Asymmetric hydrogen bonds in centrosymmetric environment: neutron study of very short hydrogen bonds in potassium hydrogen dichloromaleate

Olovsson, I.; Ptasiewicz-Bak, H.; Gustafsson, T.; Majerz, I.

doi:10.1107/S0108768101003779

Asymmetric hydrogen bonds in centrosymmetric environment: neutron study of very short hydrogen bonds in potassium hydrogen dichloromaleate

I. Olovsson, H. Ptasiewicz-Bak, T. Gustafsson and I. Majerz

The structure of the title compound has been studied by neutron diffraction at 30 and 295 K, with the emphasis on the location of the protons. There are two crystallographically independent H atoms in two very short hydrogen bonds, 2.437 (2) and 2.442 (2) Å at 30 K. The structure could be refined successfully in the centrosymmetric space group P $\bar 1$ , with the H atoms located at the centres of symmetry. However, the form of the thermal ellipsoids of hydrogen indicated either asymmetric hydrogen bonds or overlap of two closely spaced, partially occupied positions around the centres of symmetry. Several different types of refinements have then been applied, including unconventional models; with all atoms except hydrogen constrained in $P\bar 1$ , but with hydrogen allowed to refine without any constraints in P1, anisotropic refinement of all atoms resulted in clearly off-centred hydrogen positions. Significance tests clearly showed that the results from this constrained refinement give the most satisfactory description of the structure. This structure may be described as `pseudo-centrosymmetric with non-centred protons'. The results demonstrate that it is very important to also include refinement models with non-centrosymmetric hydrogen in a centrosymmetric environment when studying very short hydrogen bonds. The shifts of the two H atoms from the centres of symmetry are 0.15 (1) and 0.12 (1) Å, respectively, at 30 K, and 0.15 (1) Å for both H atoms at room temperature. At 30 K: R(F) = 0.036 for 1485 reflections; at 295 K: R(F) = 0.035 for 1349 reflections.

Keywords: hydrogen bonds; centrosymmetric; asymmetric.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768101003779/os0070sup1.cif Contains datablocks text, xray, neutron
	Structure factor file (SHELXL table format) https://doi.org/10.1107/S0108768101003779/os0070xraysup2.sft Supplementary material
	Structure factor file (SHELXL table format) https://doi.org/10.1107/S0108768101003779/os0070neutronsup3.sft Supplementary material

CCDC references: 166496; 166497

Comment top

%T {βf (Comment section to be typeset from manuscript)}

Computing details top

For both compounds, data collection: Aracor Diffractometer Control Program; cell refinement: STOE 4-circle X-ray Diffractometer Control Program; data reduction: ARACOR-DATRED vers. 950320; program(s) used to refine structure: UPALS Lundgren (1982).

Figures top

%T {βf (Figure captions to be typeset from manuscript)}

(xray) top

Crystal data top

K₂Cl₄O₈C₈H₂	γ = 89.59 (5)°
M_r = 446.1	V = 349.9 (2) Å³
Triclinic, P1	Z = 1
Hall symbol: P 1	D_x = 2.130 Mg m⁻³
a = 5.083 (3) Å	Neutron radiation, λ = 1.207 Å
b = 7.881 (5) Å	µ = 0.09 mm⁻¹
c = 8.863 (5) Å	T = 295 K
α = 81.72 (5)°	Plate with 6 faces, colourless
β = 84.78 (5)°	4.2 × 3.5 × 1.0 mm

Data collection top

Huber-Aracor 400 mm diameter four-circle diffractometer	R_int = 0.023
θ–2θ scans	θ_max = 52°
Absorption correction: numerical gaussian (Coppens, Leiserowitz & Rabinovich, 1965)	h = 0→6
T_min = 0.721, T_max = 0.925	k = −10→10
2002 measured reflections	l = −11→11
2002 independent reflections	3 standard reflections every 33 reflections
1716 reflections with F_o² > 3σ(F_o²)	intensity decay: stable

Refinement top

Refinement on F²	All H-atom parameters refined
R[F² > 2σ(F²)] = 0.064	(Δ/σ)_max = 0.05
wR(F²) = 0.082	Δρ_max = 0.05 e Å⁻³
S = 1.04	Δρ_min = −0.05 e Å⁻³
1349 reflections	Extinction correction: Lorentzian type I isotropic (Becker & Coppens, 1974, 1975)
119 parameters	Extinction coefficient: 9210.6

Crystal data top

K₂Cl₄O₈C₈H₂	γ = 89.59 (5)°
M_r = 446.1	V = 349.9 (2) Å³
Triclinic, P1	Z = 1
a = 5.083 (3) Å	Neutron radiation, λ = 1.207 Å
b = 7.881 (5) Å	µ = 0.09 mm⁻¹
c = 8.863 (5) Å	T = 295 K
α = 81.72 (5)°	4.2 × 3.5 × 1.0 mm
β = 84.78 (5)°

Data collection top

Huber-Aracor 400 mm diameter four-circle diffractometer	1716 reflections with F_o² > 3σ(F_o²)
Absorption correction: numerical gaussian (Coppens, Leiserowitz & Rabinovich, 1965)	R_int = 0.023
T_min = 0.721, T_max = 0.925	3 standard reflections every 33 reflections
2002 measured reflections	intensity decay: stable
2002 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.064	119 parameters
wR(F²) = 0.082	All H-atom parameters refined
S = 1.04	Δρ_max = 0.05 e Å⁻³
1349 reflections	Δρ_min = −0.05 e Å⁻³

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
K	0.3020 (4)	−0.1562 (2)	0.6231 (2)	0.0300 (8)
Cl1	0.4644 (1)	−0.2475 (1)	0.0566 (1)	0.0293 (4)
Cl2	0.1282 (2)	−0.5706 (1)	0.2002 (1)	0.0345 (4)
O1	0.2368 (2)	−0.0052 (1)	0.3322 (1)	0.0300 (6)
O2	0.0284 (2)	0.0470 (1)	0.1236 (1)	0.0265 (5)
O3	−0.2492 (2)	−0.2221 (1)	0.4025 (1)	0.0296 (5)
O4	−0.2996 (2)	−0.5053 (1)	0.4134 (1)	0.0292 (5)
C1	0.1503 (2)	−0.0523 (1)	0.2206 (1)	0.0185 (4)
C2	0.1979 (2)	−0.2340 (1)	0.1873 (1)	0.0176 (4)
C3	0.0526 (2)	−0.3719 (1)	0.2503 (1)	0.0188 (4)
C4	−0.1834 (2)	−0.3612 (1)	0.3646 (1)	0.0190 (4)
H2	0.0296 (18)	−0.0042 (18)	0.0008 (17)	0.035 (2)
H4	−0.510 (3)	−0.5122 (15)	0.5146 (14)	0.033 (3)
K1	−0.3020 (4)	0.1562 (2)	−0.6231 (2)	0.0300 (8)
Cl11	−0.4644 (1)	0.2475 (1)	−0.0566 (1)	0.0293 (4)
Cl21	−0.1282 (2)	0.5706 (1)	−0.2002 (1)	0.0345 (4)
O11	−0.2368 (2)	0.0052 (1)	−0.3322 (1)	0.0300 (6)
O21	−0.0284 (2)	−0.0470 (1)	−0.1236 (1)	0.0265 (5)
O31	0.2492 (2)	0.2221 (1)	−0.4025 (1)	0.0296 (5)
O41	0.2996 (2)	0.5053 (1)	−0.4134 (1)	0.0292 (5)
C11	−0.1503 (2)	0.0523 (1)	−0.2206 (1)	0.0185 (4)
C21	−0.1979 (2)	0.2340 (1)	−0.1873 (1)	0.0176 (4)
C31	−0.0526 (2)	0.3719 (1)	−0.2503 (1)	0.0188 (4)
C41	0.1834 (2)	0.3612 (1)	−0.3646 (1)	0.0190 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
K	0.0322 (9)	0.0228 (7)	0.0341 (8)	−0.0031 (7)	0.0062 (7)	−0.0062 (7)
Cl1	0.0241 (4)	0.0306 (3)	0.0307 (4)	0.0005 (3)	0.0119 (3)	0.0042 (3)
Cl2	0.0389 (4)	0.0177 (3)	0.0447 (4)	0.0004 (3)	0.0190 (3)	−0.0102 (3)
O1	0.0352 (6)	0.0292 (5)	0.0297 (6)	−0.0010 (3)	−0.0101 (3)	−0.0130 (3)
O2	0.0386 (6)	0.0183 (4)	0.0235 (5)	0.0052 (4)	−0.0052 (4)	−0.0041 (4)
O3	0.0311 (6)	0.0188 (4)	0.0371 (6)	0.0007 (4)	0.0150 (4)	−0.0083 (4)
O4	0.0269 (5)	0.0191 (5)	0.0399 (6)	−0.0043 (4)	0.0163 (4)	−0.0072 (4)
C1	0.0202 (4)	0.0166 (4)	0.0193 (4)	−0.0009 (3)	0.0001 (3)	−0.0048 (3)
C2	0.0170 (4)	0.0157 (4)	0.0193 (4)	−0.0001 (3)	0.0030 (3)	−0.0027 (3)
C3	0.0189 (4)	0.0149 (4)	0.0216 (4)	0.0004 (3)	0.0053 (3)	−0.0034 (3)
C4	0.0185 (4)	0.0159 (4)	0.0214 (4)	0.0004 (3)	0.0057 (3)	−0.0037 (3)
H2	0.019 (4)	0.0304 (16)	0.0547 (18)	0.011 (3)	−0.006 (3)	−0.0006 (13)
H4	0.040 (2)	0.018 (3)	0.032 (4)	−0.0095 (18)	0.008 (2)	0.006 (2)

Geometric parameters (Å, º) top

K—O1	2.728 (3)	C1—C2	1.517 (1)
K—O41ⁱ	2.734 (3)	C2—C3	1.342 (1)
C2—Cl1	1.713 (2)	C3—C4	1.508 (2)
C3—Cl2	1.720 (1)	O2—H2	1.214 (15)
C1—O1	1.223 (2)	O21—H2	1.259 (15)
C1—O2	1.277 (2)	O4—H4	1.327 (13)
C4—O3	1.227 (2)	O41ⁱⁱ—H4	1.129 (13)
C4—O4	1.284 (2)

C2—C1—O1	120.1 (1)	C2—C3—C4	122.5 (1)
C2—C1—O2	116.6 (1)	C3—C4—O3	119.8 (1)
O1—C1—O2	123.3 (1)	C3—C4—O4	114.4 (1)
C1—C2—C3	125.5 (1)	O3—C4—O4	125.8 (1)
C1—C2—Cl1	112.4 (1)	C1—O2—H2	113.1 (6)
Cl1—C2—C3	122.1 (1)	H2—O21—C11	122.8 (6)
C2—C3—Cl2	120.4 (1)	C4—O4—H4	119.9 (5)
Cl2—C3—C4	117.0 (1)	H4ⁱⁱⁱ—O41—C41	111.5 (6)

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

(neutron) top

Crystal data top

K₂Cl₄O₈C₈H₂	γ = 88.95 (2)°
M_r = 446.1	V = 341.8 (2) Å³
Triclinic, P1	Z = 1
Hall symbol: P 1	D_x = 2.180 Mg m⁻³
a = 5.022 (2) Å	Neutron radiation, λ = 1.207 Å
b = 7.827 (4) Å	µ = 0.09 mm⁻¹
c = 8.838 (4) Å	T = 30 K
α = 80.99 (2)°	Plate with 6 faces, colourless
β = 85.13 (2)°	4.2 × 3.5 × 1.0 mm

Data collection top

Huber-Aracor 400 mm diameter four-circle diffractometer	R_int = 0.046
θ–2θ scans	θ_max = 52°
Absorption correction: numerical gaussian (Coppens, Leiserowitz & Rabinovich, 1965)	h = 0→6
T_min = 0.720, T_max = 0.925	k = −10→10
2104 measured reflections	l = −11→11
2104 independent reflections	3 standard reflections every 33 reflections
1871 reflections with F_o² > 3σ(F_o²)	intensity decay: stable

Refinement top

Refinement on F²	All H-atom parameters refined
R[F² > 2σ(F²)] = 0.058	(Δ/σ)_max = 0.05
wR(F²) = 0.081	Δρ_max = 0.05 e Å⁻³
S = 1.77	Δρ_min = −0.05 e Å⁻³
1485 reflections	Extinction correction: Lorentzian type I isotropic (Becker & Coppens, 1974, 1975)
119 parameters	Extinction coefficient: 7245.1

Crystal data top

K₂Cl₄O₈C₈H₂	γ = 88.95 (2)°
M_r = 446.1	V = 341.8 (2) Å³
Triclinic, P1	Z = 1
a = 5.022 (2) Å	Neutron radiation, λ = 1.207 Å
b = 7.827 (4) Å	µ = 0.09 mm⁻¹
c = 8.838 (4) Å	T = 30 K
α = 80.99 (2)°	4.2 × 3.5 × 1.0 mm
β = 85.13 (2)°

Data collection top

Huber-Aracor 400 mm diameter four-circle diffractometer	1871 reflections with F_o² > 3σ(F_o²)
Absorption correction: numerical gaussian (Coppens, Leiserowitz & Rabinovich, 1965)	R_int = 0.046
T_min = 0.720, T_max = 0.925	3 standard reflections every 33 reflections
2104 measured reflections	intensity decay: stable
2104 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.058	119 parameters
wR(F²) = 0.081	All H-atom parameters refined
S = 1.77	Δρ_max = 0.05 e Å⁻³
1485 reflections	Δρ_min = −0.05 e Å⁻³

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
K	0.3016 (3)	−0.1559 (2)	0.6242 (2)	0.0062 (7)
Cl1	0.4754 (1)	−0.2442 (1)	0.0603 (1)	0.0065 (3)
Cl2	0.1381 (1)	−0.5711 (1)	0.2032 (1)	0.0072 (3)
O1	0.2346 (2)	−0.0015 (1)	0.3347 (1)	0.0071 (4)
O2	0.0246 (2)	0.0508 (1)	0.1215 (1)	0.0072 (4)
O3	−0.2508 (2)	−0.2200 (1)	0.4018 (1)	0.0076 (5)
O4	−0.2962 (2)	−0.5066 (1)	0.4153 (1)	0.0072 (5)
C1	0.1507 (2)	−0.0491 (1)	0.2216 (1)	0.0052 (4)
C2	0.2044 (2)	−0.2316 (1)	0.1902 (1)	0.0056 (4)
C3	0.0592 (2)	−0.3710 (1)	0.2526 (1)	0.0059 (4)
C4	−0.1812 (2)	−0.3605 (1)	0.3656 (1)	0.0055 (4)
H2	0.023 (2)	0.0065 (17)	−0.0104 (11)	0.0147 (18)
H4	−0.491 (3)	−0.4957 (18)	0.5116 (15)	0.0160 (18)
K1	−0.3016 (3)	0.1559 (2)	−0.6242 (2)	0.0062 (7)
Cl11	−0.4754 (1)	0.2442 (1)	−0.0603 (1)	0.0065 (3)
Cl21	−0.1381 (1)	0.5711 (1)	−0.2032 (1)	0.0072 (3)
O11	−0.2346 (2)	0.0015 (1)	−0.3347 (1)	0.0071 (4)
O21	−0.0246 (2)	−0.0508 (1)	−0.1215 (1)	0.0072 (4)
O31	0.2508 (2)	0.2200 (1)	−0.4018 (1)	0.0076 (5)
O41	0.2962 (2)	0.5066 (1)	−0.4153 (1)	0.0072 (5)
C11	−0.1507 (2)	0.0491 (1)	−0.2216 (1)	0.0052 (4)
C21	−0.2044 (2)	0.2316 (1)	−0.1902 (1)	0.0056 (4)
C31	−0.0592 (2)	0.3710 (1)	−0.2526 (1)	0.0059 (4)
C41	0.1812 (2)	0.3605 (1)	−0.3656 (1)	0.0055 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
K	0.0052 (7)	0.0049 (7)	0.0085 (6)	−0.0003 (6)	0.0000 (5)	−0.0011 (5)
Cl1	0.0055 (3)	0.0052 (3)	0.0084 (3)	−0.0002 (2)	0.0005 (2)	−0.0006 (2)
Cl2	0.0078 (3)	0.0033 (3)	0.0103 (3)	0.0002 (2)	0.0013 (2)	−0.0018 (2)
O1	0.0084 (5)	0.0058 (4)	0.0077 (4)	0.0001 (4)	−0.0032 (3)	−0.0019 (3)
O2	0.0086 (5)	0.0053 (4)	0.0079 (4)	0.0010 (4)	−0.0027 (3)	−0.0009 (3)
O3	0.0074 (5)	0.0045 (5)	0.0106 (4)	−0.0001 (4)	0.0019 (3)	−0.0018 (3)
O4	0.0067 (5)	0.0039 (5)	0.0105 (4)	−0.0011 (4)	0.0023 (3)	−0.0008 (3)
C1	0.0049 (4)	0.0034 (4)	0.0074 (4)	0.0001 (3)	−0.0009 (3)	−0.0010 (3)
C2	0.0061 (4)	0.0034 (4)	0.0073 (4)	−0.0001 (3)	−0.0006 (3)	−0.0008 (3)
C3	0.0055 (4)	0.0035 (4)	0.0084 (4)	−0.0004 (3)	0.0000 (3)	−0.0011 (3)
C4	0.0051 (4)	0.0039 (4)	0.0075 (4)	0.0001 (3)	0.0003 (3)	−0.0011 (3)
H2	0.009 (2)	0.0135 (14)	0.021 (2)	−0.0046 (15)	0.0061 (14)	0.0041 (14)
H4	0.023 (2)	0.0137 (13)	0.015 (2)	−0.0024 (14)	−0.0084 (15)	−0.0080 (14)

Geometric parameters (Å, º) top

K—O1	2.699 (2)	C1—C2	1.513 (1)
K—O41ⁱ	2.719 (2)	C2—C3	1.341 (1)
C2—Cl1	1.716 (1)	C3—C4	1.510 (1)
C3—Cl2	1.721 (1)	O2—H2	1.268 (12)
C1—O1	1.229 (1)	O21—H2	1.185 (12)
C1—O2	1.287 (1)	O4—H4	1.253 (15)
C4—O3	1.229 (1)	O41ⁱⁱ—H4	1.201 (15)
C4—O4	1.287 (1)

C2—C1—O1	120.1 (1)	C2—C3—C4	122.3 (1)
C2—C1—O2	116.3 (1)	C3—C4—O3	119.7 (1)
O1—C1—O2	123.5 (1)	C3—C4—O4	114.2 (1)
C1—C2—C3	125.4 (1)	O3—C4—O4	126.0 (1)
C1—C2—Cl1	112.5 (1)	C1—O2—H2	116.9 (6)
Cl1—C2—C3	122.1 (1)	H2—O21—C11	116.7 (6)
C2—C3—Cl2	120.6 (1)	C4—O4—H4	113.2 (6)
Cl2—C3—C4	117.0 (1)	H4ⁱⁱⁱ—O41—C41	117.6 (6)

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

Experimental details

	(xray)	(neutron)
Crystal data
Chemical formula	K₂Cl₄O₈C₈H₂	K₂Cl₄O₈C₈H₂
M_r	446.1	446.1
Crystal system, space group	Triclinic, P1	Triclinic, P1
Temperature (K)	295	30
a, b, c (Å)	5.083 (3), 7.881 (5), 8.863 (5)	5.022 (2), 7.827 (4), 8.838 (4)
α, β, γ (°)	81.72 (5), 84.78 (5), 89.59 (5)	80.99 (2), 85.13 (2), 88.95 (2)
V (Å³)	349.9 (2)	341.8 (2)
Z	1	1
Radiation type	Neutron, λ = 1.207 Å	Neutron, λ = 1.207 Å
µ (mm⁻¹)	0.09	0.09
Crystal size (mm)	4.2 × 3.5 × 1.0	4.2 × 3.5 × 1.0

Data collection
Diffractometer	Huber-Aracor 400 mm diameter four-circle diffractometer	Huber-Aracor 400 mm diameter four-circle diffractometer
Absorption correction	Numerical gaussian (Coppens, Leiserowitz & Rabinovich, 1965)	Numerical gaussian (Coppens, Leiserowitz & Rabinovich, 1965)
T_min, T_max	0.721, 0.925	0.720, 0.925
No. of measured, independent and observed [F_o² > 3σ(F_o²)] reflections	2002, 2002, 1716	2104, 2104, 1871
R_int	0.023	0.046
(sin θ/λ)_max (Å⁻¹)	0.653	0.653

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.064, 0.082, 1.04	0.058, 0.081, 1.77
No. of reflections	1349	1485
No. of parameters	119	119
No. of restraints	?	?
H-atom treatment	All H-atom parameters refined	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.05, −0.05	0.05, −0.05

Computer programs: Aracor Diffractometer Control Program, STOE 4-circle X-ray Diffractometer Control Program, ARACOR-DATRED vers. 950320, UPALS Lundgren (1982).

Selected geometric parameters (Å, º) for (xray) top

K—O1	2.728 (3)	C4—O3	1.227 (2)
C2—Cl1	1.713 (2)	C4—O4	1.284 (2)
C3—Cl2	1.720 (1)	C1—C2	1.517 (1)
C1—O1	1.223 (2)	C2—C3	1.342 (1)
C1—O2	1.277 (2)	C3—C4	1.508 (2)

C2—C1—O1	120.1 (1)	C3—C4—O4	114.4 (1)
C2—C1—O2	116.6 (1)	O3—C4—O4	125.8 (1)
O1—C1—O2	123.3 (1)	C1—O2—H2	113.1 (6)
C3—C4—O3	119.8 (1)	C4—O4—H4	119.9 (5)

Selected geometric parameters (Å, º) for (neutron) top

K—O1	2.699 (2)	C4—O3	1.229 (1)
C2—Cl1	1.716 (1)	C4—O4	1.287 (1)
C3—Cl2	1.721 (1)	C1—C2	1.513 (1)
C1—O1	1.229 (1)	C2—C3	1.341 (1)
C1—O2	1.287 (1)	C3—C4	1.510 (1)

C2—C1—O1	120.1 (1)	C3—C4—O4	114.2 (1)
C2—C1—O2	116.3 (1)	O3—C4—O4	126.0 (1)
O1—C1—O2	123.5 (1)	C1—O2—H2	116.9 (6)
C3—C4—O3	119.7 (1)	C4—O4—H4	113.2 (6)

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