J. Am. Chem. Soc. 1998, 120, 7107-7108
7107
Crystal Structure Change for the Thermochromy of
N-Salicylideneanilines. The First Observation by
X-ray Diffraction
Keiichiro Ogawa,* Yoshiro Kasahara, Yohko Ohtani, and
Jun Harada
Department of Chemistry, Graduate School of Arts and
Sciences, The UniVersity of Tokyo, Komaba
Meguro-ku, Tokyo, 153-8902 Japan
ReceiVed March 23, 1998
Reversible change in color of substances with variation of the
temperature is known as thermochromism and has attracted much
1
interest from chemists for a long time. N-Salicylideneanilines
belong to a class of the most popular thermochromic compounds.2
For example, the crystals of N-(5-chloro-2-hydroxybenzylidene)-
aniline (1) are orange-red at room temperature and pale yellow
at 77 K, and their color changes reversibly with variation of
temperature.3 Extensive studies have revealed that the thermo-
chromism of N-salicylideneanilines originates from the tautom-
erism between the OH and NH forms.4 A change in the crystal
structure for their thermochromy has, however, never been
observed, although an attempt to do so was reported for 1 by
Bregman et al.5 We wish to report the first observation of a
crystal structure change for the thermochromy of N-salicylidene-
anilines, using variable temperature X-ray analysis of N-(5-chloro-
Figure 1. Perspective views of 2 with the atom numbering scheme: (a)
at 298 K and (b) at 90 K. The ellipsoids are drawn at the 50% probability
level.
Table 1. Selected Bond Lengths of 1 and 2 (Å)
compd
T (K)
O2-C2
C2-C1
C1-C7
C7-N1
1
2
90
375
98
20
60
1.350(2)
1.320(2)
1.321(2)
1.318(2)
1.313(2)
1.310(1)
1.412(3)
1.414(3)
1.422(3)
1.427(2)
1.427(2)
1.433(2)
1.457(3)
1.434(3)
1.433(2)
1.428(2)
1.429(2)
1.425(1)
1.291(2)
1.288(3)
1.293(2)
1.297(2)
1.303(2)
1.308(1)
-hydroxybenzylidene)-4-hydroxyaniline (2).6
2
2
2
1
9
0
9
are regarded as of the pure OH form, are also listed in Table 1
for comparison.
Perspective views of the molecule of 2 are shown in Figure 1.
Selected bond lengths obtained from the X-ray crystallographic
7
8
analyses of 2 are listed in Table 1. Bond lengths of 1, which
(
1) Review: (a) Day, J. H. Chem. ReV. 1963, 63, 65-80. (b) Nassau, K.
Table 1 shows that the length of each of the bonds which could
change in bond order by the tautomerism is significantly different
between 1 and 2. Thus, O2-C2 bond of 2 is shorter than that of
The Physics and Chemistry of Color; John Wiley and Sons: New York, 1983;
pp 132-133, 347-348.
(
2) Review: (a) Hadjoudis, E.; Vittorakis, M.; Moustakali-Mavridis, I.
Tetrahedron 1987, 43, 1345-1360. (b) Hadjoudis, E. Tautomerism by
Hydrogen Transfer in Anil, Aci-Nitro and Related Compounds. In Photo-
chromism; D u¨ rr, H., Bouas-Laurent, H., Eds.; Studies in Organic Chemistry
1
and C1-C7 bond of 2 is also shorter than that of 1; C2-C1
bond of 2 is longer than that of 1 and C7-N1 bond of 2 is also
longer than that of 1. The results suggest that the NH form might
coexist in the crystals of 2.
The most important point is that lengths of these bonds of 2
systematically vary with the temperature. Thus, the lengths of
4
0; Elsevier: Amsterdam, 1990; pp 685-712. (c) Inabe, T. New J. Chem.
1
991, 15, 129-136. (d) E. Hadjoudis, E. Molecular Eng. 1995, 5, 301-337.
(
3) (a) Cohen, M. D.; Schmidt, G. M. J. Phys. Chem. 1962, 66, 2442-
2
2
445. (b) Cohen, M. D.; Schmidt, M. J.; Flavin, S. J. Chem. Soc. 1964, 2041-
051.
(
4) (a) Dudek, G. O.; Dudek, E. P. J. Am. Chem. Soc. 1966, 88, 2407-
2
1
412. (b) Becker, R. S.; Richey, W. F. J. Am. Chem. Soc. 1967, 89, 1298-
(7) Crystallographic data for 2: C13
2
H10ClNO , MW ) 247.67, monoclinic,
302. (c) Hadjoudis, E.; Milia, F.; Seliger, J.; Blinc, R.; Zagar, V. Chem.
space group P2
1
/a, Z ) 4, λ(Mo, KR) ) 0.71073 Å. T ) 375 K, a ) 7.2240-
3
Phys. 1980, 47, 105-109. (d) Inabe, T.; Gautier-Luneau, S.; Hoshino, N.;
Okaniwa, K.; Okamoto, H.; Mitani, T.; Nagashima, U.; Maruyama, Y. Bull.
Chem. Soc. Jpn. 1991, 64, 801-810. (e) Inabe, T.; Luneau I.; Mitani, T.;
Maruyama, Y.; Takeda, S. Bull. Chem. Soc. Jpn. 1994, 67, 612-621. (f)
Wozniak, K.; He, H.; Klinowski, J.; Jones, W.; Dziembowska, T.; Grech, E.
J. Chem. Soc., Faraday Trans. 1995, 91, 77-85. (g) Katritzky, A. R.;
Ghiviriga, I.; Leeming, P.; Soti, F. Magn. Reson. Chem. 1996, 34, 518-526.
(3), b ) 12.6908(8), c ) 12.5188(7), â ) 93.606(5)°, V ) 1145.4(1) Å , R
) 0.0486, GOF ) 0.991. T ) 298 K, a ) 7.1805(4), b ) 12.638(1), c )
3
12.514(1), â ) 93.184(7)°, V ) 1133.9(2) Å , R ) 0.0430, GOF ) 0.991. T
) 220 K, a ) 7.119(2), b ) 12.563(2), c ) 12.490(2), â ) 92.71(2)°, V )
3
1115.8(4) Å , R ) 0.0469, GOF ) 0.996. T ) 160 K, a ) 7.086(2), b )
3
12.518(2), c ) 12.485(2), â ) 92.42(2)°, V ) 1106.5(4) Å , R ) 0.0458,
GOF ) 1.033. T ) 90 K, a ) 7.043(2), b ) 12.459(3), c ) 12.4827(19), â
3
(
h) Alarc o´ n, S. H.; Olivieri, A. C.; Nordon, A.; Harris, R. K. J. Chem. Soc.,
) 92.031(18)°, V ) 1094.7(4) Å , R ) 0.0388, GOF ) 1.057.
Perkin 2 1996, 2293-2296. (i) Sekikawa, T.; Kobayashi, T.; Inabe, T. J. Phys.
(8) The X-ray structure of 1 was redetermined with higher accuracy in
Chem. A. 1997, 101, 644-649.
this study. Our structure was essentially identical with that determined by
(
5) Bregman, J.; Leriserowitz, L.; Schmidt, G. M. J. Chem. Soc. 1964,
13
Bregman et al. The crystallographic data: C H10ClNO, MW ) 231.67,
2
068-2085.
orthorhombic, space group Pca2 , Z ) 4, λ(Mo, KR) ) 0.71073 Å. T ) 298
1
3
(
6) Compound 2 was prepared by the condenstation of 5-chlorosalicylal-
K, a ) 12.177(3), b ) 4.483(3), c ) 19.271(3), V ) 1051.9(7) Å , R )
0.0350, GOF ) 1.042.
dehyde with p-aminophenol in methanol at room temperature. Single crystals
for the X-ray measurement were obtained via a slow evaporation of methanol
solution at room temperature. Mp 516-517 K.
(9) It was proved by Schmidt and co-workers that 1 exists exclusively as
3
,
the OH form at 90 K in crystals.
S0002-7863(98)00972-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/03/1998