2-Amino­pyrimidine–3,3,3-triphenyl­propanoic acid (1/1)

The title bimolecular compound, C₄H₅N₃·C₂₁H₁₈O₂, construc­ted from 2-amino­pyrimidine and 3,3,3-triphenyl­propanoic acid, forms a tetra­molecular hydrogen-bonded motif via O—H...N, N—H...O and N—H...N contacts. This aggregate organizes to give crystal-packing motifs with hydro­philic and hydro­phobic regions.

S1. Comment

Over the past decade, the field of supramolecular chemistry has emerged as a significant contributor to the broad area of materials science owing in part to advances in decoding the structural features responsible for molecular cohesion. While much of this progress has been documented in the literature, many areas still require attention before prediction of complex high-order motifs can be successfully achieved with regularity. To this end, two areas that continue to prove useful for understanding the fundamental principles of supramolecular chemistry include new synthon identification and thorough assessment of the recognition profiles of known molecular contacts.

The packing tendencies of Ph₃X groups (X = C or P; Scudder & Dance, 1998, 2000; Steiner, 2000) and their use in practical applications (Garcia-Garibay, 2005; Jarowski et al., 2007) have been reported in the literature. Crystallographic studies of molecules containing Ph₃X groups show several salient packing motifs, such as the sixfold (6PE) and fourfold (4PE) phenyl embraces (Scudder & Dance, 2000). Although these phenyl embrace motifs have been exploited as a tool for constructing supramolecular assemblies, extending their use to include additional molecular contacts (e.g. hydrogen bonds) has seen less attention. It has been reported by Steiner (1999) that 3,3,3-triphenylpropanoic acid crystallizes with molecules organized into linear motifs via a combination of carboxyl–carboxyl and 6PE interactions. We wondered if the observed linear assemblage could be transferred and extended by cocrystallizing the triphenylpropanoic acid with a complementary hydrogen-bond spacer such as 2-aminopyrimidine.

Cocrystallization of 3,3,3-triphenylpropanoic acid and 2-aminopyrimidine produced the expected bimolecular compound (I); the C—O distances in the acid component (Table 1) are consistent with the location of the hydroxyl H atom, as deduced from the refinement. The asymmetric unit of (I) shows the formation of a hydrogen-bonded R²₂(8) motif involving both 2-aminopyrimidine and 3,3,3-triphenylpropanoic acid components (Fig. 1). As anticipated, this molecular assemblage is further linked to give a tetrameric motif by use of two additional inversion-related N—H···N hydrogen bonds (Table 2; Lynch et al., 1998). Unlike the structure of 3,3,3-triphenylpropanoic acid, the terminal triphenylmethyl (TPM) groups of our tetrameric unit lack participation in 6PE interactions. Rather, the TPM groups of (I) assemble by use of van der Waals contacts to give hydrophobic and hydrophilic regions (Fig. 2)

The most effective packing of 6PE motifs involves a concerted cycle of six local edge-to-face Ph···Ph interactions. Compounds that align in this manner possess TPM conformations that approach a rotor with pseudo-threefold symmetry. This structural feature is easily quantified by assessing the twist of the three phenyl groups around their C—C_ipso bond. Cases that exhibit rotor conformations show similar twist angles of the phenyl groups. For (I), these torsion angles (Table 1) differ markedly and they are consistent with the previously described `flipper' conformation (Scudder & Dance, 2000). Although this arrangement of phenyl groups is capable of forming several phenyl embrace motifs (e.g. 6PE and 4PE), (I) crystallizes with phenyl groups aligned in a skewed 4PE arrangement. In conclusion, this study highlights the successful use of building blocks (i.e. 3,3,3-triphenylpropanoic acid and 2-aminopyrimidine) that form the expected hydrogen-bonded tetramolecular unit with additional, less well defined, phenyl embrace contacts for organizing the supramolecular assembly.

Related literature

For related literature, see: Garcia-Garibay (2005); Jarowski et al. (2007); Lynch et al. (1998); Scudder & Dance (1998, 2000); Steiner (1999, 2000).

S2. Experimental

Single crystals of (I) were prepared by slow evaporation at room temperature of an acetone solution containing equimolar quantities of 2-aminopyrimidine and 3,3,3-triphenylpropionic acid (m.p. 383–384 K).

S3. Refinement

H atoms bonded to N or O atoms were refined without constraint. All other H atoms were included as riding atoms in geometrically idealized positions [C—H = 0.93–0.97 Å and U_iso(H) = 1.2U_eq(C)].

Computing details

Data collection: XSCANS (Bruker, 1999); cell refinement: XSCANS (Bruker, 1999); data reduction: XPREP (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: X-SEED (Barbour, 2001).

Figures

	Fig. 1. A molecular diagram of (I), showing the labeling scheme, asymmetric unit (50% probability displacement ellipsoids) and hydrogen bonded tetramer. [Symmetry code: (i) −x + 1, −y + 2, −z + 1.]
	Fig. 2. A projection of the unit-cell contents of (I), showing hydrophobic and hydrophilic crystal regions. For the sake of clarity, H atoms have been omitted.

2-Aminopyrimidine–3,3,3-triphenylpropanoic acid (1/1)

Crystal data

C4H5N3·C21H18O2	F(000) = 840
Mr = 397.46	Dx = 1.278 Mg m^−3
Monoclinic, P21/c	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: -P 2ybc	Cell parameters from 23 reflections
a = 20.590 (2) Å	θ = 53.3–54.4°
b = 9.5109 (8) Å	µ = 0.66 mm^−1
c = 10.640 (2) Å	T = 298 K
β = 97.518 (15)°	Transparent plate, colourless
V = 2065.6 (5) Å^3	0.45 × 0.42 × 0.20 mm
Z = 4

Data collection

Bruker P4 diffractometer	2048 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.043
Graphite monochromator	θmax = 61.8°, θmin = 4.3°
θ//2θ scans	h = −23→23
Absorption correction: analytical (XPREP; Bruker, 2001)	k = −10→1
Tmin = 0.757, Tmax = 0.880	l = −1→12
4193 measured reflections	3 standard reflections every 97 reflections
3144 independent reflections	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)] = 0.057	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.149	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0693P)^2 + 0.2673P] where P = (Fo^2 + 2Fc^2)/3
3144 reflections	(Δ/σ)max < 0.001
278 parameters	Δρmax = 0.17 e Å^−3
0 restraints	Δρmin = −0.23 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
O1	0.33412 (10)	0.5739 (2)	0.5844 (2)	0.0648 (7)
O2	0.28867 (11)	0.7839 (2)	0.5572 (3)	0.0736 (8)
N1	0.42512 (12)	0.6656 (3)	0.4299 (3)	0.0633 (8)
N2	0.41846 (16)	0.8917 (4)	0.5024 (4)	0.0878 (11)
N3	0.51321 (15)	0.8273 (4)	0.4269 (3)	0.0835 (10)
C2	0.45260 (16)	0.7924 (4)	0.4509 (3)	0.0620 (9)
C4	0.5445 (2)	0.7287 (5)	0.3695 (4)	0.0872 (13)
H4	0.5865	0.7492	0.3515	0.105*
C5	0.51947 (18)	0.6004 (5)	0.3354 (4)	0.0799 (12)
H5	0.5416	0.5357	0.2911	0.094 (14)*
C6	0.45898 (17)	0.5731 (4)	0.3710 (4)	0.0765 (11)
H6	0.4407	0.4849	0.3528	0.092*
C11	0.29037 (14)	0.6687 (3)	0.6065 (3)	0.0495 (8)
C12	0.24507 (14)	0.6278 (3)	0.6995 (3)	0.0462 (8)
H12A	0.2153	0.7056	0.7065	0.055*
H12B	0.2710	0.6163	0.7817	0.055*
C13	0.20315 (12)	0.4920 (3)	0.6707 (2)	0.0365 (6)
C21	0.24573 (12)	0.3580 (3)	0.6781 (3)	0.0354 (6)
C22	0.29166 (13)	0.3375 (3)	0.7856 (3)	0.0459 (7)
H22	0.3013	0.4111	0.8425	0.055*
C23	0.32285 (14)	0.2099 (4)	0.8088 (3)	0.0515 (8)
H23	0.3528	0.1983	0.8814	0.062*
C24	0.31003 (14)	0.0997 (3)	0.7257 (3)	0.0490 (8)
H24	0.3306	0.0135	0.7424	0.059*
C25	0.26660 (14)	0.1182 (3)	0.6180 (3)	0.0469 (8)
H25	0.2585	0.0448	0.5604	0.056*
C26	0.23440 (13)	0.2468 (3)	0.5940 (3)	0.0409 (7)
H26	0.2050	0.2578	0.5206	0.049*
C31	0.15745 (12)	0.4691 (3)	0.7737 (3)	0.0387 (7)
C32	0.15060 (14)	0.5643 (3)	0.8695 (3)	0.0489 (8)
H32	0.1744	0.6476	0.8742	0.059*
C33	0.10850 (16)	0.5371 (4)	0.9589 (3)	0.0609 (9)
H33	0.1043	0.6025	1.0223	0.073*
C34	0.07316 (15)	0.4148 (4)	0.9542 (3)	0.0594 (10)
H34	0.0456	0.3964	1.0148	0.071*
C35	0.07881 (14)	0.3191 (4)	0.8589 (3)	0.0545 (9)
H35	0.0547	0.2362	0.8546	0.065*
C36	0.12032 (13)	0.3465 (3)	0.7700 (3)	0.0449 (7)
H36	0.1236	0.2813	0.7059	0.054*
C41	0.16147 (12)	0.5175 (3)	0.5409 (3)	0.0370 (6)
C42	0.18735 (13)	0.5039 (3)	0.4278 (3)	0.0418 (7)
H42	0.2304	0.4734	0.4294	0.050*
C43	0.15100 (14)	0.5343 (3)	0.3129 (3)	0.0493 (8)
H43	0.1697	0.5240	0.2385	0.059*
C44	0.08718 (15)	0.5797 (3)	0.3073 (3)	0.0528 (8)
H44	0.0623	0.5987	0.2298	0.063*
C45	0.06106 (14)	0.5964 (3)	0.4189 (3)	0.0514 (8)
H45	0.0183	0.6286	0.4167	0.062*
C46	0.09744 (13)	0.5661 (3)	0.5344 (3)	0.0432 (7)
H46	0.0788	0.5783	0.6087	0.052*
H1C	0.360 (2)	0.610 (5)	0.522 (4)	0.134 (18)*
H2A	0.3782 (19)	0.874 (4)	0.521 (3)	0.087 (13)*
H2B	0.439 (2)	0.979 (6)	0.517 (5)	0.15 (2)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0507 (12)	0.0464 (13)	0.1030 (19)	0.0066 (11)	0.0322 (13)	0.0108 (13)
O2	0.0684 (15)	0.0384 (13)	0.121 (2)	0.0018 (11)	0.0374 (15)	0.0146 (14)
N1	0.0466 (15)	0.0569 (18)	0.088 (2)	−0.0135 (14)	0.0129 (15)	−0.0018 (17)
N2	0.069 (2)	0.069 (2)	0.134 (3)	−0.0219 (19)	0.045 (2)	−0.013 (2)
N3	0.0678 (19)	0.079 (2)	0.111 (3)	−0.0307 (18)	0.0421 (19)	−0.006 (2)
C2	0.0490 (18)	0.068 (2)	0.071 (2)	−0.0192 (19)	0.0119 (17)	0.004 (2)
C4	0.068 (3)	0.102 (3)	0.098 (3)	−0.025 (3)	0.035 (2)	0.002 (3)
C5	0.059 (2)	0.088 (3)	0.096 (3)	−0.009 (2)	0.023 (2)	−0.010 (3)
C6	0.055 (2)	0.070 (3)	0.104 (3)	−0.009 (2)	0.009 (2)	−0.011 (2)
C11	0.0392 (16)	0.0361 (18)	0.074 (2)	−0.0056 (14)	0.0105 (15)	−0.0032 (17)
C12	0.0436 (16)	0.0379 (16)	0.0581 (19)	−0.0024 (13)	0.0105 (15)	−0.0032 (15)
C13	0.0368 (14)	0.0353 (16)	0.0383 (15)	0.0005 (12)	0.0082 (12)	−0.0008 (13)
C21	0.0338 (14)	0.0359 (16)	0.0377 (15)	0.0008 (12)	0.0085 (12)	0.0019 (13)
C22	0.0415 (16)	0.0510 (19)	0.0451 (18)	0.0034 (15)	0.0046 (14)	−0.0044 (15)
C23	0.0416 (16)	0.064 (2)	0.0477 (19)	0.0091 (16)	0.0022 (14)	0.0063 (17)
C24	0.0436 (16)	0.0437 (19)	0.061 (2)	0.0066 (14)	0.0109 (16)	0.0075 (16)
C25	0.0511 (17)	0.0361 (16)	0.0555 (19)	0.0013 (14)	0.0152 (16)	−0.0027 (15)
C26	0.0412 (16)	0.0397 (17)	0.0421 (16)	0.0003 (13)	0.0066 (13)	−0.0022 (14)
C31	0.0348 (14)	0.0425 (17)	0.0391 (16)	0.0054 (13)	0.0063 (12)	−0.0008 (14)
C32	0.0554 (18)	0.0477 (18)	0.0447 (17)	0.0084 (15)	0.0112 (15)	0.0001 (15)
C33	0.074 (2)	0.068 (2)	0.0446 (19)	0.020 (2)	0.0215 (17)	0.0003 (18)
C34	0.055 (2)	0.073 (3)	0.054 (2)	0.0180 (19)	0.0250 (17)	0.0178 (19)
C35	0.0457 (17)	0.055 (2)	0.066 (2)	0.0046 (16)	0.0187 (16)	0.0141 (18)
C36	0.0418 (15)	0.0458 (18)	0.0489 (18)	0.0000 (14)	0.0126 (14)	−0.0030 (15)
C41	0.0390 (14)	0.0324 (15)	0.0410 (16)	−0.0022 (12)	0.0098 (12)	0.0017 (13)
C42	0.0375 (14)	0.0419 (17)	0.0474 (18)	0.0033 (13)	0.0109 (14)	0.0006 (15)
C43	0.0586 (19)	0.0492 (19)	0.0423 (18)	0.0050 (16)	0.0146 (15)	0.0028 (15)
C44	0.0539 (18)	0.058 (2)	0.0449 (18)	0.0061 (16)	0.0015 (15)	0.0074 (16)
C45	0.0399 (15)	0.057 (2)	0.057 (2)	0.0073 (15)	0.0052 (15)	0.0078 (17)
C46	0.0388 (15)	0.0482 (18)	0.0440 (17)	0.0046 (14)	0.0111 (13)	0.0008 (15)

Geometric parameters (Å, º)

O1—C11	1.318 (3)	C24—C25	1.369 (4)
O1—H1C	0.96 (5)	C24—H24	0.9300
O2—C11	1.213 (4)	C25—C26	1.398 (4)
N1—C2	1.338 (4)	C25—H25	0.9300
N1—C6	1.329 (4)	C26—H26	0.9300
N2—C2	1.336 (5)	C31—C32	1.384 (4)
N2—H2A	0.89 (4)	C31—C36	1.393 (4)
N2—H2B	0.94 (5)	C32—C33	1.392 (4)
N3—C2	1.348 (4)	C32—H32	0.9300
N3—C4	1.331 (5)	C33—C34	1.370 (5)
C4—C5	1.355 (6)	C33—H33	0.9300
C4—H4	0.9300	C34—C35	1.378 (4)
C5—C6	1.373 (5)	C34—H34	0.9300
C5—H5	0.9300	C35—C36	1.381 (4)
C6—H6	0.9300	C35—H35	0.9300
C11—C12	1.496 (4)	C36—H36	0.9300
C12—C13	1.562 (4)	C41—C42	1.385 (4)
C12—H12A	0.9700	C41—C46	1.390 (3)
C12—H12B	0.9700	C42—C43	1.378 (4)
C13—C21	1.542 (4)	C42—H42	0.9300
C13—C31	1.550 (4)	C43—C44	1.377 (4)
C13—C41	1.547 (4)	C43—H43	0.9300
C21—C26	1.385 (4)	C44—C45	1.375 (4)
C21—C22	1.400 (4)	C44—H44	0.9300
C22—C23	1.380 (4)	C45—C46	1.383 (4)
C22—H22	0.9300	C45—H45	0.9300
C23—C24	1.374 (4)	C46—H46	0.9300
C23—H23	0.9300
C11—O1—H1C	109 (3)	C25—C24—H24	120.3
C2—N1—C6	116.0 (3)	C24—C25—C26	120.5 (3)
N1—C2—N2	118.1 (3)	C24—C25—H25	119.8
C2—N2—H2A	121 (3)	C26—C25—H25	119.8
C2—N2—H2B	116 (3)	C21—C26—C25	121.0 (3)
H2A—N2—H2B	123 (4)	C21—C26—H26	119.5
C2—N3—C4	115.4 (3)	C25—C26—H26	119.5
N2—C2—N3	117.0 (3)	C13—C31—C32	124.0 (3)
N1—C2—N3	124.9 (4)	C13—C31—C36	118.6 (2)
N3—C4—C5	124.6 (4)	C32—C31—C36	117.4 (3)
N3—C4—H4	117.7	C33—C32—C31	120.9 (3)
C5—C4—H4	117.7	C31—C32—H32	119.5
C4—C5—C6	115.0 (4)	C33—C32—H32	119.5
C4—C5—H5	122.5	C32—C33—C34	120.6 (3)
C6—C5—H5	122.5	C32—C33—H33	119.7
N1—C6—C5	123.7 (4)	C34—C33—H33	119.7
N1—C6—H6	118.1	C33—C34—C35	119.5 (3)
C5—C6—H6	118.1	C33—C34—H34	120.3
O1—C11—C12	116.1 (3)	C35—C34—H34	120.3
O1—C11—O2	121.5 (3)	C34—C35—C36	119.9 (3)
O2—C11—C12	122.4 (3)	C34—C35—H35	120.0
C11—C12—C13	117.5 (2)	C36—C35—H35	120.0
C11—C12—H12A	107.9	C31—C36—C35	121.7 (3)
C11—C12—H12B	107.9	C31—C36—H36	119.2
C13—C12—H12A	107.9	C35—C36—H36	119.2
C13—C12—H12B	107.9	C42—C41—C46	117.3 (3)
H12A—C12—H12B	107.2	C13—C41—C42	122.0 (2)
C12—C13—C21	112.2 (2)	C13—C41—C46	120.6 (2)
C12—C13—C31	110.4 (2)	C41—C42—C43	121.7 (3)
C12—C13—C41	105.8 (2)	C41—C42—H42	119.2
C21—C13—C31	104.0 (2)	C43—C42—H42	119.2
C21—C13—C41	114.9 (2)	C42—C43—C44	120.6 (3)
C31—C13—C41	109.6 (2)	C42—C43—H43	119.7
C13—C21—C22	118.4 (2)	C44—C43—H43	119.7
C13—C21—C26	123.5 (2)	C43—C44—C45	118.5 (3)
C22—C21—C26	117.4 (3)	C43—C44—H44	120.7
C21—C22—C23	121.2 (3)	C45—C44—H44	120.7
C21—C22—H22	119.4	C44—C45—C46	121.0 (3)
C23—C22—H22	119.4	C44—C45—H45	119.5
C22—C23—C24	120.6 (3)	C46—C45—H45	119.5
C24—C23—H23	119.7	C41—C46—C45	120.9 (3)
C22—C23—H23	119.7	C41—C46—H46	119.6
C23—C24—C25	119.3 (3)	C45—C46—H46	119.6
C23—C24—H24	120.3
C6—N1—C2—N2	175.7 (4)	C41—C13—C31—C32	−110.1 (3)
C6—N1—C2—N3	−6.0 (6)	C12—C13—C31—C32	6.1 (4)
C4—N3—C2—N2	−176.5 (4)	C21—C13—C31—C36	−54.1 (3)
C4—N3—C2—N1	5.1 (6)	C41—C13—C31—C36	69.2 (3)
C2—N1—C6—C5	1.7 (6)	C12—C13—C31—C36	−174.6 (2)
N1—C6—C5—C4	2.7 (6)	C36—C31—C32—C33	0.5 (4)
C2—N3—C4—C5	0.1 (7)	C13—C31—C32—C33	179.9 (3)
C6—C5—C4—N3	−3.7 (7)	C31—C32—C33—C34	0.3 (5)
O2—C11—C12—C13	125.1 (3)	C32—C33—C34—C35	−0.9 (5)
O1—C11—C12—C13	−57.2 (4)	C33—C34—C35—C36	0.6 (5)
C11—C12—C13—C21	66.7 (3)	C34—C35—C36—C31	0.3 (4)
C11—C12—C13—C41	−59.3 (3)	C32—C31—C36—C35	−0.8 (4)
C11—C12—C13—C31	−177.9 (2)	C13—C31—C36—C35	179.7 (3)
C41—C13—C21—C26	−19.2 (4)	C21—C13—C41—C42	−45.8 (3)
C31—C13—C21—C26	100.6 (3)	C31—C13—C41—C42	−162.4 (2)
C12—C13—C21—C26	−140.0 (3)	C12—C13—C41—C42	78.5 (3)
C41—C13—C21—C22	171.1 (2)	C21—C13—C41—C46	139.3 (3)
C31—C13—C21—C22	−69.1 (3)	C31—C13—C41—C46	22.6 (3)
C12—C13—C21—C22	50.3 (3)	C12—C13—C41—C46	−96.4 (3)
C26—C21—C22—C23	−2.0 (4)	C46—C41—C42—C43	−1.3 (4)
C13—C21—C22—C23	168.4 (3)	C13—C41—C42—C43	−176.4 (3)
C21—C22—C23—C24	0.7 (4)	C41—C42—C43—C44	0.1 (5)
C22—C23—C24—C25	1.0 (4)	C42—C43—C44—C45	1.1 (5)
C23—C24—C25—C26	−1.5 (4)	C43—C44—C45—C46	−1.1 (5)
C22—C21—C26—C25	1.5 (4)	C44—C45—C46—C41	−0.1 (5)
C13—C21—C26—C25	−168.3 (2)	C42—C41—C46—C45	1.3 (4)
C24—C25—C26—C21	0.2 (4)	C13—C41—C46—C45	176.5 (3)
C21—C13—C31—C32	126.6 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1C···N1	0.96 (5)	1.85 (5)	2.790 (3)	166 (4)
N2—H2A···O2	0.89 (4)	2.11 (4)	2.990 (4)	167 (4)
N2—H2B···N3^i	0.94 (5)	2.13 (5)	3.068 (5)	173 (4)

Symmetry code: (i) −x+1, −y+2, −z+1.