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In the title compound, [Ca(C
6H
5O
4)
2(C
6H
6O
4)
2]·4H
2O, which is a kojic acid-Ca
2+ complex, the Ca atom is on a twofold axis and is octacoordinated by O atoms from four pyrone ligand molecules. The hydroxyl and ketone O atoms of each ligand form a five-membered chelate ring with the Ca atom. The crystal structure is stabilized by partial stacking and O-H
O hydrogen bonds.
Supporting information
CCDC reference: 195604
Yellow pillar-shaped crystals of (II) were obtained by slow evaporation from an
80% ethanol–water solution of kojic acid and calcium nitrate tetrahydrate in
a 4:1 molar ratio at room temperature.
The H atoms of the ligand molecules, except for H26 and those of the disorderd
methyl group, were placed in calculated positions and refined as riding atoms.
H26, H4A, H4B and the water H atoms were located from difference Fourier maps
and were fixed, except of H26. The long O2—H26 bond [1.24 (2) Å] is due to
the strong O2—H26···O6 hydrogen bond. Three H atoms bonded to O10 was
located as the disordered atoms that exist as H10A—O10—H10B and
H10A—O10—H10C.
Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation,
1992); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 2000); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: TEXSAN.
Crystal data top
[Ca(C6H5O4)2(C6H6O4)2]·4H2O | F(000) = 1416.0 |
Mr = 678.56 | Dx = 1.550 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.7107 Å |
Hall symbol: -C 2yc | Cell parameters from 24 reflections |
a = 22.020 (4) Å | θ = 10.1–12.5° |
b = 6.223 (4) Å | µ = 0.31 mm−1 |
c = 21.225 (3) Å | T = 296 K |
β = 91.61 (1)° | Pillar, yellow |
V = 2907 (2) Å3 | 0.20 × 0.10 × 0.10 mm |
Z = 4 | |
Data collection top
Rigaku AFC-5R diffractometer | Rint = 0.062 |
ω–2θ scans | θmax = 27.5° |
Absorption correction: ψ scan (North et al., 1968) | h = 0→28 |
Tmin = 0.942, Tmax = 0.970 | k = 0→8 |
3773 measured reflections | l = −27→27 |
3332 independent reflections | 3 standard reflections every 150 reflections |
1748 reflections with I > 2σ(I) | intensity decay: 4.3% |
Refinement top
Refinement on F2 | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.048 | w = 1/[σ2(Fo2) + (0.0563P)2 + 3.2041P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.152 | (Δ/σ)max = 0.001 |
S = 1.00 | Δρmax = 0.30 e Å−3 |
3332 reflections | Δρmin = −0.52 e Å−3 |
217 parameters | |
Crystal data top
[Ca(C6H5O4)2(C6H6O4)2]·4H2O | V = 2907 (2) Å3 |
Mr = 678.56 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 22.020 (4) Å | µ = 0.31 mm−1 |
b = 6.223 (4) Å | T = 296 K |
c = 21.225 (3) Å | 0.20 × 0.10 × 0.10 mm |
β = 91.61 (1)° | |
Data collection top
Rigaku AFC-5R diffractometer | 1748 reflections with I > 2σ(I) |
Absorption correction: ψ scan (North et al., 1968) | Rint = 0.062 |
Tmin = 0.942, Tmax = 0.970 | 3 standard reflections every 150 reflections |
3773 measured reflections | intensity decay: 4.3% |
3332 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.048 | 217 parameters |
wR(F2) = 0.152 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.00 | Δρmax = 0.30 e Å−3 |
3332 reflections | Δρmin = −0.52 e Å−3 |
Special details top
Refinement. Refinement using reflections with F2 > 0.0 σ(F2). The
weighted R-factor (wR), goodness of fit (S) and
R-factor (gt) are based on F, with F set to zero for
negative F. The threshold expression of F2 > 2.0
σ(F2) is used only for calculating R-factor (gt). |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | Occ. (<1) |
Ca1 | 0.5000 | 0.1509 (2) | 0.7500 | 0.0244 (2) | |
O1 | 0.4529 (1) | 0.1946 (4) | 0.6431 (1) | 0.0374 (6) | |
O2 | 0.5058 (1) | −0.1697 (4) | 0.6825 (1) | 0.0323 (5) | |
O3 | 0.4501 (1) | −0.3188 (4) | 0.5263 (1) | 0.0468 (7) | |
O4A | 0.3552 (2) | 0.0074 (8) | 0.4293 (2) | 0.057 (1) | 0.60 |
O4B | 0.3240 (4) | −0.232 (1) | 0.4573 (4) | 0.075 (3) | 0.40 |
O5 | 0.3886 (1) | 0.1163 (4) | 0.7655 (1) | 0.0351 (6) | |
O6 | 0.4506 (1) | 0.4781 (4) | 0.7889 (1) | 0.0334 (6) | |
O7 | 0.3015 (1) | 0.6194 (4) | 0.8432 (1) | 0.0378 (6) | |
O8 | 0.1671 (1) | 0.3252 (4) | 0.8119 (1) | 0.0450 (7) | |
O9 | 0.1512 (1) | −0.0474 (5) | 0.8753 (2) | 0.069 (1) | |
O10 | 0.2338 (2) | 0.0468 (8) | 0.4745 (2) | 0.109 (2) | |
C1 | 0.4511 (1) | 0.0360 (5) | 0.6066 (2) | 0.0277 (7) | |
C2 | 0.4206 (2) | 0.0359 (6) | 0.5462 (2) | 0.0357 (8) | |
C3 | 0.4202 (2) | −0.1393 (7) | 0.5094 (2) | 0.0397 (9) | |
C4 | 0.4793 (2) | −0.3278 (6) | 0.5832 (2) | 0.0421 (9) | |
C5 | 0.4802 (1) | −0.1634 (5) | 0.6248 (2) | 0.0264 (7) | |
C6 | 0.3865 (2) | −0.1658 (8) | 0.4481 (2) | 0.060 (1) | |
C7 | 0.3599 (2) | 0.2720 (5) | 0.7883 (2) | 0.0272 (7) | |
C8 | 0.2971 (2) | 0.2699 (6) | 0.8016 (2) | 0.0326 (8) | |
C9 | 0.2706 (2) | 0.4402 (6) | 0.8288 (2) | 0.0310 (8) | |
C10 | 0.3615 (2) | 0.6325 (6) | 0.8299 (2) | 0.0364 (8) | |
C11 | 0.3916 (1) | 0.4706 (5) | 0.8033 (2) | 0.0250 (7) | |
C12 | 0.2064 (2) | 0.4566 (7) | 0.8484 (2) | 0.0435 (10) | |
H2 | 0.4008 | 0.1596 | 0.5322 | 0.0428* | |
H4 | 0.4998 | −0.4536 | 0.5942 | 0.0506* | |
H4A | 0.3577 | 0.1396 | 0.4368 | 0.0862* | 0.60 |
H4B | 0.3051 | −0.4079 | 0.4571 | 0.1128* | 0.40 |
H6A | 0.4155 | −0.2050 | 0.4162 | 0.0718* | 0.60 |
H6B | 0.3584 | −0.2854 | 0.4518 | 0.0718* | 0.60 |
H6C | 0.3861 | −0.0314 | 0.4257 | 0.0718* | 0.40 |
H6D | 0.4079 | −0.2712 | 0.4227 | 0.0718* | 0.40 |
H8 | 0.2739 | 0.1494 | 0.7914 | 0.0392* | |
H8M | 0.1532 | 0.3942 | 0.7819 | 0.0675* | |
H9A | 0.1604 | 0.0456 | 0.8421 | 0.0824* | |
H9B | 0.1153 | −0.1280 | 0.8720 | 0.0824* | |
H10 | 0.3824 | 0.7585 | 0.8397 | 0.0437* | |
H10A | 0.2178 | 0.0452 | 0.4370 | 0.1306* | |
H10B | 0.2754 | 0.0527 | 0.4568 | 0.1306* | 0.60 |
H10C | 0.2514 | −0.0889 | 0.4654 | 0.1306* | 0.40 |
H12A | 0.2040 | 0.4155 | 0.8923 | 0.0522* | |
H12B | 0.1931 | 0.6047 | 0.8446 | 0.0522* | |
H26 | 0.531 (1) | −0.345 (3) | 0.692 (2) | 0.0388* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Ca1 | 0.0234 (5) | 0.0203 (5) | 0.0293 (5) | 0.0000 | −0.0034 (4) | 0.0000 |
O1 | 0.053 (2) | 0.025 (1) | 0.034 (1) | 0.010 (1) | −0.011 (1) | −0.003 (1) |
O2 | 0.039 (1) | 0.025 (1) | 0.032 (1) | 0.009 (1) | −0.009 (1) | −0.001 (1) |
O3 | 0.070 (2) | 0.036 (2) | 0.034 (1) | 0.007 (1) | −0.009 (1) | −0.009 (1) |
O4A | 0.079 (4) | 0.047 (3) | 0.045 (3) | −0.003 (3) | −0.019 (3) | 0.012 (2) |
O4B | 0.079 (6) | 0.072 (6) | 0.073 (6) | −0.014 (5) | −0.032 (5) | 0.000 (5) |
O5 | 0.027 (1) | 0.025 (1) | 0.053 (2) | −0.001 (1) | −0.001 (1) | −0.010 (1) |
O6 | 0.027 (1) | 0.025 (1) | 0.049 (2) | −0.0076 (10) | 0.004 (1) | −0.008 (1) |
O7 | 0.031 (1) | 0.030 (1) | 0.053 (2) | 0.001 (1) | 0.009 (1) | −0.011 (1) |
O8 | 0.031 (1) | 0.039 (2) | 0.065 (2) | −0.005 (1) | −0.009 (1) | 0.018 (1) |
O9 | 0.056 (2) | 0.044 (2) | 0.105 (3) | −0.014 (2) | −0.022 (2) | 0.026 (2) |
O10 | 0.096 (3) | 0.138 (4) | 0.092 (3) | −0.013 (3) | −0.019 (2) | −0.018 (3) |
C1 | 0.026 (2) | 0.027 (2) | 0.030 (2) | 0.001 (1) | 0.000 (1) | 0.002 (1) |
C2 | 0.038 (2) | 0.035 (2) | 0.033 (2) | 0.007 (2) | −0.004 (2) | 0.003 (2) |
C3 | 0.045 (2) | 0.043 (2) | 0.030 (2) | −0.001 (2) | −0.001 (2) | −0.002 (2) |
C4 | 0.060 (2) | 0.030 (2) | 0.036 (2) | 0.011 (2) | −0.009 (2) | −0.003 (2) |
C5 | 0.027 (2) | 0.024 (2) | 0.028 (2) | 0.000 (1) | 0.001 (1) | 0.001 (1) |
C6 | 0.075 (3) | 0.066 (3) | 0.037 (2) | −0.004 (3) | −0.014 (2) | −0.002 (2) |
C7 | 0.029 (2) | 0.025 (2) | 0.028 (2) | 0.001 (1) | −0.004 (1) | −0.002 (1) |
C8 | 0.026 (2) | 0.029 (2) | 0.042 (2) | −0.006 (1) | −0.002 (1) | −0.003 (2) |
C9 | 0.027 (2) | 0.031 (2) | 0.036 (2) | −0.001 (1) | −0.002 (1) | −0.001 (2) |
C10 | 0.032 (2) | 0.027 (2) | 0.051 (2) | −0.006 (2) | 0.006 (2) | −0.008 (2) |
C11 | 0.022 (2) | 0.022 (2) | 0.031 (2) | −0.002 (1) | 0.001 (1) | 0.002 (1) |
C12 | 0.029 (2) | 0.040 (2) | 0.062 (3) | 0.002 (2) | 0.008 (2) | −0.001 (2) |
Geometric parameters (Å, º) top
CA1—O1 | 2.483 (2) | O10—H10B | 1.000 |
CA1—O2 | 2.462 (2) | O10—H10C | 0.951 |
CA1—O5 | 2.494 (2) | C1—C2 | 1.431 (5) |
CA1—O6 | 2.462 (2) | C1—C5 | 1.443 (5) |
O1—C1 | 1.255 (4) | C2—C3 | 1.342 (5) |
O2—C5 | 1.335 (4) | C2—H2 | 0.930 |
O2—H26 | 1.24 (2) | C3—C6 | 1.487 (6) |
O3—C3 | 1.341 (5) | C4—C5 | 1.351 (5) |
O3—C4 | 1.353 (4) | C4—H4 | 0.930 |
O4A—C6 | 1.335 (7) | C6—H6A | 0.975 (5) |
O4A—H4A | 0.840 (5) | C6—H6B | 0.972 (5) |
O4B—C6 | 1.46 (1) | C6—H6C | 0.962 (5) |
O4B—H4B | 1.170 (9) | C6—H6D | 0.978 (5) |
O5—C7 | 1.261 (4) | C7—C8 | 1.418 (5) |
O6—C11 | 1.342 (4) | C7—C11 | 1.451 (4) |
O6—H26i | 1.24 (2) | C8—C9 | 1.347 (5) |
O7—C9 | 1.337 (4) | C8—H8 | 0.930 |
O7—C10 | 1.362 (4) | C9—C12 | 1.490 (5) |
O8—C12 | 1.406 (5) | C10—C11 | 1.339 (5) |
O8—H8M | 0.820 | C10—H10 | 0.930 |
O9—H9A | 0.937 | C12—H12A | 0.970 |
O9—H9B | 0.937 | C12—H12B | 0.970 |
O10—H10A | 0.861 | | |
| | | |
O1···O9ii | 2.818 (4) | O5···O8vii | 2.715 (4) |
O1···C4iii | 3.291 (4) | O5···C12vii | 3.305 (5) |
O2···C10iv | 3.188 (4) | O5···C10v | 3.367 (4) |
O2···C11iv | 3.188 (4) | O8···C10vii | 3.285 (5) |
O2···O6v | 3.396 (3) | O8···C1ii | 3.427 (4) |
O3···O3vi | 3.360 (6) | O8···C11vii | 3.513 (4) |
O3···O9vii | 3.411 (4) | O8···C7ii | 3.540 (4) |
O3···C4vi | 3.585 (5) | O8···C5ii | 3.547 (4) |
O4A···C10viii | 3.084 (6) | O9···O10xi | 2.744 (5) |
O4A···O7viii | 3.163 (5) | O9···C4ii | 3.324 (5) |
O4A···C8ix | 3.431 (6) | O9···C12v | 3.371 (5) |
O4A···C7ix | 3.465 (6) | O9···C1vii | 3.464 (4) |
O4B···O10x | 2.77 (1) | O9···C2vii | 3.486 (5) |
O4B···C9ix | 3.211 (9) | O10···O10xii | 2.835 (10) |
O4B···C8ix | 3.349 (9) | C6···C7ix | 3.490 (5) |
O4B···O7ix | 3.441 (9) | | |
| | | |
O1—CA1—O1xiii | 167.4 (1) | C2—C1—C5 | 115.6 (3) |
O1—CA1—O2 | 65.41 (7) | C1—C2—C3 | 121.2 (3) |
O1—CA1—O2xiii | 126.41 (8) | C1—C2—H2 | 119.4 |
O1—CA1—O5 | 75.14 (8) | C3—C2—H2 | 119.4 |
O1—CA1—O5xiii | 105.99 (8) | O3—C3—C2 | 121.7 (3) |
O1—CA1—O6 | 92.21 (8) | O3—C3—C6 | 111.8 (3) |
O1—CA1—O6xiii | 77.31 (8) | C2—C3—C6 | 126.5 (4) |
O1xiii—CA1—O2 | 126.41 (8) | O3—C4—C5 | 123.3 (3) |
O1xiii—CA1—O2xiii | 65.41 (7) | O3—C4—H4 | 118.3 |
O1xiii—CA1—O5 | 105.99 (8) | C5—C4—H4 | 118.3 |
O1xiii—CA1—O5xiii | 75.14 (8) | O2—C5—C1 | 116.3 (3) |
O1xiii—CA1—O6 | 77.31 (8) | O2—C5—C4 | 125.1 (3) |
O1xiii—CA1—O6xiii | 92.21 (8) | C1—C5—C4 | 118.6 (3) |
O2—CA1—O2xiii | 71.7 (1) | O4A—C6—C3 | 114.4 (4) |
O2—CA1—O5 | 94.26 (8) | O4A—C6—H6A | 109.7 (5) |
O2—CA1—O5xiii | 77.63 (8) | O4A—C6—H6B | 108.5 (5) |
O2—CA1—O6 | 153.62 (7) | O4B—C6—C3 | 111.4 (5) |
O2—CA1—O6xiii | 116.40 (8) | O4B—C6—H6C | 108.5 (6) |
O2xiii—CA1—O5 | 77.63 (8) | O4B—C6—H6D | 110.7 (5) |
O2xiii—CA1—O5xiii | 94.26 (8) | C3—C6—H6A | 108.4 (4) |
O2xiii—CA1—O6 | 116.40 (8) | C3—C6—H6B | 108.5 (4) |
O2xiii—CA1—O6xiii | 153.62 (7) | C3—C6—H6C | 109.4 (4) |
O5—CA1—O5xiii | 170.1 (1) | C3—C6—H6D | 108.7 (4) |
O5—CA1—O6 | 65.25 (7) | H6A—C6—H6B | 107.1 (5) |
O5—CA1—O6xiii | 124.16 (8) | H6C—C6—H6D | 108.0 (4) |
O5xiii—CA1—O6 | 124.16 (8) | O5—C7—C8 | 124.8 (3) |
O5xiii—CA1—O6xiii | 65.25 (7) | O5—C7—C11 | 119.6 (3) |
O6—CA1—O6xiii | 68.4 (1) | C8—C7—C11 | 115.5 (3) |
CA1—O1—C1 | 118.9 (2) | C7—C8—C9 | 120.9 (3) |
CA1—O2—C5 | 118.9 (2) | C7—C8—H8 | 119.6 |
CA1—O2—H26 | 130.1 (19) | C9—C8—H8 | 119.6 |
C5—O2—H26 | 110.9 (16) | O7—C9—C8 | 122.1 (3) |
C3—O3—C4 | 119.4 (3) | O7—C9—C12 | 111.1 (3) |
C6—O4A—H4A | 134.7 (5) | C8—C9—C12 | 126.8 (3) |
C6—O4B—H4B | 127.1 (8) | O7—C10—C11 | 122.5 (3) |
CA1—O5—C7 | 119.4 (2) | O7—C10—H10 | 118.7 |
CA1—O6—C11 | 119.2 (2) | C11—C10—H10 | 118.7 |
CA1—O6—H26i | 134.7 | O6—C11—C7 | 116.3 (3) |
C11—O6—H26i | 105.3 | O6—C11—C10 | 124.3 (3) |
C9—O7—C10 | 119.5 (3) | C7—C11—C10 | 119.4 (3) |
C12—O8—H8M | 109.5 | O8—C12—C9 | 112.4 (3) |
H9A—O9—H9B | 118.26 | O8—C12—H12A | 109.1 |
H10A—O10—H10B | 90.5 (4) | O8—C12—H12B | 109.1 |
H10A—O10—H10C | 87.7 (4) | C9—C12—H12A | 109.1 |
O1—C1—C2 | 124.0 (3) | C9—C12—H12B | 109.1 |
O1—C1—C5 | 120.4 (3) | H12A—C12—H12B | 107.9 |
| | | |
CA1—O1—C1—C2 | 174.3 (2) | O3—C4—C5—C1 | −3.1 (5) |
CA1—O1—C1—C5 | −4.9 (4) | O4A—C6—C3—C2 | 1.2 (7) |
CA1—O1xiii—C1xiii—C2xiii | 174.3 (2) | O4B—C6—C3—C2 | −84.5 (6) |
CA1—O1xiii—C1xiii—C5xiii | −4.9 (4) | O5—CA1—O1—C1 | −98.4 (2) |
CA1—O2—C5—C1 | 0.4 (4) | O5—CA1—O1xiii—C1xiii | 71.4 (2) |
CA1—O2—C5—C4 | −179.1 (3) | O5—CA1—O2—C5 | 69.7 (2) |
CA1—O2xiii—C5xiii—C1xiii | 0.4 (4) | O5—CA1—O2xiii—C5xiii | −116.1 (2) |
CA1—O2xiii—C5xiii—C4xiii | −179.1 (3) | O5—CA1—O6—C11 | 5.1 (2) |
CA1—O5—C7—C8 | −177.6 (3) | O5—CA1—O6xiii—C11xiii | −171.4 (2) |
CA1—O5—C7—C11 | 1.8 (4) | O5—C7—C8—C9 | 176.7 (3) |
CA1—O5xiii—C7xiii—C8xiii | −177.6 (3) | O5—C7—C11—O6 | 2.9 (4) |
CA1—O5xiii—C7xiii—C11xiii | 1.8 (4) | O5—C7—C11—C10 | −177.2 (3) |
CA1—O6—C11—C7 | −6.3 (4) | O6—CA1—O1—C1 | −162.0 (2) |
CA1—O6—C11—C10 | 173.9 (3) | O6—CA1—O1xiii—C1xiii | 130.7 (2) |
CA1—O6xiii—C11xiii—C7xiii | −6.3 (4) | O6—CA1—O2—C5 | 32.3 (3) |
CA1—O6xiii—C11xiii—C10xiii | 173.9 (3) | O6—CA1—O2xiii—C5xiii | −62.0 (2) |
O1—CA1—O1xiii—C1xiii | 164.8 (2) | O6—CA1—O5—C7 | −3.5 (2) |
O1—CA1—O2—C5 | −1.8 (2) | O6—CA1—O5xiii—C7xiii | −40.1 (3) |
O1—CA1—O2xiii—C5xiii | −176.9 (2) | O6—CA1—O6xiii—C11xiii | 153.0 (3) |
O1—CA1—O5—C7 | −103.1 (2) | O6—C11—C7—C8 | −177.6 (3) |
O1—CA1—O5xiii—C7xiii | 63.9 (2) | O6—C11—C10—O7 | 179.3 (3) |
O1—CA1—O6—C11 | 77.6 (2) | O7—C9—C8—C7 | 1.5 (5) |
O1—CA1—O6xiii—C11xiii | −109.4 (2) | O7—C9—C12—O8 | 153.9 (3) |
O1—C1—C2—C3 | −179.8 (3) | O7—C10—C11—C7 | −0.6 (5) |
O1—C1—C5—O2 | 3.0 (5) | O8—C12—C9—C8 | −27.8 (5) |
O1—C1—C5—C4 | −177.4 (3) | C1—C2—C3—C6 | 175.1 (4) |
O2—CA1—O1—C1 | 3.5 (2) | C2—C1—C5—C4 | 3.3 (5) |
O2—CA1—O1xiii—C1xiii | −36.5 (3) | C2—C3—O3—C4 | 3.2 (5) |
O2—CA1—O2xiii—C5xiii | 145.2 (3) | C3—O3—C4—C5 | −0.2 (5) |
O2—CA1—O5—C7 | −166.3 (2) | C3—C2—C1—C5 | −0.6 (5) |
O2—CA1—O5xiii—C7xiii | 123.5 (2) | C4—O3—C3—C6 | −174.9 (3) |
O2—CA1—O6—C11 | 46.8 (3) | C7—C8—C9—C12 | −176.7 (3) |
O2—CA1—O6xiii—C11xiii | −55.5 (2) | C8—C7—C11—C10 | 2.2 (5) |
O2—C5—C1—C2 | −176.2 (3) | C8—C9—O7—C10 | 0.3 (5) |
O2—C5—C4—O3 | 176.4 (3) | C9—O7—C10—C11 | −0.8 (5) |
O3—C3—C2—C1 | −2.7 (6) | C9—C8—C7—C11 | −2.7 (5) |
O3—C3—C6—O4A | 179.2 (4) | C10—O7—C9—C12 | 178.7 (3) |
O3—C3—C6—O4B | 93.5 (6) | C10—O7—C9—C12 | 178.7 (3) |
Symmetry codes: (i) −x+1, y+1, −z+3/2; (ii) −x+1/2, y+1/2, −z+3/2; (iii) x, y+1, z; (iv) −x+1, y−1, −z+3/2; (v) x, y−1, z; (vi) −x+1, −y−1, −z+1; (vii) −x+1/2, y−1/2, −z+3/2; (viii) x, −y+1, z−1/2; (ix) x, −y, z−1/2; (x) −x+1/2, −y−1/2, −z+1; (xi) x, −y, z+1/2; (xii) −x+1/2, −y+1/2, −z+1; (xiii) −x+1, y, −z+3/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O8—H8M···O5ii | 0.82 | 1.93 | 2.715 (3) | 160 |
O9—H9A···O8 | 0.94 | 1.86 | 2.708 (4) | 149 |
O9—H9B···O1vii | 0.94 | 1.89 | 2.818 (4) | 173 |
O10—H10A···O9ix | 0.86 | 1.94 | 2.744 (5) | 155 |
O10—H10B···O4A | 1.00 | 1.89 | 2.874 (7) | 169 |
O10—H10C···O4B | 0.95 | 1.84 | 2.670 (10) | 144 |
O2—H26···O6iv | 1.24 (2) | 1.24 (2) | 2.462 (4) | 168 (3) |
Symmetry codes: (ii) −x+1/2, y+1/2, −z+3/2; (iv) −x+1, y−1, −z+3/2; (vii) −x+1/2, y−1/2, −z+3/2; (ix) x, −y, z−1/2. |
Experimental details
Crystal data |
Chemical formula | [Ca(C6H5O4)2(C6H6O4)2]·4H2O |
Mr | 678.56 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 296 |
a, b, c (Å) | 22.020 (4), 6.223 (4), 21.225 (3) |
β (°) | 91.61 (1) |
V (Å3) | 2907 (2) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.31 |
Crystal size (mm) | 0.20 × 0.10 × 0.10 |
|
Data collection |
Diffractometer | Rigaku AFC-5R diffractometer |
Absorption correction | ψ scan (North et al., 1968) |
Tmin, Tmax | 0.942, 0.970 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3773, 3332, 1748 |
Rint | 0.062 |
(sin θ/λ)max (Å−1) | 0.650 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.048, 0.152, 1.00 |
No. of reflections | 3332 |
No. of parameters | 217 |
No. of restraints | ? |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.30, −0.52 |
Selected geometric parameters (Å, º) topCA1—O1 | 2.483 (2) | CA1—O5 | 2.494 (2) |
CA1—O2 | 2.462 (2) | CA1—O6 | 2.462 (2) |
| | | |
O1—CA1—O1i | 167.4 (1) | O2—CA1—O6 | 153.62 (7) |
O1—CA1—O2 | 65.41 (7) | O2—CA1—O6i | 116.40 (8) |
O1—CA1—O2i | 126.41 (8) | O5—CA1—O5i | 170.1 (1) |
O1—CA1—O5 | 75.14 (8) | O5—CA1—O6 | 65.25 (7) |
O1—CA1—O5i | 105.99 (8) | O5—CA1—O6i | 124.16 (8) |
O1—CA1—O6 | 92.21 (8) | O6—CA1—O6i | 68.4 (1) |
O1—CA1—O6i | 77.31 (8) | CA1—O1—C1 | 118.9 (2) |
O2—CA1—O2i | 71.7 (1) | CA1—O2—C5 | 118.9 (2) |
O2—CA1—O5 | 94.26 (8) | CA1—O5—C7 | 119.4 (2) |
O2—CA1—O5i | 77.63 (8) | CA1—O6—C11 | 119.2 (2) |
Symmetry code: (i) −x+1, y, −z+3/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O8—H8M···O5ii | 0.82 | 1.93 | 2.715 (3) | 160 |
O9—H9A···O8 | 0.94 | 1.86 | 2.708 (4) | 149 |
O9—H9B···O1iii | 0.94 | 1.89 | 2.818 (4) | 173 |
O10—H10A···O9iv | 0.86 | 1.94 | 2.744 (5) | 155 |
O10—H10B···O4A | 1.00 | 1.89 | 2.874 (7) | 169 |
O10—H10C···O4B | 0.95 | 1.84 | 2.670 (10) | 144 |
O2—H26···O6v | 1.24 (2) | 1.24 (2) | 2.462 (4) | 168 (3) |
Symmetry codes: (ii) −x+1/2, y+1/2, −z+3/2; (iii) −x+1/2, y−1/2, −z+3/2; (iv) x, −y, z−1/2; (v) −x+1, y−1, −z+3/2. |
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Kojic acid [5-hydroxy-2-hydroxymethyl-4-pyrone, (I)] is a metabolic product of several species of the genus Aspergillus. It has been reported that kojic acid is an efficient inhibitor of mashroom tyrosinase and other polyphenol oxidases (Chen et al., 1991), which consequently suppresses biosynthesis of melanin in melanocytes. Kojic acid is also widely known to be an iron chelator (McBryde & Atkinson, 1961; Mitani et al., 2001) and a radical scavenger (Niwa & Akamatsu, 1991). Metal complexes containing kojic acid has been studied in solution (Barret et al., 2001; Malhotra et al., 2001; Buglyo et al., 2000; Yuen et al., 1997; Katoh et al., 1992), however, with regard to the crystal structures of kojic acid–metal chelate complexes, only the methyltin(IV) (Lockhart & Davidson, 1987) and dioxomolybdenum(VI) (Lord et al., 1999) complexes have been reported. To clarify the chelating mode of kojic acid to the alkaline earth metal, we have analyzed the crystal structure of the kojic acid–Ca2+ complex, (II), and present its structure here.
In (II), the Ca atom lies on a twofold axis and is octacoordinated by the O atoms of four ligand molecules, in which two of four hydroxyl groups are ionized (Fig. 1 and Table 1). The hydroxyl and ketone O atoms of each ligand form a five-membered chelate ring with the Ca atom. Until now, the crystal structures of only two kojic acid–metal complexes, viz. the Me2Sn4+ and MoO26+ complexes, have been analyzed. Although the number of ligand molecules is different in the Ca2+ complex, the five-membered ring between each ligand and the metal are similar.
In (II), the ketone C ═O bond lengths are somewhat longer [O1—C1 1.255 (4) Å and O5—C7 1.261 (4) Å] than that in kojic acid [1.244 (1) Å; Lokaj et al., 1991], but they are similar to those in other complexes [Me2Sn4+ 1.254 (7)–1.267 (7) Å and MoO26+ 1.272 (3) and 1.278 (3) Å].
The Ca—Oketone bond lengths in (II) are slightly longer [Ca1—O1 2.483 (2) Å and Ca1—O5 2.494 (2) Å] than the Ca—OOH distances [Ca1—O2 2.462 (2) Å and Ca1—O6 2.462 (2) Å]. In the [Me2Sn]4+ and [MoO2]6+ complexes, the M—Oketone bond lengths are markedly longer than the M—OOH distances [Sn—Oketone 2.365 (4)–2.435 (4) Å and Sn—OOH(deprotonated) 2.106 (4)–2.145 (4) Å; Mo—Oketone O 2.236 (2) and 2.286 (2) Å, and Mo—OOH(deprotonated) 1.981 (2) and 1.994 (2) Å], which indicates a distinction between Lewis acid–base and ionic bonding for the two types of O atoms. In the case of (II), the complex molecules are connected by strong hydrogen bonding [O2—H26···O6, with O2···O6 = 2.462 (4) Å; Table 2], and consequently atom H26 is shared by two hydroxylate anions. Therefore, the Ca—OOH distances reflect the co-existence of deprotonated O atoms and hydroxyl groups.
The crystal structure of (II) is stabilized by partial stacking between the ligand molecules of neighboring compounds [O3···C2i 3.176 (5) Å and C2···O3i 3.176 (5) Å; symmetry code: (i) 1 - x, -y, 1 - z] and hydrogen bonds between chelate complexes and water molecules (Table 2). In the ligand molecules, the hydroxymethyl groups are disordered over two positions (C6—O4A and C6—O4B). This may be due to comparatively loose packing, in which four water molecules are cocrystallized per Ca2+ complex molecule.