Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100008118/sk1395sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270100008118/sk1395Isup2.hkl |
CCDC reference: 150322
A solution of FeCl3·6H2O (270 mg, 1 mmol) in ethanol (20 ml) and 1 N HCl (1 ml) was overlaid on a solid pill of 6-MP·H2O and stored at a temperature of 333 K in a closed vessel. After 2 d red-brown hexagonal prismatic crystals of (I) suitable for X-ray analysis had grown on the surface of the pill. Crystals of the same composition were also synthesized by heating a solution of 6-MP·H2O (681 mg, 4 mmol) and FeCl3·6H2O (1081 mg, 4 mmol) in 1 N HCl (2 ml) and ethanol (100 ml). The reaction mixture was filtered and kept at a temperature of 333 K for crystallization. Within a few hours, a red-brown microcrystalline product, (I), could be separated from the solution.
The structure had been refined previously (ref?) with SHELX76 (Sheldrick, 1976) on Fo based on room-temperature measurements (three different crystals were used), with relatively bad R values of about 0.08. Improvement of refinement techniques (e.g. SHELXL97) and the possibility of user-friendly twin refinements with SHELXL97 (Sheldrick, 1997; Herbst-Irmer & Sheldrick, 1998) led us to remeasure one of the example crystals at 173 (1) K with an image-plate detector system (Stoe IPDS) in order to resolve this old problem structure. Repeating the refinement of the known model with the new data set showed the same result for R1 = 0.09, wR2 = 0.143, based on Fo2 using all unique reflections. Application of the twin matrix (010, 100, 00–1) led to a remarkable improvement of the final R values, as shown in the Experimental section; the twinning ratio was 0.286:0.714. The positions of the H atoms were determined from difference electron-density maps but they were finally calculated after each cycle of refinement using a riding model.
Data collection: IPDS (Stoe & Cie, 1999); cell refinement: IPDS; data reduction: X-RED in IPDS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1990) and PLUTON (Spek, 1991); software used to prepare material for publication: SHELXL97.
[Fe(C5H4N4S)3][FeCl4]Cl | Dx = 1.820 Mg m−3 |
Mr = 745.50 | Mo Kα radiation, λ = 0.71073 Å |
Trigonal, P63 | Cell parameters from 7998 reflections |
Hall symbol: P 6c | θ = 3.6–30.4° |
a = 10.3499 (6) Å | µ = 1.82 mm−1 |
c = 14.6652 (11) Å | T = 173 K |
V = 1360.48 (15) Å3 | Prism, red-brown |
Z = 2 | 0.28 × 0.25 × 0.24 mm |
F(000) = 742 |
STOE IPDS diffractometer | 2717 independent reflections |
Radiation source: fine-focus sealed tube | 2484 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.031 |
ϕ rotation scan | θmax = 30.4°, θmin = 3.6° |
Absorption correction: numerical (Coppens et al., 1965) | h = −12→14 |
Tmin = 0.630, Tmax = 0.669 | k = −14→14 |
16156 measured reflections | l = −20→20 |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.021 | w = 1/[σ2(Fo2) + (0.01P)2] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.038 | (Δ/σ)max < 0.001 |
S = 1.10 | Δρmax = 0.26 e Å−3 |
2717 reflections | Δρmin = −0.24 e Å−3 |
114 parameters | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
1 restraint | Extinction coefficient: 0.0107 (4) |
Primary atom site location: structure-invariant direct methods | Absolute structure: Flack (1983); 1306 Friedel pairs |
Secondary atom site location: difference Fourier map | Absolute structure parameter: −0.05 (2) |
[Fe(C5H4N4S)3][FeCl4]Cl | Z = 2 |
Mr = 745.50 | Mo Kα radiation |
Trigonal, P63 | µ = 1.82 mm−1 |
a = 10.3499 (6) Å | T = 173 K |
c = 14.6652 (11) Å | 0.28 × 0.25 × 0.24 mm |
V = 1360.48 (15) Å3 |
STOE IPDS diffractometer | 2717 independent reflections |
Absorption correction: numerical (Coppens et al., 1965) | 2484 reflections with I > 2σ(I) |
Tmin = 0.630, Tmax = 0.669 | Rint = 0.031 |
16156 measured reflections |
R[F2 > 2σ(F2)] = 0.021 | H-atom parameters constrained |
wR(F2) = 0.038 | Δρmax = 0.26 e Å−3 |
S = 1.10 | Δρmin = −0.24 e Å−3 |
2717 reflections | Absolute structure: Flack (1983); 1306 Friedel pairs |
114 parameters | Absolute structure parameter: −0.05 (2) |
1 restraint |
Experimental. The crystal represents a twin with twin law (010, 100, 00–1), refined with the twin option of SHELXL97. |
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 | ||
Fe2 | 2/3 | 1/3 | 0.40989 (4) | 0.02359 (12) | |
Cl1 | 2/3 | 1/3 | −0.16182 (5) | 0.01632 (15) | |
Cl2 | 2/3 | 1/3 | 0.55907 (7) | 0.0501 (3) | |
Cl3 | 0.43881 (8) | 0.25114 (9) | 0.36101 (5) | 0.0479 (2) | |
Fe1 | 0 | 0 | 0.15255 (3) | 0.01517 (9) | |
S6 | −0.23600 (6) | −0.12766 (8) | 0.25433 (3) | 0.01852 (10) | |
N3 | −0.4658 (3) | −0.5425 (3) | 0.07443 (13) | 0.0312 (5) | |
N7 | −0.1220 (2) | −0.1982 (2) | 0.06987 (11) | 0.0177 (4) | |
C8 | −0.1196 (3) | −0.2637 (2) | −0.00670 (13) | 0.0200 (4) | |
H8 | −0.0390 | −0.2212 | −0.0487 | 0.024* | |
N1 | −0.4545 (2) | −0.4048 (2) | 0.20667 (13) | 0.0254 (4) | |
H1 | −0.5018 | −0.4051 | 0.2566 | 0.030* | |
C6 | −0.3192 (3) | −0.2824 (3) | 0.18914 (14) | 0.0177 (4) | |
N9 | −0.2433 (2) | −0.3970 (2) | −0.01909 (12) | 0.0221 (4) | |
H9 | −0.2627 | −0.4564 | −0.0663 | 0.026* | |
C5 | −0.2565 (2) | −0.2976 (3) | 0.10827 (14) | 0.0168 (5) | |
C4 | −0.3339 (3) | −0.4234 (3) | 0.05506 (15) | 0.0215 (5) | |
C2 | −0.5206 (3) | −0.5268 (3) | 0.1512 (2) | 0.0344 (6) | |
H2 | −0.6144 | −0.6071 | 0.1699 | 0.041* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Fe2 | 0.02305 (17) | 0.02305 (17) | 0.0247 (2) | 0.01152 (8) | 0 | 0 |
Cl1 | 0.0183 (2) | 0.0183 (2) | 0.0123 (3) | 0.00916 (12) | 0 | 0 |
Cl2 | 0.0625 (5) | 0.0625 (5) | 0.0252 (4) | 0.0312 (2) | 0 | 0 |
Cl3 | 0.0291 (4) | 0.0554 (5) | 0.0562 (4) | 0.0188 (4) | −0.0125 (3) | −0.0111 (4) |
Fe1 | 0.01680 (13) | 0.01680 (13) | 0.01192 (18) | 0.00840 (6) | 0 | 0 |
S6 | 0.0209 (2) | 0.0208 (3) | 0.01322 (16) | 0.0099 (3) | 0.0010 (2) | −0.0031 (3) |
N3 | 0.0252 (13) | 0.0259 (13) | 0.0347 (10) | 0.0070 (9) | 0.0001 (12) | −0.0135 (12) |
N7 | 0.0211 (11) | 0.0191 (9) | 0.0130 (7) | 0.0102 (8) | −0.0003 (7) | −0.0012 (7) |
C8 | 0.0256 (14) | 0.0255 (12) | 0.0132 (7) | 0.0159 (11) | 0.0010 (10) | −0.0017 (8) |
N1 | 0.0229 (11) | 0.0257 (12) | 0.0213 (8) | 0.0075 (10) | 0.0042 (8) | −0.0056 (9) |
C6 | 0.0180 (11) | 0.0200 (11) | 0.0155 (9) | 0.0099 (10) | −0.0020 (9) | −0.0016 (8) |
N9 | 0.0269 (10) | 0.0276 (11) | 0.0159 (7) | 0.0167 (9) | −0.0029 (8) | −0.0098 (9) |
C5 | 0.0186 (11) | 0.0158 (11) | 0.0171 (10) | 0.0094 (9) | −0.0028 (8) | −0.0032 (8) |
C4 | 0.0230 (11) | 0.0207 (12) | 0.0238 (10) | 0.0133 (11) | −0.0044 (10) | −0.0076 (9) |
C2 | 0.0223 (14) | 0.0254 (16) | 0.0439 (11) | 0.0034 (12) | 0.0022 (13) | −0.0077 (13) |
Fe2—Cl2 | 2.1878 (11) | N7—C8 | 1.318 (3) |
Fe2—Cl3i | 2.1892 (7) | N7—C5 | 1.371 (3) |
Fe2—Cl3ii | 2.1892 (7) | C8—N9 | 1.345 (3) |
Fe2—Cl3 | 2.1892 (7) | C8—H8 | 0.9500 |
Fe1—N7iii | 2.1638 (19) | N1—C6 | 1.363 (3) |
Fe1—N7 | 2.1638 (19) | N1—C2 | 1.364 (3) |
Fe1—N7iv | 2.1638 (19) | N1—H1 | 0.8800 |
Fe1—S6iv | 2.5908 (6) | C6—C5 | 1.398 (3) |
Fe1—S6 | 2.5908 (6) | N9—C4 | 1.371 (3) |
Fe1—S6iii | 2.5909 (6) | N9—H9 | 0.8800 |
S6—C6 | 1.686 (2) | C5—C4 | 1.380 (3) |
N3—C2 | 1.307 (3) | C2—H2 | 0.9500 |
N3—C4 | 1.335 (4) | ||
Cl2—Fe2—Cl3i | 109.11 (3) | C8—N7—Fe1 | 144.36 (17) |
Cl2—Fe2—Cl3ii | 109.11 (3) | C5—N7—Fe1 | 111.92 (13) |
Cl3i—Fe2—Cl3ii | 109.83 (2) | N7—C8—N9 | 112.9 (2) |
Cl2—Fe2—Cl3 | 109.11 (3) | N7—C8—H8 | 123.5 |
Cl3i—Fe2—Cl3 | 109.83 (2) | N9—C8—H8 | 123.5 |
Cl3ii—Fe2—Cl3 | 109.83 (2) | C6—N1—C2 | 123.7 (2) |
N7iii—Fe1—N7 | 91.66 (7) | C6—N1—H1 | 118.2 |
N7iii—Fe1—N7iv | 91.66 (7) | C2—N1—H1 | 118.2 |
N7—Fe1—N7iv | 91.66 (7) | N1—C6—C5 | 112.0 (2) |
N7iii—Fe1—S6iv | 171.45 (6) | N1—C6—S6 | 125.13 (17) |
N7—Fe1—S6iv | 95.44 (5) | C5—C6—S6 | 122.85 (19) |
N7iv—Fe1—S6iv | 83.39 (5) | C8—N9—C4 | 107.62 (18) |
N7iii—Fe1—S6 | 95.44 (5) | C8—N9—H9 | 126.2 |
N7—Fe1—S6 | 83.39 (5) | C4—N9—H9 | 126.2 |
N7iv—Fe1—S6 | 171.45 (6) | N7—C5—C4 | 111.59 (19) |
S6iv—Fe1—S6 | 90.122 (19) | N7—C5—C6 | 128.2 (2) |
N7iii—Fe1—S6iii | 83.39 (5) | C4—C5—C6 | 120.2 (2) |
N7—Fe1—S6iii | 171.45 (6) | N3—C4—N9 | 129.4 (2) |
N7iv—Fe1—S6iii | 95.44 (5) | N3—C4—C5 | 126.5 (2) |
S6iv—Fe1—S6iii | 90.122 (19) | N9—C4—C5 | 104.1 (2) |
S6—Fe1—S6iii | 90.123 (19) | N3—C2—N1 | 125.5 (2) |
C6—S6—Fe1 | 93.51 (8) | N3—C2—H2 | 117.2 |
C2—N3—C4 | 112.1 (2) | N1—C2—H2 | 117.2 |
C8—N7—C5 | 103.72 (19) | ||
N7iii—Fe1—S6—C6 | 93.98 (10) | Fe1—S6—C6—C5 | −3.42 (18) |
N7—Fe1—S6—C6 | 2.93 (9) | N7—C8—N9—C4 | −0.9 (3) |
N7iv—Fe1—S6—C6 | −52.0 (4) | C8—N7—C5—C4 | 0.7 (3) |
S6iv—Fe1—S6—C6 | −92.53 (8) | Fe1—N7—C5—C4 | 179.81 (15) |
S6iii—Fe1—S6—C6 | 177.34 (8) | C8—N7—C5—C6 | −177.7 (2) |
N7iii—Fe1—N7—C8 | 80.6 (3) | Fe1—N7—C5—C6 | 1.4 (3) |
N7iv—Fe1—N7—C8 | −11.1 (3) | N1—C6—C5—N7 | −179.4 (2) |
S6iv—Fe1—N7—C8 | −94.6 (3) | S6—C6—C5—N7 | 2.0 (3) |
S6—Fe1—N7—C8 | 175.9 (3) | N1—C6—C5—C4 | 2.4 (3) |
S6iii—Fe1—N7—C8 | 135.1 (3) | S6—C6—C5—C4 | −176.23 (19) |
N7iii—Fe1—N7—C5 | −97.90 (18) | C2—N3—C4—N9 | −179.0 (3) |
N7iv—Fe1—N7—C5 | 170.39 (16) | C2—N3—C4—C5 | 2.1 (4) |
S6iv—Fe1—N7—C5 | 86.87 (15) | C8—N9—C4—N3 | −177.9 (3) |
S6—Fe1—N7—C5 | −2.62 (14) | C8—N9—C4—C5 | 1.3 (3) |
S6iii—Fe1—N7—C5 | −43.5 (4) | N7—C5—C4—N3 | 177.9 (2) |
C5—N7—C8—N9 | 0.1 (3) | C6—C5—C4—N3 | −3.6 (4) |
Fe1—N7—C8—N9 | −178.45 (19) | N7—C5—C4—N9 | −1.2 (3) |
C2—N1—C6—C5 | −0.4 (3) | C6—C5—C4—N9 | 177.29 (19) |
C2—N1—C6—S6 | 178.2 (2) | C4—N3—C2—N1 | 0.2 (4) |
Fe1—S6—C6—N1 | 178.1 (2) | C6—N1—C2—N3 | −1.0 (5) |
Symmetry codes: (i) −y+1, x−y, z; (ii) −x+y+1, −x+1, z; (iii) −x+y, −x, z; (iv) −y, x−y, z. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···Cl1v | 0.88 | 2.48 | 3.273 (2) | 150 |
N9—H9···Cl1vi | 0.88 | 2.38 | 3.231 (2) | 164 |
C2—H2···S6vii | 0.95 | 2.78 | 3.693 (3) | 161 |
Symmetry codes: (v) x−y−1, x−1, z+1/2; (vi) x−1, y−1, z; (vii) −x+y−1, −x−1, z. |
Experimental details
Crystal data | |
Chemical formula | [Fe(C5H4N4S)3][FeCl4]Cl |
Mr | 745.50 |
Crystal system, space group | Trigonal, P63 |
Temperature (K) | 173 |
a, c (Å) | 10.3499 (6), 14.6652 (11) |
V (Å3) | 1360.48 (15) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 1.82 |
Crystal size (mm) | 0.28 × 0.25 × 0.24 |
Data collection | |
Diffractometer | STOE IPDS diffractometer |
Absorption correction | Numerical (Coppens et al., 1965) |
Tmin, Tmax | 0.630, 0.669 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 16156, 2717, 2484 |
Rint | 0.031 |
(sin θ/λ)max (Å−1) | 0.711 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.021, 0.038, 1.10 |
No. of reflections | 2717 |
No. of parameters | 114 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.26, −0.24 |
Absolute structure | Flack (1983); 1306 Friedel pairs |
Absolute structure parameter | −0.05 (2) |
Computer programs: IPDS (Stoe & Cie, 1999), X-RED in IPDS, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1990) and PLUTON (Spek, 1991), SHELXL97.
Fe2—Cl2 | 2.1878 (11) | N7—C5 | 1.371 (3) |
Fe2—Cl3 | 2.1892 (7) | C8—N9 | 1.345 (3) |
Fe1—N7 | 2.1638 (19) | N1—C6 | 1.363 (3) |
Fe1—S6 | 2.5908 (6) | N1—C2 | 1.364 (3) |
S6—C6 | 1.686 (2) | C6—C5 | 1.398 (3) |
N3—C2 | 1.307 (3) | N9—C4 | 1.371 (3) |
N3—C4 | 1.335 (4) | C5—C4 | 1.380 (3) |
N7—C8 | 1.318 (3) | ||
Cl2—Fe2—Cl3 | 109.11 (3) | C6—N1—C2 | 123.7 (2) |
Cl3i—Fe2—Cl3 | 109.83 (2) | N1—C6—C5 | 112.0 (2) |
N7—Fe1—N7ii | 91.66 (7) | N1—C6—S6 | 125.13 (17) |
N7—Fe1—S6ii | 95.44 (5) | C5—C6—S6 | 122.85 (19) |
N7—Fe1—S6 | 83.39 (5) | C8—N9—C4 | 107.62 (18) |
N7ii—Fe1—S6 | 171.45 (6) | N7—C5—C4 | 111.59 (19) |
S6ii—Fe1—S6 | 90.122 (19) | N7—C5—C6 | 128.2 (2) |
C6—S6—Fe1 | 93.51 (8) | C4—C5—C6 | 120.2 (2) |
C2—N3—C4 | 112.1 (2) | N3—C4—N9 | 129.4 (2) |
C8—N7—C5 | 103.72 (19) | N3—C4—C5 | 126.5 (2) |
C8—N7—Fe1 | 144.36 (17) | N9—C4—C5 | 104.1 (2) |
C5—N7—Fe1 | 111.92 (13) | N3—C2—N1 | 125.5 (2) |
N7—C8—N9 | 112.9 (2) |
Symmetry codes: (i) −y+1, x−y, z; (ii) −y, x−y, z. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···Cl1iii | 0.880 | 2.482 | 3.273 (2) | 149.8 |
N9—H9···Cl1iv | 0.880 | 2.375 | 3.231 (2) | 164.2 |
C2—H2···S6v | 0.950 | 2.783 | 3.693 (3) | 160.7 |
Symmetry codes: (iii) x−y−1, x−1, z+1/2; (iv) x−1, y−1, z; (v) −x+y−1, −x−1, z. |
6-mercaptopurine (6-MP), the synthetic thio analogue of the naturally occurring purine derivative hypoxanthine, is a clinical agent routinely administered for the therapy of human leukaemia. 6-MP is converted intracellularly to the corresponding ribonucleotide, which inhibits purine biosynthesis (Elion, 1989). Metal complexes of 6-MP and related drugs are of special interest in view of their possibly enhanced therapeutic effect with respect to the free base, which may also be a consequence of the protection of the molecule from enzymatic biological degradation by metal complexation. Metal complexes of drug molecules could, in addition, be used as slow-release drugs (Farrell, 1989). Preliminary investigations by UV spectroscopy of the enzymatic degradation of 6-MP in aqueous solutions by xanthine oxidase, supported by catalase, show a significant decrease of the decomposition reaction rate of 6-MP in the form of the title iron complex, (I), compared with the corresponding rate of the free ligand. \sch
A review of metal complexes of sulfur-containing purine derivatives has recently been given by Dubler (1996). It has been shown that, depending on the protonation status of the ligand and on the hardness or softness of the corresponding metal atom, 6-MP variously coordinates monodentately through S6, N7 or N3, by chelating through N7/S6 and/or by bridging two metal atoms through S6, S6/N7 or N1/N7. As part of a program elucidating the coordination properties of oxo- and thiopurines (Zhu et al., 1998), we present here the synthesis and structure of the title complex, (I).
There are three building units in the structure (Fig.1): octahedral [Fe(C5H4N4S)3]2+ cations with three N7/S6 chelating neutral 6-MP ligands, tetrahedral [FeCl4]− anions and free chloride anions. The FeN3S3-octahedron is significantly distorted, with octahedral angles ranging from 83.39 (5) to 95.44 (5)°. The neutral 6-MP ligand is protonated at N1 and N9, but not at the coordinating N7 atom. A common feature of most coordinating purine bases is a slight non-planarity in the pseudoaromatic ring system. Small deviations from planarity occur also in Fe2(6-MP)3Cl5, where the maximum distances of an atom from the best plane through the nine purine ring atoms are −0.029 (2) for N9 and 0.025 (2) Å for N7. The `bite distance' S6···N7 of the chelating 6-MP ligand is 3.179 (2) Å, compared with the corresponding distance of 3.342 (1) Å for the non-coordinating molecule in 6-mercaptopurine monohydrate (Sletten et al., 1969). This fact is in agreement with the observation that the decrease of the bite distance is more pronounced the smaller the metal atom is. The distance may vary from about 3.32 Å in CdII-complexes to 3.04 Å in CuII complexes (Dubler & Gyr, 1988).
The [Fe(C5H4N4S)3]2+ cations are separated from each other by the [FeCl4]− anions, and there is no evidence for stacking interactions between the purine planes. The mean Fe—Cl distance in the [FeIIICl4]− anion is 2.189 (1) Å. This distance clearly indicates the FeIII oxidation state of the central atom, since for a tetrahedral [FeIICl4]2− anion the expected mean bonding distance is about 2.30 Å (query) (Pelizzi et al., 1977).
The [Fe(C5H4N4S)3]2+ cations and the free Cl− anions are connected through a network of hydrogen bonds of the type N—H···Cl, where the Cl− anion acts as a six-coordinated acceptor. In addition, weak interactions of the type C—H···S are observed (Table 2 and Fig. 2).