
C11—C21—C31—C41	−0.8 (5)	C11—P—C13—C23	170.5 (2)
C21—C31—C41—C51	1.7 (5)	C12—P—C13—C23	−79.1 (3)
C31—C41—C51—C61	−0.9 (5)	O—P—C13—C63	−129.0 (3)
C41—C51—C61—C11	−0.8 (5)	C11—P—C13—C63	−5.1 (3)
C21—C11—C61—C51	1.7 (4)	C12—P—C13—C63	105.3 (3)
P—C11—C61—C51	−176.9 (2)	C63—C13—C23—C33	−1.1 (5)
O—P—C12—C62	−135.0 (3)	P—C13—C23—C33	−176.9 (3)
C13—P—C12—C62	−8.3 (3)	C13—C23—C33—C43	1.2 (6)
C11—P—C12—C62	104.2 (3)	C23—C33—C43—C53	−0.5 (6)
O—P—C12—C22	43.6 (3)	C33—C43—C53—C63	−0.4 (6)
C13—P—C12—C22	170.3 (2)	C43—C53—C63—C13	0.5 (5)
C11—P—C12—C22	−77.1 (3)	C23—C13—C63—C53	0.2 (5)
C62—C12—C22—C32	0.6 (5)	P—C13—C63—C53	175.7 (3)