H2O2 in water addn. of 10percent H2O2 to an aq. soln. of CoCl2*6H2O and dipyridyl; heating on a water-bath; addn. of concd. HCl-soln.; evaporation;; drying the residue in vac. over CaO; extraction with alcohol for several times; residue is trans-(CoCl2dpy2)Cl; pptn. of cis-(CoCl2dpy2)Cl*2H2O on cooling down of the alc. soln.;;

dihydrogen peroxide in water stoich. amt. of netal-salt and N-compd. were mixed in H2O, stoich. amt. of H2O2 was added, excess of HCl was added; crystals of trans-isomer were filtered off, washed with EtOH and Et2O, dried, filtrate was evapd. for several days with formation of cis-isomer;