NITRO-NITRITO LINKAGE PHOTOISOMERIZATION IN CRYSTALS OF PENTAAMMINENITROCOBALT(III) DICHLORIDE

Photoisomerization in [Co(NH3)5NO2]Cl2 has been investigated by single-crystal X-ray diffraction: M(r) = 261.0, monoclinic, C2/c, Z = 4, D(x) = 1.83 Mg m-3, lambda(Mo Kalpha) = 0.71073 angstrom, mu = 2.35 mm-1 F(000) = 536, T = 116K. Before illumination with an Xe lamp, (Ia), a = 10.176 (2), b = 8.692 (1), c = 10.746 (2) angstrom, beta = 95.45 (2)-degrees, V = 946.2 (3) angstrom3, R = 0.028 for 1263 observed unique reflections. After illumination with an Xe lamp for 40 min, (Ib), R = 0.042 for 1216 reflections. After illumination for 150 min, (Ic), R = 0.062 for 730 reflections. Variation of the lattice constants was less than 0.6%. Nitrito coordination, induced by photochemical reaction, was detected on electron density maps and the populations were refined to (Ib) 8.9 (5)% and (Ic) 14.5 (8)%. Thermodynamical linkage isomerization in [Co(NH3)5ONO]Cl2, (II), was reinvestigated based on the X-ray intensity data measured by Grenthe & Nordin [Inorg. Chem. (1979), 18(7), 1869-1874]. Linkage isomerization occurs in the original plane of NO2- in (I). However, the nitro plane is inclined during isomerization of (II) because of steric hindrance to rotation in the original plane.