Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270109024093/eg3019sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270109024093/eg3019Isup2.hkl | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270109024093/eg3019IIsup3.hkl |
CCDC references: 742259; 742260
For related literature, see: Bell et al. (2004); Cernerud et al. (2004); Chen et al. (2006); Gala et al. (2003); Gawronski & Gawronska (1999); Langkilde et al. (2002); Leiserowitz (1976); Spek (2003).
Enantiomeric pure (2S,3S)-tartaric acid and (S)- and (R)-2-methylpiperazine were manufactured by Toray Fine Chemicals Co. Ltd (Japan). Both salts were prepared by heating 1 mmol quantities of (2S,3S)-tartaric acid and (S)-2-methylpiperazine [for (I)] or (R)-2-methylpiperazine [for (II)] under reflux in water, and then cooling to room temperature afforded a crop of colourless prisms [m.p. 518–519 K for (I) and 498–499 K for (II)]. Their melting points were measured on melting point apparatus. The solubility of these salts in water was established by the equilibration method, i.e. preparation of a saturated solution at room temperature and determination of its concentration.
In the refinement of (I), the positions of the alcohol, ammonium and water H atoms were determined by differential Fourier analysis near atoms O1, O2, N1, N2, O1W and O2W, and refined isotropically. In the refinement of (II), the positions of the alcohol, ammonium and water H atoms were determined by differential Fourier analysis near atoms O1, O2, N1, N2, O1W and O2W, and refined isotropically, except for the alcohol H atoms, which were refined with a Uiso(H) value of 1.5Ueq(O). The positions of all other H atoms in both compounds were calculated geometrically and refined as riding, with C—H bond lengths of 0.99–1.00 Å, and with Uiso(H) values of 1.2Ueq(C). In both (I) and (II), in the absence of significant anomalous scattering effects, Friedel pairs were merged, and the absolute configuration was determined from the known configuration of (2S,3S)-tartaric acid.
For both compounds, data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO (Rigaku, 1998); data reduction: CrystalStructure (Rigaku/MSC, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).
C5H14N22+·C4H4O62−·2H2O | F(000) = 308 |
Mr = 286.29 | Dx = 1.523 Mg m−3 |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71075 Å |
Hall symbol: P 2yb | Cell parameters from 10478 reflections |
a = 6.0830 (9) Å | θ = 3.5–27.4° |
b = 10.8648 (16) Å | µ = 0.13 mm−1 |
c = 9.6826 (14) Å | T = 123 K |
β = 102.621 (5)° | Prism, colourless |
V = 624.47 (16) Å3 | 0.60 × 0.60 × 0.20 mm |
Z = 2 |
Rigaku R-AXIS RAPID diffractometer | 1507 independent reflections |
Radiation source: rotating anode | 1502 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.022 |
ω scans | θmax = 27.5°, θmin = 3.4° |
Absorption correction: multi-scan (ABSCOR; Higashi, 1995) | h = −7→7 |
Tmin = 0.924, Tmax = 0.974 | k = −14→12 |
10636 measured reflections | l = −12→12 |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.020 | w = 1/[σ2(Fo2) + (0.0298P)2 + 0.1273P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.050 | (Δ/σ)max < 0.001 |
S = 1.05 | Δρmax = 0.24 e Å−3 |
1507 reflections | Δρmin = −0.15 e Å−3 |
214 parameters | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
1 restraint | Extinction coefficient: 0.112 (7) |
Primary atom site location: structure-invariant direct methods | Absolute structure: see text |
Secondary atom site location: difference Fourier map |
C5H14N22+·C4H4O62−·2H2O | V = 624.47 (16) Å3 |
Mr = 286.29 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 6.0830 (9) Å | µ = 0.13 mm−1 |
b = 10.8648 (16) Å | T = 123 K |
c = 9.6826 (14) Å | 0.60 × 0.60 × 0.20 mm |
β = 102.621 (5)° |
Rigaku R-AXIS RAPID diffractometer | 1507 independent reflections |
Absorption correction: multi-scan (ABSCOR; Higashi, 1995) | 1502 reflections with I > 2σ(I) |
Tmin = 0.924, Tmax = 0.974 | Rint = 0.022 |
10636 measured reflections |
R[F2 > 2σ(F2)] = 0.020 | 1 restraint |
wR(F2) = 0.050 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.05 | Δρmax = 0.24 e Å−3 |
1507 reflections | Δρmin = −0.15 e Å−3 |
214 parameters | Absolute structure: see text |
Experimental. Higashi, T. (1995). Program for Absorption Correction. Rigaku Corporation, Tokyo, Japan. |
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 | ||
N1 | 0.35235 (17) | −0.04270 (11) | 0.39134 (10) | 0.0089 (2) | |
H1 | 0.281 (3) | −0.0948 (19) | 0.446 (2) | 0.017 (4)* | |
H2 | 0.483 (3) | −0.017 (2) | 0.4451 (19) | 0.020 (5)* | |
N2 | 0.03960 (18) | −0.05456 (11) | 0.12366 (11) | 0.0097 (2) | |
H3 | 0.110 (3) | −0.005 (2) | 0.068 (2) | 0.022 (5)* | |
H4 | −0.092 (3) | −0.085 (2) | 0.067 (2) | 0.021 (5)* | |
O1 | 0.28928 (15) | 0.54793 (9) | 0.11093 (9) | 0.01071 (19) | |
H5 | 0.388 (4) | 0.567 (2) | 0.071 (2) | 0.028 (5)* | |
O2 | 0.02065 (16) | 0.35088 (9) | 0.16880 (9) | 0.0126 (2) | |
H6 | −0.095 (4) | 0.339 (2) | 0.201 (2) | 0.025 (5)* | |
O3 | 0.35913 (15) | 0.32765 (9) | −0.00708 (9) | 0.01114 (19) | |
O4 | 0.58822 (15) | 0.26506 (9) | 0.19308 (10) | 0.0131 (2) | |
O5 | −0.08400 (15) | 0.55150 (10) | 0.31454 (9) | 0.0144 (2) | |
O6 | 0.25014 (15) | 0.54817 (9) | 0.46468 (9) | 0.0118 (2) | |
C1 | 0.2033 (2) | 0.06457 (12) | 0.33950 (13) | 0.0107 (2) | |
H7 | 0.2826 | 0.1225 | 0.2882 | 0.013* | |
H8 | 0.1664 | 0.1087 | 0.4210 | 0.013* | |
C2 | −0.0119 (2) | 0.02020 (12) | 0.24158 (13) | 0.0112 (2) | |
H9 | −0.0993 | −0.0301 | 0.2959 | 0.013* | |
H10 | −0.1051 | 0.0920 | 0.2023 | 0.013* | |
C3 | 0.1923 (2) | −0.16021 (12) | 0.17565 (12) | 0.0105 (2) | |
H11 | 0.2272 | −0.2050 | 0.0940 | 0.013* | |
H12 | 0.1159 | −0.2180 | 0.2289 | 0.013* | |
C4 | 0.4098 (2) | −0.11472 (12) | 0.27110 (13) | 0.0094 (2) | |
H13 | 0.4886 | −0.0591 | 0.2153 | 0.011* | |
C5 | 0.5664 (2) | −0.22025 (13) | 0.33006 (13) | 0.0117 (2) | |
H14 | 0.6988 | −0.1878 | 0.3965 | 0.017* | |
H15 | 0.6144 | −0.2626 | 0.2523 | 0.017* | |
H16 | 0.4870 | −0.2783 | 0.3794 | 0.017* | |
C6 | 0.4487 (2) | 0.33921 (13) | 0.12254 (12) | 0.0087 (2) | |
C7 | 0.3766 (2) | 0.44923 (13) | 0.20251 (12) | 0.0086 (2) | |
H17 | 0.5084 | 0.4788 | 0.2757 | 0.010* | |
C8 | 0.1914 (2) | 0.40408 (12) | 0.27509 (12) | 0.0090 (2) | |
H18 | 0.2561 | 0.3384 | 0.3445 | 0.011* | |
C9 | 0.1093 (2) | 0.50994 (12) | 0.35615 (12) | 0.0091 (2) | |
O1W | 0.83727 (17) | 0.28450 (9) | 0.46011 (10) | 0.0128 (2) | |
H1W | 0.827 (3) | 0.213 (2) | 0.490 (2) | 0.022 (5)* | |
H2W | 0.743 (3) | 0.2807 (19) | 0.376 (2) | 0.017 (4)* | |
O2W | 0.28825 (16) | 0.07860 (9) | −0.03701 (10) | 0.0117 (2) | |
H3W | 0.217 (4) | 0.070 (2) | −0.116 (3) | 0.032 (6)* | |
H4W | 0.300 (3) | 0.158 (2) | −0.028 (2) | 0.023 (5)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0082 (4) | 0.0100 (5) | 0.0078 (4) | −0.0003 (4) | 0.0003 (4) | −0.0004 (4) |
N2 | 0.0093 (5) | 0.0104 (5) | 0.0083 (4) | 0.0006 (4) | −0.0001 (4) | 0.0007 (4) |
O1 | 0.0109 (4) | 0.0089 (4) | 0.0128 (4) | 0.0000 (3) | 0.0036 (3) | 0.0021 (4) |
O2 | 0.0102 (4) | 0.0169 (5) | 0.0110 (4) | −0.0060 (4) | 0.0032 (3) | −0.0043 (4) |
O3 | 0.0124 (4) | 0.0119 (4) | 0.0087 (4) | 0.0005 (4) | 0.0013 (3) | −0.0013 (4) |
O4 | 0.0121 (4) | 0.0135 (5) | 0.0126 (4) | 0.0036 (4) | 0.0005 (3) | 0.0001 (4) |
O5 | 0.0104 (4) | 0.0192 (5) | 0.0126 (4) | 0.0049 (4) | 0.0006 (3) | −0.0006 (4) |
O6 | 0.0116 (4) | 0.0123 (4) | 0.0104 (4) | 0.0017 (3) | −0.0005 (3) | −0.0019 (4) |
C1 | 0.0117 (5) | 0.0083 (6) | 0.0116 (5) | 0.0011 (5) | 0.0012 (4) | −0.0013 (5) |
C2 | 0.0098 (5) | 0.0124 (6) | 0.0110 (5) | 0.0014 (5) | 0.0011 (4) | −0.0020 (5) |
C3 | 0.0116 (6) | 0.0088 (6) | 0.0098 (5) | 0.0015 (5) | −0.0004 (4) | −0.0003 (5) |
C4 | 0.0097 (5) | 0.0102 (6) | 0.0083 (5) | 0.0000 (4) | 0.0023 (4) | −0.0008 (4) |
C5 | 0.0109 (6) | 0.0124 (6) | 0.0110 (5) | 0.0027 (5) | 0.0008 (4) | 0.0004 (5) |
C6 | 0.0065 (5) | 0.0097 (6) | 0.0105 (5) | −0.0015 (4) | 0.0033 (4) | −0.0012 (5) |
C7 | 0.0082 (5) | 0.0090 (5) | 0.0082 (5) | 0.0007 (4) | 0.0012 (4) | −0.0010 (5) |
C8 | 0.0092 (5) | 0.0096 (6) | 0.0079 (5) | −0.0008 (4) | 0.0013 (4) | −0.0008 (4) |
C9 | 0.0108 (5) | 0.0089 (6) | 0.0083 (5) | −0.0002 (4) | 0.0039 (4) | 0.0008 (4) |
O1W | 0.0165 (5) | 0.0108 (5) | 0.0112 (4) | 0.0002 (4) | 0.0033 (4) | 0.0015 (4) |
O2W | 0.0130 (4) | 0.0109 (5) | 0.0101 (4) | −0.0010 (4) | 0.0007 (3) | −0.0011 (4) |
N1—C1 | 1.4946 (17) | C2—H9 | 0.9900 |
N1—C4 | 1.5060 (16) | C2—H10 | 0.9900 |
N1—H1 | 0.94 (2) | C3—C4 | 1.5216 (17) |
N1—H2 | 0.89 (2) | C3—H11 | 0.9900 |
N2—C2 | 1.4893 (16) | C3—H12 | 0.9900 |
N2—C3 | 1.4930 (16) | C4—C5 | 1.5198 (18) |
N2—H3 | 0.93 (2) | C4—H13 | 1.0000 |
N2—H4 | 0.93 (2) | C5—H14 | 0.9800 |
O1—C7 | 1.4187 (16) | C5—H15 | 0.9800 |
O1—H5 | 0.81 (2) | C5—H16 | 0.9800 |
O2—C8 | 1.4160 (15) | C6—C7 | 1.5391 (18) |
O2—H6 | 0.84 (2) | C7—C8 | 1.5329 (16) |
O3—C6 | 1.2605 (15) | C7—H17 | 1.0000 |
O4—C6 | 1.2580 (16) | C8—C9 | 1.5362 (17) |
O5—C9 | 1.2416 (15) | C8—H18 | 1.0000 |
O6—C9 | 1.2718 (15) | O1W—H1W | 0.83 (2) |
C1—C2 | 1.5173 (16) | O1W—H2W | 0.89 (2) |
C1—H7 | 0.9900 | O2W—H3W | 0.80 (2) |
C1—H8 | 0.9900 | O2W—H4W | 0.86 (3) |
C1—N1—C4 | 111.83 (9) | N1—C4—C5 | 109.50 (10) |
C1—N1—H1 | 109.7 (12) | N1—C4—C3 | 108.68 (10) |
C4—N1—H1 | 109.6 (12) | C5—C4—C3 | 111.94 (11) |
C1—N1—H2 | 110.2 (14) | N1—C4—H13 | 108.9 |
C4—N1—H2 | 106.8 (12) | C5—C4—H13 | 108.9 |
H1—N1—H2 | 108.6 (16) | C3—C4—H13 | 108.9 |
C2—N2—C3 | 112.35 (9) | C4—C5—H14 | 109.5 |
C2—N2—H3 | 109.0 (13) | C4—C5—H15 | 109.5 |
C3—N2—H3 | 108.0 (13) | H14—C5—H15 | 109.5 |
C2—N2—H4 | 110.5 (12) | C4—C5—H16 | 109.5 |
C3—N2—H4 | 108.4 (13) | H14—C5—H16 | 109.5 |
H3—N2—H4 | 108.4 (16) | H15—C5—H16 | 109.5 |
C7—O1—H5 | 106.2 (16) | O4—C6—O3 | 124.77 (12) |
C8—O2—H6 | 109.5 (14) | O4—C6—C7 | 117.18 (10) |
N1—C1—C2 | 109.84 (11) | O3—C6—C7 | 118.01 (11) |
N1—C1—H7 | 109.7 | O1—C7—C8 | 108.42 (10) |
C2—C1—H7 | 109.7 | O1—C7—C6 | 112.43 (9) |
N1—C1—H8 | 109.7 | C8—C7—C6 | 107.50 (11) |
C2—C1—H8 | 109.7 | O1—C7—H17 | 109.5 |
H7—C1—H8 | 108.2 | C8—C7—H17 | 109.5 |
N2—C2—C1 | 110.80 (10) | C6—C7—H17 | 109.5 |
N2—C2—H9 | 109.5 | O2—C8—C7 | 107.06 (9) |
C1—C2—H9 | 109.5 | O2—C8—C9 | 114.09 (10) |
N2—C2—H10 | 109.5 | C7—C8—C9 | 110.38 (11) |
C1—C2—H10 | 109.5 | O2—C8—H18 | 108.4 |
H9—C2—H10 | 108.1 | C7—C8—H18 | 108.4 |
N2—C3—C4 | 110.46 (11) | C9—C8—H18 | 108.4 |
N2—C3—H11 | 109.6 | O5—C9—O6 | 124.65 (12) |
C4—C3—H11 | 109.6 | O5—C9—C8 | 119.81 (11) |
N2—C3—H12 | 109.6 | O6—C9—C8 | 115.54 (11) |
C4—C3—H12 | 109.6 | H1W—O1W—H2W | 101.4 (19) |
H11—C3—H12 | 108.1 | H3W—O2W—H4W | 103 (2) |
C4—N1—C1—C2 | 58.20 (13) | O4—C6—C7—C8 | −82.22 (13) |
C3—N2—C2—C1 | 55.51 (14) | O3—C6—C7—C8 | 95.61 (13) |
N1—C1—C2—N2 | −55.17 (13) | O1—C7—C8—O2 | 67.06 (13) |
C2—N2—C3—C4 | −56.76 (13) | C6—C7—C8—O2 | −54.73 (12) |
C1—N1—C4—C5 | 178.47 (10) | O1—C7—C8—C9 | −57.65 (12) |
C1—N1—C4—C3 | −58.98 (13) | C6—C7—C8—C9 | −179.44 (10) |
N2—C3—C4—N1 | 57.02 (13) | O2—C8—C9—O5 | −8.91 (17) |
N2—C3—C4—C5 | 178.09 (10) | C7—C8—C9—O5 | 111.68 (13) |
O4—C6—C7—O1 | 158.52 (11) | O2—C8—C9—O6 | 170.61 (10) |
O3—C6—C7—O1 | −23.64 (16) | C7—C8—C9—O6 | −68.80 (14) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O1Wi | 0.943 (19) | 1.83 (2) | 2.7657 (15) | 171.1 (18) |
O1W—H1W···O6i | 0.84 (2) | 1.93 (2) | 2.7523 (14) | 169.5 (19) |
N1—H2···O6i | 0.894 (19) | 1.811 (19) | 2.7004 (15) | 172.6 (17) |
O1W—H2W···O4 | 0.889 (19) | 1.823 (19) | 2.7043 (14) | 171.0 (19) |
N2—H3···O2W | 0.93 (2) | 1.88 (2) | 2.7981 (15) | 171.4 (18) |
O2W—H3W···O5ii | 0.80 (3) | 1.93 (3) | 2.7189 (13) | 172 (3) |
N2—H4···O1ii | 0.927 (19) | 2.36 (2) | 2.9010 (15) | 116.7 (16) |
N2—H4···O2ii | 0.927 (19) | 2.514 (19) | 2.9589 (14) | 109.8 (14) |
N2—H4···O3ii | 0.927 (19) | 1.86 (2) | 2.7565 (15) | 161.5 (18) |
O2W—H4W···O3 | 0.87 (2) | 1.88 (2) | 2.7454 (14) | 173.8 (18) |
O1—H5···O2Wiii | 0.81 (2) | 2.07 (2) | 2.8340 (14) | 157 (2) |
O2—H6···O4iv | 0.84 (2) | 2.07 (2) | 2.8486 (14) | 153.3 (19) |
C7—H17···O5v | 1.00 | 2.55 | 3.4091 (16) | 144 |
Symmetry codes: (i) −x+1, y−1/2, −z+1; (ii) −x, y−1/2, −z; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) x+1, y, z. |
C5H14N22+·C4H4O62−·2H2O | F(000) = 616 |
Mr = 286.29 | Dx = 1.493 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71075 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 12156 reflections |
a = 6.1303 (2) Å | θ = 3.5–27.4° |
b = 11.3207 (5) Å | µ = 0.13 mm−1 |
c = 18.3570 (5) Å | T = 108 K |
V = 1273.96 (8) Å3 | Prism, colourless |
Z = 4 | 0.60 × 0.60 × 0.60 mm |
Rigaku RAXIS-RAPID diffractometer | 1697 independent reflections |
Radiation source: rotating anode | 1670 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.016 |
ω scans | θmax = 27.5°, θmin = 3.5° |
Absorption correction: multi-scan (ABSCOR; Higashi, 1995) | h = −7→7 |
Tmin = 0.926, Tmax = 0.926 | k = −14→14 |
12586 measured reflections | l = −23→23 |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.022 | w = 1/[σ2(Fo2) + (0.0386P)2 + 0.2769P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.060 | (Δ/σ)max = 0.001 |
S = 1.05 | Δρmax = 0.31 e Å−3 |
1697 reflections | Δρmin = −0.18 e Å−3 |
212 parameters | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.091 (4) |
Primary atom site location: structure-invariant direct methods | Absolute structure: see text |
Secondary atom site location: difference Fourier map |
C5H14N22+·C4H4O62−·2H2O | V = 1273.96 (8) Å3 |
Mr = 286.29 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 6.1303 (2) Å | µ = 0.13 mm−1 |
b = 11.3207 (5) Å | T = 108 K |
c = 18.3570 (5) Å | 0.60 × 0.60 × 0.60 mm |
Rigaku RAXIS-RAPID diffractometer | 1697 independent reflections |
Absorption correction: multi-scan (ABSCOR; Higashi, 1995) | 1670 reflections with I > 2σ(I) |
Tmin = 0.926, Tmax = 0.926 | Rint = 0.016 |
12586 measured reflections |
R[F2 > 2σ(F2)] = 0.022 | 0 restraints |
wR(F2) = 0.060 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.05 | Δρmax = 0.31 e Å−3 |
1697 reflections | Δρmin = −0.18 e Å−3 |
212 parameters | Absolute structure: see text |
Experimental. Higashi, T. (1995). Program for Absorption Correction. Rigaku Corporation, Tokyo, Japan. |
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 | ||
N1 | 0.79592 (19) | 0.82184 (10) | 0.92596 (6) | 0.0098 (2) | |
H1 | 0.722 (3) | 0.7603 (18) | 0.9426 (9) | 0.019 (4)* | |
H2 | 0.904 (3) | 0.8326 (16) | 0.9564 (10) | 0.019 (5)* | |
N2 | 0.55081 (19) | 0.89368 (9) | 0.79978 (6) | 0.0095 (2) | |
H3 | 0.631 (3) | 0.9553 (17) | 0.7809 (9) | 0.018 (4)* | |
H4 | 0.432 (3) | 0.8801 (18) | 0.7707 (10) | 0.021 (5)* | |
O1 | 0.38481 (17) | 0.38355 (8) | 0.86726 (5) | 0.0118 (2) | |
H5 | 0.296 (3) | 0.3621 (17) | 0.8947 (10) | 0.018* | |
O2 | 0.74561 (17) | 0.51208 (8) | 0.80713 (5) | 0.0110 (2) | |
H6 | 0.868 (4) | 0.5174 (16) | 0.7896 (10) | 0.017* | |
O3 | 0.61974 (16) | 0.61528 (8) | 0.97595 (5) | 0.0114 (2) | |
O4 | 0.33199 (16) | 0.61587 (8) | 0.90128 (5) | 0.0135 (2) | |
O5 | 0.83065 (16) | 0.22810 (8) | 0.89099 (5) | 0.0123 (2) | |
O6 | 0.78964 (16) | 0.28333 (8) | 0.77496 (5) | 0.0119 (2) | |
C1 | 0.6882 (2) | 0.78480 (11) | 0.79843 (6) | 0.0107 (2) | |
H7 | 0.7444 | 0.7717 | 0.7485 | 0.013* | |
H8 | 0.5985 | 0.7156 | 0.8122 | 0.013* | |
C2 | 0.8777 (2) | 0.79690 (11) | 0.85092 (6) | 0.0112 (2) | |
H9 | 0.9639 | 0.7230 | 0.8511 | 0.013* | |
H10 | 0.9742 | 0.8620 | 0.8348 | 0.013* | |
C3 | 0.6594 (2) | 0.93110 (11) | 0.92723 (6) | 0.0112 (2) | |
H11 | 0.7505 | 0.9999 | 0.9137 | 0.013* | |
H12 | 0.6040 | 0.9442 | 0.9772 | 0.013* | |
C4 | 0.4679 (2) | 0.92184 (11) | 0.87488 (6) | 0.0105 (2) | |
H13 | 0.3693 | 0.8567 | 0.8914 | 0.013* | |
C5 | 0.3400 (2) | 1.03709 (11) | 0.87345 (7) | 0.0143 (3) | |
H14 | 0.2182 | 1.0300 | 0.8391 | 0.021* | |
H15 | 0.4362 | 1.1016 | 0.8580 | 0.021* | |
H16 | 0.2832 | 1.0539 | 0.9223 | 0.021* | |
C6 | 0.4932 (2) | 0.56718 (11) | 0.92898 (6) | 0.0094 (2) | |
C7 | 0.5493 (2) | 0.43856 (11) | 0.90949 (6) | 0.0092 (2) | |
H17 | 0.5676 | 0.3929 | 0.9557 | 0.011* | |
C8 | 0.7629 (2) | 0.43311 (11) | 0.86694 (6) | 0.0089 (2) | |
H18 | 0.8863 | 0.4580 | 0.8991 | 0.011* | |
C9 | 0.7975 (2) | 0.30406 (10) | 0.84220 (7) | 0.0091 (2) | |
O1W | 0.12467 (18) | 0.33211 (9) | 0.98185 (5) | 0.0157 (2) | |
H1W | 0.025 (4) | 0.287 (2) | 0.9637 (13) | 0.043 (6)* | |
H2W | 0.165 (3) | 0.3040 (17) | 1.0237 (11) | 0.022 (5)* | |
O2W | 0.17068 (16) | 0.55667 (8) | 0.76452 (5) | 0.0114 (2) | |
H3W | 0.224 (4) | 0.5613 (19) | 0.8065 (12) | 0.032 (5)* | |
H4W | 0.193 (4) | 0.631 (2) | 0.7482 (12) | 0.037 (6)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0111 (5) | 0.0100 (5) | 0.0084 (5) | 0.0002 (4) | −0.0019 (4) | −0.0004 (4) |
N2 | 0.0102 (5) | 0.0099 (5) | 0.0083 (5) | 0.0004 (4) | −0.0007 (4) | 0.0004 (4) |
O1 | 0.0107 (4) | 0.0136 (4) | 0.0112 (4) | −0.0040 (4) | 0.0013 (4) | −0.0011 (3) |
O2 | 0.0110 (4) | 0.0111 (4) | 0.0109 (4) | −0.0001 (4) | 0.0022 (4) | 0.0031 (3) |
O3 | 0.0134 (4) | 0.0107 (4) | 0.0102 (4) | −0.0006 (4) | 0.0014 (4) | −0.0020 (3) |
O4 | 0.0144 (5) | 0.0130 (4) | 0.0132 (4) | 0.0034 (4) | −0.0003 (4) | 0.0000 (3) |
O5 | 0.0154 (5) | 0.0107 (4) | 0.0107 (4) | 0.0017 (4) | −0.0004 (4) | 0.0011 (3) |
O6 | 0.0149 (5) | 0.0115 (4) | 0.0093 (4) | 0.0016 (4) | 0.0003 (3) | −0.0020 (3) |
C1 | 0.0135 (6) | 0.0091 (5) | 0.0095 (5) | 0.0008 (5) | −0.0007 (5) | −0.0013 (4) |
C2 | 0.0114 (6) | 0.0122 (5) | 0.0099 (5) | 0.0013 (5) | 0.0010 (5) | −0.0008 (4) |
C3 | 0.0130 (6) | 0.0104 (5) | 0.0100 (5) | 0.0019 (5) | −0.0013 (5) | −0.0018 (4) |
C4 | 0.0101 (6) | 0.0123 (5) | 0.0090 (5) | 0.0000 (5) | 0.0005 (5) | −0.0002 (4) |
C5 | 0.0144 (6) | 0.0148 (6) | 0.0136 (6) | 0.0044 (5) | −0.0009 (5) | −0.0011 (5) |
C6 | 0.0115 (6) | 0.0096 (5) | 0.0070 (5) | −0.0003 (5) | 0.0039 (4) | 0.0010 (4) |
C7 | 0.0103 (6) | 0.0086 (5) | 0.0087 (5) | 0.0002 (5) | 0.0004 (5) | −0.0006 (4) |
C8 | 0.0104 (6) | 0.0085 (5) | 0.0080 (5) | 0.0002 (5) | 0.0005 (4) | −0.0004 (4) |
C9 | 0.0061 (5) | 0.0097 (5) | 0.0114 (5) | −0.0002 (4) | 0.0009 (4) | −0.0007 (4) |
O1W | 0.0163 (5) | 0.0185 (5) | 0.0123 (4) | −0.0054 (4) | −0.0027 (4) | 0.0042 (4) |
O2W | 0.0133 (4) | 0.0101 (4) | 0.0109 (4) | −0.0004 (4) | −0.0005 (4) | 0.0012 (3) |
N1—C2 | 1.4928 (15) | C2—H9 | 0.9900 |
N1—C3 | 1.4937 (16) | C2—H10 | 0.9900 |
N1—H1 | 0.89 (2) | C3—C4 | 1.5211 (18) |
N1—H2 | 0.88 (2) | C3—H11 | 0.9900 |
N2—C1 | 1.4931 (16) | C3—H12 | 0.9900 |
N2—C4 | 1.5036 (15) | C4—C5 | 1.5225 (17) |
N2—H3 | 0.92 (2) | C4—H13 | 1.0000 |
N2—H4 | 0.91 (2) | C5—H14 | 0.9800 |
O1—C7 | 1.4159 (15) | C5—H15 | 0.9800 |
O1—H5 | 0.78 (2) | C5—H16 | 0.9800 |
O2—C8 | 1.4198 (14) | C6—C7 | 1.5383 (17) |
O2—H6 | 0.82 (2) | C7—C8 | 1.5261 (18) |
O3—C6 | 1.2811 (16) | C7—H17 | 1.0000 |
O4—C6 | 1.2408 (16) | C8—C9 | 1.5445 (16) |
O5—C9 | 1.2581 (15) | C8—H18 | 1.0000 |
O6—C9 | 1.2575 (15) | O1W—H1W | 0.86 (3) |
C1—C2 | 1.5152 (18) | O1W—H2W | 0.87 (2) |
C1—H7 | 0.9900 | O2W—H3W | 0.84 (2) |
C1—H8 | 0.9900 | O2W—H4W | 0.90 (2) |
C2—N1—C3 | 111.04 (9) | N2—C4—C3 | 109.44 (11) |
C2—N1—H1 | 110.0 (12) | N2—C4—C5 | 109.89 (10) |
C3—N1—H1 | 110.9 (13) | C3—C4—C5 | 110.44 (10) |
C2—N1—H2 | 111.1 (13) | N2—C4—H13 | 109.0 |
C3—N1—H2 | 107.5 (12) | C3—C4—H13 | 109.0 |
H1—N1—H2 | 106.2 (16) | C5—C4—H13 | 109.0 |
C1—N2—C4 | 112.40 (9) | C4—C5—H14 | 109.5 |
C1—N2—H3 | 108.7 (12) | C4—C5—H15 | 109.5 |
C4—N2—H3 | 111.3 (11) | H14—C5—H15 | 109.5 |
C1—N2—H4 | 107.4 (13) | C4—C5—H16 | 109.5 |
C4—N2—H4 | 107.6 (12) | H14—C5—H16 | 109.5 |
H3—N2—H4 | 109.3 (17) | H15—C5—H16 | 109.5 |
C7—O1—H5 | 106.2 (14) | O4—C6—O3 | 124.70 (12) |
C8—O2—H6 | 106.3 (13) | O4—C6—C7 | 120.20 (11) |
N2—C1—C2 | 110.32 (10) | O3—C6—C7 | 115.07 (11) |
N2—C1—H7 | 109.6 | O1—C7—C8 | 108.24 (10) |
C2—C1—H7 | 109.6 | O1—C7—C6 | 112.62 (10) |
N2—C1—H8 | 109.6 | C8—C7—C6 | 110.42 (10) |
C2—C1—H8 | 109.6 | O1—C7—H17 | 108.5 |
H7—C1—H8 | 108.1 | C8—C7—H17 | 108.5 |
N1—C2—C1 | 110.28 (11) | C6—C7—H17 | 108.5 |
N1—C2—H9 | 109.6 | O2—C8—C7 | 107.83 (10) |
C1—C2—H9 | 109.6 | O2—C8—C9 | 112.24 (10) |
N1—C2—H10 | 109.6 | C7—C8—C9 | 107.86 (10) |
C1—C2—H10 | 109.6 | O2—C8—H18 | 109.6 |
H9—C2—H10 | 108.1 | C7—C8—H18 | 109.6 |
N1—C3—C4 | 111.44 (10) | C9—C8—H18 | 109.6 |
N1—C3—H11 | 109.3 | O6—C9—O5 | 125.27 (11) |
C4—C3—H11 | 109.3 | O6—C9—C8 | 117.38 (11) |
N1—C3—H12 | 109.3 | O5—C9—C8 | 117.34 (10) |
C4—C3—H12 | 109.3 | H1W—O1W—H2W | 108.9 (19) |
H11—C3—H12 | 108.0 | H3W—O2W—H4W | 101 (2) |
C4—N2—C1—C2 | −56.76 (13) | O4—C6—C7—C8 | 112.99 (12) |
C3—N1—C2—C1 | −57.60 (13) | O3—C6—C7—C8 | −68.89 (13) |
N2—C1—C2—N1 | 56.84 (13) | O1—C7—C8—O2 | 70.93 (12) |
C2—N1—C3—C4 | 57.38 (14) | C6—C7—C8—O2 | −52.78 (13) |
C1—N2—C4—C3 | 55.41 (13) | O1—C7—C8—C9 | −50.49 (12) |
C1—N2—C4—C5 | 176.85 (10) | C6—C7—C8—C9 | −174.20 (10) |
N1—C3—C4—N2 | −55.19 (13) | O2—C8—C9—O6 | −5.24 (17) |
N1—C3—C4—C5 | −176.29 (10) | C7—C8—C9—O6 | 113.41 (12) |
O4—C6—C7—O1 | −8.14 (15) | O2—C8—C9—O5 | 175.01 (11) |
O3—C6—C7—O1 | 169.97 (10) | C7—C8—C9—O5 | −66.35 (15) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O3 | 0.885 (19) | 1.86 (2) | 2.7344 (15) | 168.5 (18) |
O1W—H1W···O5i | 0.86 (2) | 1.91 (2) | 2.7234 (14) | 157 (2) |
N1—H2···O3ii | 0.875 (19) | 1.908 (18) | 2.7730 (15) | 169.6 (17) |
O1W—H2W···O5iii | 0.87 (2) | 1.90 (2) | 2.7401 (13) | 162.1 (17) |
N2—H3···O2Wiv | 0.921 (19) | 1.868 (18) | 2.7772 (14) | 168.7 (17) |
O2W—H3W···O1 | 0.84 (2) | 2.50 (2) | 3.0201 (13) | 120.8 (18) |
O2W—H3W···O4 | 0.84 (2) | 1.96 (2) | 2.7802 (13) | 165 (2) |
N2—H4···O2iv | 0.916 (18) | 2.337 (19) | 2.9917 (15) | 128.3 (16) |
N2—H4···O6iv | 0.916 (18) | 1.936 (19) | 2.7926 (15) | 154.9 (18) |
O2W—H4W···O6iv | 0.90 (2) | 1.78 (2) | 2.6774 (13) | 172 (2) |
O1—H5···O1W | 0.781 (18) | 1.944 (18) | 2.7032 (14) | 164.3 (18) |
O2—H6···O2Wv | 0.82 (2) | 1.96 (2) | 2.7671 (14) | 167.3 (17) |
C1—H7···O1iv | 0.99 | 2.60 | 3.2713 (15) | 125 |
C1—H8···O2 | 0.99 | 2.48 | 3.1115 (15) | 122 |
C1—H8···O4 | 0.99 | 2.57 | 3.4627 (15) | 150 |
C8—H18···O1Wv | 1.00 | 2.54 | 3.2673 (16) | 129 |
Symmetry codes: (i) x−1, y, z; (ii) x+1/2, −y+3/2, −z+2; (iii) x−1/2, −y+1/2, −z+2; (iv) −x+1, y+1/2, −z+3/2; (v) x+1, y, z. |
Experimental details
(I) | (II) | |
Crystal data | ||
Chemical formula | C5H14N22+·C4H4O62−·2H2O | C5H14N22+·C4H4O62−·2H2O |
Mr | 286.29 | 286.29 |
Crystal system, space group | Monoclinic, P21 | Orthorhombic, P212121 |
Temperature (K) | 123 | 108 |
a, b, c (Å) | 6.0830 (9), 10.8648 (16), 9.6826 (14) | 6.1303 (2), 11.3207 (5), 18.3570 (5) |
α, β, γ (°) | 90, 102.621 (5), 90 | 90, 90, 90 |
V (Å3) | 624.47 (16) | 1273.96 (8) |
Z | 2 | 4 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.13 | 0.13 |
Crystal size (mm) | 0.60 × 0.60 × 0.20 | 0.60 × 0.60 × 0.60 |
Data collection | ||
Diffractometer | Rigaku R-AXIS RAPID diffractometer | Rigaku RAXIS-RAPID diffractometer |
Absorption correction | Multi-scan (ABSCOR; Higashi, 1995) | Multi-scan (ABSCOR; Higashi, 1995) |
Tmin, Tmax | 0.924, 0.974 | 0.926, 0.926 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10636, 1507, 1502 | 12586, 1697, 1670 |
Rint | 0.022 | 0.016 |
(sin θ/λ)max (Å−1) | 0.649 | 0.649 |
Refinement | ||
R[F2 > 2σ(F2)], wR(F2), S | 0.020, 0.050, 1.05 | 0.022, 0.060, 1.05 |
No. of reflections | 1507 | 1697 |
No. of parameters | 214 | 212 |
No. of restraints | 1 | 0 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.24, −0.15 | 0.31, −0.18 |
Absolute structure | See text | See text |
Computer programs: PROCESS-AUTO (Rigaku, 1998), CrystalStructure (Rigaku/MSC, 2003), SHELXS97 (Sheldrick, 2008), ORTEPIII (Burnett & Johnson, 1996) and PLATON (Spek, 2009), SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).
O3—C6 | 1.2605 (15) | O5—C9 | 1.2416 (15) |
O4—C6 | 1.2580 (16) | O6—C9 | 1.2718 (15) |
C1—N1—C4—C5 | 178.47 (10) | O1—C7—C8—O2 | 67.06 (13) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O1Wi | 0.943 (19) | 1.83 (2) | 2.7657 (15) | 171.1 (18) |
O1W—H1W···O6i | 0.84 (2) | 1.93 (2) | 2.7523 (14) | 169.5 (19) |
N1—H2···O6i | 0.894 (19) | 1.811 (19) | 2.7004 (15) | 172.6 (17) |
O1W—H2W···O4 | 0.889 (19) | 1.823 (19) | 2.7043 (14) | 171.0 (19) |
N2—H3···O2W | 0.93 (2) | 1.88 (2) | 2.7981 (15) | 171.4 (18) |
O2W—H3W···O5ii | 0.80 (3) | 1.93 (3) | 2.7189 (13) | 172 (3) |
N2—H4···O3ii | 0.927 (19) | 1.86 (2) | 2.7565 (15) | 161.5 (18) |
O2W—H4W···O3 | 0.87 (2) | 1.88 (2) | 2.7454 (14) | 173.8 (18) |
O1—H5···O2Wiii | 0.81 (2) | 2.07 (2) | 2.8340 (14) | 157 (2) |
O2—H6···O4iv | 0.84 (2) | 2.07 (2) | 2.8486 (14) | 153.3 (19) |
Symmetry codes: (i) −x+1, y−1/2, −z+1; (ii) −x, y−1/2, −z; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z. |
O3—C6 | 1.2811 (16) | O5—C9 | 1.2581 (15) |
O4—C6 | 1.2408 (16) | O6—C9 | 1.2575 (15) |
C1—N2—C4—C5 | 176.85 (10) | O1—C7—C8—O2 | 70.93 (12) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O3 | 0.885 (19) | 1.86 (2) | 2.7344 (15) | 168.5 (18) |
O1W—H1W···O5i | 0.86 (2) | 1.91 (2) | 2.7234 (14) | 157 (2) |
N1—H2···O3ii | 0.875 (19) | 1.908 (18) | 2.7730 (15) | 169.6 (17) |
O1W—H2W···O5iii | 0.87 (2) | 1.90 (2) | 2.7401 (13) | 162.1 (17) |
N2—H3···O2Wiv | 0.921 (19) | 1.868 (18) | 2.7772 (14) | 168.7 (17) |
O2W—H3W···O1 | 0.84 (2) | 2.50 (2) | 3.0201 (13) | 120.8 (18) |
O2W—H3W···O4 | 0.84 (2) | 1.96 (2) | 2.7802 (13) | 165 (2) |
N2—H4···O2iv | 0.916 (18) | 2.337 (19) | 2.9917 (15) | 128.3 (16) |
N2—H4···O6iv | 0.916 (18) | 1.936 (19) | 2.7926 (15) | 154.9 (18) |
O2W—H4W···O6iv | 0.90 (2) | 1.78 (2) | 2.6774 (13) | 172 (2) |
O1—H5···O1W | 0.781 (18) | 1.944 (18) | 2.7032 (14) | 164.3 (18) |
O2—H6···O2Wv | 0.82 (2) | 1.96 (2) | 2.7671 (14) | 167.3 (17) |
Symmetry codes: (i) x−1, y, z; (ii) x+1/2, −y+3/2, −z+2; (iii) x−1/2, −y+1/2, −z+2; (iv) −x+1, y+1/2, −z+3/2; (v) x+1, y, z. |
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Tartaric acid is one of the most accessible enantiomerically pure compounds, and it has emerged as a useful class of chiral resolving reagent for racemic amines (Gawronski & Gawronska, 1999). Although a variety of amines have been resolved by the formation of a diastereomeric salt with tartaric acid, systematic research on the crystal structure of diastereomers is still of importance if the process is to become non-heuristic. Here we report the crystal structures of a pair of diastereomeric 1:1 salts, (I) and (II), of (2S,3S)-tartaric acid with (S)- and (R)-2-methylpiperazine, which is a valuable compound as a raw material for various drugs and candidates for clinical compounds designed to treat HIV infection (Gala et al., 2003), obesity (Chen et al., 2006), hypertension (Bell et al., 2004) and diabetes (Cernerud et al., 2004).
In both crystal structures, all the N atoms of 2-methylpiperazine have two H atoms, showing that these amines are completely converted to quaternary ammonium cations (Figs. 1 and 2). It is also found that the O3—C6, O4—C6, O5—C9 and O6—C9 bond lengths of the tartaric acid moieties lie between 1.2416 (15) and 1.2811 (16) Å (Tables 1 and 3), which means that the O—C bonds are longer than the standard double bond of a carboxylic acid (1.200 Å) but shorter than a single bond (1.317 Å) (Leiserowitz, 1976), indicating the formation of well defined carboxylate anions. In addition, the geometries of 2-methylpiperazinium are almost identical except for the symmetry. The torsion angles C1—N1—C4—C5 in (I) and C1—N2—C4—C5 in (II) are 178.5 (1) and 176.9 (1)°, respectively, indicating that these methyl groups are in the most stable equatorial position in the chair conformation of six-membered ring piperazine. The conformations of the tartrate moieties also have roughly the same geometry around the C7—C8 axis, and the O1—C7—C8—O2 torsion angles are 67.1 (1) in (I), and 70.9 (1)° in (II).
In the crystal packing, the molecules are linked via strong intermolecular O—H···O and N—H···O hydrogen bonds (Fig. 3 and 4). The crystal packing of (I) reveals neat alternating columns of tartrate and ammonium in a grid around the a axis that incorporate water molecules at regular intervals, whereas in (II) the columns are more interconnected. The solubility of 5.0 g/100 g H2O for (I) is less than that of 63.6 g/100 g H2O for (II) at 298 K, and the crystal density of 1.523 g cm-3 for (I) is greater than that of 1.493 g cm-3 for (II). The increased efficiency of packing for (I) is also evident in its lower `packing coefficient' (Spek, 2009) (77.1%), which differs by 2.4% from the value found for (II) (75.3%), indicating the presence of a stronger molecular interaction in the less soluble salt (I). In contrast, there are more hydrogen bonds in (II) than in (I). Additionally, a scatter diagram of angles (D—H···A) versus distances (H···A) for individual intermolecular hydrogen bonds shows two weak hydrogen bonds in (I), which correspond to the interactions of carboxylate hydroxy groups and water molecules (Figs. 5 and 6). These hydrogen bonds form columns of tartrate ions around the a axis in (I). On the other hand, as shown Fig. 7, the weaker two hydrogen bonds in (II) take the form of bifurcated hydrogen bonds, whose values are estimated as being weaker than those of ordinary hydrogen bonds constituted geometrically with a donor and an acceptor. From the number of hydrogen bonds and the correlation between length and angle, we predict that these interactions are stronger in the more soluble salt (II). Although the less soluble diastereomeric salts are commonly stabilized by intermolecular interactions to a much greater extent than the corresponding more soluble diastereomeric salts, it has been reported that the number of hydrogen bonds does not necessarily lead to greater stability and less solubility in hydrated salts (Langkilde et al., 2002). Therefore, other than hydrogen bonds, the Coulomb interaction and the van der Waals interaction make a large contribution to the stabilization of the packing structure of the less soluble salt (I). In contrast, the more soluble salt (II) is structurally disadvantaged in close packing, and adopts the less stable packing structure supported by intermolecular hydrogen bonds.