Phase transition and proton ordering at 50 K in 3-(pyridin-4-yl)pentane-2,4-dione

Single-crystal neutron diffraction experiments at 100 and 2.5 K have been performed to determine the structure of 3-(pyridin-4-yl)pentane-2,4-dione (HacacPy) with respect to its protonation pattern and to monitor a low-temperature phase transition. Solid HacacPy exists as the enol tautomer with a short intramolecular hydrogen bond. At 100 K, its donor···acceptor distance is 2.450 (8) Å and the compound adopts space group C2/c, with the N and para-C atoms of the pyridyl ring and the central C of the acetyl­acetone substituent on the twofold crystallographic axis. As a consequence of the axial symmetry, the bridging hydrogen is disordered over two symmetrically equivalent positions, and the carbon–oxygen bond distances adopt intermediate values between single and double bonds. Upon cooling, a structural phase transition to the t₂ subgroup P occurs; the resulting twins show an ordered acetyl­acetone moiety. The phase transition is fully reversible but associated with an appreciable hysteresis in the large single crystal under study: transition to the low-temperature phase requires several hours at 2.5 K and heating to 80 K is required to revert the transformation. No significant hysteresis is observed in a powder sample, in agreement with the second-order nature of the phase transition.

Computing details

Data collection: PRON2010 for 100k. For both structures, program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2014).

(100k)

Crystal data

C10H11NO2	Z = 4
Mr = 177.20	F(000) = 18
Monoclinic, C2/c	Dx = 1.276 Mg m^−3
a = 11.0366 (4) Å	Neutrons radiation, λ = 0.793 Å
b = 13.2899 (5) Å	µ = 0.001 mm^−1
c = 6.3763 (2) Å	T = 100 K
β = 99.548 (2)°	Prism, colourless
V = 922.29 (6) Å^3	4.4 × 4.3 × 3.3 mm

Data collection

Closed Eulerian cradle HEiDi diffractometer	Rint = 0.097
Radiation source: FRM II	θmax = 35.6°, θmin = 2.7°
rocking scan	h = −14→14
1688 measured reflections	k = −19→16
1055 independent reflections	l = −8→9
718 reflections with I > 2σ(I)

Refinement

Refinement on F^2	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.082	w = 1/[σ^2(Fo^2) + (0.1P)^2 + 0.4P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.221	(Δ/σ)max = 0.002
S = 1.09	Δρmax = 0.14 e Å^−3
1055 reflections	Δρmin = −0.15 e Å^−3
114 parameters	Extinction correction: SHELXL-2014/7 (Sheldrick 2014, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
6 restraints	Extinction coefficient: 2.0 (4)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	1.1125 (4)	1.0523 (3)	0.7871 (6)	0.0261 (8)
H1O	1.018 (3)	1.0743 (10)	0.759 (9)	0.037 (6)	0.5
N1	1.000000	0.5766 (2)	0.750000	0.0258 (7)
C2	1.0367 (3)	0.6292 (2)	0.5918 (5)	0.0252 (7)
H2	1.0648 (9)	0.5853 (6)	0.4665 (12)	0.049 (2)
C3	1.0385 (3)	0.7340 (2)	0.5855 (5)	0.0234 (7)
H3	1.0708 (8)	0.7727 (5)	0.4548 (11)	0.0443 (18)
C4	1.000000	0.7890 (3)	0.750000	0.0172 (8)
C7	1.2345 (3)	0.9042 (3)	0.8345 (6)	0.0304 (8)
H7A	1.232 (2)	0.848 (2)	0.953 (4)	0.071 (7)*	0.53 (4)
H7B	1.2488 (17)	0.8589 (16)	0.693 (3)	0.056 (6)*	0.53 (4)
H7C	1.306 (2)	0.9568 (19)	0.883 (5)	0.066 (6)*	0.53 (4)
H7D	1.2380 (18)	0.8294 (16)	0.782 (3)	0.051 (6)*	0.47 (4)
H7E	1.262 (2)	0.8971 (19)	1.006 (4)	0.059 (6)*	0.47 (4)
H7F	1.3073 (18)	0.9511 (16)	0.789 (4)	0.050 (5)*	0.47 (4)
C8	1.1111 (3)	0.9549 (2)	0.7874 (5)	0.0214 (6)
C9	1.000000	0.9012 (3)	0.750000	0.0206 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.035 (2)	0.0184 (16)	0.0248 (15)	−0.0057 (15)	0.0047 (13)	−0.0022 (13)
H1O	0.041 (19)	0.026 (5)	0.042 (9)	0.008 (6)	0.000 (14)	−0.002 (8)
N1	0.0314 (16)	0.0170 (14)	0.0288 (15)	0.000	0.0045 (12)	0.000
C2	0.0331 (16)	0.0182 (14)	0.0251 (14)	0.0009 (12)	0.0070 (12)	0.0002 (11)
H2	0.078 (6)	0.036 (4)	0.041 (4)	0.001 (4)	0.030 (4)	−0.013 (3)
C3	0.0294 (15)	0.0208 (14)	0.0209 (13)	0.0012 (12)	0.0065 (11)	−0.0008 (10)
H3	0.073 (5)	0.029 (3)	0.035 (3)	−0.001 (3)	0.023 (3)	0.003 (3)
C4	0.0198 (18)	0.0136 (16)	0.0183 (16)	0.000	0.0036 (13)	0.000
C7	0.0247 (14)	0.0303 (17)	0.0368 (17)	−0.0032 (13)	0.0072 (13)	−0.0034 (14)
C8	0.0253 (14)	0.0189 (13)	0.0197 (11)	−0.0012 (11)	0.0029 (10)	0.0001 (11)
C9	0.0265 (19)	0.0160 (18)	0.0189 (17)	0.000	0.0023 (14)	0.000

Geometric parameters (Å, º)

O1—C8	1.294 (5)	C7—C8	1.504 (5)
O1—H1O	1.07 (3)	C7—H7A	1.07 (3)
N1—C2^i	1.344 (4)	C7—H7B	1.12 (2)
N1—C2	1.344 (4)	C7—H7C	1.06 (3)
C2—C3	1.393 (4)	C7—H7D	1.05 (2)
C2—H2	1.076 (7)	C7—H7E	1.09 (2)
C3—C4	1.401 (4)	C7—H7F	1.09 (2)
C3—H3	1.088 (7)	C8—C9	1.404 (4)
C4—C9	1.491 (6)
C8—O1—H1O	105.3 (9)	H7A—C7—H7C	111 (2)
C2^i—N1—C2	117.3 (3)	H7B—C7—H7C	113.1 (18)
N1—C2—C3	123.3 (3)	C8—C7—H7D	116.1 (11)
N1—C2—H2	115.8 (5)	C8—C7—H7E	109.1 (12)
C3—C2—H2	120.9 (5)	H7D—C7—H7E	102.8 (18)
C2—C3—C4	119.5 (3)	C8—C7—H7F	111.9 (11)
C2—C3—H3	120.1 (5)	H7D—C7—H7F	112.7 (17)
C4—C3—H3	120.4 (5)	H7E—C7—H7F	102.9 (17)
C3^i—C4—C3	117.1 (4)	O1—C8—C9	121.2 (3)
C3^i—C4—C9	121.45 (18)	O1—C8—C7	116.0 (3)
C3—C4—C9	121.45 (18)	C9—C8—C7	122.8 (3)
C8—C7—H7A	109.2 (13)	C8—C9—C8^i	118.9 (4)
C8—C7—H7B	108.9 (10)	C8—C9—C4	120.53 (19)
H7A—C7—H7B	102.5 (18)	C8^i—C9—C4	120.53 (19)
C8—C7—H7C	111.6 (13)
C2^i—N1—C2—C3	0.1 (2)	O1—C8—C9—C4	179.7 (3)
N1—C2—C3—C4	−0.3 (5)	C7—C8—C9—C4	−1.6 (3)
C2—C3—C4—C3^i	0.1 (2)	C3^i—C4—C9—C8	108.8 (2)
C2—C3—C4—C9	−179.9 (2)	C3—C4—C9—C8	−71.2 (2)
O1—C8—C9—C8^i	−0.3 (3)	C3^i—C4—C9—C8^i	−71.2 (2)
C7—C8—C9—C8^i	178.4 (3)	C3—C4—C9—C8^i	108.8 (2)

Symmetry code: (i) −x+2, y, −z+3/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···O1^i	1.07 (3)	1.45 (3)	2.450 (8)	152.3 (12)

Symmetry code: (i) −x+2, y, −z+3/2.

(2k5)

Crystal data

C10H11NO2	Z = 2
Mr = 177.20	F(000) = 18
Triclinic, P1	Dx = 1.299 Mg m^−3
a = 6.2755 (2) Å	Neutrons radiation, λ = 0.793 Å
b = 8.6368 (2) Å	Cell parameters from 34 reflections
c = 8.6570 (2) Å	µ = 0.001 mm^−1
α = 101.482 (3)°	T = 3 K
β = 96.2307 (13)°	Prism, colourless
γ = 96.0785 (13)°	4.4 × 4.3 × 3.3 mm
V = 453.17 (2) Å^3

Data collection

Closed Eulerian cradle HEiDi diffractometer	Rint = 0.073
Radiation source: FRM II	θmax = 36.1°, θmin = 2.7°
rocking scan	h = −8→7
2315 measured reflections	k = −11→11
1555 independent reflections	l = −11→10
1121 reflections with I > 2σ(I)

Refinement

Refinement on F^2	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.107	w = 1/[σ^2(Fo^2) + (0.120P)^2 + 0.3P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.284	(Δ/σ)max = 0.002
S = 1.08	Δρmax = 0.27 e Å^−3
1555 reflections	Δρmin = −0.19 e Å^−3
160 parameters	Extinction correction: SHELXL-2014/7 (Sheldrick 2014, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
67 restraints	Extinction coefficient: 1.9 (8)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refined as a 2-component twin; twin law is a twofold axis.

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

	x	y	z	Uiso*/Ueq
O1	0.2910 (14)	0.5563 (10)	0.6676 (10)	0.0183 (17)*
H1O	0.255 (3)	0.4448 (14)	0.5948 (16)	0.036 (3)
O2	0.2195 (16)	0.3361 (11)	0.4370 (11)	0.026 (2)*
N1	0.2422 (12)	0.9204 (6)	0.0759 (7)	0.0233 (8)
C2	0.0833 (13)	0.9040 (10)	0.1666 (10)	0.0241 (18)*
H2	−0.043 (2)	0.981 (2)	0.157 (2)	0.034 (4)
C3	0.0819 (13)	0.8013 (10)	0.2749 (11)	0.0258 (18)*
H3	−0.059 (3)	0.791 (2)	0.344 (2)	0.039 (4)
C4	0.2464 (14)	0.7082 (9)	0.2872 (9)	0.0197 (10)*
C5	0.4106 (12)	0.7264 (10)	0.1913 (9)	0.0187 (15)*
H5	0.536 (3)	0.657 (2)	0.195 (2)	0.039 (4)
C6	0.4005 (12)	0.8329 (9)	0.0869 (9)	0.0196 (16)*
H6	0.532 (4)	0.852 (3)	0.019 (3)	0.049 (5)
C7	0.3386 (13)	0.8261 (9)	0.6446 (9)	0.0221 (15)*
H7A	0.261 (4)	0.855 (2)	0.751 (3)	0.058 (5)
H7B	0.288 (4)	0.9095 (19)	0.5690 (19)	0.051 (4)
H7C	0.520 (3)	0.853 (2)	0.685 (3)	0.061 (5)
C8	0.2870 (12)	0.6557 (9)	0.5660 (9)	0.0180 (14)*
C9	0.2541 (15)	0.6009 (9)	0.4030 (9)	0.0197 (10)*
C10	0.2142 (13)	0.4325 (9)	0.3400 (10)	0.0221 (15)*
C11	0.1715 (13)	0.3650 (9)	0.1635 (9)	0.0214 (16)*
H11A	0.140 (3)	0.2315 (14)	0.1491 (19)	0.036 (3)
H11B	0.308 (3)	0.395 (2)	0.1022 (19)	0.051 (4)
H11C	0.034 (3)	0.405 (2)	0.1195 (19)	0.046 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
H1O	0.044 (7)	0.013 (5)	0.041 (7)	0.002 (5)	0.011 (7)	−0.015 (5)
N1	0.0267 (19)	0.015 (3)	0.024 (3)	0.000 (2)	0.006 (2)	−0.0067 (12)
H2	0.014 (6)	0.042 (8)	0.049 (8)	0.009 (6)	0.004 (6)	0.012 (6)
H3	0.041 (9)	0.030 (7)	0.055 (9)	0.012 (6)	0.031 (7)	0.012 (6)
H5	0.034 (8)	0.032 (7)	0.047 (8)	−0.009 (6)	0.013 (7)	0.002 (6)
H6	0.059 (10)	0.049 (9)	0.048 (9)	0.015 (8)	0.029 (8)	0.013 (7)
H7A	0.069 (11)	0.052 (9)	0.062 (10)	0.032 (8)	0.035 (9)	0.008 (7)
H7B	0.082 (11)	0.039 (7)	0.035 (7)	0.029 (8)	−0.009 (7)	0.015 (6)
H7C	0.038 (7)	0.046 (8)	0.074 (10)	−0.022 (6)	0.000 (7)	−0.028 (7)
H11A	0.046 (8)	0.012 (5)	0.043 (7)	0.006 (5)	0.011 (6)	−0.013 (5)
H11B	0.046 (8)	0.060 (9)	0.031 (7)	−0.017 (7)	0.020 (6)	−0.020 (6)
H11C	0.034 (7)	0.050 (8)	0.040 (7)	0.011 (6)	0.000 (6)	−0.020 (6)

Geometric parameters (Å, º)

O1—C8	1.346 (11)	C5—H5	1.04 (2)
O1—H1O	1.028 (12)	C6—H6	1.08 (2)
O2—C10	1.296 (13)	C7—C8	1.479 (10)
O2—H1O	1.475 (14)	C7—H7A	1.09 (2)
N1—C6	1.317 (11)	C7—H7B	1.113 (16)
N1—C2	1.348 (11)	C7—H7C	1.140 (18)
C2—C3	1.413 (12)	C8—C9	1.382 (11)
C2—H2	1.09 (2)	C9—C10	1.433 (11)
C3—C4	1.382 (9)	C10—C11	1.507 (11)
C3—H3	1.125 (18)	C11—H11A	1.128 (14)
C4—C5	1.407 (9)	C11—H11B	1.092 (18)
C4—C9	1.495 (7)	C11—H11C	1.025 (19)
C5—C6	1.413 (10)
C8—O1—H1O	103.9 (11)	H7A—C7—H7B	105.6 (17)
C10—O2—H1O	103.1 (9)	C8—C7—H7C	108.5 (11)
C6—N1—C2	117.8 (4)	H7A—C7—H7C	106.2 (18)
N1—C2—C3	123.3 (8)	H7B—C7—H7C	109.8 (19)
N1—C2—H2	115.6 (13)	O1—C8—C9	122.3 (7)
C3—C2—H2	121.0 (13)	O1—C8—C7	113.9 (7)
C4—C3—C2	119.6 (8)	C9—C8—C7	123.7 (7)
C4—C3—H3	121.0 (13)	C8—C9—C10	118.8 (4)
C2—C3—H3	119.3 (12)	C8—C9—C4	123.5 (8)
C3—C4—C5	116.4 (5)	C10—C9—C4	117.6 (8)
C3—C4—C9	121.3 (8)	O2—C10—C9	119.2 (8)
C5—C4—C9	122.2 (7)	O2—C10—C11	119.3 (8)
C4—C5—C6	120.4 (7)	C9—C10—C11	121.5 (7)
C4—C5—H5	119.0 (13)	C10—C11—H11A	106.0 (10)
C6—C5—H5	120.5 (13)	C10—C11—H11B	112.6 (10)
N1—C6—C5	122.6 (7)	H11A—C11—H11B	109.4 (15)
N1—C6—H6	117.2 (15)	C10—C11—H11C	107.9 (10)
C5—C6—H6	120.1 (15)	H11A—C11—H11C	109.2 (15)
C8—C7—H7A	112.2 (13)	H11B—C11—H11C	111.4 (18)
C8—C7—H7B	114.3 (11)
C6—N1—C2—C3	1.7 (13)	O1—C8—C9—C4	179.3 (8)
N1—C2—C3—C4	−2.0 (13)	C7—C8—C9—C4	−5.9 (14)
C2—C3—C4—C5	1.7 (14)	C3—C4—C9—C8	−66.4 (13)
C2—C3—C4—C9	178.5 (9)	C5—C4—C9—C8	110.2 (11)
C3—C4—C5—C6	−1.2 (13)	C3—C4—C9—C10	110.4 (10)
C9—C4—C5—C6	−178.0 (8)	C5—C4—C9—C10	−73.0 (12)
C2—N1—C6—C5	−1.2 (12)	C8—C9—C10—O2	−3.0 (15)
C4—C5—C6—N1	1.0 (12)	C4—C9—C10—O2	−180.0 (9)
O1—C8—C9—C10	2.6 (15)	C8—C9—C10—C11	178.4 (7)
C7—C8—C9—C10	177.3 (7)	C4—C9—C10—C11	1.5 (13)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···O2	1.028 (12)	1.475 (14)	2.432 (8)	152.3 (15)