metal-organic compounds
Dioxidobis(2-oxo-1,2-dihydropyridin-3-olato)molybdenum(VI)
aDepartment of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, India, and bDepartment of Chemistry and Biochemistry and Center for Nanoscience, University of Missouri-St Louis, One University Boulevard, St Louis, MO 63121-4499, USA
*Correspondence e-mail: manojtri@gmail.com
In the title compound, [Mo(C5H4NO2)2O2], the MoVI atom exhibits a distorted octahedral coordination geometry formed by two terminal oxo ligands and two monoanionic O,O-bidentate pyridinone ligands. The two terminal oxo ligands lie in a cis arrangement, the ketonic O atoms of the pyridinone ligands are coordinated trans to the oxo ligands and the deprotonated hydroxyl O atoms are located trans to each other. The contains intermolecular N—H⋯O hydrogen bonds, C—H⋯O contacts and face-to-face π–π stacking interactions with an interplanar separation of 3.25 (1) Å.
Related literature
For general background, see: Veiros et al. (2006); Tucci et al. (1998); Collison et al. (1996); Hille (1996). For related structures, see: Brown et al. (2004); Hanna et al. (2000); Thompson et al. (1999); Zhang et al. (1992). For related literature, see: Braga et al. (1997); Grasselli (1999); Hozba et al. (1997); Ranganathan et al. (1998); Schrock (1998); Schultz et al. (1993).
Experimental
Crystal data
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Refinement
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Data collection: APEX2 (Bruker, 2006); cell SAINT (Bruker, 2006); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXL97; software used to prepare material for publication: SHELXL97.
Supporting information
10.1107/S1600536808007782/bi2282sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536808007782/bi2282Isup2.hkl
The title compound was prepared by suspension of 2,3-pyridinediol (0.111 g, 1 mmol) in methanol (30 ml), followed by addition of KOH (0.112 g, 2 mmol). Stirring at room temperature for 30 min gave a clear red solution. This solution was treated with (NH4)2Mo2O7 (0.170 g, 0.50 mmol) and stirred overnight. The resulting orange-red solution was filtered and allowed to cool at room temperature. Over a couple of days, orange irregular needle-shaped diffraction-quality crystals separated, which were isolated and dried in air.
All H atoms were added in calculated positions and were refined as riding with Uiso(H) = 1.2Ueq(C).
Data collection: APEX2 (Bruker, 2006); cell
SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXL97 (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).[Mo(C5H4NO2)2O2] | F(000) = 688 |
Mr = 348.12 | Dx = 2.065 Mg m−3 Dm = no Mg m−3 Dm measured by not measured |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 9899 reflections |
a = 13.263 (3) Å | θ = 1.8–29.6° |
b = 7.2470 (14) Å | µ = 1.20 mm−1 |
c = 13.264 (3) Å | T = 100 K |
β = 118.540 (9)° | Needle, orange |
V = 1120.0 (4) Å3 | 0.29 × 0.16 × 0.09 mm |
Z = 4 |
Bruker APEXII CCD diffractometer | 3123 independent reflections |
Radiation source: fine-focus sealed tube | 2772 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.045 |
ϕ and ω scans | θmax = 29.6°, θmin = 1.8° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2007) | h = −18→18 |
Tmin = 0.723, Tmax = 0.899 | k = −10→10 |
37847 measured reflections | l = −18→18 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.025 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.058 | H-atom parameters constrained |
S = 1.08 | w = 1/[σ2(Fo2) + (0.0224P)2 + 1.1984P] where P = (Fo2 + 2Fc2)/3 |
3123 reflections | (Δ/σ)max = 0.001 |
172 parameters | Δρmax = 0.70 e Å−3 |
0 restraints | Δρmin = −0.52 e Å−3 |
[Mo(C5H4NO2)2O2] | V = 1120.0 (4) Å3 |
Mr = 348.12 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 13.263 (3) Å | µ = 1.20 mm−1 |
b = 7.2470 (14) Å | T = 100 K |
c = 13.264 (3) Å | 0.29 × 0.16 × 0.09 mm |
β = 118.540 (9)° |
Bruker APEXII CCD diffractometer | 3123 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2007) | 2772 reflections with I > 2σ(I) |
Tmin = 0.723, Tmax = 0.899 | Rint = 0.045 |
37847 measured reflections |
R[F2 > 2σ(F2)] = 0.025 | 0 restraints |
wR(F2) = 0.058 | H-atom parameters constrained |
S = 1.08 | Δρmax = 0.70 e Å−3 |
3123 reflections | Δρmin = −0.52 e Å−3 |
172 parameters |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
Mo1 | 0.248605 (14) | 0.91497 (2) | 0.414412 (14) | 0.01513 (6) | |
O1 | 0.08144 (11) | 0.8541 (2) | 0.33241 (11) | 0.0172 (3) | |
O2 | 0.20602 (12) | 0.8648 (2) | 0.55242 (12) | 0.0176 (3) | |
O3 | 0.40951 (12) | 0.8995 (2) | 0.53830 (12) | 0.0173 (3) | |
O4 | 0.27660 (12) | 0.6185 (2) | 0.44705 (12) | 0.0177 (3) | |
O5 | 0.25461 (12) | 0.8903 (2) | 0.28946 (12) | 0.0196 (3) | |
O6 | 0.25285 (12) | 1.1491 (2) | 0.43339 (12) | 0.0204 (3) | |
N1 | 0.06163 (14) | 0.7521 (2) | 0.58314 (14) | 0.0166 (3) | |
H1N | 0.1075 | 0.7516 | 0.6578 | 0.020* | |
N2 | 0.41302 (15) | 0.4130 (2) | 0.56670 (15) | 0.0181 (3) | |
H2N | 0.3655 | 0.3201 | 0.5347 | 0.022* | |
C1 | −0.04904 (17) | 0.6950 (3) | 0.54263 (18) | 0.0185 (4) | |
H1 | −0.0754 | 0.6548 | 0.5942 | 0.022* | |
C2 | −0.12129 (17) | 0.6964 (3) | 0.42750 (18) | 0.0206 (4) | |
H2 | −0.1989 | 0.6594 | 0.3987 | 0.025* | |
C3 | −0.08198 (17) | 0.7519 (3) | 0.35098 (17) | 0.0189 (4) | |
H3 | −0.1325 | 0.7526 | 0.2706 | 0.023* | |
C4 | 0.02965 (17) | 0.8049 (3) | 0.39344 (16) | 0.0160 (4) | |
C5 | 0.10352 (16) | 0.8086 (3) | 0.51457 (16) | 0.0148 (4) | |
C6 | 0.37661 (17) | 0.5850 (3) | 0.52910 (16) | 0.0157 (4) | |
C7 | 0.45352 (17) | 0.7346 (3) | 0.58207 (16) | 0.0166 (4) | |
C8 | 0.56213 (17) | 0.7023 (3) | 0.66842 (17) | 0.0203 (4) | |
H8 | 0.6140 | 0.8016 | 0.7037 | 0.024* | |
C9 | 0.59590 (18) | 0.5190 (3) | 0.70425 (18) | 0.0231 (5) | |
H9 | 0.6710 | 0.4941 | 0.7645 | 0.028* | |
C10 | 0.52126 (18) | 0.3776 (3) | 0.65289 (18) | 0.0218 (4) | |
H10 | 0.5444 | 0.2542 | 0.6770 | 0.026* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Mo1 | 0.01552 (9) | 0.01402 (9) | 0.01085 (9) | 0.00111 (6) | 0.00226 (6) | 0.00057 (6) |
O1 | 0.0157 (6) | 0.0197 (7) | 0.0102 (6) | 0.0007 (6) | 0.0014 (5) | 0.0007 (5) |
O2 | 0.0159 (6) | 0.0189 (7) | 0.0120 (6) | −0.0009 (6) | 0.0019 (5) | −0.0005 (5) |
O3 | 0.0148 (6) | 0.0167 (7) | 0.0146 (7) | −0.0010 (5) | 0.0023 (5) | 0.0004 (5) |
O4 | 0.0166 (6) | 0.0152 (7) | 0.0150 (7) | 0.0016 (5) | 0.0025 (5) | 0.0001 (5) |
O5 | 0.0200 (7) | 0.0226 (8) | 0.0122 (7) | 0.0020 (6) | 0.0045 (6) | 0.0012 (6) |
O6 | 0.0233 (7) | 0.0158 (7) | 0.0198 (7) | 0.0012 (6) | 0.0084 (6) | 0.0010 (6) |
N1 | 0.0181 (8) | 0.0156 (8) | 0.0113 (7) | 0.0011 (7) | 0.0031 (6) | −0.0005 (7) |
N2 | 0.0213 (8) | 0.0172 (8) | 0.0168 (8) | 0.0037 (7) | 0.0099 (7) | 0.0026 (7) |
C1 | 0.0205 (10) | 0.0137 (9) | 0.0201 (10) | 0.0017 (8) | 0.0086 (8) | −0.0009 (8) |
C2 | 0.0162 (9) | 0.0193 (10) | 0.0217 (10) | 0.0000 (8) | 0.0053 (8) | −0.0043 (8) |
C3 | 0.0155 (9) | 0.0184 (10) | 0.0143 (9) | 0.0021 (8) | 0.0003 (7) | −0.0031 (8) |
C4 | 0.0183 (9) | 0.0122 (9) | 0.0120 (9) | 0.0028 (7) | 0.0028 (7) | −0.0011 (7) |
C5 | 0.0166 (9) | 0.0089 (8) | 0.0131 (9) | 0.0017 (7) | 0.0025 (7) | −0.0016 (7) |
C6 | 0.0168 (9) | 0.0183 (10) | 0.0117 (9) | 0.0024 (8) | 0.0066 (7) | 0.0016 (7) |
C7 | 0.0172 (9) | 0.0209 (10) | 0.0112 (9) | 0.0016 (8) | 0.0065 (7) | 0.0003 (8) |
C8 | 0.0168 (9) | 0.0312 (12) | 0.0114 (9) | 0.0001 (8) | 0.0055 (8) | 0.0001 (8) |
C9 | 0.0178 (9) | 0.0384 (13) | 0.0115 (9) | 0.0088 (9) | 0.0057 (8) | 0.0072 (9) |
C10 | 0.0236 (10) | 0.0270 (11) | 0.0158 (10) | 0.0114 (9) | 0.0103 (8) | 0.0091 (8) |
Mo1—O1 | 1.9972 (14) | N2—H2N | 0.880 |
Mo1—O2 | 2.1886 (15) | C1—C2 | 1.361 (3) |
Mo1—O3 | 1.9790 (14) | C1—H1 | 0.950 |
Mo1—O4 | 2.1882 (15) | C2—C3 | 1.403 (3) |
Mo1—O5 | 1.7062 (15) | C2—H2 | 0.950 |
Mo1—O6 | 1.7124 (16) | C3—C4 | 1.364 (3) |
O1—C4 | 1.336 (3) | C3—H3 | 0.950 |
O2—C5 | 1.270 (2) | C4—C5 | 1.427 (3) |
O3—C7 | 1.335 (2) | C6—C7 | 1.423 (3) |
O4—C6 | 1.274 (2) | C7—C8 | 1.366 (3) |
N1—C5 | 1.337 (3) | C8—C9 | 1.410 (3) |
N1—C1 | 1.364 (3) | C8—H8 | 0.950 |
N1—H1N | 0.880 | C9—C10 | 1.360 (3) |
N2—C6 | 1.344 (3) | C9—H9 | 0.950 |
N2—C10 | 1.366 (3) | C10—H10 | 0.950 |
O5—Mo1—O6 | 103.48 (7) | C1—C2—C3 | 120.52 (19) |
O5—Mo1—O3 | 105.57 (7) | C1—C2—H2 | 119.7 |
O6—Mo1—O3 | 89.27 (6) | C3—C2—H2 | 119.7 |
O5—Mo1—O1 | 90.16 (6) | C4—C3—C2 | 119.16 (18) |
O6—Mo1—O1 | 104.40 (6) | C4—C3—H3 | 120.4 |
O3—Mo1—O1 | 156.33 (6) | C2—C3—H3 | 120.4 |
O5—Mo1—O4 | 90.40 (6) | O1—C4—C3 | 126.57 (18) |
O6—Mo1—O4 | 162.43 (6) | O1—C4—C5 | 113.69 (17) |
O3—Mo1—O4 | 76.49 (6) | C3—C4—C5 | 119.74 (19) |
O1—Mo1—O4 | 86.00 (6) | O2—C5—N1 | 122.93 (17) |
O5—Mo1—O2 | 161.00 (6) | O2—C5—C4 | 118.70 (18) |
O6—Mo1—O2 | 92.59 (6) | N1—C5—C4 | 118.37 (18) |
O3—Mo1—O2 | 84.43 (6) | O4—C6—N2 | 122.44 (19) |
O1—Mo1—O2 | 75.87 (6) | O4—C6—C7 | 119.02 (18) |
O4—Mo1—O2 | 76.04 (5) | N2—C6—C7 | 118.53 (18) |
C4—O1—Mo1 | 119.16 (12) | O3—C7—C8 | 125.8 (2) |
C5—O2—Mo1 | 112.20 (12) | O3—C7—C6 | 113.95 (17) |
C7—O3—Mo1 | 119.05 (12) | C8—C7—C6 | 120.3 (2) |
C6—O4—Mo1 | 111.40 (13) | C7—C8—C9 | 118.8 (2) |
C5—N1—C1 | 122.94 (17) | C7—C8—H8 | 120.6 |
C5—N1—H1N | 118.5 | C9—C8—H8 | 120.6 |
C1—N1—H1N | 118.5 | C10—C9—C8 | 120.20 (19) |
C6—N2—C10 | 122.19 (19) | C10—C9—H9 | 119.9 |
C6—N2—H2N | 118.9 | C8—C9—H9 | 119.9 |
C10—N2—H2N | 118.9 | C9—C10—N2 | 120.0 (2) |
C2—C1—N1 | 119.2 (2) | C9—C10—H10 | 120.0 |
C2—C1—H1 | 120.4 | N2—C10—H10 | 120.0 |
N1—C1—H1 | 120.4 | ||
O5—Mo1—O1—C4 | 162.99 (15) | C2—C3—C4—O1 | 177.13 (19) |
O6—Mo1—O1—C4 | −93.04 (15) | C2—C3—C4—C5 | −1.9 (3) |
O3—Mo1—O1—C4 | 30.6 (2) | Mo1—O2—C5—N1 | 173.36 (15) |
O4—Mo1—O1—C4 | 72.60 (14) | Mo1—O2—C5—C4 | −6.4 (2) |
O2—Mo1—O1—C4 | −3.99 (13) | C1—N1—C5—O2 | 178.72 (18) |
O5—Mo1—O2—C5 | −38.2 (3) | C1—N1—C5—C4 | −1.5 (3) |
O6—Mo1—O2—C5 | 109.76 (14) | O1—C4—C5—O2 | 3.4 (3) |
O3—Mo1—O2—C5 | −161.22 (14) | C3—C4—C5—O2 | −177.45 (18) |
O1—Mo1—O2—C5 | 5.55 (13) | O1—C4—C5—N1 | −176.45 (17) |
O4—Mo1—O2—C5 | −83.79 (13) | C3—C4—C5—N1 | 2.7 (3) |
O5—Mo1—O3—C7 | −88.95 (15) | Mo1—O4—C6—N2 | 178.53 (15) |
O6—Mo1—O3—C7 | 167.25 (15) | Mo1—O4—C6—C7 | −2.4 (2) |
O1—Mo1—O3—C7 | 41.0 (2) | C10—N2—C6—O4 | 178.42 (19) |
O4—Mo1—O3—C7 | −2.36 (14) | C10—N2—C6—C7 | −0.6 (3) |
O2—Mo1—O3—C7 | 74.58 (14) | Mo1—O3—C7—C8 | −179.11 (16) |
O5—Mo1—O4—C6 | 108.44 (14) | Mo1—O3—C7—C6 | 1.9 (2) |
O6—Mo1—O4—C6 | −34.2 (3) | O4—C6—C7—O3 | 0.6 (3) |
O3—Mo1—O4—C6 | 2.52 (13) | N2—C6—C7—O3 | 179.69 (17) |
O1—Mo1—O4—C6 | −161.43 (14) | O4—C6—C7—C8 | −178.48 (19) |
O2—Mo1—O4—C6 | −85.01 (14) | N2—C6—C7—C8 | 0.6 (3) |
C5—N1—C1—C2 | −0.6 (3) | O3—C7—C8—C9 | −179.41 (19) |
N1—C1—C2—C3 | 1.4 (3) | C6—C7—C8—C9 | −0.4 (3) |
C1—C2—C3—C4 | −0.1 (3) | C7—C8—C9—C10 | 0.3 (3) |
Mo1—O1—C4—C3 | −177.08 (16) | C8—C9—C10—N2 | −0.3 (3) |
Mo1—O1—C4—C5 | 2.0 (2) | C6—N2—C10—C9 | 0.5 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1N···O5i | 0.88 | 2.16 | 2.900 (2) | 142 |
N2—H2N···O6ii | 0.88 | 1.91 | 2.776 (3) | 167 |
C3—H3···O6iii | 0.95 | 2.51 | 3.428 (3) | 162 |
C9—H9···O2iv | 0.95 | 2.38 | 3.235 (3) | 150 |
Symmetry codes: (i) x, −y+3/2, z+1/2; (ii) x, y−1, z; (iii) −x, y−1/2, −z+1/2; (iv) −x+1, y−1/2, −z+3/2. |
Experimental details
Crystal data | |
Chemical formula | [Mo(C5H4NO2)2O2] |
Mr | 348.12 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 100 |
a, b, c (Å) | 13.263 (3), 7.2470 (14), 13.264 (3) |
β (°) | 118.540 (9) |
V (Å3) | 1120.0 (4) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 1.20 |
Crystal size (mm) | 0.29 × 0.16 × 0.09 |
Data collection | |
Diffractometer | Bruker APEXII CCD diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2007) |
Tmin, Tmax | 0.723, 0.899 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 37847, 3123, 2772 |
Rint | 0.045 |
(sin θ/λ)max (Å−1) | 0.694 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.025, 0.058, 1.08 |
No. of reflections | 3123 |
No. of parameters | 172 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.70, −0.52 |
Computer programs: APEX2 (Bruker, 2006), SAINT (Bruker, 2006), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008).
Mo1—O1 | 1.9972 (14) | Mo1—O4 | 2.1882 (15) |
Mo1—O2 | 2.1886 (15) | Mo1—O5 | 1.7062 (15) |
Mo1—O3 | 1.9790 (14) | Mo1—O6 | 1.7124 (16) |
O5—Mo1—O6 | 103.48 (7) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1N···O5i | 0.88 | 2.16 | 2.900 (2) | 141.6 |
N2—H2N···O6ii | 0.88 | 1.91 | 2.776 (3) | 166.8 |
C3—H3···O6iii | 0.95 | 2.51 | 3.428 (3) | 162.2 |
C9—H9···O2iv | 0.95 | 2.38 | 3.235 (3) | 150.0 |
Symmetry codes: (i) x, −y+3/2, z+1/2; (ii) x, y−1, z; (iii) −x, y−1/2, −z+1/2; (iv) −x+1, y−1/2, −z+3/2. |
Acknowledgements
This work was supported by the Council of Scientific and Industrial Research, New Delhi. We also thank the Head, Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi. We acknowledge funding from the National Science Foundation (CHE0420497) for the purchase of the APEXII diffractometer.
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There has been growing interest in the study of MoVI complexes because of their biochemical significance (Collison et al., 1996; Hille, 1996). For example, dioxomolybdenum(VI) complexes are studied as models for oxidized forms of molybdoenzymes, e.g. aldehyde oxidase and sulfite oxidase which are supposed to contain cis-MoX2 units (X = O,S) coordinated to S, N and O donor atoms of the protein structure (Tucci et al., 1998; Schultz et al., 1993). The present view of these enzymes indicates that the formal oxidation state of Mo cycles between +4 and +6 in reactions with substrate and oxidant. The two electron O atom transfer seems to be the relevant mechanism in understanding the chemical role of enzymatic reactions. A large number of important chemical reactions are catalysed by MoVI complexes. Several industrial processes such as ammoxidation of propene to acrylonitrile (Grasselli, 1999), olefin epoxidation (Veiros et al., 2006) and olefin metathesis (Schrock, 1998) reactions are carried out over Mo catalysts.
In the title compound, the coordination sphere about the MoVI atom consists of six O atoms arranged in a distorted octahedral geometry (Fig. 1 and Table 1). There is a cis arrangement of dioxo ligands, as predicted by spectroscopic and other structural data. The O=Mo=O angle is 103.48 (7) and the Mo=O distances are 1.706 (15) and 1.712 (16) Å [average 1.709 (15) Å], comparable to those found in other cis-dioxomolybdenum(VI) complexes (Hanna et al., 2000; Brown et al., 2004). The two ketonic O atoms of the pyridinone ligands are trans to the oxo ligands and the stronger field hydroxyl O atoms are trans to one another. As expected, a slight lengthening of the ketone C=O bond is observed upon complexation, with a mean distance of 1.272 (2) Å, and the Mo—O(ketone) bonds [average 2.188 (15) Å] are somewhat longer than the Mo—O(hydroxyl) distances [average 1.988 (14) Å]. A pronounced localization of the formal double bonds in the pyridinone rings is clearly indicated by the short C1—C2 and C9—C10 bonds [average 1.360 (3) Å], long C4—C5 and C6—C7 bonds [average 1.425 (3) Å], and short ketone C5—O2 and C6—O4 [average 1.272 (2) Å] bonds. Resonance forms for pyridinone ligands have been described in detail elsewhere (Thompson et al., 1999; Zhang et al., 1992).
The NH and CH groups of the pyridinone ligands form a hydrogen bond with an oxo ligand attached to Mo in a neighbouring molecule (Table 2) (Braga et al., 1997). Repetition of this hydrogen bond generates parallel chains along the b axis (Fig. 2). There are face-to-face π–π stacking interactions involving the pyridinone rings of adjacent pyridinone molecules, with π–π distances of 3.295–3.389 Å (Fig. 3) (Ranganathan et al., 1998; Hozba et al., 1997). One potential driving force for alignment of the motifs might be the N···O interactions (N···O distance = 2.904 Å) that exists between adjacent motifs, resulting in a columnar architecture with a dimension of 7.2 × 6.7 Å (Fig. 4).