fac-Tris(2-ethyl-4-oxo-4H-pyran-3-olato-[kappa]²O³,O⁴)­iron(III) and its aluminium(III) analog

The crystal structures of the title iron(III) and aluminium(III) ethyl maltolate complexes, [Fe(C₇H₇O₃)₃] and [Al(C₇H₇O₃)₃], respectively, are isomorphous. In each case, the three bidentate ligand mol­ecules are bound to the metal atom, forming a distorted octahedral coordination geometry in a fac configuration.

S1. Comment

Pyranone ligands have remarkable properties for clinical purposes. These ligands are relevant to the control of metal levels in the body and so far have been tested for administration for the amelioration of anaemia (Hider et al., 1984a,b), and the removal of iron (Kontoghiorghes et al., 1990) and aluminium (Kontoghiorghes, 1995) overload. One of these ligands, viz. ethyl maltol (2-ethyl-3-hydroxyl-4-pyranone), (I), is suitable for oral administration since it has no toxic effect. It has been tested for the characteristics of iron uptake (Levey et al., 1988; Maxton et al., 1994). In this study, to determine the chelating mode of ethyl maltol to Fe³⁺ and Al³⁺ atoms, we have analyzed the crystal structures of the title complexes fac-tris(2-ethyl-3-oxo-4H-pyran-4-onato)iron(III), (II), and fac-tris(2-ethyl-3-oxo-4H-pyran-4-onato)aluminium(III), (III), which are isomorphous.

In (II), the Fe atom is bound by the deprotonated hydroxyl and keto O atoms of three bidentate ligands to form a distorted octahedral structure (Fig. 1). These O atoms of each ligand form a five-membered chelate ring with the Fe atom. In the ligand molecule, the C—O_keto bond lengths [O3—C4 = 1.262 (4) Å, O6—C11 = 1.259 (4) Å and O9—C18 = 1.262 (4) Å] are longer than those of free ethyl maltol in the crystal [1.235 (2)–1.256 (6) Å; Brown et al., 1995], and the C—O_OH bonds [O2—C3 = 1.330 (4) Å, O5—C10 = 1.326 (3) Å and O8—C17 = 1.321 (4) Å] are shorter than those of the free molecule [1.347 (3)–1.356 (6) Å]. This indicates the distinction between the two types of Lewis acid–base interactions. The Fe atom lies in a trigonally distorted octahedral environment, coordinated to the six O atoms of three bidentate ligands in a fac configuration, that is, the three longer Fe—O_keto bonds (Fe—O3, Fe—O6 and Fe—O9) are cis to each other, and the three shorter Fe—O_OH bonds (Fe—O2, Fe—O5 and Fe—O8) are also cis. The distortion of the octahedral environment is due to the differences found in the Fe—O bond lengths [Fe—O_keto = 2.074 (2)–2.090 (2) Å and Fe—O_OH = 1.960 (2)–1.969 (2) Å]. This situation is similar to those in the crystal structure of the maltolate–Fe³⁺ complex (Ahmet et al., 1988). The differences between the Fe—O_keto and Fe—O_OH bond lengths are due to the negative charge at the deprotonated O atoms.

In (III), coordination about the Al atom is similar to that in (II). The Al atom is surrounded by six O atoms of three bidentate ligands in a fac configuration in a distorted octahedral environment (Fig. 2). In the ligand molecule, the C—O_keto bond lengths [O3—C4 = 1.274 (6) Å, O6—C11 = 1.263 (6) Å and O9—C18 = 1.268 (6) Å] are longer than those of free ethyl maltol and the C—O_OH bonds [O2—C3 = 1.315 (5) Å, O5—C10 = 1.329 (5) Å and O8—C17 = 1.321 (5) Å] are shorter than those of the free molecule. The overall conformational tendency of (III) is similar to that in the crystal structures of maltolate–Al³⁺ complexes (Finnegan et al., 1986; Yu et al., 2002).

Despite the conformational similarity of the crystal structures of (II) and (III), the bite angles, O—M—O, of the ethyl maltolate ligands are different. Those for the Fe³⁺ complex [range 80.39 (9)–80.79 (9)°] are smaller than those for the Al³⁺ complex [range 84.3 (1)–84.6 (1)°]. This correlates to the M—O bond lengths [Fe—O = 1.960 (2)–2.090 (2) Å and Al—O = 1.860 (3)–1.956 (4) Å], namely the steric constraint imposed by the ionic radii (0.79 Å for Fe³⁺ and 0.68 Å for Al³⁺; Shannon, 1976).

Until now, the crystal structures of the Sn⁴⁺ (Lu et al., 1999; Alshehri et al., 2000), Ti⁴⁺ (Alshehri et al., 2000) and Bi³⁺ (Burgess et al., 1994) complexes of ethyl maltol have been reported. In these complexes, similar to (II) and (III), the metal atoms are bound by bidentate ligand molecules to form five membered chelate rings. These structures, except for the Ti⁴⁺ complex, show the same trends consistent with the increasing radius of the metal ion. The M—O bond lengths increase and the O—M—O bond angles decrease with increasing ionic radius.

Comparing the present two complexes with the corresponding maltolate complexes shows that all four crystal structures are similar in the fact that the metal atoms are bound by six O atoms of bidentate ligand molecules to form distorted octahedral structures, but are different with regard to their geometrical isomerism properties. In the ethyl maltolate complexes, the ligand molecules are coordinated in a fac configuration, in contrast in the maltolate complexes, which exhibit a mer configuration. This may be due to the bulky hydrophobic ethyl groups of the ethyl maltolate ligand molecules.

S2. Experimental

For the preparation of (II), ethyl maltol and Fe(NO₃)₃·9H₂O (8:1 molar ratio) were dissolved in ethanol–water (4:6). Red pillar-shaped crystals of (II) were obtained by slow evaporation at room temperature. For the preparation of (III), ethyl maltol and Al(NO₃)₃·9H₂O (3:1 molar ratio) were dissolved in ethanol–water (1:1). The pH of this solution was raised to about 8 by adding ammonia solution, and the resulting solution was then heated for a few minutes and cooled to room temperature. Colorless plate-shaped crystals of (III) were obtained by slow evaporation.

S3. Refinement

Intensity decay of standard reflections for (III) was 7.3%, which was corrected. For both compounds, all H atoms were generated by calculation and refined as riding atoms.

Computing details

For both compounds, 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.

Figures

	Fig. 1. ORTEPII (Johnson, 1976) drawing of (II), with the atomic numbering schemes. Ellipsoids for non-H atoms are shown at the 50% probability level.
	Fig. 2. ORTEPII (Johnson, 1976) drawing of (III), with the atomic numbering schemes. Ellipsoids for non-H atoms are shown at the 50% probability level.

(II)

Crystal data

[Fe(C7H7O3)3]	F(000) = 980.0
Mr = 473.23	Dx = 1.473 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: -P 2yn	Cell parameters from 25 reflections
a = 7.878 (3) Å	θ = 12.8–14.3°
b = 8.818 (4) Å	µ = 0.76 mm^−1
c = 30.721 (2) Å	T = 296 K
β = 90.80 (2)°	Pillar, red
V = 2133.9 (13) Å^3	0.40 × 0.10 × 0.10 mm
Z = 4

Data collection

Rigaku AFC-5R diffractometer	θmax = 27.5°
ω scans	h = 0→10
5604 measured reflections	k = 0→11
4911 independent reflections	l = −39→39
2768 reflections with I > 2σ(I)	3 standard reflections every 150 reflections
Rint = 0.026	intensity decay: 0.1%

Refinement

Refinement on F^2	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.042	w = 1/[σ^2(Fo^2) + (0.0624P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.135	(Δ/σ)max = 0.001
S = 0.99	Δρmax = 0.41 e Å^−3
4911 reflections	Δρmin = −0.32 e Å^−3
283 parameters

Special details

Refinement. Refinement using reflections with F² > 0.0 σ(F²). The weighted R-factor (wR) and goodness of fit (S) are based on F². R-factor (gt) are based on 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 (Ų)

	x	y	z	Uiso*/Ueq
Fe	0.91203 (5)	0.12025 (5)	0.35538 (1)	0.0415 (1)
O1	1.1404 (3)	−0.3863 (3)	0.41162 (8)	0.0605 (6)
O2	1.0216 (3)	0.0083 (2)	0.40356 (7)	0.0450 (5)
O3	0.9325 (3)	−0.0920 (2)	0.32598 (7)	0.0474 (5)
O4	1.2065 (4)	0.3993 (3)	0.23226 (8)	0.0721 (8)
O5	1.1230 (3)	0.2053 (2)	0.33272 (6)	0.0440 (5)
O6	0.8199 (3)	0.2078 (3)	0.29701 (7)	0.0543 (6)
O7	0.4438 (3)	0.3857 (3)	0.44021 (9)	0.0713 (7)
O8	0.8442 (3)	0.2949 (2)	0.39097 (7)	0.0469 (5)
O9	0.6622 (3)	0.0578 (3)	0.36875 (7)	0.0524 (6)
C2	1.1189 (4)	−0.2376 (4)	0.4230 (1)	0.0528 (8)
C3	1.0496 (4)	−0.1370 (4)	0.39445 (9)	0.0407 (7)
C4	0.9996 (4)	−0.1878 (4)	0.3514 (1)	0.0416 (7)
C5	1.0268 (5)	−0.3414 (4)	0.3417 (1)	0.0542 (9)
C6	1.0944 (5)	−0.4334 (4)	0.3722 (1)	0.0601 (9)
C7	1.1705 (5)	−0.2035 (5)	0.4688 (1)	0.071 (1)
C8	1.0324 (7)	−0.2270 (7)	0.4992 (1)	0.109 (2)
C9	1.2356 (5)	0.3299 (4)	0.2714 (1)	0.0532 (8)
C10	1.1039 (4)	0.2707 (3)	0.29411 (9)	0.0422 (7)
C11	0.9352 (4)	0.2735 (4)	0.2762 (1)	0.0482 (8)
C12	0.9144 (5)	0.3509 (4)	0.2356 (1)	0.064 (1)
C13	1.0481 (6)	0.4086 (5)	0.2164 (1)	0.075 (1)
C14	1.4171 (5)	0.3282 (5)	0.2848 (1)	0.065 (1)
C15	1.4823 (6)	0.4715 (6)	0.3030 (2)	0.111 (2)
C16	0.6105 (4)	0.3990 (4)	0.4279 (1)	0.0561 (9)
C17	0.6854 (4)	0.2887 (4)	0.40421 (9)	0.0429 (7)
C18	0.5901 (4)	0.1569 (4)	0.3916 (1)	0.0471 (8)
C19	0.4187 (4)	0.1495 (5)	0.4053 (1)	0.0605 (10)
C20	0.3555 (5)	0.2632 (6)	0.4283 (1)	0.074 (1)
C21	0.6876 (5)	0.5458 (5)	0.4417 (1)	0.073 (1)
C22	0.6230 (6)	0.6792 (6)	0.4161 (2)	0.111 (2)
H1	0.9982	−0.3792	0.3143	0.0650*
H2	1.1098	−0.5351	0.3653	0.0721*
H3	1.2653	−0.2681	0.4771	0.0852*
H4	1.2083	−0.0991	0.4708	0.0852*
H5	1.0011	−0.3322	0.4993	0.1628*
H6	0.9364	−0.1668	0.4904	0.1628*
H7	1.0689	−0.1975	0.5279	0.1628*
H8	0.8072	0.3604	0.2228	0.0772*
H9	1.0311	0.4591	0.1901	0.0901*
H10	1.4336	0.2490	0.3064	0.0777*
H11	1.4843	0.3018	0.2597	0.0777*
H12	1.4163	0.4997	0.3277	0.1669*
H13	1.4743	0.5496	0.2813	0.1669*
H14	1.5988	0.4587	0.3118	0.1669*
H15	0.3517	0.0660	0.3983	0.0726*
H16	0.2426	0.2571	0.4366	0.0891*
H17	0.8097	0.5395	0.4386	0.0880*
H18	0.6644	0.5623	0.4722	0.0880*
H19	0.6533	0.6677	0.3861	0.1669*
H20	0.6726	0.7706	0.4275	0.1669*
H21	0.5017	0.6846	0.4182	0.1669*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe	0.0382 (2)	0.0453 (3)	0.0409 (2)	−0.0007 (2)	−0.0028 (2)	−0.0026 (2)
O1	0.067 (2)	0.050 (1)	0.065 (2)	0.008 (1)	0.001 (1)	0.009 (1)
O2	0.051 (1)	0.044 (1)	0.041 (1)	−0.001 (1)	−0.0060 (9)	−0.0050 (10)
O3	0.052 (1)	0.050 (1)	0.041 (1)	0.001 (1)	−0.0064 (10)	−0.0079 (10)
O4	0.081 (2)	0.083 (2)	0.053 (1)	0.003 (2)	0.007 (1)	0.023 (1)
O5	0.041 (1)	0.054 (1)	0.037 (1)	0.0000 (10)	−0.0035 (9)	0.0063 (10)
O6	0.043 (1)	0.066 (2)	0.054 (1)	0.004 (1)	−0.012 (1)	0.005 (1)
O7	0.050 (1)	0.092 (2)	0.072 (2)	0.006 (1)	0.019 (1)	−0.009 (2)
O8	0.039 (1)	0.047 (1)	0.055 (1)	−0.0046 (10)	0.0046 (9)	−0.007 (1)
O9	0.046 (1)	0.055 (1)	0.056 (1)	−0.009 (1)	−0.001 (1)	−0.008 (1)
C2	0.053 (2)	0.052 (2)	0.054 (2)	0.001 (2)	−0.002 (2)	0.004 (2)
C3	0.036 (1)	0.047 (2)	0.039 (1)	−0.008 (1)	−0.001 (1)	0.000 (1)
C4	0.035 (2)	0.047 (2)	0.043 (2)	−0.004 (1)	0.004 (1)	−0.005 (1)
C5	0.063 (2)	0.048 (2)	0.052 (2)	−0.001 (2)	0.008 (2)	−0.012 (2)
C6	0.071 (2)	0.047 (2)	0.062 (2)	0.001 (2)	0.013 (2)	−0.008 (2)
C7	0.080 (3)	0.074 (3)	0.058 (2)	0.002 (2)	−0.020 (2)	0.011 (2)
C8	0.109 (4)	0.163 (6)	0.053 (2)	−0.008 (4)	−0.001 (3)	−0.010 (3)
C9	0.059 (2)	0.053 (2)	0.047 (2)	0.005 (2)	0.005 (2)	0.006 (2)
C10	0.048 (2)	0.041 (2)	0.038 (2)	0.007 (1)	−0.004 (1)	−0.001 (1)
C11	0.050 (2)	0.048 (2)	0.047 (2)	0.011 (2)	−0.008 (1)	−0.004 (1)
C12	0.074 (3)	0.066 (2)	0.052 (2)	0.013 (2)	−0.022 (2)	0.006 (2)
C13	0.099 (3)	0.078 (3)	0.049 (2)	0.013 (3)	−0.011 (2)	0.019 (2)
C14	0.053 (2)	0.069 (2)	0.073 (2)	0.003 (2)	0.014 (2)	0.011 (2)
C15	0.086 (4)	0.091 (4)	0.156 (5)	−0.003 (3)	−0.037 (3)	−0.004 (4)
C16	0.049 (2)	0.067 (2)	0.053 (2)	0.003 (2)	0.004 (2)	−0.005 (2)
C17	0.039 (2)	0.053 (2)	0.037 (1)	−0.001 (1)	−0.002 (1)	0.004 (1)
C18	0.039 (2)	0.066 (2)	0.036 (2)	−0.004 (2)	−0.004 (1)	0.008 (1)
C19	0.041 (2)	0.088 (3)	0.053 (2)	−0.014 (2)	0.004 (2)	0.003 (2)
C20	0.040 (2)	0.114 (4)	0.069 (3)	−0.003 (2)	0.014 (2)	0.004 (3)
C21	0.066 (2)	0.072 (3)	0.082 (3)	0.006 (2)	0.012 (2)	−0.026 (2)
C22	0.079 (3)	0.077 (3)	0.178 (6)	−0.002 (3)	0.023 (4)	−0.003 (4)

Geometric parameters (Å, º)

Fe—O2	1.969 (2)	C8—H6	0.960
Fe—O3	2.085 (2)	C8—H7	0.960
Fe—O5	1.960 (2)	C9—C10	1.362 (5)
Fe—O6	2.074 (2)	C9—C14	1.483 (5)
Fe—O8	1.967 (2)	C10—C11	1.432 (4)
Fe—O9	2.090 (2)	C11—C12	1.428 (5)
O1—C2	1.368 (4)	C12—C13	1.316 (6)
O1—C6	1.327 (4)	C12—H8	0.930
O2—C3	1.330 (4)	C13—H9	0.930
O3—C4	1.262 (4)	C14—C15	1.471 (7)
O4—C9	1.366 (4)	C14—H10	0.970
O4—C13	1.336 (6)	C14—H11	0.970
O5—C10	1.326 (3)	C15—H12	0.960
O6—C11	1.259 (4)	C15—H13	0.960
O7—C16	1.377 (4)	C15—H14	0.960
O7—C20	1.333 (5)	C16—C17	1.356 (5)
O8—C17	1.321 (4)	C16—C21	1.488 (6)
O9—C18	1.262 (4)	C17—C18	1.434 (5)
C2—C3	1.358 (4)	C18—C19	1.421 (5)
C2—C7	1.490 (5)	C19—C20	1.327 (6)
C3—C4	1.446 (4)	C19—H15	0.930
C4—C5	1.404 (5)	C20—H16	0.930
C5—C6	1.344 (5)	C21—C22	1.500 (7)
C5—H1	0.930	C21—H17	0.970
C6—H2	0.930	C21—H18	0.970
C7—C8	1.458 (7)	C22—H19	0.960
C7—H3	0.970	C22—H20	0.960
C7—H4	0.970	C22—H21	0.960
C8—H5	0.960
O1···O7^i	3.236 (4)	O5···C6^vii	3.417 (4)
O1···C20^i	3.559 (5)	O5···C20^ii	3.477 (4)
O2···C19^ii	3.367 (4)	O6···C14^viii	3.362 (4)
O2···C20^ii	3.535 (5)	O6···C15^viii	3.540 (6)
O2···C8^iii	3.585 (5)	O8···C6^vii	3.161 (4)
O3···C12^iv	3.340 (5)	O8···C8^iii	3.548 (5)
O3···O4^v	3.382 (4)	O9···C13^iv	3.347 (5)
O4···C4^vi	3.567 (4)	C6···C10^ix	3.545 (5)
O5···C19^ii	3.241 (4)
O2—Fe—O3	80.79 (9)	C10—C9—C14	126.3 (3)
O2—Fe—O5	95.38 (9)	O5—C10—C9	123.2 (3)
O2—Fe—O6	168.89 (9)	O5—C10—C11	116.4 (3)
O2—Fe—O8	95.42 (9)	C9—C10—C11	120.4 (3)
O2—Fe—O9	97.16 (9)	O6—C11—C10	117.9 (3)
O3—Fe—O5	96.81 (9)	O6—C11—C12	126.0 (3)
O3—Fe—O6	89.31 (9)	C10—C11—C12	116.0 (3)
O3—Fe—O8	165.16 (9)	C11—C12—C13	119.5 (4)
O3—Fe—O9	85.83 (9)	C11—C12—H8	120.3
O5—Fe—O6	80.71 (8)	C13—C12—H8	120.2
O5—Fe—O8	97.83 (9)	O4—C13—C12	124.2 (4)
O5—Fe—O9	167.45 (9)	O4—C13—H9	117.9
O6—Fe—O8	95.42 (9)	C12—C13—H9	117.9
O6—Fe—O9	87.08 (9)	C9—C14—C15	115.3 (4)
O8—Fe—O9	80.39 (9)	C9—C14—H10	108.5
C2—O1—C6	120.1 (3)	C9—C14—H11	108.4
Fe—O2—C3	113.4 (2)	C15—C14—H10	108.5
Fe—O3—C4	111.5 (2)	C15—C14—H11	108.5
C9—O4—C13	119.5 (3)	H10—C14—H11	107.5
Fe—O5—C10	113.5 (2)	C14—C15—H12	109.5
Fe—O6—C11	111.4 (2)	C14—C15—H13	109.5
C16—O7—C20	119.4 (3)	C14—C15—H14	109.5
Fe—O8—C17	113.9 (2)	H12—C15—H13	109.5
Fe—O9—C18	111.1 (2)	H12—C15—H14	109.5
O1—C2—C3	120.7 (3)	H13—C15—H14	109.5
O1—C2—C7	113.7 (3)	O7—C16—C17	120.7 (3)
C3—C2—C7	125.5 (3)	O7—C16—C21	112.6 (3)
O2—C3—C2	124.0 (3)	C17—C16—C21	126.7 (3)
O2—C3—C4	116.6 (3)	O8—C17—C16	123.8 (3)
C2—C3—C4	119.4 (3)	O8—C17—C18	116.4 (3)
O3—C4—C3	117.7 (3)	C16—C17—C18	119.8 (3)
O3—C4—C5	125.3 (3)	O9—C18—C17	118.2 (3)
C3—C4—C5	117.0 (3)	O9—C18—C19	124.8 (3)
C4—C5—C6	119.6 (3)	C17—C18—C19	116.9 (3)
C4—C5—H1	120.2	C18—C19—C20	119.2 (4)
C6—C5—H1	120.2	C18—C19—H15	120.4
O1—C6—C5	123.2 (3)	C20—C19—H15	120.4
O1—C6—H2	118.4	O7—C20—C19	124.0 (3)
C5—C6—H2	118.4	O7—C20—H16	118.0
C2—C7—C8	112.3 (4)	C19—C20—H16	118.0
C2—C7—H3	109.1	C16—C21—C22	113.5 (4)
C2—C7—H4	109.1	C16—C21—H17	108.9
C8—C7—H3	109.1	C16—C21—H18	108.9
C8—C7—H4	109.1	C22—C21—H17	108.9
H3—C7—H4	107.9	C22—C21—H18	108.9
C7—C8—H5	109.5	H17—C21—H18	107.7
C7—C8—H6	109.5	C21—C22—H19	109.5
C7—C8—H7	109.5	C21—C22—H20	109.5
H5—C8—H6	109.5	C21—C22—H21	109.5
H5—C8—H7	109.5	H19—C22—H20	109.5
H6—C8—H7	109.5	H19—C22—H21	109.5
O4—C9—C10	120.2 (3)	H20—C22—H21	109.5
O4—C9—C14	113.5 (3)
Fe—O2—C3—C2	−177.9 (3)	O6—Fe—O8—C17	85.1 (2)
Fe—O2—C3—C4	1.2 (3)	O6—Fe—O9—C18	−95.4 (2)
Fe—O3—C4—C3	−0.4 (3)	O6—C11—C10—C9	175.0 (3)
Fe—O3—C4—C5	178.3 (3)	O6—C11—C12—C13	−176.9 (4)
Fe—O5—C10—C9	−176.4 (3)	O7—C16—C17—O8	179.3 (3)
Fe—O5—C10—C11	2.0 (3)	O7—C16—C17—C18	0.1 (5)
Fe—O6—C11—C10	2.9 (4)	O7—C16—C21—C22	−72.1 (4)
Fe—O6—C11—C12	−177.6 (3)	O7—C20—C19—C18	−0.9 (6)
Fe—O8—C17—C16	−177.9 (3)	O8—Fe—O2—C3	164.5 (2)
Fe—O8—C17—C18	1.2 (3)	O8—Fe—O3—C4	−75.4 (4)
Fe—O9—C18—C17	−0.2 (3)	O8—Fe—O5—C10	−94.7 (2)
Fe—O9—C18—C19	178.5 (3)	O8—Fe—O6—C11	95.7 (2)
O1—C2—C3—O2	178.6 (3)	O8—Fe—O9—C18	0.7 (2)
O1—C2—C3—C4	−0.6 (5)	O8—C17—C16—C21	2.6 (5)
O1—C2—C7—C8	−88.1 (4)	O8—C17—C18—O9	−0.7 (4)
O1—C6—C5—C4	−1.1 (6)	O8—C17—C18—C19	−179.5 (3)
O2—Fe—O3—C4	0.8 (2)	O9—Fe—O2—C3	83.5 (2)
O2—Fe—O5—C10	169.1 (2)	O9—Fe—O3—C4	−97.2 (2)
O2—Fe—O6—C11	−71.5 (5)	O9—Fe—O5—C10	−13.8 (5)
O2—Fe—O8—C17	−97.4 (2)	O9—Fe—O6—C11	175.7 (2)
O2—Fe—O9—C18	95.0 (2)	O9—Fe—O8—C17	−1.0 (2)
O2—C3—C2—C7	1.5 (5)	O9—C18—C17—C16	178.5 (3)
O2—C3—C4—O3	−0.6 (4)	O9—C18—C19—C20	−178.0 (3)
O2—C3—C4—C5	−179.3 (3)	C2—O1—C6—C5	0.4 (5)
O3—Fe—O2—C3	−1.1 (2)	C2—C3—C4—C5	−0.1 (4)
O3—Fe—O5—C10	87.8 (2)	C3—C2—O1—C6	0.5 (5)
O3—Fe—O6—C11	−98.4 (2)	C3—C2—C7—C8	89.1 (5)
O3—Fe—O8—C17	−23.0 (4)	C3—C4—C5—C6	0.9 (5)
O3—Fe—O9—C18	175.1 (2)	C4—C3—C2—C7	−177.6 (3)
O3—C4—C3—C2	178.6 (3)	C6—O1—C2—C7	177.8 (3)
O3—C4—C5—C6	−177.7 (3)	C9—O4—C13—C12	−1.9 (6)
O4—C9—C10—O5	−178.3 (3)	C9—C10—C11—C12	−4.6 (5)
O4—C9—C10—C11	3.4 (5)	C10—C9—O4—C13	−0.1 (5)
O4—C9—C14—C15	78.3 (5)	C10—C9—C14—C15	−101.6 (5)
O4—C13—C12—C11	0.5 (6)	C10—C11—C12—C13	2.7 (5)
O5—Fe—O2—C3	−97.1 (2)	C11—C10—C9—C14	−176.8 (3)
O5—Fe—O3—C4	95.1 (2)	C13—O4—C9—C14	−180.0 (3)
O5—Fe—O6—C11	−1.4 (2)	C16—O7—C20—C19	0.8 (6)
O5—Fe—O8—C17	166.4 (2)	C16—C17—C18—C19	−0.3 (4)
O5—Fe—O9—C18	−82.2 (5)	C17—C16—O7—C20	−0.4 (5)
O5—C10—C9—C14	1.6 (5)	C17—C16—C21—C22	104.9 (5)
O5—C10—C11—O6	−3.4 (4)	C17—C18—C19—C20	0.7 (5)
O5—C10—C11—C12	177.0 (3)	C18—C17—C16—C21	−176.6 (3)
O6—Fe—O2—C3	−28.4 (6)	C20—O7—C16—C21	176.8 (3)
O6—Fe—O3—C4	175.7 (2)	C20—O7—C16—C21	176.8 (3)
O6—Fe—O5—C10	−0.4 (2)

Symmetry codes: (i) x+1, y−1, z; (ii) x+1, y, z; (iii) −x+2, −y, −z+1; (iv) −x+3/2, y−1/2, −z+1/2; (v) −x+5/2, y−1/2, −z+1/2; (vi) −x+5/2, y+1/2, −z+1/2; (vii) x, y+1, z; (viii) x−1, y, z; (ix) x, y−1, z.

(III)

Crystal data

[Al(C7H7O3)3]	F(000) = 928.0
Mr = 444.36	Dx = 1.395 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: -P 2yn	Cell parameters from 10 reflections
a = 7.897 (4) Å	θ = 10.4–11.8°
b = 8.696 (9) Å	µ = 0.15 mm^−1
c = 30.801 (4) Å	T = 296 K
β = 91.40 (3)°	Plate, colorless
V = 2115 (2) Å^3	0.20 × 0.20 × 0.10 mm
Z = 4

Data collection

Rigaku AFC-5R diffractometer	Rint = 0.127
ω scans	θmax = 27.5°
Absorption correction: ψ scan (North et al., 1968)	h = 0→10
Tmin = 0.952, Tmax = 0.999	k = 0→11
5552 measured reflections	l = −39→40
4868 independent reflections	3 standard reflections every 150 reflections
1804 reflections with I > 2σ(I)	intensity decay: 7.3%

Refinement

Refinement on F^2	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.064	w = 1/[σ^2(Fo^2) + (0.1054P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.228	(Δ/σ)max < 0.001
S = 0.94	Δρmax = 0.37 e Å^−3
4868 reflections	Δρmin = −0.42 e Å^−3
280 parameters

Special details

Refinement. Refinement using reflections with F² > −10.0 σ(F²). The weighted R-factor (wR) and goodness of fit (S) are based on F². R-factor (gt) are based on 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 (Ų)

	x	y	z	Uiso*/Ueq
Al	0.4051 (2)	0.1075 (2)	0.35649 (4)	0.0452 (4)
O1	0.6317 (4)	−0.3904 (4)	0.4135 (1)	0.0644 (9)
O2	0.5087 (4)	0.0069 (4)	0.40387 (9)	0.0482 (8)
O3	0.4337 (4)	−0.0891 (4)	0.32664 (9)	0.0498 (8)
O4	0.6793 (5)	0.3827 (5)	0.2350 (1)	0.075 (1)
O5	0.6057 (3)	0.1899 (4)	0.33642 (8)	0.0456 (7)
O6	0.3054 (4)	0.1895 (4)	0.3028 (1)	0.0552 (8)
O7	−0.0579 (4)	0.3645 (5)	0.4369 (1)	0.076 (1)
O8	0.3448 (4)	0.2795 (4)	0.38932 (9)	0.0507 (8)
O9	0.1779 (4)	0.0351 (4)	0.3695 (1)	0.0568 (9)
C2	0.6080 (6)	−0.2412 (6)	0.4249 (1)	0.053 (1)
C3	0.5415 (5)	−0.1382 (5)	0.3955 (1)	0.044 (1)
C4	0.4977 (5)	−0.1901 (6)	0.3521 (1)	0.046 (1)
C5	0.5270 (6)	−0.3455 (6)	0.3425 (2)	0.055 (1)
C6	0.5904 (6)	−0.4395 (6)	0.3733 (2)	0.061 (1)
C7	0.6544 (7)	−0.2070 (7)	0.4709 (2)	0.070 (2)
C8	0.5171 (10)	−0.236 (1)	0.5003 (2)	0.114 (3)
C9	0.7128 (6)	0.3145 (6)	0.2741 (2)	0.058 (1)
C10	0.5861 (5)	0.2540 (5)	0.2974 (1)	0.046 (1)
C11	0.4154 (6)	0.2569 (6)	0.2806 (1)	0.050 (1)
C12	0.3861 (7)	0.3321 (6)	0.2403 (2)	0.065 (1)
C13	0.5177 (9)	0.3916 (7)	0.2198 (2)	0.078 (2)
C14	0.8971 (6)	0.3122 (7)	0.2859 (2)	0.074 (2)
C15	0.9666 (8)	0.4613 (8)	0.3011 (3)	0.110 (2)
C16	0.1084 (6)	0.3853 (7)	0.4254 (2)	0.061 (1)
C17	0.1867 (5)	0.2729 (6)	0.4022 (1)	0.048 (1)
C18	0.0989 (6)	0.1352 (6)	0.3910 (1)	0.053 (1)
C19	−0.0742 (6)	0.1208 (7)	0.4034 (2)	0.064 (1)
C20	−0.1423 (7)	0.2379 (9)	0.4254 (2)	0.079 (2)
C21	0.1799 (7)	0.5315 (7)	0.4391 (2)	0.079 (2)
C22	0.1116 (9)	0.6696 (9)	0.4145 (3)	0.124 (3)
H1	0.5024	−0.3831	0.3148	0.0659*
H2	0.6063	−0.5426	0.3665	0.0730*
H3	0.7511	−0.2695	0.4796	0.0844*
H4	0.6879	−0.1000	0.4733	0.0844*
H5	0.5475	−0.1973	0.5286	0.1712*
H6	0.4968	−0.3446	0.5020	0.1712*
H7	0.4164	−0.1851	0.4897	0.1712*
H8	0.2771	0.3399	0.2284	0.0783*
H9	0.4970	0.4420	0.1936	0.0939*
H10	0.9165	0.2363	0.3085	0.0890*
H11	0.9592	0.2796	0.2607	0.0890*
H12	1.0870	0.4527	0.3053	0.1645*
H13	0.9159	0.4889	0.3280	0.1645*
H14	0.9419	0.5391	0.2797	0.1645*
H15	−0.1372	0.0334	0.3964	0.0762*
H16	−0.2551	0.2300	0.4330	0.0949*
H17	0.3016	0.5275	0.4358	0.0949*
H18	0.1586	0.5456	0.4697	0.0949*
H19	0.1639	0.7614	0.4258	0.1854*
H20	−0.0088	0.6758	0.4178	0.1854*
H21	0.1364	0.6594	0.3843	0.1854*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Al	0.0424 (7)	0.0506 (8)	0.0424 (7)	−0.0022 (6)	−0.0065 (5)	−0.0003 (6)
O1	0.070 (2)	0.062 (2)	0.062 (2)	0.008 (2)	−0.001 (2)	0.004 (2)
O2	0.052 (2)	0.050 (2)	0.042 (2)	0.001 (1)	−0.009 (1)	−0.005 (1)
O3	0.052 (2)	0.057 (2)	0.041 (2)	0.001 (2)	−0.009 (1)	−0.003 (2)
O4	0.079 (3)	0.091 (3)	0.057 (2)	0.001 (2)	0.005 (2)	0.025 (2)
O5	0.038 (2)	0.059 (2)	0.040 (2)	−0.002 (1)	−0.007 (1)	0.007 (1)
O6	0.045 (2)	0.070 (2)	0.049 (2)	0.003 (2)	−0.011 (1)	0.008 (2)
O7	0.052 (2)	0.101 (3)	0.076 (3)	0.000 (2)	0.016 (2)	−0.004 (2)
O8	0.042 (2)	0.053 (2)	0.056 (2)	−0.003 (1)	0.000 (1)	−0.006 (2)
O9	0.046 (2)	0.066 (2)	0.058 (2)	−0.008 (2)	0.004 (1)	−0.007 (2)
C2	0.059 (3)	0.052 (3)	0.047 (3)	0.000 (2)	−0.008 (2)	0.002 (2)
C3	0.043 (2)	0.048 (3)	0.040 (2)	−0.005 (2)	0.000 (2)	0.000 (2)
C4	0.035 (2)	0.059 (3)	0.043 (2)	−0.005 (2)	0.004 (2)	−0.008 (2)
C5	0.062 (3)	0.052 (3)	0.050 (3)	0.005 (3)	0.004 (2)	−0.007 (2)
C6	0.066 (3)	0.046 (3)	0.071 (4)	0.005 (3)	0.011 (3)	−0.010 (3)
C7	0.085 (4)	0.069 (4)	0.057 (3)	−0.004 (3)	−0.013 (3)	0.016 (3)
C8	0.115 (5)	0.164 (8)	0.063 (4)	−0.007 (5)	−0.008 (3)	−0.011 (4)
C9	0.060 (3)	0.064 (3)	0.050 (3)	−0.004 (3)	−0.002 (2)	0.006 (3)
C10	0.047 (3)	0.049 (3)	0.041 (2)	0.006 (2)	−0.001 (2)	0.000 (2)
C11	0.052 (3)	0.053 (3)	0.045 (3)	0.013 (2)	−0.011 (2)	0.001 (2)
C12	0.073 (3)	0.068 (4)	0.054 (3)	0.013 (3)	−0.021 (3)	0.009 (3)
C13	0.102 (5)	0.083 (4)	0.049 (3)	0.015 (4)	−0.010 (3)	0.017 (3)
C14	0.056 (3)	0.091 (4)	0.076 (4)	−0.001 (3)	0.012 (3)	0.006 (3)
C15	0.079 (4)	0.088 (5)	0.161 (7)	0.001 (4)	−0.032 (4)	−0.016 (5)
C16	0.049 (3)	0.080 (4)	0.054 (3)	0.008 (3)	−0.001 (2)	−0.003 (3)
C17	0.042 (2)	0.056 (3)	0.044 (3)	0.006 (2)	−0.005 (2)	0.004 (2)
C18	0.045 (3)	0.076 (4)	0.037 (2)	−0.004 (3)	−0.004 (2)	0.007 (2)
C19	0.049 (3)	0.078 (4)	0.064 (3)	−0.009 (3)	0.001 (2)	0.000 (3)
C20	0.048 (3)	0.105 (5)	0.085 (4)	−0.004 (3)	0.006 (3)	0.000 (4)
C21	0.073 (4)	0.064 (4)	0.101 (5)	0.000 (3)	0.010 (3)	−0.019 (4)
C22	0.094 (5)	0.095 (6)	0.182 (8)	0.002 (5)	−0.001 (5)	0.008 (6)

Geometric parameters (Å, º)

Al—O2	1.872 (3)	C8—H6	0.960
Al—O3	1.956 (3)	C8—H7	0.960
Al—O5	1.858 (3)	C9—C10	1.353 (6)
Al—O6	1.949 (3)	C9—C14	1.491 (7)
Al—O8	1.874 (3)	C10—C11	1.432 (6)
Al—O9	1.952 (3)	C11—C12	1.417 (7)
O1—C2	1.359 (6)	C12—C13	1.333 (9)
O1—C6	1.343 (6)	C12—H8	0.930
O2—C3	1.315 (5)	C13—H9	0.930
O3—C4	1.274 (5)	C14—C15	1.479 (10)
O4—C9	1.362 (6)	C14—H10	0.970
O4—C13	1.350 (8)	C14—H11	0.970
O5—C10	1.329 (5)	C15—H12	0.960
O6—C11	1.263 (6)	C15—H13	0.960
O7—C16	1.380 (6)	C15—H14	0.960
O7—C20	1.330 (8)	C16—C17	1.368 (7)
O8—C17	1.321 (5)	C16—C21	1.449 (8)
O9—C18	1.268 (6)	C17—C18	1.422 (7)
C2—C3	1.369 (6)	C18—C19	1.434 (7)
C2—C7	1.485 (7)	C19—C20	1.343 (9)
C3—C4	1.445 (6)	C19—H15	0.930
C4—C5	1.403 (7)	C20—H16	0.930
C5—C6	1.338 (7)	C21—C22	1.51 (1)
C5—H1	0.930	C21—H17	0.970
C6—H2	0.930	C21—H18	0.970
C7—C8	1.451 (9)	C22—H19	0.960
C7—H3	0.970	C22—H20	0.960
C7—H4	0.970	C22—H21	0.960
C8—H5	0.960
O1···O7^i	3.314 (5)	O6···C14^vi	3.424 (6)
O2···C19^ii	3.439 (6)	O6···C15^vi	3.569 (8)
O2···C20^ii	3.461 (7)	O8···C6^v	3.166 (6)
O2···C8^iii	3.571 (8)	O8···C8^iii	3.565 (7)
O3···C12^iv	3.293 (6)	O9···C13^iv	3.362 (7)
O5···C19^ii	3.279 (6)	O9···C22^vii	3.512 (9)
O5···C20^ii	3.373 (6)	C6···C10^vii	3.544 (7)
O5···C6^v	3.420 (6)
O2—Al—O3	84.6 (1)	C10—C9—C14	126.6 (4)
O2—Al—O5	94.6 (1)	O5—C10—C9	124.9 (4)
O2—Al—O6	172.7 (2)	O5—C10—C11	114.9 (4)
O2—Al—O8	93.7 (1)	C9—C10—C11	120.2 (4)
O2—Al—O9	94.4 (1)	O6—C11—C10	116.8 (4)
O3—Al—O5	94.1 (1)	O6—C11—C12	126.0 (4)
O3—Al—O6	88.3 (1)	C10—C11—C12	117.2 (4)
O3—Al—O8	170.0 (1)	C11—C12—C13	118.8 (5)
O3—Al—O9	86.1 (1)	C11—C12—H8	120.6
O5—Al—O6	84.6 (1)	C13—C12—H8	120.6
O5—Al—O8	95.8 (1)	O4—C13—C12	123.7 (5)
O5—Al—O9	171.0 (1)	O4—C13—H9	118.2
O6—Al—O8	93.6 (1)	C12—C13—H9	118.2
O6—Al—O9	86.4 (1)	C9—C14—C15	114.7 (5)
O8—Al—O9	84.3 (1)	C9—C14—H10	108.6
C2—O1—C6	120.7 (4)	C9—C14—H11	108.6
Al—O2—C3	112.3 (2)	C15—C14—H10	108.6
Al—O3—C4	111.2 (3)	C15—C14—H11	108.6
C9—O4—C13	119.5 (4)	H10—C14—H11	107.6
Al—O5—C10	112.4 (2)	C14—C15—H12	109.5
Al—O6—C11	111.1 (3)	C14—C15—H13	109.5
C16—O7—C20	120.9 (5)	C14—C15—H14	109.5
Al—O8—C17	112.4 (3)	H12—C15—H13	109.5
Al—O9—C18	110.6 (3)	H12—C15—H14	109.5
O1—C2—C3	120.5 (4)	H13—C15—H14	109.5
O1—C2—C7	113.9 (4)	O7—C16—C17	119.0 (5)
C3—C2—C7	125.5 (5)	O7—C16—C21	114.0 (5)
O2—C3—C2	125.0 (4)	C17—C16—C21	127.0 (5)
O2—C3—C4	115.9 (4)	O8—C17—C16	124.6 (4)
C2—C3—C4	119.1 (4)	O8—C17—C18	115.0 (4)
O3—C4—C3	115.9 (4)	C16—C17—C18	120.3 (4)
O3—C4—C5	126.9 (4)	O9—C18—C17	117.5 (4)
C3—C4—C5	117.3 (4)	O9—C18—C19	124.3 (5)
C4—C5—C6	120.0 (5)	C17—C18—C19	118.1 (5)
C4—C5—H1	120.0	C18—C19—C20	117.6 (5)
C6—C5—H1	120.0	C18—C19—H15	121.2
O1—C6—C5	122.4 (5)	C20—C19—H15	121.2
O1—C6—H2	118.8	O7—C20—C19	123.9 (5)
C5—C6—H2	118.8	O7—C20—H16	118.0
C2—C7—C8	113.0 (5)	C19—C20—H16	118.0
C2—C7—H3	109.0	C16—C21—C22	114.8 (5)
C2—C7—H4	109.0	C16—C21—H17	108.6
C8—C7—H3	109.0	C16—C21—H18	108.6
C8—C7—H4	109.0	C22—C21—H17	108.6
H3—C7—H4	107.8	C22—C21—H18	108.6
C7—C8—H5	109.5	H17—C21—H18	107.5
C7—C8—H6	109.5	C21—C22—H19	109.5
C7—C8—H7	109.5	C21—C22—H20	109.5
H5—C8—H6	109.5	C21—C22—H21	109.5
H5—C8—H7	109.5	H19—C22—H20	109.5
H6—C8—H7	109.5	H19—C22—H21	109.5
O4—C9—C10	120.5 (4)	H20—C22—H21	109.5
O4—C9—C14	112.8 (4)
Al—O2—C3—C2	−176.1 (4)	O6—Al—O9—C18	−91.3 (3)
Al—O2—C3—C4	1.9 (4)	O6—C11—C10—C9	175.5 (4)
Al—O3—C4—C3	−2.7 (4)	O6—C11—C12—C13	−176.7 (5)
Al—O3—C4—C5	176.2 (4)	O7—C16—C17—O8	179.9 (4)
Al—O5—C10—C9	−175.9 (4)	O7—C16—C17—C18	−1.5 (7)
Al—O5—C10—C11	4.5 (5)	O7—C16—C21—C22	−71.1 (7)
Al—O6—C11—C10	2.7 (5)	O7—C20—C19—C18	−1.1 (8)
Al—O6—C11—C12	−178.7 (4)	O8—Al—O2—C3	167.6 (3)
Al—O8—C17—C16	−177.8 (4)	O8—Al—O5—C10	−95.6 (3)
Al—O8—C17—C18	3.5 (5)	O8—Al—O6—C11	95.3 (3)
Al—O9—C18—C17	−1.5 (5)	O8—Al—O9—C18	2.7 (3)
Al—O9—C18—C19	176.1 (4)	O8—C17—C16—C21	1.7 (8)
O1—C2—C3—O2	177.6 (4)	O8—C17—C18—O9	−1.3 (6)
O1—C2—C3—C4	−0.3 (6)	O8—C17—C18—C19	−179.1 (4)
O1—C2—C7—C8	−86.4 (6)	O9—Al—O2—C3	83.0 (3)
O1—C6—C5—C4	−1.6 (7)	O9—Al—O3—C4	−91.8 (3)
O2—Al—O3—C4	3.0 (3)	O9—Al—O6—C11	179.3 (3)
O2—Al—O5—C10	170.3 (3)	O9—Al—O8—C17	−3.4 (3)
O2—Al—O8—C17	−97.5 (3)	O9—C18—C17—C16	−180.0 (4)
O2—Al—O9—C18	96.0 (3)	O9—C18—C19—C20	−178.6 (5)
O2—C3—C2—C7	−0.1 (7)	C2—O1—C6—C5	1.0 (7)
O2—C3—C4—O3	0.7 (5)	C2—C3—C4—C5	−0.2 (6)
O2—C3—C4—C5	−178.4 (4)	C3—C2—O1—C6	0.0 (7)
O3—Al—O2—C3	−2.6 (3)	C3—C2—C7—C8	91.5 (7)
O3—Al—O5—C10	85.4 (3)	C3—C4—C5—C6	1.1 (6)
O3—Al—O6—C11	−94.5 (3)	C4—C3—C2—C7	−178.0 (4)
O3—Al—O9—C18	−179.8 (3)	C6—O1—C2—C7	177.9 (4)
O3—C4—C3—C2	178.8 (4)	C9—O4—C13—C12	−2.4 (8)
O3—C4—C5—C6	−177.8 (4)	C9—C10—C11—C12	−3.3 (7)
O4—C9—C10—O5	−177.6 (4)	C10—C9—O4—C13	0.9 (7)
O4—C9—C10—C11	1.9 (7)	C10—C9—C14—C15	−105.7 (7)
O4—C9—C14—C15	76.1 (6)	C10—C11—C12—C13	1.9 (7)
O4—C13—C12—C11	0.9 (9)	C11—C10—C9—C14	−176.2 (5)
O5—Al—O2—C3	−96.3 (3)	C13—O4—C9—C14	179.3 (5)
O5—Al—O3—C4	97.2 (3)	C16—O7—C20—C19	1.9 (8)
O5—Al—O6—C11	−0.2 (3)	C16—C17—C18—C19	2.2 (7)
O5—Al—O8—C17	167.6 (3)	C17—C16—O7—C20	−0.5 (7)
O5—C10—C9—C14	4.2 (8)	C17—C16—C21—C22	107.1 (7)
O5—C10—C11—O6	−4.9 (6)	C17—C18—C19—C20	−0.9 (7)
O5—C10—C11—C12	176.3 (4)	C18—C17—C16—C21	−179.7 (5)
O6—Al—O3—C4	−178.3 (3)	C20—O7—C16—C21	177.9 (5)
O6—Al—O5—C10	−2.5 (3)	C20—O7—C16—C21	177.9 (5)
O6—Al—O8—C17	82.6 (3)

Symmetry codes: (i) x+1, y−1, z; (ii) x+1, y, z; (iii) −x+1, −y, −z+1; (iv) −x+1/2, y−1/2, −z+1/2; (v) x, y+1, z; (vi) x−1, y, z; (vii) x, y−1, z.