Cooperative assistance in a very short O-H···O, hydrogen bond. Low-temperature X-ray crystal structures of 2,3,5,6-pyrazinetetracarboxylic and related acids

Article abstract of DOI:10.1039/b007346f

In contrast to the well documented role of charge- and resonance-assistance in very short hydrogen bonds, a very short O-H_acid···O_water hydrogen bond [O···O 2.4791(13) A] in the title acid is ascribed to the cumulative stabilisation from σ- and π-bond cooperativity.

Full text of DOI:10.1039/b007346f

Cooperative assistance in a very short O–H···O hydrogen bond.
Low-temperature X-ray crystal structures of 2,3,5,6-pyrazinetetracarboxylic
and related acids
a
a
b
Peddy Vishweshwar, Ashwini Nangia* and Vincent M. Lynch
a
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India. E-mail: ansc@uohyd.ernet.in
Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712, USA
b
Received (in Columbia, MO, USA) 30th August 2000, Accepted 7th November 2000
First published as an Advance Article on the web 4th January 2001
3
In contrast to the well documented role of charge- and
resonance-assistance in very short hydrogen bonds, a very
short O–Hacid…Owater hydrogen bond [O…O 2.4791(13) Å]
in the title acid is ascribed to the cumulative stabilisation
from s- and p-bond cooperativity.
through p-bonds (RAHB) results in unusual bond shortening.
We show here that a composite array with s- and p-bond
cooperativity,
O–H…ONC–O–Hacid…Owater–H…O,
can
shorten an intermolecular O–Hacid…Owater hydrogen bond into
the regime of the very short H-bond (O…O < 2.50 Å). This kind
of H-bond array has been referred to as ‘polarisation enhanced
hydrogen bonding’ by Jeffrey.1a Our example of a very short
hydrogen bond is: (i) intermolecular, (ii) not of the charge-
Very short (very strong) O–H…O hydrogen bonds are formed
with unusually activated donors and acceptors, as between an
–
4
5
acid and its conjugate base (O–H…O ) or in the hydrates of
assisted type, (iii) not of the acid–conjugate-base type and (iv)
+
6
strong acids (O –H…O). With H…O distances in the range
does not contain highly activated donor/acceptor groups.
1
.2–1.5 Å (O…O 2.2–2.5 Å), very short H-bonds have a
Recrystallisation of 2,3,5,6-pyrazinetetracarboxylic acid 1†
from 20% aqueous HCl afforded diffraction quality crystals of
the dihydrate. Low-temperature (123 K) single crystal X-ray
significant covalent component (O–H ≈ H…O) and bond
energies in the range 15–40 kcal mol . The substantial
covalent character of very short H-bonds, a result of three-
centre–four-electron contribution, O – H… O Ô O …H – O,
is responsible for their distinctive properties: the near linear
geometry (q = 170–180°), the lengthening of O–H distance (up
to 0.2 Å) and the very large IR bathochromic shifts (up to 2000
2
1
¯
2
analysis of 1·2H O (P1, Z = 1)‡ showed it to contain a very
•
•
••
••
• •
short O–Hacid…Owater H-bond [d = 1.50 Å, D = 2.4791(13) Å,
q = 170.3°]§ that is part of cooperative array I [Figs. 1 and
2(a)]. In this very short H-bond, both the carboxylic acid O–H
donor ability and the water O atom acceptor basicity are
simultaneously enhanced through polarisation, as shown in Fig.
2(b). Such a strong polarising effect involving water was noted
2
1
1
cm in n
s
). Typical examples are the intramolecular hydrogen
2
bonds in monobasic salts of dicarboxylic acids. Very strong
hydrogen bonds are relevant in the context of proton transfer
phenomena in chemical and biological systems and they have
been studied with spectroscopic, crystallographic and computa-
tional methods.1a The overall picture that emerges from such
studies is that very short H-bonds have a quasi-covalent
character. This is in contrast to strong hydrogen bonds (H…O
3 2
recently in the complex, Ph PNO–1,4-diethynylbenzene–H O
7
(4+1+2). The other O–H…O/N bonds in the crystal are in the
short to medium range (Table 1).
In order to probe such a polarisation-induced H-bond
shortening in related acids, the crystal structures of pyrazine-
2,3-dicarboxylic acid 2 and 5,6-dimethylpyrazine-2,3-dicar-
2
1
1
.5–2.2 Å, O…O 2.5–3.2 Å, energy 4–15 kcal mol ) that are
1b
largely electrostatic in nature.
In addition to charge-assisted hydrogen bonding (CAHB: O–
–
+
H…O , O –H…O) in carboxylic acids, very short hydrogen
bonds have been observed in the neutral b-diketone enol
fragment, …ONC–CNC–OH…, wherein resonance-assistance
Fig. 1 Crystal structure of tetra-acid 1 showing the cooperative O–H…O
synthon I. The water molecule acts as a H-bond donor to the CO
2
H group
Fig. 2 (a) Cooperative synthon I in tetra-acid 1. The acid group marked # is
of the next layer (shaded differently). Metrics of the very short O–H…O
bond are indicated. Displacement ellipsoids are drawn at the 50%
probability level for non-H atoms.
2
replaced with H O in diacids 2 and 3. (b) Donor and acceptor groups
enhanced by polarisation in I. (c) Tautomer synthons IA and IB (not
observed).
DOI: 10.1039/b007346f
Chem. Commun., 2001, 179–180
This journal is © The Royal Society of Chemistry 2001
179

Table 1 Geometry of O–H…O/N hydrogen bonds and C–O bond lengths
Acid
Hydrogen bond geometry
O–H…O
O–H…N
O–H/Å
0.85(3)
Bond length
C–O/Å
O–H/Å
D/Å
da/Å
q/°
D/Å
da/Å
q/°
CNO/Å
1b
0.96(3)
2.4791(13)
2.7010(12)
2.7811(12)
2.562
2.922
2.5269(12)
2.8747(12)
1.50
1.74
1.80
1.58
2.04
1.55
1.92
170.3
162.6
171.9
170.9
147.4
167.2
162.4
2.9393(16)
2.01
156.1
1.3113(17)
1.2957(16)
1.2022(15)
1.2174(14)
0
0
.91(2)
.89(2)
2c
3b
a
1.05
.86
0.968(18)
.872(18)
0.73
2.840
1.87
1.97
166.4
155.1
1.304
1.208
0
0.87(2)
2.8963(13)
1.3143(13)
1.2122(13)
0
d Values are neutron-normalised (O–H 0.983 Å). b This work. c Ref. 8.
boxylic acid 3 were analysed. Diacid 2 is reported as a dihydrate
into the very strong regime. This study adds to our knowledge
of the traditional H-bond shortening phenomena, namely
through charge- and resonance-assistance.
A. N. thanks the DST for research funding (SP/S1/G29/98).
V. M. L. thanks the NSF (CHE-9807702) for support. We thank
Professor Gautam R. Desiraju for suggestions.
8
(
C2/c). Diacid 3 was also determined to be a dihydrate by low-
temperature X-ray diffraction (Pbcn).‡ Both these crystal
structures contain synthon I with O…O distances in the short
2 2
(strong) regime [2·2H O 2.562, 3·2H O 2.5269(12) Å]. The
very short O–H…O bond in 1 compared to the short bond in 2
and 3 may be rationalised through differences in their extended
arrays: the CO
replaced by H
H…O bond in 3 compared to 2 could be because the donor O–
acid is more polarised by the stronger O–Hwater…O = C–O–H
2
H donor in 1 [marked with # in Fig. 2(a)] is
O in 2 and 3. The relative shortness of the O–
2
Notes and references
H
†
4
Synthesis: tetra-acid 1: oxidation of phenazine with KMnO (R. J. Light
bond in 3 [2.922 vs. 2.8747(12) Å].
and C. R. Hauser, J. Org. Chem., 1961, 26, 1296). Diacid 3: by the oxidation
of 2,3-dimethylquinoxaline under identical conditions.
Another reason for the very short O–Hacid…Owater bond in
tetra-acid 1 compared to the short H-bond in diacids 2 and 3 is
the presence of twice as many electron-withdrawing groups in
‡ Crystal data: tetra-acid 1: 2,3,5,6-pyrazinetetracarboxylic acid dihydrate
¯
2
O, M = 292.16); triclinic, space group P1, a = 5.4409(3),
8 4 2 8
(C H N O ·2H
b = 6.4041(3), c = 8.6995(3) Å, a = 98.572(3), b = 107.374(3), g =
2
the former structure. Thus, molecular (4 CO H groups on a N-
3
23
1
05.519(3)°, V = 269.97(2) Å , Z = 1, D
CCD area detector, T = 123 K, m = 0.171 mm , l(Mo-Ka) = 0.71073 Å,
w scan mode, 1219 unique reflections, 1125 with F 4s(F ), no
c
= 1.797 Mg m , Nonius Kappa
heterocycle) and supramolecular (extended cooperative array I)
features act in concert, resulting in the very short O–H…O bond
in 1. An analysis of the Cambridge Structural Database (April
21
o
>
o
absorption corrections. Structure solution and refinement with standard
methods (SHELX97); H-atoms refined isotropically. Final R = 0.030
2 2
2000 update) substantiates our observation. While CO H…OH
H-bonding is present in many carboxylic acids (ca. 150 contacts
in the range O…O 2.40–2.80 Å),¶ the very short H-bond region
(obs.), 0.032 (all); wR(F
Diacid 3: 5,6-dimethylpyrazine-2,3-dicarboxylic acid dihydrate
·2H O, M = 232.19); orthorhombic, space group Pbcn; a =
2.6454(3), b = 9.0812(3), c = 8.8800(3) Å, V = 1019.74(5) Å , Z = 4,
2
) = 0.080 (obs.), 0.082 (all).
(
< 2.50 Å) contains mostly the oxalic acid dihydrates (11/13).
In these crystal structures, activation of the donor O–H in the
,2-dicarboxylic acid moiety results in very short O–Hacid···O-
(C
1
H N O
8 8 2 4
2
3
23
D
0
c
= 1.512 Mg m , Nonius Kappa CCD area detector, T = 123 K, m =
1
21
.131 mm , l(Mo-Ka)
=
0.71073 Å, w scan mode, 1161 unique
water bonds, a point not mentioned in the original publica-
reflections, 1059 with F
o
> 4s(F ), no absorption corrections. Structure
o
tions.9
solution and refinement with standard methods (SHELX97); H-atoms
refined isotropically. Final R = 0.031 (obs.), 0.034 (all); wR(F ) = 0.084
A novel feature of this work is the influence on H-bond
shortening of cooperative stabilisation, a phenomenon hitherto
2
(obs.), 0.086 (all). CCDC 182/1850. See http://www.rsc.org/suppdata/cc/
1
–6
not discussed in the extensive literature
on very short
b0/b007346f/ for crystallographic files in .cif format.
§ d Values in this study are neutron-normalised (O-H 0.983 Å).
¶ Screens 228, 35, 255, 57, 85, 88, 153 were applied. Organometallic
crystal structures were excluded.
hydrogen bonds. Once again, akin to polarisation by water,7
precedent for H-bond shortening through cooperative assistance
comes from the weak C–H…O category, namely 2-ethynylada-
mantan-2-ol.10 The presence of two types of CO
∑ See ref. 1(a), p. 222.
2
H groups in
the same crystal, one that engages in a very short H-bond and
the other with a normal H-bond, permits an assessment of O–H
bond lengthening (Table 1). Thus, the very short O–H…O bond
in 1 displays the expected characteristics: near linear geometry
1 (a) G. A. Jeffrey, An Introduction to Hydrogen Bonding, OUP, Oxford,
1997; (b) G. R. Desiraju and T. Steiner, The Weak Hydrogen Bond in
Structural Chemistry and Biology, OUP, Oxford, 1999, ch. 1.
2
M. Currie and J. C. Speakman, J. Chem. Soc. A, 1970, 1923.
(
s
q = 170.3°), O–H lengthening (0.1 Å) and O–H n in
2
1
3 P. Gilli, V. Bertolasi, V. Ferretti and G. Gilli, J. Am. Chem. Soc., 1994,
agreement with the reported correlation (1398 cm ).∑
1
1
16, 909; V. Bertolasi, P. Gilli, V. Ferretti and G. Gilli, Chem. Eur. J.,
996, 2, 925.
In order that our s- and p-bond cooperativity argument
through synthon I is tenable, the presence of tautomers IA and IB
in tetra-acid 1 [Fig. 2(c)] must be rigorously excluded, because
such motifs would contribute towards resonance stabilisation (I
Ô IAÔ IB), and in effect negate the present hypothesis.
Carboxylic acid groups may be characterised as CNO and C–O
or as a delocalised carboxylate by their single and double bond
4
5
D. Braga, L. Maini, F. Grepioni, A. D. Cian, O. Félix, J. Fischer and
M. W. Hosseini, New J. Chem., 2000, 24, 547.
T. Steiner, A. M. M. Schreurs, M. Lutz and J. Kroon, Acta Crystallogr.,
Sect. C, 2000, 56, 577.
6 T. Steiner, C. C. Wilson and I. Majerz, Chem. Commun., 2000, 1231.
7 B. M. Kariuki, K. D. M. Harris, D. Philp and J. M. A. Robinson, J. Am.
Chem. Soc., 1997, 119, 12 679.
lengths.11 A difference of > 0.1 Å implies a static CO
2
H group
8
9
F. Takusagawa and A. Shimada, Chem. Lett., 1973, 1121.
Y. Wang, C. J. Tsai, W. L. Liu and L. D. Calvert, Acta Crystallogr.,
Sect. B, 1985, 41, 131; D. Zobel, P. Luger, W. Dreissig and T.
Koritsanszky, Acta Crystallogr., Sect. B, 1992, 48, 837.
while a smaller difference ( < 0.02 Å) means a resonating or
disordered carboxylate. The > 0.1 Å difference between C–O
and CNO bond distances in 1–3 (Table 1) confirms that synthon
I is present in their crystal structures, and not a resonance-
stabilised motif.
1
0 F. H. Allen, J. A. K. Howard, V. J. Hoy, G. R. Desiraju, D. S. Reddy and
C. C. Wilson, J. Am. Chem. Soc., 1996, 118, 4081.
In summary, we have shown that polarisation through a finite
s- and p-bond cooperative array can shorten an O–H…O bond
11 D. A. Diedrich, I. C. Paul and D. Y. Curtin, J. Am. Chem. Soc., 1974, 96,
6372.
180
Chem. Commun., 2001, 179–180