Thermal reactions of the complexes [Ni(H2O)2(NN-deen)2]X2·nH2O (NN-deen is N,N-diethylethylene-diamine and X is Cl or Br) were investigated. It was found by derivatography and spectral and magnetic measurements that the bromide undergoes transformation from octahedral to square planar structure by “deaquation” upon heating, whereas the chloride turned to the dichloro complex by thermal “deaquation-anation” losing the coordinated water and drawing chloride ion into the coordination sphere with retention of octahedral structure around the central metal. No such transformation could be found in the corresponding iodide and nitrate, since only diamagnetic complexes, [Ni(NN-deen)2]X2 (X is I or NO3), and no paramagentic complexes were obtained.

The reaction involving the increase of the coordination number from four to six, viz, the transformation from square planar to octahedral was found in the benzimidazole complex, [Ni(bimd)4](NO3)2·2.5C2H5OH upon heating. The transformation was considered to be due to the approach of the nitrate ions toward the central ion along the vertical axis.

Wie derivatographische, elektronenspektroskopische und magnetische Untersuchungen bestätigen, unterwerfen sich die nach bekannter Methode synthetisierten oktaedrischen Diaquo‐Ni(II)‐halogenide (II) einer thermischen Umlagerung.