Potassium trans-diaqua­bis[oxalato(2–)-κ²O,O′]chromate(III)

The title compound, K[Cr(C₂O₄)₂(H₂O)₂], was crystallized from an aqueous solution. It is the first member without uncoordinated water molecules of formula A_m[M(C₂O₄)₂(H₂O)₂]·xH₂O, where A = monovalent cation, m = 1 or 2, M = metal(II) or metal(III), x ≥ 0. The crystal packing is governed by electrostatic and coordinative inter­actions, and inter­molecular hydrogen bonds help to stabilize the packing. The coordination of the Cr sites is quasi-octa­hedral, and the K ions are eight-coordinated by O atoms of oxalate ligands, forming strongly distorted square anti­prisms.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.044
• wR factor = 0.137
• Data-to-parameter ratio = 13.8

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT369_ALERT_2_C Long   C(sp2)-C(sp2) Bond  C      -   C_f    ...       1.56 Ang.
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.29 Ratio

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion

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Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999).

Potassium trans-diaquabis[oxalato(2-)-κ²O,O']chromate(III)

Crystal data

K[Cr(C2O4)2(H2O)2]	F(000) = 302
Mr = 303.17	Dx = 2.134 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2y	Cell parameters from 3283 reflections
a = 6.6012 (10) Å	θ = 2.1–28.3°
b = 7.2585 (11) Å	µ = 1.70 mm^−1
c = 9.8539 (16) Å	T = 298 K
β = 92.228 (3)°	Needle, pink
V = 471.79 (13) Å^3	0.32 × 0.10 × 0.08 mm
Z = 2

Data collection

Bruker APEX CCD area-detector diffractometer	636 independent reflections
Radiation source: fine-focus sealed tube	625 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.064
integration method scans	θmax = 28.3°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Bruker, 2001)	h = −8→8
Tmin = 0.772, Tmax = 0.873	k = −9→9
3283 measured reflections	l = −13→13

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)] = 0.044	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.137	All H-atom parameters refined
S = 1.15	w = 1/[σ^2(Fo^2) + (0.0805P)^2 + 1.7264P] where P = (Fo^2 + 2Fc^2)/3
636 reflections	(Δ/σ)max < 0.001
46 parameters	Δρmax = 0.43 e Å^−3
0 restraints	Δρmin = −1.51 e Å^−3

Special details

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
Cr	0.0000	0.5000	0.5000	0.0133 (3)
K	0.0000	0.0000	0.0000	0.0443 (5)
O1	0.0638 (3)	0.3215 (3)	0.3590 (2)	0.0195 (5)
O2	0.1862 (4)	0.3070 (4)	0.1521 (2)	0.0341 (6)
C	0.1285 (4)	0.3925 (4)	0.2473 (3)	0.0203 (6)
O3	−0.2885 (5)	0.5000	0.4385 (3)	0.0235 (7)
H	−0.334 (6)	0.585 (6)	0.400 (4)	0.026 (10)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cr	0.0153 (5)	0.0094 (4)	0.0156 (5)	0.000	0.0045 (3)	0.000
K	0.0533 (11)	0.0412 (10)	0.0391 (9)	0.000	0.0120 (8)	0.000
O1	0.0261 (10)	0.0134 (9)	0.0194 (9)	0.0009 (7)	0.0057 (8)	−0.0014 (7)
O2	0.0473 (14)	0.0315 (13)	0.0245 (11)	0.0020 (11)	0.0132 (10)	−0.0082 (9)
C	0.0216 (13)	0.0189 (14)	0.0205 (12)	0.0008 (10)	0.0034 (10)	−0.0020 (10)
O3	0.0189 (14)	0.0137 (14)	0.0377 (17)	0.000	−0.0022 (12)	0.000

Geometric parameters (Å, º)

Cr—O1	1.9575 (19)	K—O2^ix	2.956 (3)
Cr—O1^i	1.9575 (19)	K—O2^x	2.956 (3)
Cr—O1^ii	1.9575 (19)	K—K^xi	4.9057 (5)
Cr—O1^iii	1.9575 (19)	K—K^vii	4.9057 (5)
Cr—O3	1.976 (3)	K—K^xii	4.9057 (5)
Cr—O3^i	1.976 (3)	K—K^xiii	4.9057 (5)
K—O2^iv	2.929 (3)	O1—C	1.302 (3)
K—O2	2.929 (3)	O2—C	1.200 (4)
K—O2^v	2.929 (3)	O2—K^xi	2.956 (3)
K—O2^vi	2.929 (3)	C—C^iii	1.561 (6)
K—O2^vii	2.956 (3)	O3—H	0.78 (4)
K—O2^viii	2.956 (3)
O1—Cr—O1^i	180	O2^v—K—K^xi	72.91 (5)
O1—Cr—O1^ii	97.13 (12)	O2^vi—K—K^xi	107.09 (5)
O1^i—Cr—O1^ii	82.87 (12)	O2^vii—K—K^xi	146.64 (5)
O1—Cr—O1^iii	82.87 (12)	O2^viii—K—K^xi	97.70 (5)
O1^i—Cr—O1^iii	97.13 (12)	O2^ix—K—K^xi	33.36 (5)
O1^ii—Cr—O1^iii	180	O2^x—K—K^xi	82.30 (5)
O1—Cr—O3	90.80 (10)	O2^iv—K—K^vii	33.71 (5)
O1^i—Cr—O3	89.20 (10)	O2—K—K^vii	146.29 (5)
O1^ii—Cr—O3	89.20 (10)	O2^v—K—K^vii	107.09 (5)
O1^iii—Cr—O3	90.80 (10)	O2^vi—K—K^vii	72.91 (5)
O1—Cr—O3^i	89.20 (10)	O2^vii—K—K^vii	33.36 (5)
O1^i—Cr—O3^i	90.80 (10)	O2^viii—K—K^vii	82.30 (5)
O1^ii—Cr—O3^i	90.80 (10)	O2^ix—K—K^vii	146.64 (5)
O1^iii—Cr—O3^i	89.20 (10)	O2^x—K—K^vii	97.70 (5)
O3—Cr—O3^i	180	K^xi—K—K^vii	180.0
O2^iv—K—O2	180	O2^iv—K—K^xii	72.91 (5)
O2^iv—K—O2^v	99.07 (11)	O2—K—K^xii	107.09 (5)
O2—K—O2^v	80.93 (11)	O2^v—K—K^xii	146.29 (5)
O2^iv—K—O2^vi	80.93 (11)	O2^vi—K—K^xii	33.71 (5)
O2—K—O2^vi	99.07 (11)	O2^vii—K—K^xii	97.70 (5)
O2^v—K—O2^vi	180.00 (7)	O2^viii—K—K^xii	146.64 (5)
O2^iv—K—O2^vii	67.07 (7)	O2^ix—K—K^xii	82.30 (5)
O2—K—O2^vii	112.93 (7)	O2^x—K—K^xii	33.36 (5)
O2^v—K—O2^vii	109.36 (4)	K^xi—K—K^xii	95.430 (12)
O2^vi—K—O2^vii	70.64 (4)	K^vii—K—K^xii	84.570 (12)
O2^iv—K—O2^viii	109.36 (4)	O2^iv—K—K^xiii	107.09 (5)
O2—K—O2^viii	70.64 (4)	O2—K—K^xiii	72.91 (5)
O2^v—K—O2^viii	67.07 (7)	O2^v—K—K^xiii	33.71 (5)
O2^vi—K—O2^viii	112.93 (7)	O2^vi—K—K^xiii	146.29 (5)
O2^vii—K—O2^viii	56.58 (10)	O2^vii—K—K^xiii	82.30 (5)
O2^iv—K—O2^ix	112.93 (7)	O2^viii—K—K^xiii	33.36 (5)
O2—K—O2^ix	67.07 (7)	O2^ix—K—K^xiii	97.70 (5)
O2^v—K—O2^ix	70.64 (4)	O2^x—K—K^xiii	146.64 (5)
O2^vi—K—O2^ix	109.36 (4)	K^xi—K—K^xiii	84.570 (12)
O2^vii—K—O2^ix	180.00 (9)	K^vii—K—K^xiii	95.430 (12)
O2^viii—K—O2^ix	123.42 (10)	K^xii—K—K^xiii	180.0
O2^iv—K—O2^x	70.64 (4)	C—O1—Cr	115.14 (17)
O2—K—O2^x	109.36 (4)	C—O2—K	130.9 (2)
O2^v—K—O2^x	112.93 (7)	C—O2—K^xi	113.7 (2)
O2^vi—K—O2^x	67.07 (7)	K—O2—K^xi	112.93 (7)
O2^vii—K—O2^x	123.42 (10)	O2—C—O1	125.5 (3)
O2^viii—K—O2^x	180.0	O2—C—C^iii	121.17 (19)
O2^ix—K—O2^x	56.58 (10)	O1—C—C^iii	113.31 (15)
O2^iv—K—K^xi	146.29 (5)	Cr—O3—H	120 (3)
O2—K—K^xi	33.71 (5)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H···O1^xiii	0.78 (4)	1.88 (4)	2.636 (3)	163 (4)

Symmetry code: (xiii) x−1/2, y+1/2, z.