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For two solid complexes, Co(NH 3 ) 5 NO 2 X 2 ( X = Cl − , Br − ), pentaamminenitrocobalt(III) dichloride/dibromide, the anisotropy of structural distortion on cooling the samples from 290 to 150 K was studied by variable-temperature single-crystal X-ray diffraction. The changes in lattice parameters were used to calculate the strain tensors and to scan linear strain in various crystallographic directions. The changes in different intra- and intermolecular distances in the structure were followed. Lattice strain on cooling was compared with lattice strain in the same structures under high hydrostatic pressure and with structural distortion in the course of homogeneous nitro–nitrito linkage isomerization. The effect of isomorphous substitution (Br − for Cl − ) with respect to structural strain was discussed. Structural strain in the monoclinic chloride and bromide was compared also with the previously obtained data Boldyreva, Kivikoski & Howard (1997). Acta Cryst. B 53 , 394–404 on strain in the orthorhombic structure of another compound of the same Co III nitropentaammine series, Co(NH 3 ) 5 NO 2 CI(NO 3 ).
Boldyreva et al. (Sun,) studied this question.