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Structure and spectroscopic behaviour of the β-phase of 2,4,6-trimethylpyridinium pentachlorophenolate
161
Journal of Molecular Structure, 273 (1992) 161-170 Elsevier Science Publishers B.V., Amsterdam
Structure and spectroscopic of 2,4,6-trimethylpyridinium
behaviour of the P-phase pentachlorophenolate
I. Majerz, Z. Malarski and W. Sawka-Dobrowolska Institute of Chemistry, University of Wroclaw, 50-333 Wroclaw (Poland) (First received 12 February 1992; in final form 13 April 1992)
Abstract The structure of the p-phase of 2,4,6trimethylpyridinium pentachlorophenolate has been determined by X-ray diffraction. The crystals are monoclinic, space group P!Z,/nwith a = 13.957(3), b = 13.432(2), c = 8.770(2) A, /I = g&79(2)” and 2 = 4. The structure has been solved by direct methods and refined to R = 0.036 for 1636 independent reflections. The O-. . .H-N+ bridge of 2.659(4) A with LOHN = 173(4)’ is characterized by strongly asymmetric proton distribution. The shortened C-O bond length of 1.264(4) A and the v(N+ -H.. .O- ) protonic absorption in the 2660cm-’ region confirm the ionic character of the complex.
INTRODUCTION
During our investigations on the structure and spectroscopic behaviour (UV and IR) of the complexes of pentachlorophenol with nitrogen bases [1,2], we found that pentachlorophenol with 2,4,6_trimethylpyridine gives two crystalline phases a and B. The a-phase crystallizes from l,l,l-trichloroethane and acetonitrile, and the P-phase from heptane, carbon tetrachloride, carbon disulphide, chloroform, dichloromethane, 1,2-dichloroethane, methanol and acetone solution. It was interesting to elucidate this polymorphism and to determine the crystallographic structures. Unfortunately, this was possible only for the b-phase; the a-phase decomposes under X-ray radiation. EXPERIMENTAL
The colourless crystals were grown from Ccl, by slow isothermal evaporation of the solvent. Correspondence to: Dr. Z. Malarski, Institute of Chemistry, University of WrocIaw, 50-383 WrocIaw, Poland.
0022-2860/92/$05.00 0 1992 Elsevier Science Publishers
B.V. All rights reserved.
162
1. Majerz et al.lJ. Mol. Struct., 273 (1992) 161-l 70
TABLE 1 Summary of crystal data, data collection and refinement conditions Compound Molecular weight a b ; VW) Z % DC Space group Temperature (K) Radiation Linear absorption coefficient, p(cm-‘) WOO) Number of unique reflections used in refinement I > 2.50(I) Final R Final R, S
C,Cl,O - C,H,, NH 387.5 13.957(3) 13.432(2) 8.779(2) 98.79(2) 1624.8(6) 4 1.59(l) Mgme3 1.584(1)Mgmm3 P2, In 292( 1) MOKa from graphite monochromatization i = 0.71069A 8.85 784 1636 0.036 0.039 3.30
“Measured by flotation in CC&/ethyl bromide.
Preliminary Weissenberg photographs showed the space group to be P2, /n (the monoclinic system). A specimen (0.65 x 0.60 x 0.65 mm) was cut from a large crystal and sealed in a capillary. A syntex P2, diffractometer was used. Cell parameters were obtained from a least-squares fit of the setting angles of 15 reflections in the range 20 < 20 < 30’. The summary of crystal and intensity collection data is given in Table 1. The diffraction data were collected at 292 + 1 K with MO Ka radiation and O-20 scan technique up to 20 = 50’. The intensities of two standard reflections, monitored after each 50 intensity scan, showed a variation of ? 3.6%. A total of 2737 reflections were collected, of which 1636 2 2.50(I) were used for the structure determination. The crystal structure was solved by direct methods using SHELXS 8s [3] and refined by block-diagonal least-squares techniques. All H-atom positions were found from a difference synthesis. An absorption correction following the DIFABS procedure [4] was applied: minimum and maximum absorption corrections were 0.846 and 1.192, respectively. Most calculations were performed with locally modified XTL/XTLE programs [5]. Neutral atomic scattering factors for all atoms were taken from the International Tables for X-ray Crystallography [6]. Real and imaginary disper-
163
I. Majerz et al./J. Mol. Struct., 273 (1992) 161-170 TABLE
2
Final atomic
parameters
Atom
x
Y
z
Biq6”)
0
0.0564(2)
0.1257(3)
- 0.3567(3)
4.3(l)
N
0.1247(3) 0.1113(l)
- 0.5089(3)
3.2(l)
Cl2
- 0.1236(2) 0.1015(l)
- 0.0214(l)
4.7(l)
Cl3
0.3223(l)
0.1010(1)
0.1014(l)
4.9(l)
Cl4
0.4721(l)
0.1176(l)
-0.1267(l)
4.9(l)
Cl5
0.3986(l)
0.1349(l)
- 0.4780(l)
5.2(l)
Cl6 Cl
0.1787(l) 0.1464(3)
0.1464(l)
5.0(l)
0.1240(3)
- 0.5993(l) - 0.3074(4)
c2
0.1838(3)
0.1161(3)
- 0.1481(4)
3.1(2)
c3
0.2817(3)
0.1136(3)
- 0.0937(4)
3.3(2)
c4 c5
0.3496(3)
0.1188(3)
- 0.1941(4)
0.3153(3)
0.1284(3)
- 0.3513(4)
3.3(2) 3.4(2)
3.1(2)
0.2175(3)
0.1327(3)
- 0.4050(4)
3.1(2)
- 0.1916(3)
0.1273(3)
- 0.4149(4)
3.3(2)
0.1302(3)
- 0.4800(4)
3.8(2)
c41
- 0.2869(3) - 0.3148(3)
0.1303(3)
c51
- 0.2414(3)
0.1273(4)
- 0.6385(4) - 0.7280(4)
3.4(2) 3.6(2)
C61
- 0.1459(3)
0.1245(3)
- 0.6656(4)
3.1(2)
Cl2
- 0.1562(3)
0.1275(4)
- 0.2447(4)
5.0(2)
Cl4
- 0.4176(3)
0.1346(4)
- 0.7097(5)
5.2(2)
Cl6
- 0.0652(3)
0.1211(4)
- 0.7552(5)
4.5(2)
C6 c21 c31
‘B,
= (1/3)x
1 Bija:aTaiaj
1 j
TABLE
3
Final H-atom
parameters
Atom
x
Y
z
Hl
- 0.063(3)
0.124(3)
- 0.466(4)
5.5(9)
H3
0.131(3) 0.129(3)
- 0.422(4)
H5
- 0.328(3) - 0.254(3)
4.0(8) 4.6(9)
H12
- 0.200(3)
0.149(3)
- 0.196(5)
7.2(12)
H13 H14
- 0.085(3) - 0.150(4)
0.152(3) 0.065(4)
- 0.217(5) - 0.212(6)
6.4(11) 11.6(18)
H15 H16
- 0.456(3) - 0.450(4)
0.084(4) 0.186(4)
- 0.655(5) - 0.685(5)
8.4(13) 9.0(15)
H17 H18 H19
- 0.428(3) - 0.017(3)
0.116(3) 0.163(3)
8.7(14) 5.9(11)
- 0.029(3) - 0.086(4)
0.064(3) 0.114(4)
- 0.811(5) - 0.722(4) - 0.726(5)
H20
- 0.829(4)
- 0.873(6)
&(A”)
6.9(12) 9.6(15)
I. Majerz et al./J. Mol. Strut.,
164
273 (1992) 161-170
TABLE 4 Bond lengths (A) and bond angles (deg) with esds in parentheses for fi-2,4,6_trimethylpyridinium pentachlorophenolate Bond length N...O 0.. . H(1) C(lW(2) c(2tc(3) C(4W(5) N-C(21) C(21kC(31) C(41&C(51) C(21)-C(12) c(6l~c(l6) C(3WW3) C(5WU5) O-H Cl(2). . . H(13) Bond angle 0. . H(l)-N o-c(ltc(2) C(2tC(ltC(6) C(2tC(3W(4) C(4tC(5tC(6) C(21tN-C(61) N-C(61tC(51) C(31~C(41~C(51) C(12tC(21tC(31) C(14tC(41tC(51) N-C(21tC(12) C1(2W(2W(l) CU3tC(3F-C(2) CU4W(4W(3) CV5W(5W(4) C1(6tC(6tC(l) @C(lW(2)
2.659(4)
1.79(4) 1.419(5) 1.377(5) 1.394(5) 1.349(5) 1.365(5) 1.382(5) 1.499(5) 1.469(5) 1.727(4) 1.729(4) 0.82(3k1.04(4) 2.94(4) 173(4) 122.3(3) 114.6(4) 121.0(4) 121.0(4) 122.9(3) 117.6(3) 116.8(4) 124.5(4) 121.2(4) 116.9(3) 117.3(3) 120.2(3) 121.3(3) 118.5(3) 117.8(3) 122.3(3)
C(3W(4) C(5W6) N-C(61) C(31kC(41) C(51tC(61) C(41kC(14) C(2Px2) C(4kW4) C(6kW6)
0.88(4) 1.264(4) 1.410(5) 1.340(5) 1.375(5) 1.362(4) 1.388(5) 1.361(5) 1.477(6) 1.718(4) 1.722(4) 1.717(3)
Cl(6). . . H(18)
2.79(4)
HOW 0-W) WkC(6)
C(lkO . . . H(1) 0-C(ltC(6) c(lkc(2kc(3) C(3kU4W(5) C(5W(6W(l) N-C(21tC(31) C(21tC(31tC(41) C(41)-C(51tC(61) C(31kC(41 jC(14) C(51tC(61tC(16) N-C(61kC(16) c1(2W(2tc(3) W3tC(3tC(4) C1(4kC(4W(5) Cl(5W5WX6) Cu6tC(6tC(5) o-WW(6)
167(1) 123.1(3) 122.6(3) 117.8(3) 122.8(3) 118.6(6) 121.6(4) 122.5(4) 122.0(4) 124.7(4) 117.6(3) 120.1(3) 118.7(3) 120.9(3) 120.5(3) 119.4(3) 123.1(3)
sion corrections were included for all non-H atoms. The function minimized was Cw(lF,I - IF,I)” w h ere w = l/r?@‘,,). The final R and R, values were 0.036 and 0.039 for the observed reflections. For the last cycle of the refinement, the maximum A/o ratio was 0.01 and the final difference map showed a general background within + 0.16 e Him3.The final atomic parameters are given in Tables 2 and 3. IR spectra of KBr pellets were recorded on a Perkin-Elmer 180 spectrophotometer.
165
1. Majerz et al&J. Mol. Struct., 273 (1992) 161-170 HI2
dH20
Fig. 1. Molecular structure and atom numbering of /?-2,4,6trimethylpyridinium pentachlorophenolate. RESULTS AND DISCUSSION
In correlating the lengths of O-H *a. N and O- - * * H-N+ hydrogen bridges with ApK, values (ApK, = pKatbasej- pKa(acid)), we found that for the complexes of pentaclorophenol with nitrogen bases, the inversion point corresponding formally to 50% proton transfer lies at 0.8 for pyridines and at 1.9 for aliphatic amines. The currently investigated complex should be located at the border of the inversion range of proton transfer complexes at this correlation. Crystallization of 2,4,6-trimethylpyridinium pentachlorophenolate (TMP PCP) from different solutions shows that it may have two phases: the a-phase, with melting point at 410 + 1 K, and the metastable B-phase, which turns into the a form at 388 +_1K, as confirmed by our DTA measurements [7].
Fig. 2. Stereoscopic phenolate.
view
of the packing
of B-2,4,6&imethylpyridinium
pentachloro.
I. Majerz et al.lJ. Mol. Struct.; 273 (1992) 161-170
166 TABLE 5
Anisotropic thermal parameters” with esd values in parentheses Atom
B,, (sd)
B,, (sd)
Wsd)
0
2.75(12) 2.77(14) 4.60(5) 5.14(6) 3.30(5) 3.94(5) 4.75(6) 3.42(17) 3.26(17) 4.17(19) 3.13(17) 3.74(M) 3.42(M) 3.49(M) 3.05(M) 2.87(17) 4.00(19) 3.37(18) 4.87(23) 3.52(21) 3.34(19)
6.64(17) 3.65(15) 6.66(7) 7.03(7) 6.70(7) 8.16(8) 7.91(8) 3.30(18) 3.55(20) 3.39(19) 3.34(19) 3.77(19) 3.62(18) 3.55(18) 4.72(21) 3.32(18) 3.77(19) 3.02(18) 7.41(28) 6.69(28) 5.86(25)
3.42(12) 3.15(13) 3.00(4) 2.32(4) 4.45(5) 3.72(5) 2.17(4) 2.66(15) 2.48(15) 2.14(14) 3.07(16) 2.73(15) 1.98(13) 2.89(15) 3.63(18) 3.93(18) 2.63(16) 2.91(15) 2.71(17) 5.04(23) 4.24(20)
N Cl2 Cl3 Cl4 Cl5 Cl6 Cl c2 c3 c4 c5 C6 c21 c31 c41 c51 C61 Cl2 Cl4 Cl6
“The temperature factor 2B,,hka*b*
+ 2B,,hZu*c*
B,,(sd)
-
-
-
-
0.25(14) 0.20(14) 0.09(6) 0.02(5) 0.07(6) 0.17(6) 0.23(6) 0.26(17) 0.13(17) 0.04(18) 0.09(17) 0.34(19) 0.23(18) 0.05(19) 0.31(20) 0.12(18) 0.09(18) 0.06(17) 0.56(26) 0.35(24) 0.30(22)
B,, (sd)
B,,(sd)
- 0.15(9)
0.27(14) - 0.08(14) 0.22(5) 0.53(4) 0.54(6) 0.46(6) 0.60(5) 0.12(15) 0.13(15) 0.07(15) 0.31(15) 0.01(16) O.ll(15) - 0.05(17) - 0.13(18) 0.01(17) - 0.06(17) - 0.26(16) 0.21(22) - 0.92(24) - 0.36(21)
-
-
-
O.Ol(lO) 1.31(4) 0.42(4) 0.46(4) 1.43(4) O.OO(4) 0.34(13) 0.56(12) O.OO(13) 0.21(13) 0.98(13) 0.21(12) 0.17(13) 0.95( 14) 0.03(13) 0.42(13) 0.33(13) 0.24(15) O.Ol(17) 0.66(15)
is of the form T = exp[ - 1/4(B,,h2a*2 + B,k’b*’
+ B,,Fc*’
+
+ 2B,kZb*c*)].
The principal interatomic distances and angles of P-TMP PCP are given in Table 4, the molecular structure of the complex and the atom numbering scheme are shown in Fig. 1 and a stereoview of the cell packing is presented in Fig. 2. The structure consists of the pyridinium cation and phenolate anion, which are linked to each other by a hydrogen bond of length 2.659(4) Hi.The OHN angle is 173(4)0. This bond is considerably elongated in comparison with that in the 2,4-dimethylpyridine pentachlorophenol complex (2.604(3) A), in spite of comparable ApK, values (1.87 and 1.60, respectively). The cation and anion rings are flat and the normals to the planes make an angle of 5.9(5)‘. Unexpectedly, they are almost coplanar in spite of steric hindrance between the Cl atoms and the H atoms of the methyl groups in the 2 and 6 positions. Intermolecular H(18). . . Cl(6) and H(13). . . Cl(2) distances are 2.79(4) and 2.94(4) Hi,respectively, and are shorter than the corresponding sum of the van der Waals radii. The Cl atoms in the 2 and 6 positions are blocked between the H atoms of the methyl group, causing
I. Majerz et al.lJ. Mol. Struct., 273 (1992) 161-170
167
TABLE 6 Atom-to-plane distances (A) and angles between normals to the planes (deg) Plane A C(1) 0.017(4) C(6) - 0.016(4) CI(6) - 0.044(l)
C(2)
- 0.004(4) Cl(2) - 0.049( 1) 0 0.026(3)
C(3) - O.OOS(4) Cl(3) 0.005( 1) B(1) 0.14(4)
CI(4) -0.022(a) N 0.151(3)
C(5) 0.005(4) CI(5) 0.026(l) B(l3) - 0.447(41)
C(41) O.OOl(4)
C(51) - O.OOl(5)
C(12) - 0.005(5)
C(14) 0.017(5)
C(4) 0.008(4)
B(l8) - 0.188(40) Plane B N 0.001(3) C(61) - O.OOO(4)
ww
- O.OOl(4) 0 0.084(3)
C(31) O.OOO(5) B(1) O.Ol(4)
0
C(l)
C(16) - 0.002(5) Plane C N O.OOO(3) A-B EC A-C
O.OOO(3)
O.OOO(4)
5.9(5) 12.4(5) 7.0(4)
“Atoms not included in the planes.
elongation of the hydrogen bond and giving it more ionic character. The methyl groups have significant thermal parameters (Table 5). The H(1) and 0 atoms lie in the phenolate ring plane as well as in the pyridinium one (Table 6). The C-C and C-Cl bond lengths in the phenolate and pyridinium rings lie within the range 1.365(5)-1.410(5) A and 1.717(3)-1.729(4) A respectively. The deviations of the Cl(2) and Cl(6) atoms from the phenolate ring plane are especially large in comparison with the other Cl atoms. The C-O bond length of l-264(4) A is the shortest among the C-O bonds for the pentachlorophenol complexes investigated by us and indicates the fully ionic character of /l-TMP PCP. IR SPECTRA
IR spectra of the solid a- and P-phases of TMP PCP are shown in Fig. 3. Transition from a- to p-phase causes drastic spectroscopic changes. The IR spectrum of a-TMA PCP is characterized by continuous proton absorption v(N+ H ***O- ) extended in the 300-3200 cm-l range and is typical for very strong hydrogen bonding. In this continuous absorption, two ranges may be
I. Majerz
168
400
800
1200
1600
et al./J.
2000
Mol. Strut.,
273 (1992) 161-170
2500
Fig. 3. IR spectra of the complexs of 2,4,6-trimethylpyridine with pentachlorophenol: a-form, obtained by crystallization from CCI.,; (b) B-form, from l,l,l-trichloroethane.
(a)
distinguished and attributed to different transitions between ground and excited split vibration levels. The absorption maxima corresponding to these transitions are located at 8OOcm-’ (intense) and 2500cm-’ (less intense). The characteristic features of the low-frequency absorption are numerous Evans transmission holes. The strongest of these at 450,624,724 and 988 cm-’ are caused by the resonance coupling of the v(N+ -H . . . O- ) protonic absorption with some internal vibrations of the pyridinium cation. Assignments are listed in Table 7. There are two reasons for the ionic character of a-TMP PCP: the coupling of proton absorption with internal pyridinium cation frequencies and the disappearance of the coupled v(C0) and the &OH) frequencies at about 1200-1300cm-’ [1,2], characteristic of the molecular form of the complex. On the basis of the IR spectroscopic behaviour of a-TMP PCP, one may assume that the N+ -H . ..O- hydrogen bond in this phase is shorter than 2.60 A. The IR spectrum of &TMP PCP is completely different. The quite narrow (Av,,, = 400 cm-‘) absorption band lies at 2660 cm-’ and is very similar to the protonic absorption of 2,4,6-trimethylpyridinium hydrobromide (2670 cm-‘), which indicates the typically ionic character of a complex with
169
1. Majerz et al.lJ. Mol. Struct., 273 (1992) 161-170 TABLE 7
Selected frequencies and Evans holes (cm-‘) below 17OOcm-’ for 2,4,6_trimethylpyridine and its hydrobromide, and for cations of a-TMP PCP and fi-TMP PCP TMP 467 w 516m 531 s 540 m 589 w 724 w 840 vs 878 VW 922 s
993 s
1029 s
1155 w 1218s 1317 w 1372 s 1407 s 1440 sh 1458 vs
1532 m 1570 vs 1610 vs
TMP * HBr 468 VW 515m 531 VW 590 VW 720 m 890s 932 m 948w 965m 994 w 1038 m 1050 sh 1176 w 1220 VW 1280 w 1330 w 1385 sh 1398 s 1430 m 1480 m 1518m 1537 m 1632 vs
a-TMP PCP
468 w 520 s 531 VW
4531
6241 7241 805 br 870sh br 923 w 942 w 958 w 9982 1035 m
1138 w 1215 m 1275 m 1315~s
1465 w 1485 w 1520 m
1632 vs
b-TMP PCP
590w 710m 843s
936 m 945 w 970w 992s 1038 m 1052 m 1113m 1164w 1211 w 1280m br 1330 w Obscured by phenolate anion 1430 vs 1465 vs 1500 s 1528 vs 1570 w 1632 vs
Assignmentsb
b,, “26 aI, v9
4, h,
“26 “16
a19 “6
4, “15 b,, “14 a2, vll
b,, vu
a19 “6
P(CW
al7 v5
b,, “23 al9 v4
UCH,)
b,, va al, v3
&,,(CH,)
b,, vzo al9 v2
“JEvans holes. bRef. 8.
a long hydrogen bond. The very well-shaped cation bands at 520, 622, 710 and 998 cm-’ of P-TMP PCP correspond to the Evans holes in the spectrum of a-TMP PCP. CONCLUSIONS
2,4,6_Trimethylpyridinium pentachlorophenolate is the first known phenol-pyridine complex which shows polymorphism. b-TMP PCP + ol-TMP PCP at 336 + 1 K is an irreversible first-order phase transition. a- and B-TMP PCP do not fulfil the correlation between the length of the N+-He** O- hydrogen bond and the ApKa value.
170
I. Majerz et al.lJ. Mol. Struct., 273 (1992) 161-170
The flat conformation of the j?-TMP PCP molecule has an elongated N+ -H . ..Om hydrogen bond (2.659(4) A) and, therefore, more ionic character. This is the result of the steric hindrances caused by the blocking of the Cl atoms in the 2 and 6 positions between the hydrogen atoms in the 2,6-methyl groups. The perpendicular conformation of a-TMP PCP has the N+ -H . ..Ohydrogen bond shortened to below 2.6OA. The protonic absorption observed in the IR spectrum shows features typical of the complexes from the inversion (HB t+PT) region. This is probably caused by the better packing of the complex components in the crystal lattice in comparison with /?-TMP PCP. REFERENCES I. Majerz, Z. Malarski and T. Lis, J. Mol. Struct., 158 (1987) 369; 161 (1987) 165; 213 (1989) 161; 243 (1991) 351; Acta Crystallogr., Sect. C, 43 (1987) 187; J. Crystallogr. Spectrosc. Res., 19 (1989) 349; Bull. Pal. Acad. Sci., Chem., 37 (1989) 349. I. Majerz, Z. Malarski and W. Sawka-Dobrowolska, J. Mol. Struct., 249 (1991) 109. G.M. Sheldrick, SHELXS 86. Program for the solution of crystal structure, University of Gottingen, 1986. N. Walker and D. Stuart, Acta Crstallogr., Sect. A, 39 (1983) 158. Syntex STL/STLE Structure Determination System, Syntex Analytical Instruments, Cupertino, CA, 1976. International Tables for X-ray Crystallography, Vol. 4, Kynoch Press, Birmingham, 1974. I. Majerz, P. Freundlich and Z. Malarski, in preparation. J.H.S. Green and D.J. Harrison, Spectrochim. Acta, Part A, 29 (1973) 293.
Journal of Molecular Structure, 273 (1992) 161-170 Elsevier Science Publishers B.V., Amsterdam
Structure and spectroscopic of 2,4,6-trimethylpyridinium
behaviour of the P-phase pentachlorophenolate
I. Majerz, Z. Malarski and W. Sawka-Dobrowolska Institute of Chemistry, University of Wroclaw, 50-333 Wroclaw (Poland) (First received 12 February 1992; in final form 13 April 1992)
Abstract The structure of the p-phase of 2,4,6trimethylpyridinium pentachlorophenolate has been determined by X-ray diffraction. The crystals are monoclinic, space group P!Z,/nwith a = 13.957(3), b = 13.432(2), c = 8.770(2) A, /I = g&79(2)” and 2 = 4. The structure has been solved by direct methods and refined to R = 0.036 for 1636 independent reflections. The O-. . .H-N+ bridge of 2.659(4) A with LOHN = 173(4)’ is characterized by strongly asymmetric proton distribution. The shortened C-O bond length of 1.264(4) A and the v(N+ -H.. .O- ) protonic absorption in the 2660cm-’ region confirm the ionic character of the complex.
INTRODUCTION
During our investigations on the structure and spectroscopic behaviour (UV and IR) of the complexes of pentachlorophenol with nitrogen bases [1,2], we found that pentachlorophenol with 2,4,6_trimethylpyridine gives two crystalline phases a and B. The a-phase crystallizes from l,l,l-trichloroethane and acetonitrile, and the P-phase from heptane, carbon tetrachloride, carbon disulphide, chloroform, dichloromethane, 1,2-dichloroethane, methanol and acetone solution. It was interesting to elucidate this polymorphism and to determine the crystallographic structures. Unfortunately, this was possible only for the b-phase; the a-phase decomposes under X-ray radiation. EXPERIMENTAL
The colourless crystals were grown from Ccl, by slow isothermal evaporation of the solvent. Correspondence to: Dr. Z. Malarski, Institute of Chemistry, University of WrocIaw, 50-383 WrocIaw, Poland.
0022-2860/92/$05.00 0 1992 Elsevier Science Publishers
B.V. All rights reserved.
162
1. Majerz et al.lJ. Mol. Struct., 273 (1992) 161-l 70
TABLE 1 Summary of crystal data, data collection and refinement conditions Compound Molecular weight a b ; VW) Z % DC Space group Temperature (K) Radiation Linear absorption coefficient, p(cm-‘) WOO) Number of unique reflections used in refinement I > 2.50(I) Final R Final R, S
C,Cl,O - C,H,, NH 387.5 13.957(3) 13.432(2) 8.779(2) 98.79(2) 1624.8(6) 4 1.59(l) Mgme3 1.584(1)Mgmm3 P2, In 292( 1) MOKa from graphite monochromatization i = 0.71069A 8.85 784 1636 0.036 0.039 3.30
“Measured by flotation in CC&/ethyl bromide.
Preliminary Weissenberg photographs showed the space group to be P2, /n (the monoclinic system). A specimen (0.65 x 0.60 x 0.65 mm) was cut from a large crystal and sealed in a capillary. A syntex P2, diffractometer was used. Cell parameters were obtained from a least-squares fit of the setting angles of 15 reflections in the range 20 < 20 < 30’. The summary of crystal and intensity collection data is given in Table 1. The diffraction data were collected at 292 + 1 K with MO Ka radiation and O-20 scan technique up to 20 = 50’. The intensities of two standard reflections, monitored after each 50 intensity scan, showed a variation of ? 3.6%. A total of 2737 reflections were collected, of which 1636 2 2.50(I) were used for the structure determination. The crystal structure was solved by direct methods using SHELXS 8s [3] and refined by block-diagonal least-squares techniques. All H-atom positions were found from a difference synthesis. An absorption correction following the DIFABS procedure [4] was applied: minimum and maximum absorption corrections were 0.846 and 1.192, respectively. Most calculations were performed with locally modified XTL/XTLE programs [5]. Neutral atomic scattering factors for all atoms were taken from the International Tables for X-ray Crystallography [6]. Real and imaginary disper-
163
I. Majerz et al./J. Mol. Struct., 273 (1992) 161-170 TABLE
2
Final atomic
parameters
Atom
x
Y
z
Biq6”)
0
0.0564(2)
0.1257(3)
- 0.3567(3)
4.3(l)
N
0.1247(3) 0.1113(l)
- 0.5089(3)
3.2(l)
Cl2
- 0.1236(2) 0.1015(l)
- 0.0214(l)
4.7(l)
Cl3
0.3223(l)
0.1010(1)
0.1014(l)
4.9(l)
Cl4
0.4721(l)
0.1176(l)
-0.1267(l)
4.9(l)
Cl5
0.3986(l)
0.1349(l)
- 0.4780(l)
5.2(l)
Cl6 Cl
0.1787(l) 0.1464(3)
0.1464(l)
5.0(l)
0.1240(3)
- 0.5993(l) - 0.3074(4)
c2
0.1838(3)
0.1161(3)
- 0.1481(4)
3.1(2)
c3
0.2817(3)
0.1136(3)
- 0.0937(4)
3.3(2)
c4 c5
0.3496(3)
0.1188(3)
- 0.1941(4)
0.3153(3)
0.1284(3)
- 0.3513(4)
3.3(2) 3.4(2)
3.1(2)
0.2175(3)
0.1327(3)
- 0.4050(4)
3.1(2)
- 0.1916(3)
0.1273(3)
- 0.4149(4)
3.3(2)
0.1302(3)
- 0.4800(4)
3.8(2)
c41
- 0.2869(3) - 0.3148(3)
0.1303(3)
c51
- 0.2414(3)
0.1273(4)
- 0.6385(4) - 0.7280(4)
3.4(2) 3.6(2)
C61
- 0.1459(3)
0.1245(3)
- 0.6656(4)
3.1(2)
Cl2
- 0.1562(3)
0.1275(4)
- 0.2447(4)
5.0(2)
Cl4
- 0.4176(3)
0.1346(4)
- 0.7097(5)
5.2(2)
Cl6
- 0.0652(3)
0.1211(4)
- 0.7552(5)
4.5(2)
C6 c21 c31
‘B,
= (1/3)x
1 Bija:aTaiaj
1 j
TABLE
3
Final H-atom
parameters
Atom
x
Y
z
Hl
- 0.063(3)
0.124(3)
- 0.466(4)
5.5(9)
H3
0.131(3) 0.129(3)
- 0.422(4)
H5
- 0.328(3) - 0.254(3)
4.0(8) 4.6(9)
H12
- 0.200(3)
0.149(3)
- 0.196(5)
7.2(12)
H13 H14
- 0.085(3) - 0.150(4)
0.152(3) 0.065(4)
- 0.217(5) - 0.212(6)
6.4(11) 11.6(18)
H15 H16
- 0.456(3) - 0.450(4)
0.084(4) 0.186(4)
- 0.655(5) - 0.685(5)
8.4(13) 9.0(15)
H17 H18 H19
- 0.428(3) - 0.017(3)
0.116(3) 0.163(3)
8.7(14) 5.9(11)
- 0.029(3) - 0.086(4)
0.064(3) 0.114(4)
- 0.811(5) - 0.722(4) - 0.726(5)
H20
- 0.829(4)
- 0.873(6)
&(A”)
6.9(12) 9.6(15)
I. Majerz et al./J. Mol. Strut.,
164
273 (1992) 161-170
TABLE 4 Bond lengths (A) and bond angles (deg) with esds in parentheses for fi-2,4,6_trimethylpyridinium pentachlorophenolate Bond length N...O 0.. . H(1) C(lW(2) c(2tc(3) C(4W(5) N-C(21) C(21kC(31) C(41&C(51) C(21)-C(12) c(6l~c(l6) C(3WW3) C(5WU5) O-H Cl(2). . . H(13) Bond angle 0. . H(l)-N o-c(ltc(2) C(2tC(ltC(6) C(2tC(3W(4) C(4tC(5tC(6) C(21tN-C(61) N-C(61tC(51) C(31~C(41~C(51) C(12tC(21tC(31) C(14tC(41tC(51) N-C(21tC(12) C1(2W(2W(l) CU3tC(3F-C(2) CU4W(4W(3) CV5W(5W(4) C1(6tC(6tC(l) @C(lW(2)
2.659(4)
1.79(4) 1.419(5) 1.377(5) 1.394(5) 1.349(5) 1.365(5) 1.382(5) 1.499(5) 1.469(5) 1.727(4) 1.729(4) 0.82(3k1.04(4) 2.94(4) 173(4) 122.3(3) 114.6(4) 121.0(4) 121.0(4) 122.9(3) 117.6(3) 116.8(4) 124.5(4) 121.2(4) 116.9(3) 117.3(3) 120.2(3) 121.3(3) 118.5(3) 117.8(3) 122.3(3)
C(3W(4) C(5W6) N-C(61) C(31kC(41) C(51tC(61) C(41kC(14) C(2Px2) C(4kW4) C(6kW6)
0.88(4) 1.264(4) 1.410(5) 1.340(5) 1.375(5) 1.362(4) 1.388(5) 1.361(5) 1.477(6) 1.718(4) 1.722(4) 1.717(3)
Cl(6). . . H(18)
2.79(4)
HOW 0-W) WkC(6)
C(lkO . . . H(1) 0-C(ltC(6) c(lkc(2kc(3) C(3kU4W(5) C(5W(6W(l) N-C(21tC(31) C(21tC(31tC(41) C(41)-C(51tC(61) C(31kC(41 jC(14) C(51tC(61tC(16) N-C(61kC(16) c1(2W(2tc(3) W3tC(3tC(4) C1(4kC(4W(5) Cl(5W5WX6) Cu6tC(6tC(5) o-WW(6)
167(1) 123.1(3) 122.6(3) 117.8(3) 122.8(3) 118.6(6) 121.6(4) 122.5(4) 122.0(4) 124.7(4) 117.6(3) 120.1(3) 118.7(3) 120.9(3) 120.5(3) 119.4(3) 123.1(3)
sion corrections were included for all non-H atoms. The function minimized was Cw(lF,I - IF,I)” w h ere w = l/r?@‘,,). The final R and R, values were 0.036 and 0.039 for the observed reflections. For the last cycle of the refinement, the maximum A/o ratio was 0.01 and the final difference map showed a general background within + 0.16 e Him3.The final atomic parameters are given in Tables 2 and 3. IR spectra of KBr pellets were recorded on a Perkin-Elmer 180 spectrophotometer.
165
1. Majerz et al&J. Mol. Struct., 273 (1992) 161-170 HI2
dH20
Fig. 1. Molecular structure and atom numbering of /?-2,4,6trimethylpyridinium pentachlorophenolate. RESULTS AND DISCUSSION
In correlating the lengths of O-H *a. N and O- - * * H-N+ hydrogen bridges with ApK, values (ApK, = pKatbasej- pKa(acid)), we found that for the complexes of pentaclorophenol with nitrogen bases, the inversion point corresponding formally to 50% proton transfer lies at 0.8 for pyridines and at 1.9 for aliphatic amines. The currently investigated complex should be located at the border of the inversion range of proton transfer complexes at this correlation. Crystallization of 2,4,6-trimethylpyridinium pentachlorophenolate (TMP PCP) from different solutions shows that it may have two phases: the a-phase, with melting point at 410 + 1 K, and the metastable B-phase, which turns into the a form at 388 +_1K, as confirmed by our DTA measurements [7].
Fig. 2. Stereoscopic phenolate.
view
of the packing
of B-2,4,6&imethylpyridinium
pentachloro.
I. Majerz et al.lJ. Mol. Struct.; 273 (1992) 161-170
166 TABLE 5
Anisotropic thermal parameters” with esd values in parentheses Atom
B,, (sd)
B,, (sd)
Wsd)
0
2.75(12) 2.77(14) 4.60(5) 5.14(6) 3.30(5) 3.94(5) 4.75(6) 3.42(17) 3.26(17) 4.17(19) 3.13(17) 3.74(M) 3.42(M) 3.49(M) 3.05(M) 2.87(17) 4.00(19) 3.37(18) 4.87(23) 3.52(21) 3.34(19)
6.64(17) 3.65(15) 6.66(7) 7.03(7) 6.70(7) 8.16(8) 7.91(8) 3.30(18) 3.55(20) 3.39(19) 3.34(19) 3.77(19) 3.62(18) 3.55(18) 4.72(21) 3.32(18) 3.77(19) 3.02(18) 7.41(28) 6.69(28) 5.86(25)
3.42(12) 3.15(13) 3.00(4) 2.32(4) 4.45(5) 3.72(5) 2.17(4) 2.66(15) 2.48(15) 2.14(14) 3.07(16) 2.73(15) 1.98(13) 2.89(15) 3.63(18) 3.93(18) 2.63(16) 2.91(15) 2.71(17) 5.04(23) 4.24(20)
N Cl2 Cl3 Cl4 Cl5 Cl6 Cl c2 c3 c4 c5 C6 c21 c31 c41 c51 C61 Cl2 Cl4 Cl6
“The temperature factor 2B,,hka*b*
+ 2B,,hZu*c*
B,,(sd)
-
-
-
-
0.25(14) 0.20(14) 0.09(6) 0.02(5) 0.07(6) 0.17(6) 0.23(6) 0.26(17) 0.13(17) 0.04(18) 0.09(17) 0.34(19) 0.23(18) 0.05(19) 0.31(20) 0.12(18) 0.09(18) 0.06(17) 0.56(26) 0.35(24) 0.30(22)
B,, (sd)
B,,(sd)
- 0.15(9)
0.27(14) - 0.08(14) 0.22(5) 0.53(4) 0.54(6) 0.46(6) 0.60(5) 0.12(15) 0.13(15) 0.07(15) 0.31(15) 0.01(16) O.ll(15) - 0.05(17) - 0.13(18) 0.01(17) - 0.06(17) - 0.26(16) 0.21(22) - 0.92(24) - 0.36(21)
-
-
-
O.Ol(lO) 1.31(4) 0.42(4) 0.46(4) 1.43(4) O.OO(4) 0.34(13) 0.56(12) O.OO(13) 0.21(13) 0.98(13) 0.21(12) 0.17(13) 0.95( 14) 0.03(13) 0.42(13) 0.33(13) 0.24(15) O.Ol(17) 0.66(15)
is of the form T = exp[ - 1/4(B,,h2a*2 + B,k’b*’
+ B,,Fc*’
+
+ 2B,kZb*c*)].
The principal interatomic distances and angles of P-TMP PCP are given in Table 4, the molecular structure of the complex and the atom numbering scheme are shown in Fig. 1 and a stereoview of the cell packing is presented in Fig. 2. The structure consists of the pyridinium cation and phenolate anion, which are linked to each other by a hydrogen bond of length 2.659(4) Hi.The OHN angle is 173(4)0. This bond is considerably elongated in comparison with that in the 2,4-dimethylpyridine pentachlorophenol complex (2.604(3) A), in spite of comparable ApK, values (1.87 and 1.60, respectively). The cation and anion rings are flat and the normals to the planes make an angle of 5.9(5)‘. Unexpectedly, they are almost coplanar in spite of steric hindrance between the Cl atoms and the H atoms of the methyl groups in the 2 and 6 positions. Intermolecular H(18). . . Cl(6) and H(13). . . Cl(2) distances are 2.79(4) and 2.94(4) Hi,respectively, and are shorter than the corresponding sum of the van der Waals radii. The Cl atoms in the 2 and 6 positions are blocked between the H atoms of the methyl group, causing
I. Majerz et al.lJ. Mol. Struct., 273 (1992) 161-170
167
TABLE 6 Atom-to-plane distances (A) and angles between normals to the planes (deg) Plane A C(1) 0.017(4) C(6) - 0.016(4) CI(6) - 0.044(l)
C(2)
- 0.004(4) Cl(2) - 0.049( 1) 0 0.026(3)
C(3) - O.OOS(4) Cl(3) 0.005( 1) B(1) 0.14(4)
CI(4) -0.022(a) N 0.151(3)
C(5) 0.005(4) CI(5) 0.026(l) B(l3) - 0.447(41)
C(41) O.OOl(4)
C(51) - O.OOl(5)
C(12) - 0.005(5)
C(14) 0.017(5)
C(4) 0.008(4)
B(l8) - 0.188(40) Plane B N 0.001(3) C(61) - O.OOO(4)
ww
- O.OOl(4) 0 0.084(3)
C(31) O.OOO(5) B(1) O.Ol(4)
0
C(l)
C(16) - 0.002(5) Plane C N O.OOO(3) A-B EC A-C
O.OOO(3)
O.OOO(4)
5.9(5) 12.4(5) 7.0(4)
“Atoms not included in the planes.
elongation of the hydrogen bond and giving it more ionic character. The methyl groups have significant thermal parameters (Table 5). The H(1) and 0 atoms lie in the phenolate ring plane as well as in the pyridinium one (Table 6). The C-C and C-Cl bond lengths in the phenolate and pyridinium rings lie within the range 1.365(5)-1.410(5) A and 1.717(3)-1.729(4) A respectively. The deviations of the Cl(2) and Cl(6) atoms from the phenolate ring plane are especially large in comparison with the other Cl atoms. The C-O bond length of l-264(4) A is the shortest among the C-O bonds for the pentachlorophenol complexes investigated by us and indicates the fully ionic character of /l-TMP PCP. IR SPECTRA
IR spectra of the solid a- and P-phases of TMP PCP are shown in Fig. 3. Transition from a- to p-phase causes drastic spectroscopic changes. The IR spectrum of a-TMA PCP is characterized by continuous proton absorption v(N+ H ***O- ) extended in the 300-3200 cm-l range and is typical for very strong hydrogen bonding. In this continuous absorption, two ranges may be
I. Majerz
168
400
800
1200
1600
et al./J.
2000
Mol. Strut.,
273 (1992) 161-170
2500
Fig. 3. IR spectra of the complexs of 2,4,6-trimethylpyridine with pentachlorophenol: a-form, obtained by crystallization from CCI.,; (b) B-form, from l,l,l-trichloroethane.
(a)
distinguished and attributed to different transitions between ground and excited split vibration levels. The absorption maxima corresponding to these transitions are located at 8OOcm-’ (intense) and 2500cm-’ (less intense). The characteristic features of the low-frequency absorption are numerous Evans transmission holes. The strongest of these at 450,624,724 and 988 cm-’ are caused by the resonance coupling of the v(N+ -H . . . O- ) protonic absorption with some internal vibrations of the pyridinium cation. Assignments are listed in Table 7. There are two reasons for the ionic character of a-TMP PCP: the coupling of proton absorption with internal pyridinium cation frequencies and the disappearance of the coupled v(C0) and the &OH) frequencies at about 1200-1300cm-’ [1,2], characteristic of the molecular form of the complex. On the basis of the IR spectroscopic behaviour of a-TMP PCP, one may assume that the N+ -H . ..O- hydrogen bond in this phase is shorter than 2.60 A. The IR spectrum of &TMP PCP is completely different. The quite narrow (Av,,, = 400 cm-‘) absorption band lies at 2660 cm-’ and is very similar to the protonic absorption of 2,4,6-trimethylpyridinium hydrobromide (2670 cm-‘), which indicates the typically ionic character of a complex with
169
1. Majerz et al.lJ. Mol. Struct., 273 (1992) 161-170 TABLE 7
Selected frequencies and Evans holes (cm-‘) below 17OOcm-’ for 2,4,6_trimethylpyridine and its hydrobromide, and for cations of a-TMP PCP and fi-TMP PCP TMP 467 w 516m 531 s 540 m 589 w 724 w 840 vs 878 VW 922 s
993 s
1029 s
1155 w 1218s 1317 w 1372 s 1407 s 1440 sh 1458 vs
1532 m 1570 vs 1610 vs
TMP * HBr 468 VW 515m 531 VW 590 VW 720 m 890s 932 m 948w 965m 994 w 1038 m 1050 sh 1176 w 1220 VW 1280 w 1330 w 1385 sh 1398 s 1430 m 1480 m 1518m 1537 m 1632 vs
a-TMP PCP
468 w 520 s 531 VW
4531
6241 7241 805 br 870sh br 923 w 942 w 958 w 9982 1035 m
1138 w 1215 m 1275 m 1315~s
1465 w 1485 w 1520 m
1632 vs
b-TMP PCP
590w 710m 843s
936 m 945 w 970w 992s 1038 m 1052 m 1113m 1164w 1211 w 1280m br 1330 w Obscured by phenolate anion 1430 vs 1465 vs 1500 s 1528 vs 1570 w 1632 vs
Assignmentsb
b,, “26 aI, v9
4, h,
“26 “16
a19 “6
4, “15 b,, “14 a2, vll
b,, vu
a19 “6
P(CW
al7 v5
b,, “23 al9 v4
UCH,)
b,, va al, v3
&,,(CH,)
b,, vzo al9 v2
“JEvans holes. bRef. 8.
a long hydrogen bond. The very well-shaped cation bands at 520, 622, 710 and 998 cm-’ of P-TMP PCP correspond to the Evans holes in the spectrum of a-TMP PCP. CONCLUSIONS
2,4,6_Trimethylpyridinium pentachlorophenolate is the first known phenol-pyridine complex which shows polymorphism. b-TMP PCP + ol-TMP PCP at 336 + 1 K is an irreversible first-order phase transition. a- and B-TMP PCP do not fulfil the correlation between the length of the N+-He** O- hydrogen bond and the ApKa value.
170
I. Majerz et al.lJ. Mol. Struct., 273 (1992) 161-170
The flat conformation of the j?-TMP PCP molecule has an elongated N+ -H . ..Om hydrogen bond (2.659(4) A) and, therefore, more ionic character. This is the result of the steric hindrances caused by the blocking of the Cl atoms in the 2 and 6 positions between the hydrogen atoms in the 2,6-methyl groups. The perpendicular conformation of a-TMP PCP has the N+ -H . ..Ohydrogen bond shortened to below 2.6OA. The protonic absorption observed in the IR spectrum shows features typical of the complexes from the inversion (HB t+PT) region. This is probably caused by the better packing of the complex components in the crystal lattice in comparison with /?-TMP PCP. REFERENCES I. Majerz, Z. Malarski and T. Lis, J. Mol. Struct., 158 (1987) 369; 161 (1987) 165; 213 (1989) 161; 243 (1991) 351; Acta Crystallogr., Sect. C, 43 (1987) 187; J. Crystallogr. Spectrosc. Res., 19 (1989) 349; Bull. Pal. Acad. Sci., Chem., 37 (1989) 349. I. Majerz, Z. Malarski and W. Sawka-Dobrowolska, J. Mol. Struct., 249 (1991) 109. G.M. Sheldrick, SHELXS 86. Program for the solution of crystal structure, University of Gottingen, 1986. N. Walker and D. Stuart, Acta Crstallogr., Sect. A, 39 (1983) 158. Syntex STL/STLE Structure Determination System, Syntex Analytical Instruments, Cupertino, CA, 1976. International Tables for X-ray Crystallography, Vol. 4, Kynoch Press, Birmingham, 1974. I. Majerz, P. Freundlich and Z. Malarski, in preparation. J.H.S. Green and D.J. Harrison, Spectrochim. Acta, Part A, 29 (1973) 293.