A second C-centred monoclinic modification of racemic potassium hydrogen malate monohydrate

The K⁺ cation in the racemic title compound, poly[aqua-μ₆-malato-potassium(I)], [K(C₄H₅O₅)(H₂O)]_n, exists in an irregular eight-coordinate environment. The anions are linked through hydrogen bonds into a three-dimensional network. The coordination environment differs from the six-coordinate environment reported in another C-centred monoclinic modification [Geise, van Loock & Lenstra (1983). Acta Cryst. C39, 69–70].

Key indicators

• Single-crystal X-ray study
• T = 291 K
• Mean [sigma](C-C) = 0.008 Å
• R factor = 0.034
• wR factor = 0.124
• Data-to-parameter ratio = 8.8

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT420_ALERT_2_B D-H Without Acceptor       O3     -   H3     ...          ?

Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......       0.96
PLAT180_ALERT_3_C Check Cell Rounding: # of Values Ending with 0 =          4
PLAT340_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...          8
PLAT416_ALERT_2_C Short Intra D-H..H-D       H3     ..  H62     ..       1.91 Ang.
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.38 Ratio

Alert level G
REFLT03_ALERT_4_G  WARNING: Large fraction of Friedel related reflns may
                     be needed to determine absolute structure
           From the CIF: _diffrn_reflns_theta_max           27.00
           From the CIF: _reflns_number_total                876
           Count of symmetry unique reflns          786
           Completeness (_total/calc)            111.45%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured        90
           Fraction of Friedel pairs measured     0.115
           Are heavy atom types Z>Si present        yes
PLAT792_ALERT_1_G Check the Absolute Configuration of C3     = ...          R
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          2

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

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   4 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

S1. Comment

In the previous C-centered monoclinic modification of racemic potassium hydrogen malate hydrate (Geize et al., 1983), the potassium atom is in an octahedron of oxygen atoms, and for the carboxylate anion the ionized and un-ionized groups cannot be distinguished. In the present C-centered monoclinic modification, the potassium atom exists in an irregular, eight-coordinate environment (Table 1). The anion features unambiguous ionized and un-ionized groups; interestingly, the double-bond oxygen atom of the ionized group is the oxygen atom that is closest to potassium despite being involved in another briding interaction.

Related literature

For the first C-centered monoclinic modification, see: Geize et al. (1983).

S2. Experimental

DL-Malic acid (27 mg, 0.2 mmol) was mixed with potassium hydroxide (12 mg, 0.2 mmol) in water (10 ml) to give a blue solution. Slow evaporation of the solution gave colorless prismatic crystals.

S3. Refinement

Carbon- and oxygen-bound H atoms were positioned geometrically (C–H 0.97 – 0.97, O–H 0.82 Å), and were included in the refinement in the riding model approximation, with U_iso(H) set to 1.2 or 1.5U_eq(C,O).

The Flack parameter was refined from 82 Friedel pairs.

Computing details

Data collection: SMART (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2007).

Figures

Fig. 1. Thermal ellipsoid plot of potassium hydrogen malate hydrate; displacement ellipsoids are drawn at the 50% probability level and hydrogen atoms as spheres of arbitrary radius. [Symmetry codes are given in Table 1.]

poly[aqua-µ₆-malato-potassium(I)]

Crystal data

[K(C4H5O5)(H2O)]	F(000) = 392
Mr = 190.20	Dx = 1.759 Mg m^−3
Monoclinic, Cc	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C -2yc	Cell parameters from 1338 reflections
a = 10.534 (1) Å	θ = 3.0–27.0°
b = 10.494 (1) Å	µ = 0.72 mm^−1
c = 7.5640 (8) Å	T = 291 K
β = 120.801 (1)°	Prism, colorless
V = 718.19 (13) Å^3	0.42 × 0.21 × 0.15 mm
Z = 4

Data collection

Bruker APEX area-detector diffractometer	876 independent reflections
Radiation source: fine-focus sealed tube	839 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.014
φ and ω scans	θmax = 27.0°, θmin = 2.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −13→10
Tmin = 0.717, Tmax = 0.900	k = −13→11
1561 measured reflections	l = −3→9

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H-atom parameters constrained
wR(F^2) = 0.124	w = 1/[σ^2(Fo^2) + (0.0732P)^2 + 2.0212P] where P = (Fo^2 + 2Fc^2)/3
S = 1.19	(Δ/σ)max = 0.001
876 reflections	Δρmax = 0.41 e Å^−3
100 parameters	Δρmin = −0.28 e Å^−3
2 restraints	Absolute structure: Flack (1983), 82 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.1 (1)

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

	x	y	z	Uiso*/Ueq
K1	0.50000 (12)	0.56252 (10)	0.50000 (14)	0.0192 (3)
O1	0.6110 (4)	0.8267 (4)	0.5299 (6)	0.0203 (8)
O2	0.8346 (4)	0.8883 (4)	0.5947 (6)	0.0203 (8)
O3	0.7334 (4)	0.6285 (3)	0.3048 (6)	0.0202 (8)
H3	0.8143	0.5933	0.3621	0.030*
O4	0.6024 (4)	0.6425 (4)	−0.1149 (6)	0.0214 (8)
O5	0.7244 (4)	0.8251 (3)	−0.0892 (6)	0.0212 (8)
H5	0.6844	0.8079	−0.2120	0.032*
O6	0.8351 (5)	0.5749 (4)	0.7211 (7)	0.0273 (9)
H61	0.8632	0.6450	0.7751	0.041*
H62	0.8621	0.5636	0.6381	0.041*
C1	0.7049 (6)	0.8543 (5)	0.4753 (8)	0.0158 (10)
C2	0.6503 (6)	0.8418 (5)	0.2466 (8)	0.0163 (10)
H2A	0.6570	0.9236	0.1921	0.020*
H2B	0.5477	0.8151	0.1729	0.020*
C3	0.7450 (6)	0.7435 (5)	0.2164 (7)	0.0163 (11)
H3A	0.8482	0.7717	0.2860	0.020*
C4	0.6835 (6)	0.7304 (5)	−0.0148 (8)	0.0153 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K1	0.0231 (5)	0.0221 (5)	0.0108 (5)	0.0012 (5)	0.0076 (4)	−0.0016 (5)
O1	0.0222 (18)	0.0286 (19)	0.0117 (18)	0.0017 (16)	0.0098 (16)	0.0009 (15)
O2	0.0234 (19)	0.0249 (18)	0.0124 (18)	−0.0062 (16)	0.0092 (16)	−0.0031 (16)
O3	0.027 (2)	0.0168 (16)	0.017 (2)	0.0058 (15)	0.0117 (17)	0.0033 (14)
O4	0.0211 (19)	0.0282 (19)	0.0129 (18)	−0.0082 (16)	0.0072 (16)	−0.0055 (15)
O5	0.026 (2)	0.0260 (19)	0.0121 (17)	−0.0078 (16)	0.0097 (16)	−0.0032 (15)
O6	0.030 (2)	0.032 (2)	0.022 (2)	−0.0099 (19)	0.0149 (18)	−0.0025 (18)
C1	0.024 (3)	0.009 (2)	0.014 (3)	0.0053 (18)	0.009 (2)	0.0013 (17)
C2	0.017 (2)	0.020 (2)	0.010 (2)	0.003 (2)	0.006 (2)	0.0007 (19)
C3	0.015 (2)	0.025 (2)	0.009 (3)	−0.0009 (19)	0.007 (2)	0.000 (2)
C4	0.019 (2)	0.017 (2)	0.014 (2)	0.0032 (19)	0.011 (2)	0.0000 (18)

Geometric parameters (Å, º)

K1—O1	2.972 (4)	O4—C4	1.222 (6)
K1—O2^i	2.858 (4)	O4—K1^ix	2.671 (4)
K1—O2^ii	2.689 (4)	O4—K1^viii	2.740 (4)
K1—O3^iii	3.094 (4)	O5—C4	1.318 (6)
K1—O4^iv	2.671 (4)	O5—K1^x	2.876 (4)
K1—O4^iii	2.740 (4)	O5—H5	0.8200
K1—O5^v	2.876 (4)	O6—H61	0.8200
K1—O6	3.038 (5)	O6—H62	0.8200
O1—C1	1.285 (7)	C1—C2	1.524 (7)
O2—C1	1.243 (6)	C2—C3	1.531 (7)
O2—K1^vi	2.689 (4)	C2—H2A	0.9700
O2—K1^vii	2.858 (4)	C2—H2B	0.9700
O3—C3	1.415 (7)	C3—C4	1.529 (6)
O3—K1^viii	3.094 (4)	C3—H3A	0.9800
O3—H3	0.8200
O4^iv—K1—O2^ii	147.89 (13)	K1^vi—O2—K1^vii	92.34 (12)
O4^iv—K1—O4^iii	126.01 (15)	C3—O3—K1^viii	115.4 (3)
O2^ii—K1—O4^iii	85.38 (12)	C3—O3—H3	108.4
O4^iv—K1—O2^i	83.42 (12)	K1^viii—O3—H3	108.4
O2^ii—K1—O2^i	106.65 (14)	C4—O4—K1^ix	132.6 (3)
O4^iii—K1—O2^i	88.08 (13)	C4—O4—K1^viii	131.3 (4)
O4^iv—K1—O5^v	85.55 (12)	K1^ix—O4—K1^viii	95.41 (12)
O2^ii—K1—O5^v	70.55 (11)	C4—O5—K1^x	136.1 (3)
O4^iii—K1—O5^v	139.62 (12)	C4—O5—H5	103.1
O2^i—K1—O5^v	69.48 (12)	K1^x—O5—H5	103.1
O4^iv—K1—O1	72.57 (11)	K1—O6—H61	109.5
O2^ii—K1—O1	84.69 (12)	K1—O6—H62	109.5
O4^iii—K1—O1	123.58 (12)	H61—O6—H62	109.5
O2^i—K1—O1	147.59 (12)	O2—C1—O1	124.9 (5)
O5^v—K1—O1	86.90 (11)	O2—C1—C2	119.0 (5)
O4^iv—K1—O6	71.32 (12)	O1—C1—C2	116.1 (5)
O2^ii—K1—O6	120.74 (12)	C1—C2—C3	109.3 (4)
O4^iii—K1—O6	70.91 (12)	C1—C2—H2A	109.8
O2^i—K1—O6	125.09 (12)	C3—C2—H2A	109.8
O5^v—K1—O6	149.39 (12)	C1—C2—H2B	109.8
O1—K1—O6	67.50 (11)	C3—C2—H2B	109.8
O4^iv—K1—O3^iii	70.60 (11)	H2A—C2—H2B	108.3
O2^ii—K1—O3^iii	141.05 (12)	O3—C3—C4	112.1 (4)
O4^iii—K1—O3^iii	55.67 (11)	O3—C3—C2	106.5 (4)
O2^i—K1—O3^iii	75.66 (11)	C4—C3—C2	107.7 (4)
O5^v—K1—O3^iii	139.64 (12)	O3—C3—H3A	110.1
O1—K1—O3^iii	114.59 (11)	C4—C3—H3A	110.1
O6—K1—O3^iii	50.32 (11)	C2—C3—H3A	110.1
C1—O1—K1	121.6 (3)	O4—C4—O5	125.6 (5)
C1—O2—K1^vi	135.4 (3)	O4—C4—C3	121.9 (5)
C1—O2—K1^vii	125.8 (3)	O5—C4—C3	112.4 (4)
O4^iv—K1—O1—C1	127.0 (4)	O1—C1—C2—C3	−119.5 (5)
O2^ii—K1—O1—C1	−76.0 (4)	K1^viii—O3—C3—C4	−21.2 (5)
O4^iii—K1—O1—C1	4.9 (4)	K1^viii—O3—C3—C2	96.4 (4)
O2^i—K1—O1—C1	171.0 (3)	C1—C2—C3—O3	57.7 (5)
O5^v—K1—O1—C1	−146.7 (4)	C1—C2—C3—C4	178.1 (4)
O6—K1—O1—C1	50.5 (4)	K1^ix—O4—C4—O5	12.0 (8)
O3^iii—K1—O1—C1	68.7 (4)	K1^viii—O4—C4—O5	−179.5 (3)
K1^viii—K1—O1—C1	−33.2 (4)	K1^ix—O4—C4—C3	−170.3 (3)
K1^vi—O2—C1—O1	−3.5 (8)	K1^viii—O4—C4—C3	−1.8 (7)
K1^vii—O2—C1—O1	−147.1 (4)	K1^x—O5—C4—O4	−126.8 (5)
K1^vi—O2—C1—C2	177.4 (3)	K1^x—O5—C4—C3	55.3 (6)
K1^vii—O2—C1—C2	33.8 (6)	O3—C3—C4—O4	17.0 (7)
K1—O1—C1—O2	−112.4 (5)	C2—C3—C4—O4	−99.9 (6)
K1—O1—C1—C2	66.7 (5)	O3—C3—C4—O5	−165.0 (4)
O2—C1—C2—C3	59.7 (6)	C2—C3—C4—O5	78.1 (5)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O6^viii	0.82	2.13	2.607 (5)	117
O5—H5···O1^ix	0.82	1.70	2.491 (5)	160
O6—H61···O1^vi	0.82	2.34	2.831 (6)	119
O6—H62···O3	0.82	2.27	2.815 (6)	124

Symmetry codes: (vi) x+1/2, −y+3/2, z+1/2; (viii) x, −y+1, z−1/2; (ix) x, y, z−1.