Buy article online - an online subscription or single-article purchase is required to access this article.
Crystallization of the hexane reaction mixture after treatment of LiGe(OCH
2CH
2NMe
2)
3 with Ph
3CN
3 gives rise to a new triclinic (space group
P) polymorph of triphenylmethylamine, C
19H
17N, (I), containing dimers formed by N—H
N hydrogen bonds, whereas the structure of the known orthorhombic (space group
P2
12
12
1) polymorph of this compound, (II), consists of isolated molecules. While the dimers in (I) lie across crystallographic inversion centres, the molecules are not truly related by them. The centrosymmetric structure is due to the statistical disordering of the amino H atoms participating in the N—H
N hydrogen-bonding interactions, and thus the inversion centre is superpositional. The conformations and geometric parameters of the molecules in (I) and (II) are very similar. It was found that the polarity of the solvent does not affect the capability of triphenylmethylamine to crystallize in the different polymorphic modifications. The orthorhombic polymorph, (II), is more thermodynamically stable under normal conditions than the triclinic polymorph, (I). The experimental data indicate the absence of a phase transition in the temperature interval 120–293 K. The densities of (I) (1.235 Mg m
−3) and (II) (1.231 Mg m
−3) at 120 K are practically equal. It would seem that either the kinetic factors or the effects of the other products of the reaction facilitating the hydrogen-bonded dimerization of triphenylmethylamine molecules are the determining factor for the isolation of the triclinic polymorph (I) of triphenylmethylamine.
Supporting information
CCDC reference: 724197
Single crystals of the new triclinic polymorph of triphenylmethylamine suitable
for X-ray diffraction analysis were grown from the hexane reaction mixture of
(Ph3CNLi)4 and Ge(OCH2CH2NMe2)2 at room temperature in air
[Please give quantities etc.]. Triphenylmethylamine is formed by
smooth hydrolysis of (Ph3CNLi)4in the presence of moisture (see second
scheme).
The amino H atoms were objectively located in the difference Fourier map and
refined in the isotropic approximation with fixed positional and displacement
parameters [Uiso(H) = 1.2Ueq(N)]. One of the two amino H
atoms is disordered over two sites with equal occupancies. The remaining H
atoms were placed in calculated positions and refined in a riding model (C—H
= 0.95 Å) with fixed displacement parameters [Uiso(H) =
1.2Ueq(C)].
Data collection: SMART (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1998); data reduction: SAINT-Plus (Bruker, 1998); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
Crystal data top
C19H17N | Z = 2 |
Mr = 259.34 | F(000) = 276 |
Triclinic, P1 | Dx = 1.235 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 8.7255 (8) Å | Cell parameters from 3710 reflections |
b = 8.9355 (9) Å | θ = 2.7–29.9° |
c = 10.6564 (10) Å | µ = 0.07 mm−1 |
α = 68.642 (2)° | T = 120 K |
β = 81.070 (2)° | Plate, light-yellow |
γ = 64.314 (2)° | 0.24 × 0.21 × 0.08 mm |
V = 697.32 (12) Å3 | |
Data collection top
Bruker SMART 1000 CCD area-detector diffractometer | 3309 independent reflections |
Radiation source: normal-focus sealed tube | 2636 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.017 |
ϕ and ω scans | θmax = 28.0°, θmin = 2.1° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1998) | h = −11→11 |
Tmin = 0.984, Tmax = 0.992 | k = −11→11 |
6598 measured reflections | l = −14→14 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.051 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.146 | H-atom parameters constrained |
S = 1.00 | w = 1/[σ2(Fo2) + (0.09P)2 + 0.18P] where P = (Fo2 + 2Fc2)/3 |
3309 reflections | (Δ/σ)max < 0.001 |
181 parameters | Δρmax = 0.32 e Å−3 |
0 restraints | Δρmin = −0.19 e Å−3 |
Crystal data top
C19H17N | γ = 64.314 (2)° |
Mr = 259.34 | V = 697.32 (12) Å3 |
Triclinic, P1 | Z = 2 |
a = 8.7255 (8) Å | Mo Kα radiation |
b = 8.9355 (9) Å | µ = 0.07 mm−1 |
c = 10.6564 (10) Å | T = 120 K |
α = 68.642 (2)° | 0.24 × 0.21 × 0.08 mm |
β = 81.070 (2)° | |
Data collection top
Bruker SMART 1000 CCD area-detector diffractometer | 3309 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1998) | 2636 reflections with I > 2σ(I) |
Tmin = 0.984, Tmax = 0.992 | Rint = 0.017 |
6598 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.051 | 0 restraints |
wR(F2) = 0.146 | H-atom parameters constrained |
S = 1.00 | Δρmax = 0.32 e Å−3 |
3309 reflections | Δρmin = −0.19 e Å−3 |
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 | x | y | z | Uiso*/Ueq | Occ. (<1) |
N1 | 0.19683 (14) | 0.86986 (14) | 0.02960 (11) | 0.0277 (3) | |
H1 | 0.2578 | 0.9261 | −0.0270 | 0.033* | |
H2 | 0.0825 | 0.9470 | 0.0190 | 0.033* | 0.50 |
H2' | 0.2150 | 0.7725 | 0.0064 | 0.033* | 0.50 |
C1 | 0.24505 (15) | 0.82049 (15) | 0.17151 (13) | 0.0219 (3) | |
C2 | 0.27333 (15) | 0.97142 (15) | 0.18679 (12) | 0.0213 (3) | |
C3 | 0.14380 (16) | 1.14127 (16) | 0.14446 (13) | 0.0252 (3) | |
H3 | 0.0433 | 1.1609 | 0.1052 | 0.030* | |
C4 | 0.16077 (19) | 1.28118 (17) | 0.15934 (14) | 0.0305 (3) | |
H4 | 0.0717 | 1.3958 | 0.1304 | 0.037* | |
C5 | 0.3075 (2) | 1.25478 (18) | 0.21634 (14) | 0.0321 (3) | |
H5 | 0.3188 | 1.3508 | 0.2265 | 0.039* | |
C6 | 0.43611 (18) | 1.08797 (18) | 0.25786 (14) | 0.0309 (3) | |
H6 | 0.5366 | 1.0690 | 0.2967 | 0.037* | |
C7 | 0.41951 (16) | 0.94683 (17) | 0.24309 (14) | 0.0263 (3) | |
H7 | 0.5092 | 0.8325 | 0.2718 | 0.032* | |
C8 | 0.09703 (15) | 0.79298 (15) | 0.26171 (13) | 0.0237 (3) | |
C9 | 0.01051 (17) | 0.71027 (17) | 0.23139 (16) | 0.0304 (3) | |
H9 | 0.0403 | 0.6765 | 0.1531 | 0.037* | |
C10 | −0.11876 (18) | 0.67676 (18) | 0.31461 (18) | 0.0369 (4) | |
H10 | −0.1764 | 0.6204 | 0.2928 | 0.044* | |
C11 | −0.16363 (18) | 0.72511 (19) | 0.42886 (17) | 0.0368 (4) | |
H11 | −0.2525 | 0.7029 | 0.4852 | 0.044* | |
C12 | −0.07844 (19) | 0.8061 (2) | 0.46071 (15) | 0.0350 (3) | |
H12 | −0.1083 | 0.8390 | 0.5394 | 0.042* | |
C13 | 0.05118 (17) | 0.83940 (17) | 0.37746 (14) | 0.0284 (3) | |
H13 | 0.1091 | 0.8948 | 0.4003 | 0.034* | |
C14 | 0.40673 (16) | 0.64732 (16) | 0.20921 (13) | 0.0233 (3) | |
C15 | 0.5325 (2) | 0.6111 (2) | 0.11387 (15) | 0.0402 (4) | |
H15 | 0.5188 | 0.6943 | 0.0254 | 0.048* | |
C16 | 0.6780 (2) | 0.4548 (2) | 0.14613 (16) | 0.0459 (4) | |
H16 | 0.7623 | 0.4321 | 0.0793 | 0.055* | |
C17 | 0.70181 (18) | 0.33187 (18) | 0.27400 (15) | 0.0329 (3) | |
H17 | 0.8012 | 0.2248 | 0.2953 | 0.039* | |
C18 | 0.57911 (17) | 0.36717 (17) | 0.37006 (15) | 0.0313 (3) | |
H18 | 0.5941 | 0.2842 | 0.4586 | 0.038* | |
C19 | 0.43303 (16) | 0.52386 (17) | 0.33814 (14) | 0.0277 (3) | |
H19 | 0.3499 | 0.5467 | 0.4057 | 0.033* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N1 | 0.0282 (6) | 0.0247 (5) | 0.0288 (6) | −0.0058 (4) | −0.0077 (5) | −0.0105 (4) |
C1 | 0.0215 (6) | 0.0187 (5) | 0.0254 (6) | −0.0064 (4) | −0.0051 (5) | −0.0074 (4) |
C2 | 0.0217 (6) | 0.0205 (6) | 0.0231 (6) | −0.0096 (5) | 0.0024 (5) | −0.0085 (4) |
C3 | 0.0237 (6) | 0.0228 (6) | 0.0269 (6) | −0.0079 (5) | 0.0010 (5) | −0.0085 (5) |
C4 | 0.0374 (7) | 0.0216 (6) | 0.0289 (7) | −0.0091 (5) | 0.0005 (6) | −0.0084 (5) |
C5 | 0.0481 (8) | 0.0274 (7) | 0.0286 (7) | −0.0215 (6) | 0.0009 (6) | −0.0107 (5) |
C6 | 0.0345 (7) | 0.0335 (7) | 0.0318 (7) | −0.0195 (6) | −0.0024 (6) | −0.0107 (6) |
C7 | 0.0241 (6) | 0.0251 (6) | 0.0301 (7) | −0.0095 (5) | −0.0009 (5) | −0.0099 (5) |
C8 | 0.0203 (6) | 0.0178 (5) | 0.0295 (6) | −0.0058 (4) | −0.0057 (5) | −0.0044 (5) |
C9 | 0.0243 (6) | 0.0231 (6) | 0.0455 (8) | −0.0081 (5) | −0.0065 (6) | −0.0125 (6) |
C10 | 0.0248 (7) | 0.0274 (7) | 0.0590 (10) | −0.0123 (6) | −0.0070 (6) | −0.0102 (6) |
C11 | 0.0266 (7) | 0.0313 (7) | 0.0461 (9) | −0.0142 (6) | 0.0008 (6) | −0.0033 (6) |
C12 | 0.0342 (7) | 0.0351 (7) | 0.0328 (8) | −0.0160 (6) | 0.0014 (6) | −0.0063 (6) |
C13 | 0.0278 (7) | 0.0272 (6) | 0.0311 (7) | −0.0135 (5) | −0.0029 (5) | −0.0065 (5) |
C14 | 0.0244 (6) | 0.0191 (6) | 0.0279 (6) | −0.0070 (5) | −0.0054 (5) | −0.0096 (5) |
C15 | 0.0417 (8) | 0.0320 (8) | 0.0260 (7) | 0.0035 (6) | −0.0020 (6) | −0.0092 (6) |
C16 | 0.0412 (9) | 0.0406 (9) | 0.0338 (8) | 0.0066 (7) | 0.0005 (7) | −0.0174 (7) |
C17 | 0.0284 (7) | 0.0239 (6) | 0.0419 (8) | −0.0017 (5) | −0.0091 (6) | −0.0135 (6) |
C18 | 0.0270 (7) | 0.0239 (6) | 0.0360 (8) | −0.0086 (5) | −0.0071 (6) | −0.0016 (5) |
C19 | 0.0229 (6) | 0.0254 (6) | 0.0312 (7) | −0.0094 (5) | −0.0014 (5) | −0.0056 (5) |
Geometric parameters (Å, º) top
N1—C1 | 1.4863 (16) | C9—C10 | 1.392 (2) |
N1—H1 | 0.9010 | C9—H9 | 0.9500 |
N1—H2 | 0.9304 | C10—C11 | 1.382 (2) |
N1—H2' | 0.9316 | C10—H10 | 0.9500 |
C1—C2 | 1.5385 (16) | C11—C12 | 1.384 (2) |
C1—C8 | 1.5396 (18) | C11—H11 | 0.9500 |
C1—C14 | 1.5417 (16) | C12—C13 | 1.394 (2) |
C2—C7 | 1.3905 (17) | C12—H12 | 0.9500 |
C2—C3 | 1.3989 (17) | C13—H13 | 0.9500 |
C3—C4 | 1.3864 (18) | C14—C15 | 1.388 (2) |
C3—H3 | 0.9500 | C14—C19 | 1.3899 (18) |
C4—C5 | 1.392 (2) | C15—C16 | 1.389 (2) |
C4—H4 | 0.9500 | C15—H15 | 0.9500 |
C5—C6 | 1.379 (2) | C16—C17 | 1.381 (2) |
C5—H5 | 0.9500 | C16—H16 | 0.9500 |
C6—C7 | 1.3951 (18) | C17—C18 | 1.377 (2) |
C6—H6 | 0.9500 | C17—H17 | 0.9500 |
C7—H7 | 0.9500 | C18—C19 | 1.3933 (18) |
C8—C13 | 1.3889 (19) | C18—H18 | 0.9500 |
C8—C9 | 1.3978 (17) | C19—H19 | 0.9500 |
| | | |
C1—N1—H1 | 110.2 | C10—C9—C8 | 120.75 (14) |
C1—N1—H2 | 107.8 | C10—C9—H9 | 119.6 |
H1—N1—H2 | 108.3 | C8—C9—H9 | 119.6 |
C1—N1—H2' | 112.5 | C11—C10—C9 | 120.32 (13) |
H1—N1—H2' | 108.0 | C11—C10—H10 | 119.8 |
H2—N1—H2' | 110.0 | C9—C10—H10 | 119.8 |
N1—C1—C2 | 108.86 (10) | C10—C11—C12 | 119.62 (13) |
N1—C1—C8 | 107.56 (10) | C10—C11—H11 | 120.2 |
C2—C1—C8 | 110.08 (10) | C12—C11—H11 | 120.2 |
N1—C1—C14 | 109.70 (10) | C11—C12—C13 | 120.05 (14) |
C2—C1—C14 | 111.20 (9) | C11—C12—H12 | 120.0 |
C8—C1—C14 | 109.37 (10) | C13—C12—H12 | 120.0 |
C7—C2—C3 | 118.42 (11) | C8—C13—C12 | 121.10 (12) |
C7—C2—C1 | 123.31 (11) | C8—C13—H13 | 119.4 |
C3—C2—C1 | 118.25 (10) | C12—C13—H13 | 119.4 |
C4—C3—C2 | 120.61 (12) | C15—C14—C19 | 117.81 (12) |
C4—C3—H3 | 119.7 | C15—C14—C1 | 120.24 (11) |
C2—C3—H3 | 119.7 | C19—C14—C1 | 121.95 (12) |
C3—C4—C5 | 120.43 (13) | C14—C15—C16 | 120.83 (14) |
C3—C4—H4 | 119.8 | C14—C15—H15 | 119.6 |
C5—C4—H4 | 119.8 | C16—C15—H15 | 119.6 |
C6—C5—C4 | 119.38 (12) | C17—C16—C15 | 120.90 (15) |
C6—C5—H5 | 120.3 | C17—C16—H16 | 119.6 |
C4—C5—H5 | 120.3 | C15—C16—H16 | 119.6 |
C5—C6—C7 | 120.36 (12) | C18—C17—C16 | 118.87 (13) |
C5—C6—H6 | 119.8 | C18—C17—H17 | 120.6 |
C7—C6—H6 | 119.8 | C16—C17—H17 | 120.6 |
C2—C7—C6 | 120.79 (12) | C17—C18—C19 | 120.41 (13) |
C2—C7—H7 | 119.6 | C17—C18—H18 | 119.8 |
C6—C7—H7 | 119.6 | C19—C18—H18 | 119.8 |
C13—C8—C9 | 118.15 (12) | C14—C19—C18 | 121.17 (13) |
C13—C8—C1 | 122.17 (11) | C14—C19—H19 | 119.4 |
C9—C8—C1 | 119.59 (12) | C18—C19—H19 | 119.4 |
| | | |
N1—C1—C2—C7 | −128.22 (13) | C1—C8—C9—C10 | 177.14 (11) |
C8—C1—C2—C7 | 114.12 (13) | C8—C9—C10—C11 | 0.0 (2) |
C14—C1—C2—C7 | −7.25 (17) | C9—C10—C11—C12 | −0.4 (2) |
N1—C1—C2—C3 | 53.18 (15) | C10—C11—C12—C13 | 0.4 (2) |
C8—C1—C2—C3 | −64.49 (14) | C9—C8—C13—C12 | −0.56 (19) |
C14—C1—C2—C3 | 174.14 (11) | C1—C8—C13—C12 | −177.14 (12) |
C7—C2—C3—C4 | −0.45 (19) | C11—C12—C13—C8 | 0.2 (2) |
C1—C2—C3—C4 | 178.23 (11) | N1—C1—C14—C15 | 34.98 (16) |
C2—C3—C4—C5 | 0.2 (2) | C2—C1—C14—C15 | −85.49 (15) |
C3—C4—C5—C6 | 0.1 (2) | C8—C1—C14—C15 | 152.73 (13) |
C4—C5—C6—C7 | −0.1 (2) | N1—C1—C14—C19 | −145.66 (12) |
C3—C2—C7—C6 | 0.4 (2) | C2—C1—C14—C19 | 93.88 (14) |
C1—C2—C7—C6 | −178.17 (12) | C8—C1—C14—C19 | −27.91 (15) |
C5—C6—C7—C2 | −0.2 (2) | C19—C14—C15—C16 | 1.3 (2) |
N1—C1—C8—C13 | −144.21 (11) | C1—C14—C15—C16 | −179.34 (15) |
C2—C1—C8—C13 | −25.74 (15) | C14—C15—C16—C17 | −0.4 (3) |
C14—C1—C8—C13 | 96.71 (13) | C15—C16—C17—C18 | −0.5 (3) |
N1—C1—C8—C9 | 39.26 (14) | C16—C17—C18—C19 | 0.4 (2) |
C2—C1—C8—C9 | 157.73 (11) | C15—C14—C19—C18 | −1.3 (2) |
C14—C1—C8—C9 | −79.82 (13) | C1—C14—C19—C18 | 179.31 (11) |
C13—C8—C9—C10 | 0.47 (19) | C17—C18—C19—C14 | 0.5 (2) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H2···N1i | 0.93 | 2.28 | 3.2069 (19) | 173 |
Symmetry code: (i) −x, −y+2, −z. |
Experimental details
Crystal data |
Chemical formula | C19H17N |
Mr | 259.34 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 120 |
a, b, c (Å) | 8.7255 (8), 8.9355 (9), 10.6564 (10) |
α, β, γ (°) | 68.642 (2), 81.070 (2), 64.314 (2) |
V (Å3) | 697.32 (12) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.07 |
Crystal size (mm) | 0.24 × 0.21 × 0.08 |
|
Data collection |
Diffractometer | Bruker SMART 1000 CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1998) |
Tmin, Tmax | 0.984, 0.992 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6598, 3309, 2636 |
Rint | 0.017 |
(sin θ/λ)max (Å−1) | 0.661 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.051, 0.146, 1.00 |
No. of reflections | 3309 |
No. of parameters | 181 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.32, −0.19 |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H2···N1i | 0.93 | 2.28 | 3.2069 (19) | 173 |
Symmetry code: (i) −x, −y+2, −z. |
Subscribe to Acta Crystallographica Section C: Structural Chemistry
The full text of this article is available to subscribers to the journal.
If you have already registered and are using a computer listed in your registration details, please email
support@iucr.org for assistance.
The design and preparation of materials with particular properties is one of the principal goals of chemists, physicists and structural biologists. Achieving that goal depends critically on understanding the relationship between the structure of a material and the properties in question. Polymorphic systems are a potential source of detailed information on structure–property relationships in organic solids, since the only variable among polymorphic forms is that of structure, and any variation in properties must therefore be due to structural differences. Moreover, the conditions and techniques required to obtain a particular polymorph, combined with knowledge of the crystal structures, can also provide information on the relative stability of the different structures (Bernstein, 2002).
On the other hand, the hydrogen bond is a subject that has attracted intense attention due to its importance in a vast number of chemical, biological and materials systems (Steiner, 2002). It has been widely used as a tool for the crystal engineering of organic and organometallic solids (Desiraju & Steiner, 1999; Braga & Grepioni, 2000; Nishio, 2004; Desiraju, 2005).
As a rule, the formation of hydrogen bonds of different types gives rise to a decrease in the total energy of a system and serves as its stabilizing factor. Taking this into consideration, it seemed surprising that triphenylmethylamine, possessing two active H atoms and a hydrogen-bond acceptor, forms only one polymorphic modification without hydrogen bonds (Glidewell & Ferguson, 1994; Clegg & Elsegood, 2005). Therefore, one could expect the existence of another polymorphic modification of this compound, which should contain N—H···N hydrogen bonds. A new triclinic polymorph, (I), of triphenylmethylamine was serendipitously obtained by crystallization of a hexane reaction mixture after treatment of LiGe(OCH2CH2NMe2)3 with Ph3CN3 and we report its structure here.
Polymorph (I) crystallizes in triclinic space group P1, rather than in the previously known orthorhombic modification of this compound (space group P212121), (II). The main difference between the two polymorphs is the formation of dimers via N—H···N hydrogen bonds in (I) (Fig. 1, Table 1), whereas (II) consists of isolated molecules. Despite the fact that the dimers lie across crystallographic inversion centres, the molecules are not really connected by them. The centrosymmetric structure is due to the statistical disordering of the amino H atoms participating in the N—H···N hydrogen bonds, and thus the inversion centre is superpositional.
The conformation of the molecules in (I) is such that there is an almost perfect staggering of the N—H and C—Ph bonds. A similar conformation is also characteristic of the molecules in polymorph (II) (Fig. 2). Nevertheless, the mutual disposition of the phenyl rings in the molecules of the two polymorphs is slightly different. In the orthorhombic structure, (II), the phenyl rings have a propeller-like arrangement, with dihedral N—C—C—C angles of -12.0 (1), -47.2 (2) and -60.3 (2)°, while in the triclinic structure, (I), the same dihedral N—C—C—C angles are -35.2 (2), -39.2 (1) and -53.2 (1)° (Fig. 2).
The aromatic C—C bond lengths in the phenyl rings and the C—Ph bond lengths of the central C atom of (I) fall in the narrow ranges of 1.377 (2)–1.400 (2) and 1.537 (2)–1.541 (2) Å, respectively, and are practically equal to the corresponding values in (II) [1.357 (5)–1.398 (3) and 1.539 (3)–1.541 (3) Å, respectively].
The crystal packings of the molecules in (I) and (II) are topologically similar. They both consist of stacks along the a axis and these stacks form layers parallel to the ab plane (Fig. 3a and b). However, the arrangements of the molecules relative to each other in neighbouring stacks, and consequently within the layers, differ considerably. In (I), molecules in neighbouring layers are oriented with the amino groups facing each other, which favours the formation of the aforementioned N—H···N hydrogen bonds, while in (II), the amino groups of neighbouring stacks both within and between the layers are oriented away from each other (Fig. 3c and d).
Since the orthorhombic polymorph was obtained by recrystallization from a solution in the polar solvent dichloromethane, while the triclinic polymorph was isolated from a nonpolar hexane solution, we decided to elucidate the influence of solvent polarity on the formation of the different polymophic modifications of triphenylmethylamine. For this purpose, we recrystallized commercially available triphenylmethylamine from solutions in the polar solvents ethanol, diethyl ether and dichloromethane, and the non-polar solvents hexane, heptane and benzene. It was found that only the orthorhombic modification of triphenylmethylamine is formed from all these solutions at room temperature. Thus, the polarity of solvent does not affect the capability of triphenylmethylamine to crystallize in the different polymorphic modifications. Moreover, the orthorhombic polymorph, (II), is more thermodynamically stable under normal conditions than the triclinic polymorph, (I). It is interesting to note that even the presence of hydrogen bonding in polymorph (I) does not result in its greater stability under ambient conditions compared with polymorph (II).
The possibility of a phase transition from the orthorhombic to the triclinic modification upon cooling was studied by X-ray diffraction analysis in the temperature interval 120–293 K. Our experimental data show that a phase transition does not occur. The densities of the orthorhombic (1.231 Mg m-3) and triclinic (1.235 Mg m-3) modifications at 120 K are practically equal. This result implies that factors other than thermodynamics might be responsible for their formation (Burger & Ramberger, 1979). In the present case, it would seem that either the kinetic factors or the effects of the other products of the reaction facilitating the hydrogen-bonded dimerization of triphenylmethylamine molecules were critical for the isolation of the triclinic polymorph of triphenylmethylamine, (I).