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In the title compound, [Fe(C4O4)(H2O)2], each Fe atom is coordinated by four squarate dianions and two water mol­ecules within a slightly distorted octahedron. The Fe atoms and the squarate dianions are located in special positions, whereas the water mol­ecules occupy general positions. There are two crystallographically independent squarate dianions in the asymmetric unit which exhibit a similar geometry. The compound represents a pseudo-polymorphic form of the previously reported Fe squarate dihydrate.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536802015647/bt6187sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536802015647/bt6187Isup2.hkl
Contains datablock I

CCDC reference: 198291

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](C-C) = 0.004 Å
  • R factor = 0.040
  • wR factor = 0.178
  • Data-to-parameter ratio = 17.3

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Amber Alert Alert Level B:
PLAT_601 Alert B Structure Contains Solvent Accessible VOIDS of 117.00 A   3
0 Alert Level A = Potentially serious problem
1 Alert Level B = Potential problem
0 Alert Level C = Please check

Comment top

Recently, we became interested in the synthesis, structures and properties of coordination polymers based on transition metals and aromatic amine ligands. During these investigations, we obtained new transition metal squarates with 4,4'-bipyridine (Näther & Jeß, 2002; Greve, 2000) and pyrazine (Greve, 2000; Näther & Jeß, 2001) as ligands. In the bipyridine compounds, additional water molecules are present which can be reversible deintercalated and reintercalated, a process which is accompanied with a change of the colour of the material (Näther & Jeß, 2002; Greve, 2000). Depending on the experimental conditions used in the synthesis of the metal squarates, mixtures of the desired compounds and additional phases are obtained. This is the case, for example, for the iron compound poly[[diaqua(µ2-squarato-O,O')(µ2-4,4'-bipyridine)iron(II)] hydrate] (Greve, 2000). To identify the additional phase and to calculate a theoretical powder pattern, we have performed a single-crystal structure analysis. This analysis reveals that a new Fe squarate hydrate was formed. Two similar compounds are known, namely the dihydrate poly[diaqua(µ4-squarato-O,O',O'',O''')iron(II)] (Lee et al., 1996) and the tetrahydrate catena[tetraaqua(µ2-squarato-O,O')iron(II)] (Frankenbach et al., 1992).

In the structure of the title compound, (I), the Fe atoms are surrounded by four O atoms of two pairs of symmetry-related squarate dianions and two water molecules within a slightly distorted octahedron. The Fe atom is located on a twofold rotation axis and the water molecules occupy general positions. There are two crystallographically independent squarate dianions in the asymmetric unit, of which the dianion formed by C1 and O1 is located around a fourfold rotation axis, whereas the second anion, formed by C2 and O2, is located around a fourfold fold rotoinversion axis. Bond lengths and angles around the Fe atoms are comparable to those obtained for the previously reported Fe squarate dihydrate and tetrahydrate (Lee et al., 1996; Frankenbach et al., 1992). The squarate dianions are coordinated by only one O atom to the metal centres and the Fe atoms are oriented in the direction of the lone pairs of the squarate dianions. Altogether, each squarate anion is coordinated to four Fe atoms, forming a three-dimensional coordination network. Within these networks, large cubic voids are found, which are bordered by six squarate dianions. There are hydrogen bonds in the structure between the O atoms of the squarate dianions and the H atoms of the water molecules. Bond lengths and angles indicate a strong interaction. The geometry of the two crystallographically independent squarate dianions is similar and comparable to that found in other metal squarate compounds retrieved from the Cambridge Structural Database (Conquest, Version 1.3 of 2002; Allen & Kennard, 1993).

The title compound is isotypic with the similar Co (Lee et al., 1996) and Zn compounds (Weiss et al., 1986). In these structures, additional solvent molecules are present in the voids. For the Co compound, 0.33 molecules of water, and for the Zn compound, 0.33 molecules of acetic acid, are found. Also, in (I), there is evidence for some additional solvent in the voids, which was not considered in the structure refinement due to disorder (see Experimental). We performed additional thermogravimetric measurements which show that the compound decomposes completely at about 493 K. Only at this point can the additional water leave the crystal. Due to its small amount relative to the complete mass loss observed one cannot determine if additional water is present in the cavities. Therefore, it is difficult to decide whether this compound is a polymorphic form of the previously reported Fe squarate dihydrate (Lee et al., 1996) or a pseudo-polymorphic form if additional solvent is present. In the structure determined by Lee et al. (1996), the stoichiometry of the compound is given exactly as [Fe(C4O4)2(H2O)2] and there is no evidence for additional solvent molecules or disorder in the structure. Interestingly, this structure is very similar to that of the title compound. In both compounds, the topology of the coordination network is very similar, but differences are found in the orientation of the squarate dianions between successive layers found in the structures. This leads to a doubling of the translational period in (I) compared to the dihydrate determined by Lee et al. (1996). This is also be reflected by the similarity of the lattice parameters. The previously reported dihydrate crystallizes with trigonal symmetry in space group R3, with a = 11.4395 (19) Å and c = 14.504 (3) Å. This trigonal unit cell can be transformed into a cubic unit cell with an a axis which is approximately half of that found for (I). However, to be sure that the previously reported Fe squarate dihydrate does not represent a substructure of our compound we have tried to perform refinement in space group R3 with half of the lattice parameters. In this case, strong disordering of the squarate dianions is found and the refinement does not work very well. The reason for the occurrence of two different dihydrates is not clear. It might be that the inclusion of solvent molecules into the voids is responsible for this. However, because we have prepared our compound at elevated temperatures, it might also be that our compound is the thermodynamically most stable form at higher temperatures, whereas the previously reported compound is more stable at lower temperatures. However, for a definite decision much more investigations are needed.

Experimental top

The title compound was prepared by the reaction of 0.5 mmol iron(II) chloride, 0.5 mmol squaric acid and 0.5 mmol 4,4'-bipyridine in 5 ml of water in a Teflon-lined steel autoclave at 423 K under hydrothermal conditions. After 5 d, the reaction mixture was cooled to room temperature, filtered and washed with water. The precipitate consisted of a mixture of large red crystals of the 4,4'-bipyridine compound poly[[diaqua(µ2-squarato-O,O')(µ2–4,4'-bipyridine)iron(II)] hydrate] (Greve, 2000), which are embedded in a yellow microcrystalline powder of the title compound. The composition of the different phases were determined by X-ray powder diffraction using Co Kα radiation.

Refinement top

The positions of the O—H H atoms were located from a difference Fourier map and then refined as rigid groups with idealized O—H bond lengths of 0.86 Å and fixed isotropic displacement parameters [Uiso(H) = 1.5Ueq(O)]. In the last refinement, significant residual electron density was found in voids of the structure, which presumably correspond to incorporated clathrate water molecules. The distances between the highest peak in the difference map and the next adjacent atom is 3.74 Å. Several peaks are found with extremely short distances indicating strong disorder of the clathrate water molecules. A structure refinement using a split model or using the Squeeze option for disordered solvent in PLATON (Spek, 2002) leads only to slightly improved realibility factors. Therefore, the disordered solvent was not considered in the structure refinement.

Computing details top

Data collection: IPDS Program Package (Stoe & Cie, 1998); cell refinement: IPDS Program Package; data reduction: IPDS Program Package; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL (Bruker, 1998); software used to prepare material for publication: CIFTAB in SHELXL97.

Figures top
[Figure 1] Fig. 1. The crystal structure of the title compound, showing the iron coordination, with labelling and displacement ellipsoids drawn at the 50% probability level [symmetry code: (i) y, x, −z + 1/2].
[Figure 2] Fig. 2. The crystal structure of the title compound viewed along the crystallographic a axis.
(I) top
Crystal data top
[Fe(C4O4)(H2O)2]Melting point: decomposition at about 200°C K
Mr = 203.92Mo Kα radiation, λ = 0.71073 Å
Cubic, Pn3nCell parameters from 800 reflections
a = 16.3606 (9) Åθ = 2.5–28°
V = 4379.2 (4) Å3µ = 2.05 mm1
Z = 24T = 293 K
F(000) = 2448Irregular polyhedron, yellow
Dx = 1.856 Mg m30.3 × 0.05 × 0.05 mm
Data collection top
Stoe IPDS
diffractometer
750 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.026
Graphite monochromatorθmax = 28.0°, θmin = 3.1°
ω scansh = 2121
27710 measured reflectionsk = 2020
881 independent reflectionsl = 2121
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.040Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.178H atoms treated by a mixture of independent and constrained refinement
S = 1.18 w = 1/[σ2(Fo2) + (0.0991P)2 + 5.2645P]
where P = (Fo2 + 2Fc2)/3
881 reflections(Δ/σ)max = 0.001
51 parametersΔρmax = 1.08 e Å3
0 restraintsΔρmin = 0.39 e Å3
Crystal data top
[Fe(C4O4)(H2O)2]Z = 24
Mr = 203.92Mo Kα radiation
Cubic, Pn3nµ = 2.05 mm1
a = 16.3606 (9) ÅT = 293 K
V = 4379.2 (4) Å30.3 × 0.05 × 0.05 mm
Data collection top
Stoe IPDS
diffractometer
750 reflections with I > 2σ(I)
27710 measured reflectionsRint = 0.026
881 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0400 restraints
wR(F2) = 0.178H atoms treated by a mixture of independent and constrained refinement
S = 1.18Δρmax = 1.08 e Å3
881 reflectionsΔρmin = 0.39 e Å3
51 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.

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 (Å2) top
xyzUiso*/Ueq
Fe0.498475 (16)0.498475 (16)0.25000.0083 (4)
C10.30900 (13)0.48407 (15)0.22728 (14)0.0140 (5)
O10.37958 (10)0.48778 (12)0.19866 (10)0.0195 (5)
C20.50044 (14)0.69069 (14)0.22811 (17)0.0165 (6)
O20.50261 (12)0.61950 (10)0.20032 (11)0.0214 (5)
O30.46029 (10)0.53742 (10)0.36497 (11)0.0188 (5)
H10.41370.52000.38180.028*
H20.47000.58690.37970.028*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Fe0.0084 (4)0.0084 (4)0.0080 (4)0.00049 (12)0.00046 (10)0.00046 (10)
C10.0097 (11)0.0222 (11)0.0101 (10)0.0011 (8)0.0001 (8)0.0002 (9)
O10.0071 (8)0.0395 (11)0.0119 (8)0.0001 (7)0.0006 (6)0.0018 (7)
C20.0282 (13)0.0107 (12)0.0107 (11)0.0001 (8)0.0007 (7)0.0007 (9)
O20.0458 (12)0.0066 (8)0.0118 (8)0.0010 (6)0.0028 (6)0.0008 (6)
O30.0197 (8)0.0190 (8)0.0176 (9)0.0045 (6)0.0077 (6)0.0076 (6)
Geometric parameters (Å, º) top
Fe—O3i2.0819 (17)C1—C1ii1.463 (3)
Fe—O32.0819 (17)C1—C1iii1.463 (3)
Fe—O12.1260 (16)C2—O21.251 (3)
Fe—O1i2.1260 (16)C2—C2iv1.463 (3)
Fe—O2i2.1414 (17)C2—C2v1.463 (3)
Fe—O22.1414 (17)O3—H10.8600
C1—O11.247 (3)O3—H20.8599
O3i—Fe—O3179.52 (9)O1i—Fe—O2176.91 (7)
O3i—Fe—O184.17 (7)O2i—Fe—O294.92 (10)
O3—Fe—O196.18 (7)O1—C1—C1ii133.9 (3)
O3i—Fe—O1i96.18 (7)O1—C1—C1iii136.0 (3)
O3—Fe—O1i84.17 (7)C1ii—C1—C1iii90.000 (1)
O1—Fe—O1i90.31 (10)C1—O1—Fe134.63 (16)
O3i—Fe—O2i93.98 (7)O2—C2—C2iv133.9 (3)
O3—Fe—O2i85.69 (7)O2—C2—C2v136.1 (3)
O1—Fe—O2i176.91 (7)C2iv—C2—C2v89.994 (4)
O1i—Fe—O2i87.42 (7)C2—O2—Fe136.24 (17)
O3i—Fe—O285.69 (7)Fe—O3—H1117.0
O3—Fe—O293.98 (7)Fe—O3—H2119.1
O1—Fe—O287.42 (7)H1—O3—H2112.7
Symmetry codes: (i) y, x, z+1/2; (ii) z, y, x+1/2; (iii) z+1/2, y, x; (iv) x+1, z+1, y1/2; (v) x+1, z+1/2, y+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H1···O1iii0.861.912.735 (2)160
O3—H2···O2v0.861.912.745 (2)164
Symmetry codes: (iii) z+1/2, y, x; (v) x+1, z+1/2, y+1.

Experimental details

Crystal data
Chemical formula[Fe(C4O4)(H2O)2]
Mr203.92
Crystal system, space groupCubic, Pn3n
Temperature (K)293
a (Å)16.3606 (9)
V3)4379.2 (4)
Z24
Radiation typeMo Kα
µ (mm1)2.05
Crystal size (mm)0.3 × 0.05 × 0.05
Data collection
DiffractometerStoe IPDS
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
27710, 881, 750
Rint0.026
(sin θ/λ)max1)0.661
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.040, 0.178, 1.18
No. of reflections881
No. of parameters51
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)1.08, 0.39

Computer programs: IPDS Program Package (Stoe & Cie, 1998), IPDS Program Package, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), XP in SHELXTL (Bruker, 1998), CIFTAB in SHELXL97.

Selected geometric parameters (Å, º) top
Fe—O3i2.0819 (17)Fe—O2i2.1414 (17)
Fe—O12.1260 (16)
O3i—Fe—O3179.52 (9)O1i—Fe—O2i87.42 (7)
O3i—Fe—O184.17 (7)O3i—Fe—O285.69 (7)
O3—Fe—O196.18 (7)O3—Fe—O293.98 (7)
O1—Fe—O1i90.31 (10)O1—Fe—O287.42 (7)
O3—Fe—O2i85.69 (7)O2i—Fe—O294.92 (10)
O1—Fe—O2i176.91 (7)
Symmetry code: (i) y, x, z+1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H1···O1ii0.861.912.735 (2)160
O3—H2···O2iii0.861.912.745 (2)164
Symmetry codes: (ii) z+1/2, y, x; (iii) x+1, z+1/2, y+1.
 

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