Sodium citrate dihydrate doped with Mn3+ ions, namely trisodium(I) managnese(III) citrate(3-) dihydrate, [Na3Mn0.011(C6H5O7)(H2O)2]n, was obtained during attempts to prepare some complex MnIII citrates from a concentrated strong alkaline solution containing Na+, Mn3+ and citrate ions. The compound is isostructural with the recently described Na3(C6H5O7)·2H2O [Fischer & Palladino (2003). Acta Cryst. E59, m1080-m1082]. The essential difference between these two structures is the presence of a very small proportion (0.205 wt%) of Mn3+ ions, which are positioned at the special 4e Wyckoff position in C2/c, where they are in a highly distorted octahedral environment of O atoms from two citrate anions.
Supporting information
CCDC reference: 749693
Into an aqueous solution containing an equimolar mixture of Mn2+ ions and
citric acid (~1 mol l-1), a solution of NaOH (~1 mol l-1) was
added slowly until a pH of ~13 was reached. The presence of Mn3+ ions
in this solution was confirmed by UV/vis spectroscopy. After about a month,
the slow evaporation of the mother liquor resulted in colourless, needle-like
(up to 20 mm long) crystals. These crystals were assumed to be one of the
known sodium citrates (Fischer & Palladino, 2003; Viossat et al., 1986)
and were not further characterized. However, after about two months, a few
brown, prismatic crystals were obtained from the honey-like slurry solution.
They were picked out, quickly washed by putting them into a drop of water to
remove the mother liquor and dried using filter paper. The presence of Mn was
confirmed by a qualitative energy dispersive X-ray spectroscopy analysis (a
quantitative determination was not possible owing to crystal decomposition
under the given experimental conditions).
With the exception of Mn, all non-H atoms were refined anisotropically. H atoms
were located in difference Fourier maps and refined isotropically with
constraints [restraints?] applied on O—H bond distances in water
molecules [O—H = 0.85 (s.u. value?) Å]. The Mn3+ ion was located
at special Wyckoff position 4e as a maximum of 1.25 e Å-3 in a
ΔF map (the next highest peak was ~0.7 e Å-3). To avoid great
correlations, the occupancy and isotropic atomic displacement parameter of Mn
were tested in subsequent cycles. The final cycles of refinement were
performed keeping the Mn isotropic atomic displacement parameter at a
reasonable value of 0.025 Å2 yielding the atom site occupancy of
0.0224 (8). The final R value for F2 > 2σ(F2) of
0.0289 may be compared with that of 0.0326 obtained when the Mn ion is not
included in the refinement. The highest residual maxima and minima in the last
difference Fourier map are located at a distance of about 0.80 Å from atom
O3, suggesting possible disorder, which was not further investigated.
Data collection: COLLECT (Nonius, 2002); cell refinement: HKL SCALEPACK (Otwinowski et al., 2003); data reduction: DENZO–SMN (Otwinowski & Minor, 1997; Otwinowski et al.,
2003); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) and WinGX (Farrugia, 1999); molecular graphics: ATOMS (Dowty, 2000); software used to prepare material for publication: publCIF (Westrip, 2009).
trisodium(I) managnese(III) citrate(3-) dihydrate
top
Crystal data top
3Na+·0.011Mn3+·C6H5O73−·2H2O | F(000) = 1202.5 |
Mr = 294.71 | Dx = 1.820 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71069 Å |
Hall symbol: -C 2yc | Cell parameters from 5321 reflections |
a = 15.7072 (3) Å | θ = 2.0–32.6° |
b = 12.4989 (2) Å | µ = 0.28 mm−1 |
c = 11.2710 (2) Å | T = 295 K |
β = 103.5991 (10)° | Prism, brown |
V = 2150.71 (7) Å3 | 0.68 × 0.64 × 0.38 mm |
Z = 8 | |
Data collection top
Nonius Kappa CCD diffractometer | 2661 independent reflections |
Radiation source: fine-focus sealed tube | 2508 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.022 |
ϕ scans | θmax = 28.3°, θmin = 2.6° |
Absorption correction: multi-scan (DENZO–SMN; Otwinowski & Minor, 1997; Otwinowski et al.,
2003) | h = −20→20 |
Tmin = 0.833, Tmax = 0.902 | k = −16→16 |
9936 measured reflections | l = −15→15 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.029 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.078 | w = 1/[σ2(Fo2) + (0.0404P)2 + 1.8573P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max = 0.001 |
2661 reflections | Δρmax = 0.70 e Å−3 |
202 parameters | Δρmin = −0.44 e Å−3 |
4 restraints | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0047 (6) |
Crystal data top
3Na+·0.011Mn3+·C6H5O73−·2H2O | V = 2150.71 (7) Å3 |
Mr = 294.71 | Z = 8 |
Monoclinic, C2/c | Mo Kα radiation |
a = 15.7072 (3) Å | µ = 0.28 mm−1 |
b = 12.4989 (2) Å | T = 295 K |
c = 11.2710 (2) Å | 0.68 × 0.64 × 0.38 mm |
β = 103.5991 (10)° | |
Data collection top
Nonius Kappa CCD diffractometer | 2661 independent reflections |
Absorption correction: multi-scan (DENZO–SMN; Otwinowski & Minor, 1997; Otwinowski et al.,
2003) | 2508 reflections with I > 2σ(I) |
Tmin = 0.833, Tmax = 0.902 | Rint = 0.022 |
9936 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.029 | 4 restraints |
wR(F2) = 0.078 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | Δρmax = 0.70 e Å−3 |
2661 reflections | Δρmin = −0.44 e Å−3 |
202 parameters | |
Special details top
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. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | Occ. (<1) |
Na1 | 0.39991 (3) | 0.49617 (4) | −0.10206 (5) | 0.02484 (13) | |
Na2 | 0.38677 (3) | 0.32748 (4) | 0.17356 (4) | 0.02492 (13) | |
Na3 | 0.31272 (3) | 0.07800 (4) | 0.12686 (5) | 0.02888 (14) | |
O1 | 0.32919 (5) | 0.34529 (6) | −0.04754 (7) | 0.02116 (18) | |
O2 | 0.24804 (5) | 0.23985 (8) | −0.18719 (9) | 0.0286 (2) | |
O3 | 0.68940 (7) | 0.06452 (11) | 0.06092 (10) | 0.0464 (3) | |
O4 | 0.59587 (6) | 0.09239 (8) | 0.17780 (8) | 0.0312 (2) | |
O5 | 0.52682 (6) | 0.37467 (7) | −0.06520 (8) | 0.0264 (2) | |
O6 | 0.52673 (6) | 0.34382 (7) | 0.12847 (8) | 0.02408 (19) | |
O7 | 0.43814 (5) | 0.16054 (6) | 0.07931 (7) | 0.01912 (17) | |
H7 | 0.4838 (13) | 0.1393 (16) | 0.1344 (18) | 0.045 (5)* | |
O8 | 0.35896 (6) | 0.51987 (8) | 0.18517 (9) | 0.0296 (2) | |
H8A | 0.3926 (13) | 0.5595 (16) | 0.157 (2) | 0.059 (6)* | |
H8B | 0.3056 (7) | 0.5365 (15) | 0.1539 (17) | 0.045 (5)* | |
O9 | 0.23669 (7) | −0.08802 (8) | 0.13221 (9) | 0.0319 (2) | |
H9A | 0.2557 (13) | −0.1081 (16) | 0.0714 (14) | 0.051 (6)* | |
H9B | 0.2431 (14) | −0.1386 (12) | 0.1841 (15) | 0.051 (6)* | |
C1 | 0.32028 (7) | 0.26728 (8) | −0.12038 (9) | 0.0172 (2) | |
C2 | 0.40138 (7) | 0.20529 (9) | −0.13208 (10) | 0.0203 (2) | |
H2A | 0.3837 (11) | 0.1330 (14) | −0.1561 (15) | 0.030 (4)* | |
H2B | 0.4229 (11) | 0.2418 (14) | −0.1944 (17) | 0.035 (4)* | |
C3 | 0.47450 (7) | 0.20323 (8) | −0.01584 (9) | 0.0161 (2) | |
C4 | 0.54984 (7) | 0.13189 (9) | −0.03640 (10) | 0.0209 (2) | |
H4A | 0.5243 (13) | 0.0675 (15) | −0.0761 (17) | 0.040 (5)* | |
H4B | 0.5811 (12) | 0.1667 (14) | −0.0893 (17) | 0.035 (4)* | |
C5 | 0.61742 (8) | 0.09578 (10) | 0.07771 (11) | 0.0234 (2) | |
C6 | 0.51200 (6) | 0.31647 (9) | 0.01859 (10) | 0.0172 (2) | |
Mn1 | 0.5 | 0.1768 (10) | 0.25 | 0.025* | 0.0224 (8) |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Na1 | 0.0208 (2) | 0.0202 (2) | 0.0307 (3) | −0.00324 (17) | 0.00030 (18) | 0.00327 (18) |
Na2 | 0.0192 (2) | 0.0308 (3) | 0.0246 (2) | −0.00394 (18) | 0.00482 (18) | −0.00540 (18) |
Na3 | 0.0179 (2) | 0.0291 (3) | 0.0379 (3) | −0.00172 (18) | 0.00300 (19) | 0.0039 (2) |
O1 | 0.0196 (4) | 0.0193 (4) | 0.0237 (4) | 0.0011 (3) | 0.0031 (3) | −0.0022 (3) |
O2 | 0.0149 (4) | 0.0354 (5) | 0.0326 (5) | −0.0019 (3) | −0.0002 (3) | −0.0087 (4) |
O3 | 0.0240 (5) | 0.0767 (8) | 0.0396 (6) | 0.0230 (5) | 0.0098 (4) | 0.0182 (5) |
O4 | 0.0249 (4) | 0.0450 (5) | 0.0225 (4) | 0.0088 (4) | 0.0033 (3) | 0.0056 (4) |
O5 | 0.0247 (4) | 0.0267 (4) | 0.0281 (4) | −0.0034 (3) | 0.0070 (3) | 0.0076 (3) |
O6 | 0.0240 (4) | 0.0253 (4) | 0.0223 (4) | −0.0069 (3) | 0.0040 (3) | −0.0052 (3) |
O7 | 0.0160 (4) | 0.0202 (4) | 0.0215 (4) | −0.0012 (3) | 0.0051 (3) | 0.0031 (3) |
O8 | 0.0226 (4) | 0.0351 (5) | 0.0300 (5) | 0.0007 (4) | 0.0038 (3) | 0.0072 (4) |
O9 | 0.0317 (5) | 0.0318 (5) | 0.0331 (5) | 0.0070 (4) | 0.0092 (4) | 0.0060 (4) |
C1 | 0.0149 (5) | 0.0185 (5) | 0.0174 (5) | −0.0003 (4) | 0.0025 (4) | 0.0030 (4) |
C2 | 0.0169 (5) | 0.0223 (5) | 0.0192 (5) | 0.0026 (4) | −0.0005 (4) | −0.0046 (4) |
C3 | 0.0138 (4) | 0.0174 (5) | 0.0166 (4) | 0.0009 (4) | 0.0026 (3) | 0.0001 (4) |
C4 | 0.0189 (5) | 0.0236 (5) | 0.0199 (5) | 0.0066 (4) | 0.0037 (4) | −0.0001 (4) |
C5 | 0.0182 (5) | 0.0264 (6) | 0.0245 (5) | 0.0046 (4) | 0.0030 (4) | 0.0031 (4) |
C6 | 0.0115 (4) | 0.0183 (5) | 0.0214 (5) | 0.0006 (4) | 0.0029 (4) | 0.0005 (4) |
Geometric parameters (Å, º) top
Na1—O8i | 2.3408 (11) | O5—C6 | 1.2565 (14) |
Na1—O1 | 2.3428 (9) | O6—C6 | 1.2528 (14) |
Na1—O6ii | 2.3617 (9) | O7—C3 | 1.4315 (12) |
Na1—O9iii | 2.3864 (11) | O7—H7 | 0.87 (2) |
Na1—O5 | 2.4623 (10) | O8—H8A | 0.841 (10) |
Na1—O5ii | 2.5425 (10) | O8—H8B | 0.854 (9) |
Na2—O2iii | 2.3169 (10) | O9—H9A | 0.847 (9) |
Na2—O6iv | 2.3326 (9) | O9—H9B | 0.851 (9) |
Na2—O6 | 2.3787 (10) | C1—C2 | 1.5230 (15) |
Na2—O1 | 2.4531 (9) | C2—C3 | 1.5259 (14) |
Na2—O8 | 2.4531 (11) | C2—H2A | 0.965 (17) |
Na2—O7 | 2.5566 (9) | C2—H2B | 0.963 (19) |
Na3—O4iv | 2.3355 (10) | C3—C4 | 1.5421 (14) |
Na3—O7 | 2.3934 (9) | C3—C6 | 1.5470 (15) |
Na3—O1iii | 2.3979 (9) | C4—C5 | 1.5306 (15) |
Na3—O9 | 2.4020 (11) | C4—H4A | 0.961 (19) |
Na3—O2iii | 2.6195 (11) | C4—H4B | 0.961 (19) |
Na3—O3v | 2.7606 (14) | Mn1—Na2 | 2.594 (9) |
O1—C1 | 1.2611 (13) | Mn1—O4 | 2.150 (6) |
O2—C1 | 1.2531 (13) | Mn1—O6 | 2.585 (10) |
O3—C5 | 1.2519 (15) | Mn1—O7 | 1.9514 (15) |
O4—C5 | 1.2525 (15) | Mn1—H7 | 1.35 (2) |
| | | |
O8i—Na1—O1 | 99.60 (4) | C6—O6—Mn1 | 106.76 (16) |
O8i—Na1—O6ii | 88.17 (4) | Na2iv—O6—Mn1 | 63.44 (9) |
O1—Na1—O6ii | 171.96 (4) | Na1ii—O6—Mn1 | 153.58 (8) |
O8i—Na1—O9iii | 82.77 (4) | Na2—O6—Mn1 | 62.87 (9) |
O1—Na1—O9iii | 87.63 (4) | C3—O7—Mn1 | 120.38 (19) |
O6ii—Na1—O9iii | 91.35 (4) | C3—O7—Na3 | 145.37 (7) |
O8i—Na1—O5 | 97.85 (4) | Mn1—O7—Na3 | 93.99 (15) |
O1—Na1—O5 | 82.78 (3) | C3—O7—Na2 | 103.15 (6) |
O6ii—Na1—O5 | 98.28 (3) | Mn1—O7—Na2 | 68.8 (3) |
O9iii—Na1—O5 | 170.36 (4) | Na3—O7—Na2 | 84.37 (3) |
O8i—Na1—O5ii | 141.39 (4) | C3—O7—H7 | 103.9 (13) |
O1—Na1—O5ii | 118.45 (3) | Na3—O7—H7 | 107.0 (13) |
O6ii—Na1—O5ii | 53.60 (3) | Na2—O7—H7 | 103.8 (13) |
O9iii—Na1—O5ii | 92.01 (4) | Na1vi—O8—Na2 | 87.78 (4) |
O5—Na1—O5ii | 93.39 (3) | Na1vi—O8—H8A | 113.4 (16) |
O2iii—Na2—O6iv | 107.71 (4) | Na2—O8—H8A | 114.9 (16) |
O2iii—Na2—O6 | 161.86 (4) | Na1vi—O8—H8B | 116.8 (13) |
O6iv—Na2—O6 | 80.63 (4) | Na2—O8—H8B | 112.7 (13) |
O2iii—Na2—O1 | 88.62 (3) | H8A—O8—H8B | 110 (2) |
O6iv—Na2—O1 | 163.04 (4) | Na1iii—O9—Na3 | 90.94 (4) |
O6—Na2—O1 | 85.05 (3) | Na1iii—O9—H9A | 120.2 (15) |
O2iii—Na2—O8 | 100.11 (4) | Na3—O9—H9A | 88.0 (14) |
O6iv—Na2—O8 | 86.22 (3) | Na1iii—O9—H9B | 114.3 (14) |
O6—Na2—O8 | 96.45 (4) | Na3—O9—H9B | 132.9 (14) |
O1—Na2—O8 | 86.42 (3) | H9A—O9—H9B | 109 (2) |
O2iii—Na2—O7 | 96.53 (3) | O2—C1—O1 | 123.30 (10) |
O6iv—Na2—O7 | 107.41 (3) | O2—C1—C2 | 117.80 (10) |
O6—Na2—O7 | 65.39 (3) | O1—C1—C2 | 118.85 (9) |
O1—Na2—O7 | 74.27 (3) | C1—C2—C3 | 114.22 (9) |
O8—Na2—O7 | 154.13 (4) | C1—C2—H2A | 108.0 (10) |
O4iv—Na3—O7 | 79.75 (3) | C3—C2—H2A | 109.5 (10) |
O4iv—Na3—O1iii | 129.21 (4) | C1—C2—H2B | 105.4 (10) |
O7—Na3—O1iii | 119.08 (3) | C3—C2—H2B | 108.2 (10) |
O4iv—Na3—O9 | 104.00 (4) | H2A—C2—H2B | 111.5 (14) |
O7—Na3—O9 | 144.90 (4) | O7—C3—C2 | 107.28 (8) |
O1iii—Na3—O9 | 86.03 (3) | O7—C3—C4 | 110.63 (8) |
O4iv—Na3—O2iii | 82.48 (4) | C2—C3—C4 | 109.27 (9) |
O7—Na3—O2iii | 93.02 (3) | O7—C3—C6 | 110.40 (8) |
O1iii—Na3—O2iii | 52.11 (3) | C2—C3—C6 | 111.42 (9) |
O9—Na3—O2iii | 122.06 (4) | C4—C3—C6 | 107.84 (8) |
O4iv—Na3—O3v | 131.79 (4) | C5—C4—C3 | 116.71 (9) |
O7—Na3—O3v | 88.20 (4) | C5—C4—H4A | 106.0 (11) |
O1iii—Na3—O3v | 97.45 (3) | C3—C4—H4A | 107.6 (12) |
O9—Na3—O3v | 62.96 (4) | C5—C4—H4B | 107.5 (11) |
O2iii—Na3—O3v | 145.13 (4) | C3—C4—H4B | 110.7 (11) |
C1—O1—Na1 | 116.01 (7) | H4A—C4—H4B | 108.0 (15) |
C1—O1—Na3iii | 96.62 (6) | O3—C5—O4 | 124.79 (11) |
Na1—O1—Na3iii | 92.11 (3) | O3—C5—C4 | 115.95 (11) |
C1—O1—Na2 | 123.31 (7) | O4—C5—C4 | 119.07 (10) |
Na1—O1—Na2 | 104.79 (3) | O6—C6—O5 | 124.14 (10) |
Na3iii—O1—Na2 | 120.22 (4) | O6—C6—C3 | 117.94 (9) |
C1—O2—Na2iii | 140.54 (8) | O5—C6—C3 | 117.91 (9) |
C1—O2—Na3iii | 86.55 (7) | O7iv—Mn1—O4iv | 78.83 (18) |
Na2iii—O2—Na3iii | 84.50 (3) | O7iv—Mn1—O4 | 95.2 (2) |
C5—O3—Na3v | 117.95 (10) | O7iv—Mn1—O6iv | 70.6 (2) |
C5—O4—Mn1 | 133.33 (18) | O4iv—Mn1—O6iv | 88.87 (13) |
C5—O4—Na3iv | 127.97 (8) | O4iv—Mn1—O4 | 121.2 (6) |
C6—O5—Na1 | 101.43 (7) | O4—Mn1—O6 | 88.87 (13) |
C6—O5—Na1ii | 86.67 (7) | O4—Mn1—O6iv | 144.4 (3) |
Na1—O5—Na1ii | 86.61 (3) | O6iv—Mn1—O6 | 72.3 (3) |
C6—O6—Na2iv | 148.48 (8) | O6—Mn1—O7 | 70.6 (2) |
C6—O6—Na1ii | 95.09 (7) | O7iv—Mn1—O7 | 168.0 (7) |
Na2iv—O6—Na1ii | 90.17 (3) | O7—Mn1—O4iv | 95.2 (2) |
C6—O6—Na2 | 102.86 (7) | O7—Mn1—O4 | 78.83 (18) |
Na2iv—O6—Na2 | 98.50 (4) | O7—Mn1—O6iv | 120.1 (4) |
Na1ii—O6—Na2 | 127.04 (4) | | |
Symmetry codes: (i) x, −y+1, z−1/2; (ii) −x+1, −y+1, −z; (iii) −x+1/2, −y+1/2, −z; (iv) −x+1, y, −z+1/2; (v) −x+1, −y, −z; (vi) x, −y+1, z+1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O7—H7···O4 | 0.872 (18) | 1.81 (2) | 2.608 (1) | 151 (2) |
O8—H8A···O5ii | 0.84 (2) | 1.99 (2) | 2.815 (1) | 167 (2) |
O8—H8B···O3vii | 0.85 (1) | 1.91 (1) | 2.759 (1) | 171 (1) |
O9—H9A···O3v | 0.85 (2) | 1.97 (2) | 2.713 (2) | 146 (2) |
O9—H9B···O2viii | 0.85 (2) | 1.91 (2) | 2.758 (1) | 172 (2) |
Symmetry codes: (ii) −x+1, −y+1, −z; (v) −x+1, −y, −z; (vii) x−1/2, y+1/2, z; (viii) x, −y, z+1/2. |
Experimental details
Crystal data |
Chemical formula | 3Na+·0.011Mn3+·C6H5O73−·2H2O |
Mr | 294.71 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 295 |
a, b, c (Å) | 15.7072 (3), 12.4989 (2), 11.2710 (2) |
β (°) | 103.5991 (10) |
V (Å3) | 2150.71 (7) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 0.28 |
Crystal size (mm) | 0.68 × 0.64 × 0.38 |
|
Data collection |
Diffractometer | Nonius Kappa CCD diffractometer |
Absorption correction | Multi-scan (DENZO–SMN; Otwinowski & Minor, 1997; Otwinowski et al.,
2003) |
Tmin, Tmax | 0.833, 0.902 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 9936, 2661, 2508 |
Rint | 0.022 |
(sin θ/λ)max (Å−1) | 0.667 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.029, 0.078, 1.04 |
No. of reflections | 2661 |
No. of parameters | 202 |
No. of restraints | 4 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.70, −0.44 |
Selected geometric parameters (Å, º) topMn1—Na2 | 2.594 (9) | Mn1—O7 | 1.9514 (15) |
Mn1—O4 | 2.150 (6) | Mn1—H7 | 1.35 (2) |
Mn1—O6 | 2.585 (10) | | |
| | | |
O4i—Mn1—O4 | 121.2 (6) | O7i—Mn1—O7 | 168.0 (7) |
O4—Mn1—O6 | 88.87 (13) | O7—Mn1—O4i | 95.2 (2) |
O4—Mn1—O6i | 144.4 (3) | O7—Mn1—O4 | 78.83 (18) |
O6i—Mn1—O6 | 72.3 (3) | O7—Mn1—O6i | 120.1 (4) |
O6—Mn1—O7 | 70.6 (2) | | |
Symmetry code: (i) −x+1, y, −z+1/2. |
Comparison of Na3Mn0.011(C6O7H5).2H2O unit cell
parameters with literature data (space group C2/c) topCompound | a(Å) | b(Å) | c(Å) | β(o) | V(Å3) |
Na3Mn0.011(C6O7H5).2H2O1 | 15.7072 (3) | 12.4989 (2) | 11.2710 (2) | 103.5991 (10) | 2150.71 (7) |
Na3(C6O7H5).H2O2 | 15.7044 (4) | 12.5010 (4) | 11.2837 (4) | 103.5841 (13) | 2153.26 (12) |
(1) This work;
(2) Fischer & Palladino (2003). |
Citric (2-hydroxypropane-1,2,3-tricarboxylic, C6H8O7) acid belongs to the group of polycarboxylic acids present in biological fluids and playing very important roles in biochemical processes. Complexes of citric acid also attract considerable attention in the production of special materials, such as high-conductive LaNiO3 and LaMnO3 (Počuča et al., 2007; Đuriš et al., 2007), using a modification of Pechini's method (Pechini, 1967; Keishi & Toshio, 2005; Petrykin & Kakihana, 2005). In spite of this, not many citrate complexes have been structurally characterized. For example, only three Mncompounds – polymeric {K[MnIII(C6H5O7)(H2O)]}n (Xie et al., 2005), as well as mononuclear (NH4)4[MnII(C6H5O7)2] and (NH4)5[MnIII(C6H4O7)2].2H2O (Matzapetakis et al., 2000) – have been reported so far. No Na-containing analogues of these complexes have been described.
During attempts to prepare single crystals of complex MnIII citrates from a strongly alkaline aqueous solution (pH ≈ 13) containing Na+ ions, crystals of the title compound, (I), were obtained together with the already described sodium citrate salts Na3(C6O7H5).2H2O (Fischer & Palladino, 2003) or Na3(C6O7H5).5.5H2O (Viossat et al., 1986). The presence and oxidation state of Mn were confirmed by a qualitative EDX analysis and crystal color, respectively.
The structure analysis indicated that the investigated compound is isostructural with the recently described Na3(C6O7H5).2H2O (Fischer & Palladino, 2003). The minor discrepancies in the unit-cell dimensions and volume (~0.1%) are negligible (see Table 2). The two structures are essentially identical with no significant differences in bond distances and angles. Both structures contain three Na+ ions bonded to a triply deprotonated citrate anion (C6O7H53-) and two water molecules (Fig. 1). The citrate anion acts as a heptadentate ligand coordinated to two Na1, three Na2 and four Na3 atoms. In addition to O atoms from COO and OH groups, the Na+ ions also coordinate two water O atoms (O8 and O9) and are in a distorted octahedral environment. The Na polyhedra create very narrow channels extending parallel to the [101] and [001] directions (Fig. 2). These channels accommodate H atoms from the citrate ions and water molecules.
The only difference between these two structures is the presence of a very small proportion (0.205 wt%) of Mn3+ ions positioned on the twofold rotation axis at special Wyckoff site 4e in C2/c. The Mn3+ ions are in a highly distorted octahedral environment of O atoms (O4, O6 and O7) arising from two citrate anions (Fig. 3). The Mn—O distances range from 1.951 (1) to 2.58 (1) Å. Four of them are close to the expected value of 2.045 Å, calculated from ionic radii (Shannon, 1976). However, the remaining two (Mn—O6) distances are much longer than the longest distance observed, for example, in (NH4)5[MnIII(C6H4O7)2].2H2O [2.224 (1) Å; Matzapetakis et al., 2000]. Values comparable to those observed here are found in the low-temperature form of the mineral bixbyite, Mn2O3, where three of the five independent Mn3+ ions have one Mn—O distance of about 2.50 Å (Geller, 1971).
At first sight the distortion of the Mn octahedron can be attributed to the Jahn–Teller effect, but in that case the two long Mn—O bonds are expected to be in trans positions. Nevertheless, a theoretical study of MnPO4 using density functional theory calculations confirmed that the existence of two long (about 2.50 Å) Mn—O bonds in cis positions is also possible (Osorio-Guillen et al., 2004). Another, probably better, explanation is that the shape of the Mn polyhedron is determined by the packing of the O atoms based on the existing sodium citrate framework. This is confirmed by calculating the centroid position of the corresponding set of O atoms in the structure reported by Fischer & Palladino (2003) and in our structure when the Mn ion is and is not included in the refinement. In all three cases the position of the centroid almost coincides with the reported position of the Mn ion.
It is notable that Mn3+ in Na3Mn0.011(C6O7H5).2H2O occupies a similar environment to Mn3+ in (NH4)5[Mn(C6H4O7)2].2H2O (Matzapetakis et al., 2000). Both ions are in a distorted octahedral coordination formed by O atoms from two citrate ligands. Each citrate ion uses the central hydroxy and carboxylate groups, as well as one of the terminal carboxylate groups, to achieve coordination around Mn3+. In our case the (Mn1)O6 polyhedron shares two edges with adjacent (Na3)O6 and two vertices with adjacent (Na1)O6 polyhedra (Fig. 2).
Refinement of the Mn3+ site occupancy factor yielded the empirical formula Na3Mn0.011(C6O7H5).2H2O, meaning that one Mn3+ ion exists in only one of about 23 unit cells, and only one of about 92 available Mn sites is occupied. At the same time, to maintain reasonable bond distances and charge balance, some Na2 and H7 atoms must be absent (Fig. 3). Therefore, when Mn3+ ions are present some O7/H7 groups in the neighbourhood should be ionized and some Na+ sites should be vacant. This resembles the mechanism of aliovalent substitution characteristic of inorganic compounds but does not quite satisfy the charge balance. Attempts to resolve this ambiguity were unsuccessful; apparently the sensitivity of the available experimental data is insufficient for this purpose.
In this case the crystallization occurred from very concentrated aqueous solution and the crystal lattice was not able to resist the entering of Mn3+ ions at a place characteristic for some other MnIII citrates. Our study confirmed the presence of Mn3+ ions at a level of only 0.2 wt%, demonstrating that when a suitable combination of light and heavy elements exists and high-quality experimental data are available, X-ray analysis can be a very powerful tool for determination of small impurities/dopants in unusual cases.