Table 2. endo-Nitrito Isomer Populations (P) and Reaction-Cavity Volumes (V_cav) per Complex Molecule Calculated for the Ni-2a Crystal Structure during Cooling and Heating Experiments^a.

	T (K)	P (%)	Vcav (Å3)
cooling	290	0.0	42.4
	240	0.0	41.0
	200	0.0	39.8
	160	8(1)	40.0
	140	11(1)	40.1
	120	11(1)	38.0
	100	8(1)	38.4
heating	120	12(1)	38.1
	140	11(1)	39.3
	160	12(1)	40.7
	180	10(1)	40.0
	200	0.0	40.3

^aCavity volumes were computed with the MERCURY program⁷⁴ (probe radius of 1.2 Å and grid spacing of 0.1 Å). Note that the standard deviation on V_cav was estimated to be ca. 0.5 ų.¹⁶