Temperature phase changes in solid bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.1]nonane-3,7-dione from powder X-ray diffraction data

The crystal structures of bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.1]­non­ane-3,7-dione have been solved by direct methods and by direct-space simulated annealing, respectively, from powder synchrotron X-ray diffraction data. Both compounds have a transition to a face-centred-cubic orientationally disordered phase (phase I) near 363 K, as shown by differential scanning calorimetry and powder diffraction measurements. Phase II of bicyclo[3.3.1]nonane-2,6-dione, which occurs below 363 K, is monoclinic, space group C2/c, with a = 7.38042 (4), b = 10.38220 (5), c = 9.75092 (5) Å and β = 95.359 (1)° at 80 K. Phase II of bicyclo[3.3.1]nonane-3,7-dione, which occurs below 365 K, is tetragonal, space group P4₁2₁2, with a = 6.8558 (1) and c = 16.9375 (1) Å at 100 K. This phase coexists in a biphasic mixture with a minor monoclinic phase II′ [a = 11.450 (6), b = 20.583 (1), c = 6.3779 (3) Å, β = 94.7555 (5)°, at 100 K] detected in the sample, which impeded indexing with standard programs. The crystal structures of phases II were solved by direct methods and by direct-space simulated annealing, employing powder synchrotron X-ray diffraction data of increased instrumental intensity and resolution from the ID31 beamline at the ESRF, and novel indexing algorithms. Ab initio molecular orbital calculations on the two systems are reported. In the solid state, the molecules pack in chair–chair conformation; molecular structures and packing are discussed.

Computing details

Figures

(Structure)

Crystal data

O8C40H48	α = 90°
Mr = 656.81	β = 90°
?, P41212	γ = 90°
Hall symbol: P_4abw_2nw	V = ? Å^3
a = 6.8558 Å	Z = ?
b = 6.8558 Å	? radiation, λ = ? Å
c = 16.9375 Å	× × mm

Data collection

h = ?→?	l = ?→?
k = ?→?

Refinement

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

	x	y	z	Uiso*/Ueq
O1	0.5505	0.1570	0.3279	?
C1	0.4679	0.3045	0.3115	?
C2	0.3270	0.4997	0.1951	?
C3	0.3169	0.3119	0.2450	?
C4	0.4932	0.4900	0.3605	?
C5	0.3253	0.6783	0.2500	?
H1	0.1994	0.5029	0.1578	?
H2	0.1754	0.3033	0.2728	?
H3	0.3333	0.1823	0.2095	?
H4	0.3957	0.4766	0.4103	?
H5	0.6398	0.4916	0.3837	?
H6	0.1937	0.7363	0.2760	?

(refine)

Crystal data

O8C34H48	α = 90°
Mr = 584.75	β = 95.359°
?, C2/c	γ = 90°
Hall symbol: -C_2yc	V = ? Å^3
a = 7.3803 Å	Z = ?
b = 10.3820 Å	? radiation, λ = ? Å
c = 9.7508 Å	× × mm

Data collection

h = ?→?	l = ?→?
k = ?→?

Refinement

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.5943	0.1352	0.0522	0.00732*
C1	0.4295	0.2404	−0.1427	0.00732*
C2	0.5775	0.1515	−0.0714	0.00732*
C3	0.6962	0.0797	−0.1660	0.00732*
C4	0.7355	0.1582	−0.2968	0.00732*
C5	0.5000	0.3287	−0.2500	0.00732*	0.500
H1	0.3771	0.2966	−0.0617	0.00732*
H2	0.6329	−0.0114	−0.1931	0.00732*
H3	0.8205	0.0558	−0.1052	0.00732*
H4	0.7931	0.0945	−0.3692	0.00732*
H5	0.8363	0.2312	−0.2690	0.00732*
H6	0.3898	0.3853	−0.2983	0.00732*