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Isotope effect and hydrogen bonding in crystalline hydrazinium hydrogen oxalate, N2H5HC2O4
Volume 3, number 2
CHEMICAL PHYSICS LETTERS
ISOTOPE
EFFECT
AND
HYDRAZINIUM
HYDROGEN
BONDING
HYDROGEN J. LINDGREN,
Laboratoire
de Chimie
February
IN
OXALATE,
1969
CRYSTALLINE
N2H5HC204
J. DE VILLEPIN
Physique
du C.N.R.S.,
94 Thiais
and A. NOVAK Laboratoire
de Specfvochimie
Molkulaire,
Facultl
des Sciences
de Paris,
France
Received 13 January 1969 Infrared speatra>of hydrazinium hydrogen oxalate, N2H6HC20a, and of its deuterated derivative, N2D6DC20 , have heemstudied at liquid nitrogen temperature in the 3600 to 200 cm-1 range. It appears that t%e symmetric 0.. H.. 0 hydrogen bond of the hydrogen oxslate chains becomes asymmetric when hydkgen is substituted by de&r&.
A positive isotope effect, i.e., the OD.. 0 distance is longer than the OH. . 0 distance, has been observed for a few hydrogen bonded systems [ 1,2] ,a”d is particularly large for short (2.40-2.60 A) hydrogen bonds such as are found in HCrO2 and HCo02 [l]. Infrared studies of these two compounds showed that the OH stretching frequency is lower than its OD analog and that the former is a singlet whel’zas the latter is a doublet. Snyder and Ibers [l] have interpreted these results in terms of different hydrogen-bond potential functions for the two isotopic species. In this communication we report the infrared spectra of hydrazinium hydrogen oxalatc and its deuterated derivative which appear to indicate that the symmetrical 0. . H. . 0 hydrogen bond becomes asymmetrical upon deuteration. The crystal structure of N2H5HC204 has been determined [3,4]. The hydrazinium ions, N2H$+, are linked into infinite zig-zag chains by NH+. . N hydrogen bonds and the hydrogen oxalate ions, HC2O4-, form infinite planar chains by short 0.. H.. 0 hydrogen bonds. The two types of chains are cross-linked by NH.. 0 bonds. Several kinds of hydrogen bonds can thus be clistinguished in ‘&is crystal (table 1). There are . weak, medium-to-strong, and very stror.g hydrogen bonds of the NH2, NH3+, and OH0 groups respectivey. Ths 0.. H.. 0 bond (2.45 A) is either symmetrical with the hydrogen at the center of sjrmmetry or there is a disordered arrangement [3,4j. -84
The infrared spectrum of N2HgHC204 shown in fig. 1 is consistent with the description of NH+. . N and NH.. 0 hydrogen bonds and supports the symmetrical 0.. H. . 0 hydrogen bond. The NH stretching bands are observed in the 36002000 cm-1 region and the absorption pattern is similar to that of solid N2H5Cl containing chains of N2Hgf ions [5] recorded for comparison. The assignment of the narrow bands at 3369 and 3299 cm-l to the antisymmetric and symmetric stretching vibrations of the weakly bonded NH2 group is straightforward (table 1). Two broad and strong bands near 3030 and 2550 cm-l, on the other hand, can be associated with the stretching vibrations of the NH3+ group which forms medium-strong interchain NH+. . 0 and strong intrachain NH+. . N h drogen bonds characterized by shorter (1.02 P ) and longer (1.04 A) N-H distances re ectively. It is thus likely that the high 3030 cm-? frequency corresponds to the
former
and the low 2550 cm-l frequency to the (table 1). The subband structure of these two absorptions is probably due to combinations and overtones. This interpretation implies that there is no OH stretching band in the 3600-2000 cm-l region. In fact, for the intermolecular hydrogen bonds of the acid salt type, (-COQHOOC-), for which it seems probable that the hydrogen atom is truly centered [S] three characteristic spectral features have been observed [?I: the existence of a single uC=O band due to the equivalent COO groups, the presence of a strong and latier
Volume 3, number 2
CHEMICAL
PHYSICS LETTERS
1600
x200
February
mo
Fig. 1. Infrared spectra of: (a) N2HsC204; (b) N2DgDC204; mulls in fluorolube (3600-1300 cm-l) (1300-200 cm-L) at liquid nitrogen temperature.
very broad absorption, usually between 3600 and 300 cm-l, and the absence of any vOH band above 1300 cm-l. If the O-H-O hydrogen bond in N2H5HC204 is symmetric the selection rules derived from the factor group analysis of the oxalate chain show that only two skeletal stretching vibrations of this chain are infrared active. In the spectrum of N2H5HC204, they have been identified at 1’748 (uC=O) and 1349 (UC-O) cm-l. Furthermore, there is a very strong absorption between 1300 and 300 cm-l on which sharper bands are superimposed. This broad absorption with a maximum near 650 cm-l is assigned to the OH stretching vibration of a symmetrical 0. . H. . 0 hydrogen bond. The above considerations can be applied to the spectra of N2H5HC204 at room temperature as well as at liquid nitrogen temperature. A comparison of the infrared spectra at 300 and -18oOC shows that, apart from the usual band sharpening, the principal differences concern the 2660 (NH+. .N) and 850 (OHO) cm-l bands
1569
I
and in nujol
freryuencies, 2550 and 650 respectively on cooling the crystal (table 1)‘. The main structural pattern remains thus probably similar while the band shifts may indicate some shortening of the intrachain, NEl+. . N and 0. . H. . 0 hydrogen-bond distances at low temperature. The behaviour of the vOH band at whi_clh shift to lawer IX-
1180 cm-l which shifts about 40 cm-1 towards higher wave-numbers on cooling appears consistent with the assumed contraction of the ca-
tionic chains. The crystalline structure of N2D5DC2O4 is not known. However, the spectrum of the deuterated (about 908) crystal at -18OoC (fig. 1) cannot be interpreted in the same way as that of N2H5HC204. Instead of a single uC=O band there is a doublet at 1723 and 1671 cm-1 and a new band appears at 1436 cm-l. The broad z.iiE! strong absorption near 650 cm-i disappears and no equivalent is observed at lower frequencies down to 200 cm-l. One finds two weaker and illdefined absorptions at higher frauencies instead: the first one is probably confined between 85
Volume 3, number 2
Stretching frequencies Assignment
Table 1 and bond distances of the hydrogen bonded groups in hydrazinium hydrogen oxalate crystal. Frequencies
t [cm-l]
Distances [A] N2H5HC204 (ref. 3,4)
V/V’ $
N2HgHG 204 3ooc -1aooc
N2D5m204 3ooc -180°C
(NH2&NH2
3357
3369
2510
2517
1.34
(NH2) vsNH2
3292
3299
2421
2424
1.36
,‘NH;)mH
3050
3030
2290
2300
1.32
-
February. 1969
CHEMICAL PHYSICS LETTERS
25OC rA-H
-18OOC 1.00
RA..B (N-H)
3.12 2.99 1
1.02
(N-H)
2.89 2.87 I
(NH$‘NH (OHO) uOH
2660
2550
850
650
2066
1980
1.29
1600
N..O
N..O
1.04
(N-H)
2.87
N..N
1.225
(G-H)
2.45
0.. 0
quency shifts accompanying the transition of a symmetric hydrogen bond into an asymmetric one have already been observed [7,8]. Crystalline potassium hydrogen bisphenylacetate for instance
shows the vOH absorption
centered
near
1000 cm-l; this band shifts to 2450 cm-l on melting of the crystal [7]. The isotope effect on the hydrogen bonds of 86
the hydrazinium ion chains does not change the type of these bonds. The isotopic frequency ratios of the vNH bands decrease with increasing strength of the hydrogen bonding (table I); the low v/v’ ratio (1.29) of the vNH frequency associated with the NH+. . N intrachain hydrogen bond may indicate some expansion of this bond upon cieuteration. On the contrary, the symmetric hydrogen bond of the hydrogen oxalate chains appears to become asymmetric when hydrogen is substituted by deuterium. This implies that there is a phase transition of the hydrazinium hydrogen oxalate crystal at low temperature caused by the isotope effect.
REFERENCES 1. W. C. Hamilton and J. A. Ihers, Hydrogen Bonding in Solids (W. A. Benjamin, New York, 1968) pp. 104, 121. 2. C. C. Cost& and G. P. Srivastava, J. Chem. Phys. 41 (1964) 1620. 3. N. A. K. Ahned, R. Liminga and I. Olovsson. Acta Chim. Scancl. 22 (1968) 88. 4. A. Nilsson, R. Liminga and I. Olovsson, Acta Chim. &and. 22 (1968) 719. K.Sakurai and Y.Tomiie. Acta Cry&. 5 (1952) 293. ii:H. H. Mills and J. C. Speakman, J. Chem. Sot. (1963) 4355; L. Manojlovid and J. C. Speakmen, Acta Cryst. B24 (1968) 323. 7. D. Had% and A. Novak, Spectrochim. Acta 18 (1962) 1059. 8. D. HadZi and A. Novak, Proc. Chem. Sot. (1960) 241.
CHEMICAL PHYSICS LETTERS
ISOTOPE
EFFECT
AND
HYDRAZINIUM
HYDROGEN
BONDING
HYDROGEN J. LINDGREN,
Laboratoire
de Chimie
February
IN
OXALATE,
1969
CRYSTALLINE
N2H5HC204
J. DE VILLEPIN
Physique
du C.N.R.S.,
94 Thiais
and A. NOVAK Laboratoire
de Specfvochimie
Molkulaire,
Facultl
des Sciences
de Paris,
France
Received 13 January 1969 Infrared speatra>of hydrazinium hydrogen oxalate, N2H6HC20a, and of its deuterated derivative, N2D6DC20 , have heemstudied at liquid nitrogen temperature in the 3600 to 200 cm-1 range. It appears that t%e symmetric 0.. H.. 0 hydrogen bond of the hydrogen oxslate chains becomes asymmetric when hydkgen is substituted by de&r&.
A positive isotope effect, i.e., the OD.. 0 distance is longer than the OH. . 0 distance, has been observed for a few hydrogen bonded systems [ 1,2] ,a”d is particularly large for short (2.40-2.60 A) hydrogen bonds such as are found in HCrO2 and HCo02 [l]. Infrared studies of these two compounds showed that the OH stretching frequency is lower than its OD analog and that the former is a singlet whel’zas the latter is a doublet. Snyder and Ibers [l] have interpreted these results in terms of different hydrogen-bond potential functions for the two isotopic species. In this communication we report the infrared spectra of hydrazinium hydrogen oxalatc and its deuterated derivative which appear to indicate that the symmetrical 0. . H. . 0 hydrogen bond becomes asymmetrical upon deuteration. The crystal structure of N2H5HC204 has been determined [3,4]. The hydrazinium ions, N2H$+, are linked into infinite zig-zag chains by NH+. . N hydrogen bonds and the hydrogen oxalate ions, HC2O4-, form infinite planar chains by short 0.. H.. 0 hydrogen bonds. The two types of chains are cross-linked by NH.. 0 bonds. Several kinds of hydrogen bonds can thus be clistinguished in ‘&is crystal (table 1). There are . weak, medium-to-strong, and very stror.g hydrogen bonds of the NH2, NH3+, and OH0 groups respectivey. Ths 0.. H.. 0 bond (2.45 A) is either symmetrical with the hydrogen at the center of sjrmmetry or there is a disordered arrangement [3,4j. -84
The infrared spectrum of N2HgHC204 shown in fig. 1 is consistent with the description of NH+. . N and NH.. 0 hydrogen bonds and supports the symmetrical 0.. H. . 0 hydrogen bond. The NH stretching bands are observed in the 36002000 cm-1 region and the absorption pattern is similar to that of solid N2H5Cl containing chains of N2Hgf ions [5] recorded for comparison. The assignment of the narrow bands at 3369 and 3299 cm-l to the antisymmetric and symmetric stretching vibrations of the weakly bonded NH2 group is straightforward (table 1). Two broad and strong bands near 3030 and 2550 cm-l, on the other hand, can be associated with the stretching vibrations of the NH3+ group which forms medium-strong interchain NH+. . 0 and strong intrachain NH+. . N h drogen bonds characterized by shorter (1.02 P ) and longer (1.04 A) N-H distances re ectively. It is thus likely that the high 3030 cm-? frequency corresponds to the
former
and the low 2550 cm-l frequency to the (table 1). The subband structure of these two absorptions is probably due to combinations and overtones. This interpretation implies that there is no OH stretching band in the 3600-2000 cm-l region. In fact, for the intermolecular hydrogen bonds of the acid salt type, (-COQHOOC-), for which it seems probable that the hydrogen atom is truly centered [S] three characteristic spectral features have been observed [?I: the existence of a single uC=O band due to the equivalent COO groups, the presence of a strong and latier
Volume 3, number 2
CHEMICAL
PHYSICS LETTERS
1600
x200
February
mo
Fig. 1. Infrared spectra of: (a) N2HsC204; (b) N2DgDC204; mulls in fluorolube (3600-1300 cm-l) (1300-200 cm-L) at liquid nitrogen temperature.
very broad absorption, usually between 3600 and 300 cm-l, and the absence of any vOH band above 1300 cm-l. If the O-H-O hydrogen bond in N2H5HC204 is symmetric the selection rules derived from the factor group analysis of the oxalate chain show that only two skeletal stretching vibrations of this chain are infrared active. In the spectrum of N2H5HC204, they have been identified at 1’748 (uC=O) and 1349 (UC-O) cm-l. Furthermore, there is a very strong absorption between 1300 and 300 cm-l on which sharper bands are superimposed. This broad absorption with a maximum near 650 cm-l is assigned to the OH stretching vibration of a symmetrical 0. . H. . 0 hydrogen bond. The above considerations can be applied to the spectra of N2H5HC204 at room temperature as well as at liquid nitrogen temperature. A comparison of the infrared spectra at 300 and -18oOC shows that, apart from the usual band sharpening, the principal differences concern the 2660 (NH+. .N) and 850 (OHO) cm-l bands
1569
I
and in nujol
freryuencies, 2550 and 650 respectively on cooling the crystal (table 1)‘. The main structural pattern remains thus probably similar while the band shifts may indicate some shortening of the intrachain, NEl+. . N and 0. . H. . 0 hydrogen-bond distances at low temperature. The behaviour of the vOH band at whi_clh shift to lawer IX-
1180 cm-l which shifts about 40 cm-1 towards higher wave-numbers on cooling appears consistent with the assumed contraction of the ca-
tionic chains. The crystalline structure of N2D5DC2O4 is not known. However, the spectrum of the deuterated (about 908) crystal at -18OoC (fig. 1) cannot be interpreted in the same way as that of N2H5HC204. Instead of a single uC=O band there is a doublet at 1723 and 1671 cm-1 and a new band appears at 1436 cm-l. The broad z.iiE! strong absorption near 650 cm-i disappears and no equivalent is observed at lower frequencies down to 200 cm-l. One finds two weaker and illdefined absorptions at higher frauencies instead: the first one is probably confined between 85
Volume 3, number 2
Stretching frequencies Assignment
Table 1 and bond distances of the hydrogen bonded groups in hydrazinium hydrogen oxalate crystal. Frequencies
t [cm-l]
Distances [A] N2H5HC204 (ref. 3,4)
V/V’ $
N2HgHG 204 3ooc -1aooc
N2D5m204 3ooc -180°C
(NH2&NH2
3357
3369
2510
2517
1.34
(NH2) vsNH2
3292
3299
2421
2424
1.36
,‘NH;)mH
3050
3030
2290
2300
1.32
-
February. 1969
CHEMICAL PHYSICS LETTERS
25OC rA-H
-18OOC 1.00
RA..B (N-H)
3.12 2.99 1
1.02
(N-H)
2.89 2.87 I
(NH$‘NH (OHO) uOH
2660
2550
850
650
2066
1980
1.29
1600
N..O
N..O
1.04
(N-H)
2.87
N..N
1.225
(G-H)
2.45
0.. 0
quency shifts accompanying the transition of a symmetric hydrogen bond into an asymmetric one have already been observed [7,8]. Crystalline potassium hydrogen bisphenylacetate for instance
shows the vOH absorption
centered
near
1000 cm-l; this band shifts to 2450 cm-l on melting of the crystal [7]. The isotope effect on the hydrogen bonds of 86
the hydrazinium ion chains does not change the type of these bonds. The isotopic frequency ratios of the vNH bands decrease with increasing strength of the hydrogen bonding (table I); the low v/v’ ratio (1.29) of the vNH frequency associated with the NH+. . N intrachain hydrogen bond may indicate some expansion of this bond upon cieuteration. On the contrary, the symmetric hydrogen bond of the hydrogen oxalate chains appears to become asymmetric when hydrogen is substituted by deuterium. This implies that there is a phase transition of the hydrazinium hydrogen oxalate crystal at low temperature caused by the isotope effect.
REFERENCES 1. W. C. Hamilton and J. A. Ihers, Hydrogen Bonding in Solids (W. A. Benjamin, New York, 1968) pp. 104, 121. 2. C. C. Cost& and G. P. Srivastava, J. Chem. Phys. 41 (1964) 1620. 3. N. A. K. Ahned, R. Liminga and I. Olovsson. Acta Chim. Scancl. 22 (1968) 88. 4. A. Nilsson, R. Liminga and I. Olovsson, Acta Chim. &and. 22 (1968) 719. K.Sakurai and Y.Tomiie. Acta Cry&. 5 (1952) 293. ii:H. H. Mills and J. C. Speakman, J. Chem. Sot. (1963) 4355; L. Manojlovid and J. C. Speakmen, Acta Cryst. B24 (1968) 323. 7. D. Had% and A. Novak, Spectrochim. Acta 18 (1962) 1059. 8. D. HadZi and A. Novak, Proc. Chem. Sot. (1960) 241.