Table 3.

Crystal data and PIXEL energies of polymorphs of Pbtl

Form	I	II	III	V a	VI	X b
References	[26]	[26]	[26]	This work	This work	[25, 48]
CCDC refcode	PHBARB07	PHBARB08	PHBARB09	–	–	LATMEA
Space group	P21/n	P $\overline{1}$	P21/c	P21/n	P21/n	C2/c
Z′	3	3	1	2	2	1
a (Å)	10.70	10.74	9.55	12.76	14.67	12.67
b (Å)	47.26	23.40	11.85	6.76	6.90	20.69
c (Å)	6.80	6.72	10.81	26.85	23.03	10.25
α (°)	90	91.0	90	90	90	90
β (°)	94.2	94.5	111.6	98.8	94.1	118.5
γ (°)	90	88.4	90	90	90	90
T exp (K)	298	173	298	173	173	173
D (g cm−3)	1.349	1.376	1.357	1.348	1.327	d
HBS	C-2 + L-3	C-2 + L-3	C-2	C-3	C-5	C-1
[N o, N t]	[4/3, 4/3]	[4/3, 4/3]	[0, 2]	[4, 0]	[2, 1]	[0, 2]
m.p. (°C) [26]	176	174	168	160	156	126
E T,Cry/ΔE intra (kJ mol−1)	c/7.3	c/7.5	−118.3/3.9	−122.4/13.1	−114.9/3.7	−118.3/8.0
E T,Σ (kJ mol−1)	−123.3	−122.4	−120.5	−124.1	−117.9	−121.1
E T,Σ(A)/ΔE intra (kJ mol−1)	−143.1/8.9	−141.4/8.7	–	−120.9/8.5	−128.3/0.3	–
E T,Σ(B)/ΔE intra (kJ mol−1)	−103.8/6.9	−104.0/8.2	–	−127.4/17.6	−107.5/7.1	–
E T,Σ(C)/ΔE intra (kJ mol−1)	−122.9/6.0	−121.9/5.5	–	–	–	–
Density order	3rd	1st	2nd	4th	5th	d
Stability order (RT) [26]	1st	2nd	3rd	4/5th	4/5th	e
Stability order (calc.)f	2nd	3rd	1st	6th	4th	5th

^aThe matrix ($10000\overline{1}\overline{1}0\overline{1}$) transforms the room temperature data reported by Williams [36] (a = 12.66, b = 6.75, c = 27.69 Å; β = 106.9°; P2₁/c) into a unit cell (a′ = 12.66, b′ = 6.75, c′ = 26.89 Å; β’ = 99.9°; P2₁/n) which matches our data

^bThe structure model for form X (Additional file 1: Section 8) was derived from the isostructural co-crystal of Pbtl with pentobarbital (the quoted CCDC refcode, unit cell data and T _exp all refer to the co-crystal)

^c E _T,Cry not determined because of Z′ > 2

^dNot applicable

^eExists only in a melt-film preparation and in the presence of a structurally analogous second barbiturate

^fBased on the results of SCDS-PIXEL calculations, corrected for ΔE _intra