catena-Poly[[bis[pentaaquaerbium(III)]-[mu]-benzenehexacarboxylato] tetrahydrate]

The title compound is composed of one-dimensional polymeric {[Er₂(C₁₂O₁₂)(H₂O)₁₀]·4H₂O}_n chains containing Er in a slightly distorted antiprismatic eightfold coordination. The benzene­hexa­carboxyl­ate ion is located about an inversion centre. Water mol­ecules of crystallization, linked by hydrogen bonding to water mol­ecules of the rare earth coordination spheres or the carboxyl­ate groups of the organic ligands, fill the space generated by the packing of the separated chains.

S1. Comment

Aromatic acids usually form rare earth salts which exhibit optical properties (strong fluorescent emission) and possess very important physical and biological properties. Mellitic acid (benzenehexacarboxylic acid) can lose from two to six H atoms, depending on the reaction conditions used, and this gives rise to a great diversity of salts. The mellitate anion is known to be a multidentate agent via its carboxylate O atoms to metal cations, such as main group metal ions (for example Ca or Al; Uchtman & Jandacek, 1980; Giacovazzo et al., 1973), transition metal ions (Cu^II, Ni^II, Co^III or Y^III; Endres & Knieszner, 1984; Robl & Hentschel 1991, 1992) or rare earth ions (La^III; Wu et al., 1996). In these materials, the dimensionality of the networks varies from three-dimensional in Al₂[C₆(CO₂)₆].16(H₂O) to two-dimensional in the Cu compound, where layers are linked to each other by hydrogen bonds, and one-dimensional in Co or Ni compounds, where infinite chains are formed. We present here the crystal structure of the title compound, (I), an Er compound with mellitate. \sch

The title compound, (I), forms a one-dimensional polymer. As shown in Fig. 1, the chains are formed by the succession of one organic ligand and a pair of Er atoms along a. Each chain is separated from neighbouring chains by free water molecules (Fig. 2).

The Er atom in (I) is eight-coordinated, by three O atoms from two mellitate ions and by five water O atoms. The Er—O distances are quite homogeneous (Table 1) and the environment of the Er atom is a slightly distorted square antiprism (Fig. 3). The mellitate ion is located about an inversion centre and each ligand is bonded to four different Er atoms. The six carboxylate groups are each linked to an Er atom via one O atom, while the other O atom remains free. The carboxylate groups are highly twisted out of the plane of the benzene ring Is this added text OK? (twist angles lie in the range 50–70°). This twisting ability of a carboxylato group involved in a rare-earth-containing coordination polymer has already been reported in a terephthalate compound (Reineke et al., 1999) and in a benzenetetracarboxylate compound (Cao et al., 2002).

In addition to the five water molecules in the first coordination sphere of the Er atoms, two water molecules per Er atom were refined (Fig. 2). This is in accordance with the results of the thermogravimetric analysis. For the two sets of sites O1W—O4W and O2W—O3W, a disorder model (0.5:0.5) was introduced. These water molecules build a complex network of hydrogen bonding between themselves, the carboxylate O atoms and the water molecules of the first coordination sphere. These O atoms from the water molecules of crystallization exhibit high thermal displacement parameters. We attribute these high parameters to the existence of numerous hydrogen bonds of comparable importance.

It is interesting to note that the crystal structure of (I) differs from the La-containing structure already reported by Wu et al. (1993). The La-containing material was synthesized by hydrothermal methods, whereas both Y– and Er-containing compounds have been obtained by slow diffusion in gel media.

S2. Experimental

Mellitic acid was supplied by Aldrich Chemical Company Inc. and oxide of erbium was supplied by Rhodia Inc. Both were used without further purification. By reaction with NaOH, the mellitic acid provided the hexasodium mellitate salt. By reaction with HCl, the erbium oxide led to the pentahydrated erbium chloride. Dilute aqueous solutions of Er^III chloride and hexasodium mellitate were allowed to diffuse slowly through an agar gel medium in a U-shaped tube. After one and a half months, pale pink single crystals of (I) were collected. Analysis calculated (found) for Er₂[C(CO₂)₆](H₂O)₁₀·4H₂O: Er 36.3 (36.3); C 15.5 (15.6); H 3.2 (3.0); O 45.3% (45.1%).

S3. Refinement

The s.u.s of the cell constants indicate the internal consistency of the measurements themselves, i.e. the precision of the measurement, not their accuracy. The maximum in the final difference map is 2.08 Å from O3W and the minimum is 0.77 Å from Er.

Computing details

Data collection: COLLECT (Nonius, 1997-2000); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandeburg, 2000); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A projection view of (I) along the b axis, showing the packing of the infinite chains. Displacement ellipsoids are at the 50% probability level. For clarity, water molecules of crystallization and all H atoms have been omitted.
	Fig. 2. A projection view of (I) along the a axis, showing the packing of the infinite chains and the location of the crystallization water molecules, together with the labelling scheme for the water molecules. Displacement ellipsoids are at the 50% probability level. For clarity, each water molecule has only been drawn once.
	Fig. 3. A projection view of the coordination polyhedron of the Er^III ions in (I), along with the atomic labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.

catena-Poly[[bis[pentaaquaerbium(III)]-µ-benzenehexacarboxylato] tetrahydrate]

Crystal data

[Er2(C12O12)(H2O)10]·4H2O	Dx = 2.444 Mg m^−3
Mr = 922.86	Melting point: not measured K
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 8.4499 (1) Å	Cell parameters from 8641 reflections
b = 9.2595 (2) Å	θ = 1.0–30.0°
c = 16.2911 (4) Å	µ = 6.76 mm^−1
β = 100.3390 (8)°	T = 298 K
V = 1253.95 (4) Å^3	Plate, pale pink
Z = 2	0.31 × 0.09 × 0.06 mm
F(000) = 832

Data collection

Nonius KappaCCD area-detector diffractometer	3648 independent reflections
Radiation source: Enraf-Nonius FR-590	2884 reflections with I > 2σ(I)
Horizonally mounted graphite crystal monochromator	Rint = 0.049
Detector resolution: 9 pixels mm^-1	θmax = 30.0°, θmin = 2.5°
CCD rotation images, thick slices scans	h = −11→9
Absorption correction: analytical (Alcock, 1970)	k = −13→11
Tmin = 0.256, Tmax = 0.646	l = −21→22
17561 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	H-atom parameters not defined
wR(F^2) = 0.093	w = 1/[σ^2(Fo^2) + (0.0438P)^2 + 4.4981P] where P = (Fo^2 + 2Fc^2)/3
S = 1.03	(Δ/σ)max < 0.001
3648 reflections	Δρmax = 2.48 e Å^−3
199 parameters	Δρmin = −2.05 e Å^−3
0 restraints

Special details

Experimental. Data collection was performed at the Centre de Diffractométrie, Université de Rennes, France. A crystal-to-detector distance of 25 mm was used and a total of 163 frames were recorded, using Δω 2° rotation scans, with exposure time = 40 sec/°.).

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Er	0.44714 (2)	0.09373 (2)	0.166967 (13)	0.01942 (9)
O1	0.3852 (5)	−0.1071 (4)	0.0788 (3)	0.0305 (9)
O2	0.2436 (4)	−0.0332 (5)	0.2225 (3)	0.0327 (9)
O3	0.5629 (5)	0.3262 (5)	0.1793 (3)	0.0432 (11)
O4	0.5821 (6)	−0.1022 (6)	0.2418 (4)	0.0666 (19)
O5	0.4831 (6)	0.1657 (8)	0.3068 (3)	0.0645 (17)
O11	0.2213 (4)	0.2442 (4)	0.1606 (2)	0.0251 (8)
O12	−0.0095 (5)	0.3468 (5)	0.1020 (3)	0.0378 (10)
C12	0.0892 (5)	0.2457 (5)	0.1092 (3)	0.0190 (10)
C11	0.0474 (5)	0.1155 (5)	0.0537 (3)	0.0162 (9)
O21	0.3902 (4)	0.1855 (4)	0.0308 (2)	0.0224 (8)
O22	0.2539 (4)	0.2518 (4)	−0.0932 (2)	0.0297 (9)
C22	0.2662 (5)	0.1823 (5)	−0.0270 (3)	0.0184 (9)
C21	0.1282 (5)	0.0886 (5)	−0.0130 (3)	0.0154 (9)
O31	0.3177 (4)	−0.0687 (4)	−0.1181 (2)	0.0274 (8)
O32	0.0834 (5)	−0.0705 (5)	−0.2082 (2)	0.0356 (10)
C32	0.1670 (5)	−0.0595 (5)	−0.1375 (3)	0.0191 (9)
C31	0.0804 (5)	−0.0276 (5)	−0.0658 (3)	0.0156 (9)
O1W	0.1943 (11)	−0.3524 (13)	0.0654 (7)	0.037 (2)	0.50
O2W	0.291 (4)	−0.3798 (18)	0.110 (2)	0.193 (16)	0.50
O3W	0.671 (6)	−0.531 (4)	0.0462 (10)	0.433 (7)	0.50
O4W	0.5025 (13)	−0.4638 (13)	0.0816 (10)	0.073 (4)	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Er	0.01265 (11)	0.02931 (15)	0.01631 (13)	−0.00125 (8)	0.00263 (8)	0.00118 (9)
O1	0.030 (2)	0.032 (2)	0.032 (2)	−0.0035 (15)	0.0102 (16)	−0.0039 (17)
O2	0.0203 (17)	0.043 (2)	0.035 (2)	−0.0008 (16)	0.0049 (15)	0.0167 (19)
O3	0.036 (2)	0.040 (3)	0.054 (3)	−0.0133 (19)	0.011 (2)	−0.021 (2)
O4	0.032 (3)	0.086 (4)	0.080 (4)	0.008 (2)	0.005 (3)	0.055 (3)
O5	0.045 (3)	0.123 (5)	0.025 (2)	−0.031 (3)	0.004 (2)	−0.014 (3)
O11	0.0181 (15)	0.028 (2)	0.0270 (19)	−0.0027 (13)	−0.0005 (13)	−0.0068 (15)
O12	0.032 (2)	0.031 (2)	0.046 (3)	0.0123 (18)	−0.0048 (17)	−0.014 (2)
C12	0.0144 (19)	0.025 (3)	0.018 (2)	0.0003 (17)	0.0040 (16)	−0.0038 (19)
C11	0.0125 (19)	0.018 (2)	0.017 (2)	0.0003 (15)	0.0015 (16)	−0.0038 (17)
O21	0.0170 (15)	0.030 (2)	0.0179 (17)	−0.0084 (13)	−0.0020 (12)	0.0014 (14)
O22	0.0258 (17)	0.038 (2)	0.0238 (19)	−0.0056 (15)	−0.0008 (14)	0.0102 (16)
C22	0.016 (2)	0.020 (2)	0.020 (2)	−0.0028 (16)	0.0034 (16)	0.0003 (18)
C21	0.0108 (18)	0.017 (2)	0.018 (2)	−0.0004 (15)	0.0017 (15)	0.0009 (17)
O31	0.0155 (16)	0.037 (2)	0.031 (2)	0.0004 (14)	0.0077 (14)	−0.0023 (17)
O32	0.028 (2)	0.062 (3)	0.0154 (19)	−0.0058 (18)	0.0028 (15)	−0.0068 (18)
C32	0.0147 (19)	0.024 (3)	0.020 (2)	−0.0027 (17)	0.0075 (17)	−0.0023 (19)
C31	0.0116 (18)	0.022 (2)	0.013 (2)	0.0012 (16)	0.0010 (15)	−0.0006 (18)
O1W	0.028 (4)	0.046 (6)	0.033 (5)	0.003 (4)	−0.004 (3)	0.005 (4)
O2W	0.31 (4)	0.041 (9)	0.31 (4)	0.013 (16)	0.27 (3)	0.027 (16)
O3W	0.80 (3)	0.422 (17)	0.036 (9)	−0.566	−0.05 (2)	0.041 (17)
O4W	0.055 (7)	0.050 (7)	0.118 (12)	−0.006 (5)	0.028 (7)	0.029 (7)

Geometric parameters (Å, º)

Er—O31^i	2.281 (3)	C11—C21	1.405 (6)
Er—O5	2.341 (5)	O21—C22	1.277 (5)
Er—O21	2.343 (3)	O22—C22	1.244 (6)
Er—O11	2.350 (3)	C22—C21	1.504 (6)
Er—O1	2.351 (4)	C21—C31	1.392 (6)
Er—O3	2.358 (4)	O31—C32	1.259 (6)
Er—O4	2.362 (5)	O31—Er^i	2.281 (3)
Er—O2	2.391 (4)	O32—C32	1.243 (6)
O11—C12	1.269 (5)	C32—C31	1.514 (6)
O12—C12	1.246 (6)	C31—C11^ii	1.394 (6)
C12—C11	1.510 (6)	O1W—O2W	1.03 (4)
C11—C31^ii	1.394 (6)	O3W—O4W	1.74 (6)
O31^i—Er—O5	113.56 (16)	O1—Er—O2	75.27 (15)
O31^i—Er—O21	75.54 (13)	O3—Er—O2	137.06 (16)
O5—Er—O21	141.9 (2)	O4—Er—O2	74.97 (16)
O31^i—Er—O11	142.76 (14)	C12—O11—Er	130.3 (3)
O5—Er—O11	80.61 (18)	O12—C12—O11	124.4 (5)
O21—Er—O11	73.49 (13)	O12—C12—C11	117.6 (4)
O31^i—Er—O1	79.55 (14)	O11—C12—C11	118.0 (4)
O5—Er—O1	142.7 (2)	C31^ii—C11—C21	120.1 (4)
O21—Er—O1	73.94 (14)	C31^ii—C11—C12	119.0 (4)
O11—Er—O1	110.62 (13)	C21—C11—C12	120.7 (4)
O31^i—Er—O3	75.44 (14)	C22—O21—Er	133.8 (3)
O5—Er—O3	71.2 (2)	O22—C22—O21	123.9 (4)
O21—Er—O3	76.19 (15)	O22—C22—C21	118.9 (4)
O11—Er—O3	77.50 (14)	O21—C22—C21	117.2 (4)
O1—Er—O3	144.88 (15)	C31—C21—C11	119.2 (4)
O31^i—Er—O4	74.43 (17)	C31—C21—C22	119.9 (4)
O5—Er—O4	75.5 (3)	C11—C21—C22	120.9 (4)
O21—Er—O4	139.9 (2)	C32—O31—Er^i	145.6 (3)
O11—Er—O4	142.33 (17)	O32—C32—O31	127.4 (5)
O1—Er—O4	75.0 (2)	O32—C32—C31	117.3 (4)
O3—Er—O4	120.19 (19)	O31—C32—C31	115.3 (4)
O31^i—Er—O2	144.37 (14)	C21—C31—C11^ii	120.6 (4)
O5—Er—O2	75.40 (17)	C21—C31—C32	120.1 (4)
O21—Er—O2	119.80 (12)	C11^ii—C31—C32	119.3 (4)
O11—Er—O2	71.02 (13)

Symmetry codes: (i) −x+1, −y, −z; (ii) −x, −y, −z.