Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S160053680703139X/hb2459sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S160053680703139X/hb2459Isup2.hkl |
CCDC reference: 657666
Key indicators
- Single-crystal X-ray study
- T = 297 K
- Mean (C-C) = 0.002 Å
- R factor = 0.043
- wR factor = 0.122
- Data-to-parameter ratio = 15.0
checkCIF/PLATON results
No syntax errors found
Alert level A PLAT353_ALERT_3_A Long N-H Bond (0.87A) N1 - H1A ... 1.41 Ang.
Author Response: There is a symmetrical intra-molecular hydrogen bond between the N1 and N3 atoms. |
PLAT353_ALERT_3_A Long N-H Bond (0.87A) N3 - H1A ... 1.28 Ang.
Author Response: There is a symmetrical intra-molecular hydrogen bond between the N1 and N3 atoms. |
PLAT771_ALERT_2_A Suspect N-H Bond in CIF: N1 -H1A .. 1.41 Ang.
Author Response: There is a symmetrical intra-molecular hydrogen bond between the N1 and N3 atoms. |
Alert level C PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low ....... 0.97 PLAT041_ALERT_1_C Calc. and Rep. SumFormula Strings Differ .... ? PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ .... ? PLAT045_ALERT_1_C Calculated and Reported Z Differ by ............ 2.00 Ratio
Alert level G PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints ....... 2
3 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 4 ALERT level C = Check and explain 1 ALERT level G = General alerts; check 3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 1 ALERT type 2 Indicator that the structure model may be wrong or deficient 4 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check
For related literature, see: Bertolasi et al. (1996, 2001); Farrugia (1999); Gilli & Gilli (2000); Gilli et al. (1994); Köroglu et al. (2005); Liebeskind et al. (1993); Mathew et al. (2002); Reetz et al. (1994); Seitz & Imming (1992); Steiner et al. (2000); Uçar et al. (2004, 2005).
Compound (I) was prepared by mixing squaric acid and 2,2'dipyridilamine in a 1:2 molar ratio in a mixed solution of methanol and water (1:1 v/v, 50 ml), with stirring at 333 K for 1 h. Crystals of (I) were obtained by slow evaporation of the solvent in about a week. The crystals wre filtered off, washed with methanol and dried in vacuo.
H atoms attached to C atoms and amine N atoms were placed in calculated positions (N—H = 0.86 Å, C—H = 0.93 Å) and refined as riding with Uiso(H) = 1.2Ueq(C). The remaining H atoms were located in a difference map. The H atoms of water molecule were refined with the O—H distance restrained to 0.82 (2) Å.
Squaric acid, H2Sq, is a very strong dibasic acid and has been studied for potential application to xerographic photoreceptors, organic solar cells and optical recording (Seitz & Imming, 1992; Liebeskind et al., 1993). It is also a useful tool for constructing crystalline architecture because of its rigid and flat four-membered ring framework (Reetz et al., 1994). Squaric acid (H2Sq) can be found in three forms, viz. (a) as uncharged H2Sq, (b) as the HSq- monoanion and (c) as Sq2- dianions on deprotonation by amines. These forms have been observed to crystallize with various types of hydrogen bonding, as summarized by Bertolasi et al. (2001). Our ongoing research on metallic and organic salts of squaric acid (Uçar et al., 2004; Uçar et al., 2005; Köroglu et al., 2005), we have synthesized the title compounds, (I), in which the dianion form of squaric acid is observed.
Each squaric acid molecule donates both its H atoms to the pyridine N atom of two 2,2'dipyridylamine molecules, forming the bis(2,2'dipyridiniumamine) squarate dihydrate salt. The C4O42- anion is centrosymmetric. (Fig. 1). The most noteworthy aspect of the structure of (I) concerns the hydrogen bonding (Table 1). Intermolecular hydrogen bonding is conventional (in terms of geometry), with each of the H atoms being donated. However, the N—H···N intramolecular hydrogen bond associated with the pyridine nitrogen atoms has much more unusual behaviour. The freely refined N—H bond length of 1.28 (2)Å is very long for an N—H covalent bond, which would be expected to be around 0.87Å in an X-ray crystallographic analysis. Consequently, the H···N distance is 1.42 (2) Å, whic is rather short. Given that the overall N···N distance is relatively short at 2.586 (2) Å, these values indicate a strong hydrogen bond, which nevertheles display unusual disorder or thermal motion. A difference Fourier map (Fig. 2; Farrugia, 1999) of the electron density associated with this H atom shows this to be smeared out between the dipyridinium N atoms, with the maximum lying closer to the N3 atom. These type hydrogen bonds have been called "positive charge assisted hydrogen bonds (N+—H···N or N···H—N+)" by Gilli and co-workers [Gilli et al., 1994; Bertolasi et al., 1996; Gilli & Gilli, 2000;] and found in organic amines and carboxylic acids [Steiner et al., 2000; Mathew et al., 2002].
In the crystal of (I), both intermolecular H bonds and van der Waals interactions combine to stabilize the extended structure (Fig. 3). The crystal water molecule and amine nitrogen atom link cations to dianions, acting as hydrogen-bond donors to the squarate oxygen atoms. These interactions mediate the formation of chains in the ac plane (Fig. 3) and adjacent chains are linked by van der Waals interactions.
For related literature, see: Bertolasi et al. (1996, 2001); Farrugia (1999); Gilli & Gilli (2000); Gilli et al. (1994); Köroglu et al. (2005); Liebeskind et al. (1993); Mathew et al. (2002); Reetz et al. (1994); Seitz & Imming (1992); Steiner et al. (2000); Uçar et al. (2004, 2005).
Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
2C10H10N3+·C4O42−·2H2O | Z = 1 |
Mr = 492.50 | F(000) = 258.0 |
Triclinic, P1 | Dx = 1.477 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71069 Å |
a = 8.072 (2) Å | Cell parameters from 1875 reflections |
b = 8.493 (3) Å | θ = 2.6–27.8° |
c = 8.833 (2) Å | µ = 0.11 mm−1 |
α = 74.34 (3)° | T = 297 K |
β = 87.26 (2)° | Block, colourless |
γ = 71.85 (4)° | 0.35 × 0.24 × 0.18 mm |
V = 553.6 (3) Å3 |
Stoe IPDS II diffractometer | 2634 independent reflections |
Radiation source: fine-focus sealed tube | 2027 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.035 |
Detector resolution: 6.67 pixels mm-1 | θmax = 28.2°, θmin = 2.6° |
ω scans | h = −9→10 |
Absorption correction: integration (X-RED32; Stoe & Cie, 2002) | k = −11→11 |
Tmin = 0.947, Tmax = 0.981 | l = −11→11 |
6024 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.044 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.122 | w = 1/[σ2(Fo2) + (0.0672P)2 + 0.0549P] where P = (Fo2 + 2Fc2)/3 |
S = 1.02 | (Δ/σ)max < 0.001 |
2634 reflections | Δρmax = 0.27 e Å−3 |
176 parameters | Δρmin = −0.20 e Å−3 |
2 restraints | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.079 (12) |
2C10H10N3+·C4O42−·2H2O | γ = 71.85 (4)° |
Mr = 492.50 | V = 553.6 (3) Å3 |
Triclinic, P1 | Z = 1 |
a = 8.072 (2) Å | Mo Kα radiation |
b = 8.493 (3) Å | µ = 0.11 mm−1 |
c = 8.833 (2) Å | T = 297 K |
α = 74.34 (3)° | 0.35 × 0.24 × 0.18 mm |
β = 87.26 (2)° |
Stoe IPDS II diffractometer | 2634 independent reflections |
Absorption correction: integration (X-RED32; Stoe & Cie, 2002) | 2027 reflections with I > 2σ(I) |
Tmin = 0.947, Tmax = 0.981 | Rint = 0.035 |
6024 measured reflections |
R[F2 > 2σ(F2)] = 0.044 | 2 restraints |
wR(F2) = 0.122 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.02 | Δρmax = 0.27 e Å−3 |
2634 reflections | Δρmin = −0.20 e Å−3 |
176 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.1787 (2) | −0.0003 (2) | 0.20087 (18) | 0.0525 (4) | |
H1 | 0.1856 | 0.0817 | 0.1086 | 0.063* | |
C2 | 0.1266 (2) | −0.1349 (2) | 0.1916 (2) | 0.0562 (4) | |
H2 | 0.1019 | −0.1468 | 0.0942 | 0.067* | |
C3 | 0.1108 (2) | −0.2539 (2) | 0.3286 (2) | 0.0518 (4) | |
H3 | 0.0732 | −0.3457 | 0.3243 | 0.062* | |
C4 | 0.15007 (19) | −0.23637 (18) | 0.46912 (19) | 0.0440 (3) | |
H4 | 0.1387 | −0.3145 | 0.5625 | 0.053* | |
C5 | 0.20815 (17) | −0.09827 (17) | 0.47064 (16) | 0.0372 (3) | |
C6 | 0.30437 (17) | 0.05217 (16) | 0.63285 (16) | 0.0367 (3) | |
C7 | 0.3349 (2) | 0.05677 (19) | 0.78463 (17) | 0.0436 (3) | |
H7 | 0.3259 | −0.0310 | 0.8710 | 0.052* | |
C8 | 0.3784 (2) | 0.1927 (2) | 0.8039 (2) | 0.0519 (4) | |
H8 | 0.3975 | 0.1990 | 0.9048 | 0.062* | |
C9 | 0.3944 (2) | 0.3214 (2) | 0.6754 (2) | 0.0535 (4) | |
H9 | 0.4246 | 0.4142 | 0.6884 | 0.064* | |
C10 | 0.3654 (2) | 0.30938 (19) | 0.5314 (2) | 0.0495 (4) | |
H10 | 0.3760 | 0.3954 | 0.4440 | 0.059* | |
C11 | 0.38626 (17) | 0.57812 (16) | −0.05777 (14) | 0.0344 (3) | |
C12 | 0.43433 (18) | 0.42336 (17) | 0.07214 (15) | 0.0371 (3) | |
N1 | 0.22009 (17) | 0.01827 (15) | 0.33788 (14) | 0.0430 (3) | |
N2 | 0.25340 (16) | −0.07779 (14) | 0.60874 (13) | 0.0392 (3) | |
H2A | 0.2493 | −0.1574 | 0.6917 | 0.047* | |
N3 | 0.32133 (16) | 0.17666 (14) | 0.50969 (14) | 0.0415 (3) | |
O1 | 0.24748 (14) | 0.67258 (13) | −0.12805 (13) | 0.0494 (3) | |
O2 | 0.35589 (16) | 0.33000 (16) | 0.15768 (15) | 0.0639 (4) | |
O3 | 0.0043 (2) | 0.4689 (2) | 0.2011 (2) | 0.0858 (5) | |
H3A | −0.058 (3) | 0.426 (3) | 0.163 (3) | 0.088 (8)* | |
H3B | 0.105 (3) | 0.435 (3) | 0.171 (3) | 0.095 (8)* | |
H1A | 0.282 (3) | 0.132 (2) | 0.392 (2) | 0.064 (5)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0580 (10) | 0.0630 (10) | 0.0364 (7) | −0.0161 (8) | 0.0007 (7) | −0.0158 (7) |
C2 | 0.0512 (9) | 0.0726 (11) | 0.0480 (9) | −0.0113 (8) | −0.0037 (7) | −0.0297 (8) |
C3 | 0.0442 (8) | 0.0512 (8) | 0.0648 (10) | −0.0109 (7) | −0.0037 (7) | −0.0270 (7) |
C4 | 0.0410 (8) | 0.0397 (7) | 0.0498 (8) | −0.0097 (6) | −0.0012 (6) | −0.0125 (6) |
C5 | 0.0327 (7) | 0.0379 (7) | 0.0375 (7) | −0.0040 (5) | 0.0010 (5) | −0.0123 (5) |
C6 | 0.0325 (6) | 0.0347 (6) | 0.0405 (7) | −0.0050 (5) | 0.0017 (5) | −0.0126 (5) |
C7 | 0.0462 (8) | 0.0453 (7) | 0.0390 (7) | −0.0134 (6) | 0.0009 (6) | −0.0116 (6) |
C8 | 0.0545 (9) | 0.0564 (9) | 0.0519 (9) | −0.0162 (7) | 0.0005 (7) | −0.0269 (7) |
C9 | 0.0591 (10) | 0.0446 (8) | 0.0655 (10) | −0.0202 (7) | 0.0059 (8) | −0.0249 (7) |
C10 | 0.0568 (9) | 0.0376 (7) | 0.0554 (9) | −0.0172 (7) | 0.0075 (7) | −0.0124 (6) |
C11 | 0.0396 (7) | 0.0343 (6) | 0.0293 (6) | −0.0137 (5) | −0.0012 (5) | −0.0055 (5) |
C12 | 0.0409 (7) | 0.0361 (6) | 0.0326 (6) | −0.0146 (5) | 0.0004 (5) | −0.0031 (5) |
N1 | 0.0483 (7) | 0.0452 (6) | 0.0355 (6) | −0.0138 (5) | 0.0023 (5) | −0.0116 (5) |
N2 | 0.0465 (7) | 0.0348 (6) | 0.0340 (6) | −0.0124 (5) | −0.0001 (5) | −0.0052 (4) |
N3 | 0.0472 (7) | 0.0363 (6) | 0.0398 (6) | −0.0117 (5) | 0.0026 (5) | −0.0101 (5) |
O1 | 0.0410 (6) | 0.0464 (6) | 0.0497 (6) | −0.0138 (5) | −0.0091 (5) | 0.0074 (4) |
O2 | 0.0490 (7) | 0.0599 (7) | 0.0655 (8) | −0.0244 (5) | 0.0033 (5) | 0.0200 (6) |
O3 | 0.0617 (9) | 0.1184 (13) | 0.1131 (13) | −0.0447 (9) | 0.0245 (9) | −0.0735 (11) |
C1—N1 | 1.333 (2) | C8—C9 | 1.380 (2) |
C1—C2 | 1.358 (3) | C8—H8 | 0.9300 |
C1—H1 | 0.9300 | C9—C10 | 1.340 (2) |
C2—C3 | 1.382 (3) | C9—H9 | 0.9300 |
C2—H2 | 0.9300 | C10—N3 | 1.3441 (19) |
C3—C4 | 1.353 (2) | C10—H10 | 0.9300 |
C3—H3 | 0.9300 | C11—O1 | 1.2335 (17) |
C4—C5 | 1.395 (2) | C11—C12i | 1.4440 (19) |
C4—H4 | 0.9300 | C11—C12 | 1.4511 (17) |
C5—N1 | 1.3366 (18) | C12—O2 | 1.2426 (16) |
C5—N2 | 1.3596 (18) | C12—C11i | 1.4440 (19) |
C6—N3 | 1.3323 (18) | N1—H1A | 1.415 (19) |
C6—N2 | 1.3605 (18) | N2—H2A | 0.8600 |
C6—C7 | 1.388 (2) | N3—H1A | 1.28 (2) |
C7—C8 | 1.360 (2) | O3—H3A | 0.832 (17) |
C7—H7 | 0.9300 | O3—H3B | 0.834 (17) |
N1—C1—C2 | 122.13 (16) | C10—C9—H9 | 120.8 |
N1—C1—H1 | 118.9 | C8—C9—H9 | 120.8 |
C2—C1—H1 | 118.9 | C9—C10—N3 | 121.90 (15) |
C1—C2—C3 | 119.11 (15) | C9—C10—H10 | 119.0 |
C1—C2—H2 | 120.4 | N3—C10—H10 | 119.0 |
C3—C2—H2 | 120.4 | O1—C11—C12i | 134.52 (12) |
C4—C3—C2 | 119.71 (15) | O1—C11—C12 | 134.30 (13) |
C4—C3—H3 | 120.1 | C12i—C11—C12 | 91.18 (11) |
C2—C3—H3 | 120.1 | O1—C11—C11i | 179.69 (14) |
C3—C4—C5 | 118.45 (15) | C12i—C11—C11i | 45.73 (8) |
C3—C4—H4 | 120.8 | C12—C11—C11i | 45.45 (8) |
C5—C4—H4 | 120.8 | O2—C12—C11i | 135.38 (13) |
N1—C5—N2 | 117.87 (12) | O2—C12—C11 | 135.79 (14) |
N1—C5—C4 | 121.56 (13) | C11i—C12—C11 | 88.82 (11) |
N2—C5—C4 | 120.57 (13) | C1—N1—C5 | 118.99 (13) |
N3—C6—N2 | 119.44 (13) | C1—N1—H1A | 138.1 (8) |
N3—C6—C7 | 120.33 (13) | C5—N1—H1A | 102.9 (8) |
N2—C6—C7 | 120.22 (12) | C5—N2—C6 | 128.48 (12) |
C8—C7—C6 | 118.39 (14) | C5—N2—H2A | 115.8 |
C8—C7—H7 | 120.8 | C6—N2—H2A | 115.8 |
C6—C7—H7 | 120.8 | C6—N3—C10 | 120.29 (13) |
C7—C8—C9 | 120.69 (15) | C6—N3—H1A | 103.3 (8) |
C7—C8—H8 | 119.7 | C10—N3—H1A | 136.4 (8) |
C9—C8—H8 | 119.7 | H3A—O3—H3B | 108 (3) |
C10—C9—C8 | 118.38 (14) | ||
N1—C1—C2—C3 | 2.0 (3) | O1—C11—C12—C11i | 179.75 (19) |
C1—C2—C3—C4 | −1.1 (2) | C12i—C11—C12—C11i | 0.0 |
C2—C3—C4—C5 | −0.9 (2) | C2—C1—N1—C5 | −0.8 (2) |
C3—C4—C5—N1 | 2.1 (2) | N2—C5—N1—C1 | 179.13 (13) |
C3—C4—C5—N2 | −178.34 (13) | C4—C5—N1—C1 | −1.3 (2) |
N3—C6—C7—C8 | 1.4 (2) | N1—C5—N2—C6 | 2.9 (2) |
N2—C6—C7—C8 | −177.22 (14) | C4—C5—N2—C6 | −176.63 (13) |
C6—C7—C8—C9 | −1.0 (2) | N3—C6—N2—C5 | −2.9 (2) |
C7—C8—C9—C10 | 0.3 (3) | C7—C6—N2—C5 | 175.82 (13) |
C8—C9—C10—N3 | 0.1 (3) | N2—C6—N3—C10 | 177.57 (13) |
O1—C11—C12—O2 | 0.8 (3) | C7—C6—N3—C10 | −1.1 (2) |
C12i—C11—C12—O2 | −178.9 (2) | C9—C10—N3—C6 | 0.3 (2) |
C11i—C11—C12—O2 | −178.9 (2) |
Symmetry code: (i) −x+1, −y+1, −z. |
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2A···O1ii | 0.86 | 1.84 | 2.7008 (17) | 178 |
O3—H3A···O1iii | 0.83 (2) | 2.03 (2) | 2.8382 (19) | 163 (2) |
N3—H1A···N1 | 1.28 (2) | 1.415 (19) | 2.5857 (18) | 147.8 (15) |
O3—H3B···O2 | 0.83 (2) | 1.95 (2) | 2.765 (2) | 165 (3) |
Symmetry codes: (ii) x, y−1, z+1; (iii) −x, −y+1, −z. |
Experimental details
Crystal data | |
Chemical formula | 2C10H10N3+·C4O42−·2H2O |
Mr | 492.50 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 297 |
a, b, c (Å) | 8.072 (2), 8.493 (3), 8.833 (2) |
α, β, γ (°) | 74.34 (3), 87.26 (2), 71.85 (4) |
V (Å3) | 553.6 (3) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 0.11 |
Crystal size (mm) | 0.35 × 0.24 × 0.18 |
Data collection | |
Diffractometer | Stoe IPDS II |
Absorption correction | Integration (X-RED32; Stoe & Cie, 2002) |
Tmin, Tmax | 0.947, 0.981 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6024, 2634, 2027 |
Rint | 0.035 |
(sin θ/λ)max (Å−1) | 0.665 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.044, 0.122, 1.02 |
No. of reflections | 2634 |
No. of parameters | 176 |
No. of restraints | 2 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.27, −0.20 |
Computer programs: X-AREA (Stoe & Cie, 2002), X-AREA, X-RED32 (Stoe & Cie, 2002), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEPIII (Farrugia, 1997), WinGX (Farrugia, 1999).
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2A···O1i | 0.86 | 1.84 | 2.7008 (17) | 178.0 |
O3—H3A···O1ii | 0.832 (17) | 2.031 (18) | 2.8382 (19) | 163 (2) |
N3—H1A···N1 | 1.28 (2) | 1.415 (19) | 2.5857 (18) | 147.8 (15) |
O3—H3B···O2 | 0.834 (17) | 1.951 (18) | 2.765 (2) | 165 (3) |
Symmetry codes: (i) x, y−1, z+1; (ii) −x, −y+1, −z. |
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Squaric acid, H2Sq, is a very strong dibasic acid and has been studied for potential application to xerographic photoreceptors, organic solar cells and optical recording (Seitz & Imming, 1992; Liebeskind et al., 1993). It is also a useful tool for constructing crystalline architecture because of its rigid and flat four-membered ring framework (Reetz et al., 1994). Squaric acid (H2Sq) can be found in three forms, viz. (a) as uncharged H2Sq, (b) as the HSq- monoanion and (c) as Sq2- dianions on deprotonation by amines. These forms have been observed to crystallize with various types of hydrogen bonding, as summarized by Bertolasi et al. (2001). Our ongoing research on metallic and organic salts of squaric acid (Uçar et al., 2004; Uçar et al., 2005; Köroglu et al., 2005), we have synthesized the title compounds, (I), in which the dianion form of squaric acid is observed.
Each squaric acid molecule donates both its H atoms to the pyridine N atom of two 2,2'dipyridylamine molecules, forming the bis(2,2'dipyridiniumamine) squarate dihydrate salt. The C4O42- anion is centrosymmetric. (Fig. 1). The most noteworthy aspect of the structure of (I) concerns the hydrogen bonding (Table 1). Intermolecular hydrogen bonding is conventional (in terms of geometry), with each of the H atoms being donated. However, the N—H···N intramolecular hydrogen bond associated with the pyridine nitrogen atoms has much more unusual behaviour. The freely refined N—H bond length of 1.28 (2)Å is very long for an N—H covalent bond, which would be expected to be around 0.87Å in an X-ray crystallographic analysis. Consequently, the H···N distance is 1.42 (2) Å, whic is rather short. Given that the overall N···N distance is relatively short at 2.586 (2) Å, these values indicate a strong hydrogen bond, which nevertheles display unusual disorder or thermal motion. A difference Fourier map (Fig. 2; Farrugia, 1999) of the electron density associated with this H atom shows this to be smeared out between the dipyridinium N atoms, with the maximum lying closer to the N3 atom. These type hydrogen bonds have been called "positive charge assisted hydrogen bonds (N+—H···N or N···H—N+)" by Gilli and co-workers [Gilli et al., 1994; Bertolasi et al., 1996; Gilli & Gilli, 2000;] and found in organic amines and carboxylic acids [Steiner et al., 2000; Mathew et al., 2002].
In the crystal of (I), both intermolecular H bonds and van der Waals interactions combine to stabilize the extended structure (Fig. 3). The crystal water molecule and amine nitrogen atom link cations to dianions, acting as hydrogen-bond donors to the squarate oxygen atoms. These interactions mediate the formation of chains in the ac plane (Fig. 3) and adjacent chains are linked by van der Waals interactions.