Table 3. Key to different crystal forms of 3CL^pro with approximate unit-cell parameters and solvent content.

Space group†	a (Å)	b (Å)	c (Å)	β or α/β/γ for P1 (°)	Molecules in asymmetric unit	Solvent content (%)
C2_a	114	53	45	101	1	39
C2_b	98	81	52	115	1	55
C2_c	109	81	53	104	1	45
C2_d	124	80	63	90	2	47
P21_a	55	99	59	108	2	45
P21_b	46	54	114	101	2	54
P212121	68	100	104		2	55
P21212	45	64	107		1	46
P6122	104	104	90		1	42
P3221	101	101	160		3	47
P1_a	47	55	62	62/61/80	2	38
P1_b	64	68	95	74/78/66	4	54
P1_c	63	68	78	78/90/73	4	46

^†In most cases the space-group symbol is extended by ‘_k’, where ‘k’ designates a distinct polymorph within the same space group.