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The crystal structure determination of the molecular proton-transfer adduct of Kemp's triacid (cis-cis-1,3,5-tri­methyl­cyclo­hexane-1,3,5-tri­carboxylic acid, KTA) with 2-amino­pyridine (2-APY), namely 2-amino­pyridinium 3,5-di­carboxy-1,3,5-tri­methyl­cyclo­hexane­carboxyl­ate, 2-APY+·KTA or C5H7N2+·C12H17O6, has revealed a centrosymmetric hydrogen-bonded cyclic KTA homodimer repeating unit [O...O 2.524 (4) Å] linked into a polymer structure through the pyridinium and amino groups of the 2-APY mol­ecule [O...N 2.736 (4), 2.989 (4) and 2.999 (4) Å].

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100012968/fr1294sup1.cif
Contains datablocks default, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270100012968/fr1294Isup2.hkl
Contains datablock I

CCDC reference: 156183

Comment top

Kemp's triacid (cis-cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid, KTA; Kemp & Petrakis, 1981; Hazell & Toftlund, 1999 [120 K]) is a unique triprotic acid, having all of its carboxylic acid groups axially oriented. The crystal structure analysis (Rebek et al., 1985; Chan et al., 1991) also indicated that the molecules had no intramolecular hydrogen-bonding associations between the carboxylic acid groups, as might have been expected with this configuration. Instead, the molecules formed into an unusual convoluted hydrogen-bonded chain structure made up of intermolecular head-to-tail cyclic hydrogen bonds [graph set R22(8); Etter, 1990; Etter & MacDonald, 1990], with two at the head and one at the tail. This is also found in the acetonitrile solvate structure (Hirose et al., 1998). This same framework structure is found in the 2:1 adduct of KTA with 8-aminoquinoline (8-AQ), where the chains are linked peripherally by hydrogen bonds through the hetero-N atom and the amino group of the substituted quinoline molecules (Smith et al., 2000). No proton transfer is found in this compound [pKa1 = 3.3 (KTA) and pKa2 (hetero-N) = 4.0 (8-AQ)]. This is in contrast with the 1:1 adduct with the analogous compound quinolin-8-ol (8-HQ) (Smith et al., 2000), where proton transfer is found [pKa2 = 5.0 (hetero-N)] in a structure which no longer retains the KTA chain backbone. Instead, the singly deprotonated KTA molecules form centrosymmetric dimer interactions, which differ from conventional hydrogen-bonded cyclic dimers in that they involve both cis-related carboxylic acid groups. One of these O atoms then links to the protonated hetero-N atom of the 8-HQ molecule, while the 8-hydroxy group of 8-HQ completes the polymer link to an adjacent dimer unit. In addition, a single intermolecular hydrogen bond is found between two of the carboxylic acid groups. This work indicated that Kemp's triacid has particular affinity for the 8-amino-substituted quinoline system, and reinforced the potential of KTA in molecular recognition processes (Bencini et al., 1992, 1994). In a continuation of this work on the self-assembly of KTA in the presence of Lewis bases, a 1:1 adduct, (I), of KTA with 2-aminopyridine was synthesized and the structure determined. \sch

The structure of (I) reveals a proton-transfer complex (Fig. 1), which is analogous to the complex with 8-HQ in having cyclic centrosymmetric hydrogen-bonded dimers [O4—H4···O2i 2.524 (4) Å and O—H—O 179 (3)°; symmetry code: (i) 1 − x, 1 − y, 1 − z] (Fig. 2). A similar short intramolecular hydrogen bond is also found [O5—H5···O1 2.552 (4) Å and O—H—O 162 (3)°]. The same carboxylate O atom is then linked to the protonated pyridinium N atom of 2-APY [O1···H12—N12 2.736 (4) Å and O—H—N 161 (3)°], while the 2-amino substituent gives a bidentate linkage to a second carboxylate O atom [N22—H2···O3 2.999 (4) Å and N—H—O 162 (3)°]. The second proton of the amino group provides the peripheral linkage between dimer units in the chain polymer structure [N22—H1···O6ii 2.989 (4) Å and N—H—O 158 (3)°; symmetry code: (ii) 1 − x, 1 − y, −z].

Although no further examples of Lewis base adducts with KTA have been isolated, the examples characterized so far indicate that there is a critical minimum pKa difference (ΔpKa) between the first dissociation constant for KTA and that for the hetero-N atom of the Lewis base, which determines which structure type exists (chain or dimer variant) [for 8-AQ, ΔpKa = 0.7 (no proton transfer, chain structure); for 8-HQ, ΔpKa = 1.7, and for 2-APY, ΔpKa = 3.4 (both proton transfer, both dimer structures)]. This threshold value appears to be considerably smaller than the corresponding ΔpKa minimum for the unsubstituted pyridine system (3.5; Johnson & Rumon, 1965). By analogy, the relatively strong nitro-substituted aromatic carboxylic acids [2,4-dinitrobenzoic acid (pKa = 3.7), 5-nitrosalicylic acid (pKa = 2.2) and 3,5-dinitrosalicylic acid (pKa = 2.1)] readily protonate the hetero-N atom in both 8-AQ and 8-HQ, giving 1:1 adducts based on cyclic hydrogen-bonded A—B heterodimers [Smith, Wermuth & White (2000). Unpublished data].

Experimental top

The synthesis of (I) was carried out by refluxing equimolar amounts (1 mmol) of 2-aminopyridine and cis-cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid for 15 min at ca 350 K in 50% aqueous ethanol (20 ml). Crystals of (I) were obtained by the evaporation of the solvent at room temperature.

Refinement top

Only the positional parameters for those H atoms involved in hydrogen bonding (H1, H2, H4, H5 and H12) were refined. All other H atoms were constrained, with C—H 0.95 Å and Uiso = 1.2Ueq of the bonded C atom.

Computing details top

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1994); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN for Windows (Molecular Structure Corporation, 1997-1999); program(s) used to solve structure: SIR92 (Altomare et al. 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: TEXSAN for Windows.

Figures top
[Figure 1] Fig. 1. The molecular configuration and atom-labelling scheme for the individual Kemp's triacid anion and the pyridinium cation in (I). Displacement ellipsoids are shown at the 30% probability level and H atoms are drawn as small spheres of arbitrary radii.
[Figure 2] Fig. 2. The dimeric KTA anion units and the cross-linking 2-aminopyridinium cations in (I), with the hydrogen-bonding scheme shown as broken lines.
(I) top
Crystal data top
C5H7N2+·C12H17O6Z = 2
Mr = 352.39F(000) = 376.00
Triclinic, P1Dx = 1.321 Mg m3
a = 8.767 (2) ÅMo Kα radiation, λ = 0.71070 Å
b = 12.228 (2) ÅCell parameters from 25 reflections
c = 8.600 (3) Åθ = 19.4–19.9°
α = 94.12 (2)°µ = 0.10 mm1
β = 90.07 (3)°T = 293 K
γ = 105.44 (1)°Plate, colourless
V = 886.2 (4) Å30.3 × 0.2 × 0.1 mm
Data collection top
Rigaku AFC-7R
diffractometer
Rint = 0.029
Radiation source: Rigaku rotating anodeθmax = 25.0°, θmin = 2.4°
Graphite monochromatorh = 010
ω/2θ scansk = 1414
3350 measured reflectionsl = 1010
3128 independent reflections3 standard reflections every 150 reflections
1699 reflections with I > 2σ(I) intensity decay: 1.8%
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.049H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.168 w = 1/[σ2(Fo2) + (0.08P)2 + 0.369P]
where P = (Fo2 + 2Fc2)/3
S = 1.02(Δ/σ)max < 0.001
3128 reflectionsΔρmax = 0.36 e Å3
242 parametersΔρmin = 0.36 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.022 (5)
Crystal data top
C5H7N2+·C12H17O6γ = 105.44 (1)°
Mr = 352.39V = 886.2 (4) Å3
Triclinic, P1Z = 2
a = 8.767 (2) ÅMo Kα radiation
b = 12.228 (2) ŵ = 0.10 mm1
c = 8.600 (3) ÅT = 293 K
α = 94.12 (2)°0.3 × 0.2 × 0.1 mm
β = 90.07 (3)°
Data collection top
Rigaku AFC-7R
diffractometer
Rint = 0.029
3350 measured reflections3 standard reflections every 150 reflections
3128 independent reflections intensity decay: 1.8%
1699 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0490 restraints
wR(F2) = 0.168H atoms treated by a mixture of independent and constrained refinement
S = 1.02Δρmax = 0.36 e Å3
3128 reflectionsΔρmin = 0.36 e Å3
242 parameters
Special details top

Experimental. The scan width was (1.57 + 0.35tanθ)° with an ω scan speed of 0° per minute (up to 5 scans to achieve I/σ(I) > 15). Stationary background counts were recorded at each end of the scan, and the scan time:background time ratio was 2:1.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.1576 (3)0.32310 (18)0.3773 (3)0.0490 (6)
O20.3246 (3)0.38352 (17)0.5806 (3)0.0467 (6)
O30.5046 (3)0.36551 (18)0.2589 (3)0.0511 (6)
O40.6839 (3)0.41459 (18)0.4510 (3)0.0461 (6)
O50.2004 (3)0.2534 (2)0.0981 (3)0.0588 (7)
O60.3963 (3)0.2132 (2)0.0291 (3)0.0626 (7)
N120.1598 (3)0.5149 (2)0.2311 (3)0.0453 (7)
N220.4167 (4)0.5671 (3)0.1445 (4)0.0539 (8)
C10.2729 (3)0.1882 (2)0.4907 (4)0.0361 (7)
C20.4448 (4)0.1909 (2)0.5323 (4)0.0380 (7)
C30.5623 (3)0.2171 (2)0.3987 (4)0.0357 (7)
C40.4990 (4)0.1328 (2)0.2567 (4)0.0405 (8)
C50.3263 (4)0.1160 (3)0.2029 (4)0.0404 (8)
C60.2175 (4)0.1070 (2)0.3445 (4)0.0410 (8)
C70.2527 (3)0.3081 (2)0.4802 (4)0.0379 (7)
C80.5825 (3)0.3405 (2)0.3611 (4)0.0338 (7)
C90.3143 (4)0.2017 (3)0.0847 (4)0.0461 (8)
C100.1660 (4)0.1406 (3)0.6265 (4)0.0509 (9)
C110.7229 (4)0.2016 (3)0.4501 (5)0.0536 (10)
C120.2726 (5)0.0006 (3)0.1030 (5)0.0604 (10)
C220.2736 (4)0.5835 (3)0.1522 (4)0.0395 (7)
C320.2322 (4)0.6703 (3)0.0773 (4)0.0477 (8)
C420.0822 (4)0.6812 (3)0.0858 (5)0.0554 (10)
C520.0314 (4)0.6078 (3)0.1688 (5)0.0581 (10)
C620.0095 (4)0.5259 (3)0.2410 (4)0.0545 (9)
H10.491 (4)0.622 (3)0.105 (4)0.042*
H20.437 (4)0.515 (3)0.198 (4)0.042*
H50.172 (4)0.263 (3)0.186 (4)0.042*
H40.681 (4)0.483 (3)0.439 (4)0.042*
H120.181 (4)0.464 (3)0.274 (4)0.054*
H210.44490.11870.56600.046*
H220.48080.24760.61540.046*
H320.30950.72170.02110.057*
H410.56430.15840.17130.049*
H420.05480.73980.03430.067*
H400.50970.06060.28100.049*
H520.13650.61550.17450.070*
H610.12060.11890.30990.050*
H620.06670.47520.29920.066*
H600.19900.03180.37590.050*
H1010.22140.16670.72280.062*
H1020.13830.05980.61560.062*
H1030.07270.16600.62440.062*
H1110.72630.20000.56040.065*
H1120.73600.13230.40270.065*
H1130.80550.26330.41920.065*
H1210.24290.05960.17000.073*
H1220.18500.00080.03820.073*
H1230.35760.00950.04010.073*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0429 (13)0.0421 (13)0.0659 (16)0.0160 (10)0.0037 (12)0.0130 (11)
O20.0493 (13)0.0283 (11)0.0603 (15)0.0080 (10)0.0014 (11)0.0022 (11)
O30.0584 (15)0.0323 (12)0.0620 (16)0.0099 (11)0.0163 (12)0.0085 (11)
O40.0437 (13)0.0266 (11)0.0643 (15)0.0035 (10)0.0103 (11)0.0011 (11)
O50.0587 (16)0.0663 (17)0.0560 (16)0.0225 (14)0.0104 (14)0.0128 (14)
O60.0634 (16)0.0709 (18)0.0478 (15)0.0062 (13)0.0005 (13)0.0120 (13)
N120.0524 (18)0.0379 (15)0.0484 (17)0.0143 (13)0.0019 (14)0.0122 (13)
N220.0474 (18)0.056 (2)0.066 (2)0.0225 (15)0.0047 (15)0.0214 (16)
C10.0371 (16)0.0258 (14)0.0444 (18)0.0052 (12)0.0025 (14)0.0077 (13)
C20.0448 (18)0.0273 (15)0.0425 (18)0.0097 (13)0.0003 (14)0.0067 (13)
C30.0360 (16)0.0271 (15)0.0457 (18)0.0102 (12)0.0025 (14)0.0071 (13)
C40.0450 (18)0.0275 (15)0.051 (2)0.0129 (13)0.0019 (15)0.0015 (14)
C50.0435 (18)0.0317 (16)0.0434 (19)0.0056 (13)0.0026 (15)0.0017 (14)
C60.0383 (17)0.0266 (15)0.057 (2)0.0046 (13)0.0006 (15)0.0086 (14)
C70.0320 (16)0.0305 (16)0.051 (2)0.0067 (13)0.0101 (15)0.0081 (15)
C80.0273 (15)0.0280 (15)0.0464 (18)0.0072 (12)0.0046 (14)0.0053 (14)
C90.0420 (19)0.0450 (19)0.045 (2)0.0013 (15)0.0080 (17)0.0040 (16)
C100.055 (2)0.0381 (18)0.056 (2)0.0040 (15)0.0097 (17)0.0108 (16)
C110.047 (2)0.0428 (19)0.076 (3)0.0209 (16)0.0098 (18)0.0074 (18)
C120.066 (2)0.041 (2)0.065 (3)0.0024 (17)0.000 (2)0.0131 (18)
C220.0391 (18)0.0354 (17)0.0443 (19)0.0107 (14)0.0047 (15)0.0018 (14)
C320.0471 (19)0.0389 (18)0.058 (2)0.0102 (15)0.0039 (16)0.0150 (16)
C420.057 (2)0.0440 (19)0.070 (3)0.0229 (17)0.0165 (19)0.0031 (18)
C520.042 (2)0.062 (2)0.074 (3)0.0222 (18)0.0018 (18)0.003 (2)
C620.046 (2)0.052 (2)0.062 (2)0.0077 (17)0.0117 (17)0.0035 (18)
Geometric parameters (Å, º) top
O1—C71.271 (4)C4—H410.95
O2—C71.252 (4)C4—H400.95
O3—C81.217 (3)C5—C91.534 (5)
O4—C81.295 (4)C5—C61.539 (5)
O4—H40.86 (3)C5—C121.556 (5)
O5—C91.317 (4)C6—H610.95
O5—H50.81 (3)C6—H600.95
O6—C91.210 (4)C10—H1010.95
N12—C221.340 (4)C10—H1020.95
N12—C621.361 (5)C10—H1030.95
N12—H120.81 (4)C11—H1110.95
N22—C221.323 (4)C11—H1120.95
N22—H10.89 (3)C11—H1130.95
N22—H20.87 (3)C12—H1210.95
C1—C71.531 (4)C12—H1220.95
C1—C61.538 (5)C12—H1230.95
C1—C21.539 (4)C22—C321.406 (4)
C1—C101.547 (4)C32—C421.358 (5)
C2—C31.537 (4)C32—H320.95
C2—H210.95C42—C521.387 (5)
C2—H220.95C42—H420.95
C3—C81.530 (4)C52—C621.341 (5)
C3—C111.538 (4)C52—H520.95
C3—C41.542 (4)C62—H620.95
C4—C51.538 (4)
C8—O4—H4113 (2)H61—C6—H60109.5
C9—O5—H5115 (2)O2—C7—O1124.3 (3)
C22—N12—C62123.3 (3)O2—C7—C1117.2 (3)
C22—N12—H12118 (3)O1—C7—C1118.4 (3)
C62—N12—H12119 (3)O3—C8—O4123.8 (3)
C22—N22—H1116 (2)O3—C8—C3122.0 (3)
C22—N22—H2118 (2)O4—C8—C3114.2 (3)
H1—N22—H2123 (3)O6—C9—O5119.4 (3)
C7—C1—C6114.8 (3)O6—C9—C5121.0 (3)
C7—C1—C2111.8 (2)O5—C9—C5119.1 (3)
C6—C1—C2109.2 (2)C1—C10—H101109.4
C7—C1—C10104.2 (2)C1—C10—H102109.4
C6—C1—C10107.8 (2)H101—C10—H102109.5
C2—C1—C10108.7 (3)C1—C10—H103109.4
C3—C2—C1115.3 (3)H101—C10—H103109.5
C3—C2—H21108.0H102—C10—H103109.5
C1—C2—H21108.1C3—C11—H111109.4
C3—C2—H22107.9C3—C11—H112109.6
C1—C2—H22108.0H111—C11—H112109.5
H21—C2—H22109.4C3—C11—H113109.4
C8—C3—C2108.4 (2)H111—C11—H113109.4
C8—C3—C11109.6 (2)H112—C11—H113109.5
C2—C3—C11109.5 (3)C5—C12—H121109.4
C8—C3—C4111.9 (2)C5—C12—H122109.5
C2—C3—C4109.1 (2)H121—C12—H122109.6
C11—C3—C4108.4 (2)C5—C12—H123109.4
C5—C4—C3118.1 (2)H121—C12—H123109.5
C5—C4—H41107.3H122—C12—H123109.5
C3—C4—H41107.2N22—C22—N12120.4 (3)
C5—C4—H40107.3N22—C22—C32122.6 (3)
C3—C4—H40107.3N12—C22—C32117.0 (3)
H41—C4—H40109.4C42—C32—C22120.0 (3)
C9—C5—C4111.1 (3)C42—C32—H32120.0
C9—C5—C6117.5 (3)C22—C32—H32119.9
C4—C5—C6110.4 (3)C32—C42—C52120.7 (3)
C9—C5—C12102.2 (3)C32—C42—H42119.6
C4—C5—C12108.1 (3)C52—C42—H42119.7
C6—C5—C12106.9 (3)C62—C52—C42118.8 (3)
C1—C6—C5119.0 (2)C62—C52—H52120.6
C1—C6—H61107.0C42—C52—H52120.6
C5—C6—H61107.1C52—C62—N12120.2 (3)
C1—C6—H60107.0C52—C62—H62119.9
C5—C6—H60107.1N12—C62—H62119.9
C7—C1—C2—C375.4 (3)C2—C1—C7—O1143.7 (3)
C6—C1—C2—C352.8 (3)C10—C1—C7—O199.1 (3)
C10—C1—C2—C3170.2 (2)C2—C3—C8—O394.3 (3)
C1—C2—C3—C867.9 (3)C11—C3—C8—O3146.3 (3)
C1—C2—C3—C11172.7 (2)C4—C3—C8—O326.0 (4)
C1—C2—C3—C454.1 (3)C2—C3—C8—O483.2 (3)
C8—C3—C4—C570.4 (3)C11—C3—C8—O436.3 (4)
C2—C3—C4—C549.5 (3)C4—C3—C8—O4156.6 (3)
C11—C3—C4—C5168.7 (3)C4—C5—C9—O651.7 (4)
C3—C4—C5—C988.9 (3)C6—C5—C9—O6180.0 (3)
C3—C4—C5—C643.2 (3)C12—C5—C9—O663.4 (4)
C3—C4—C5—C12159.8 (3)C4—C5—C9—O5136.4 (3)
C7—C1—C6—C579.5 (3)C6—C5—C9—O58.1 (4)
C2—C1—C6—C547.1 (3)C12—C5—C9—O5108.5 (3)
C10—C1—C6—C5164.9 (3)C62—N12—C22—N22178.7 (3)
C9—C5—C6—C186.6 (3)C62—N12—C22—C320.0 (5)
C4—C5—C6—C142.2 (4)N22—C22—C32—C42178.2 (4)
C12—C5—C6—C1159.5 (3)N12—C22—C32—C420.5 (5)
C6—C1—C7—O2165.6 (3)C22—C32—C42—C520.4 (6)
C2—C1—C7—O240.4 (4)C32—C42—C52—C620.2 (6)
C10—C1—C7—O276.7 (3)C42—C52—C62—N120.6 (6)
C6—C1—C7—O118.5 (4)C22—N12—C62—C520.5 (6)

Experimental details

Crystal data
Chemical formulaC5H7N2+·C12H17O6
Mr352.39
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)8.767 (2), 12.228 (2), 8.600 (3)
α, β, γ (°)94.12 (2), 90.07 (3), 105.44 (1)
V3)886.2 (4)
Z2
Radiation typeMo Kα
µ (mm1)0.10
Crystal size (mm)0.3 × 0.2 × 0.1
Data collection
DiffractometerRigaku AFC-7R
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
3350, 3128, 1699
Rint0.029
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.049, 0.168, 1.02
No. of reflections3128
No. of parameters242
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.36, 0.36

Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1994), MSC/AFC Diffractometer Control Software, TEXSAN for Windows (Molecular Structure Corporation, 1997-1999), SIR92 (Altomare et al. 1994), SHELXL97 (Sheldrick, 1997), TEXSAN for Windows.

 

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