STATIC AND DYNAMIC JAHN-TELLER DISTORTIONS IN CUN6 COMPLEXES - CRYSTAL-STRUCTURES AND EPR-SPECTRA OF COMPLEXES BETWEEN COPPER(II) AND RIGID, TRIDENTATE CIS,CIS-1,3,5-TRIAMINOCYCLOHEXANE (TACH) - CU(TACH)2(CLO4)2, CU(TACH)2(NO3)2 - CRYSTAL-STRUCTURE OF NI(TACH)2(NO3)2

The complex cation Cu(tach)22+ (tach≡cis,cis-1, 3, 5-triaminocyclohexane) was investigated in two different solids, Cu(tach)2(NO3)2 and Cu(tach)2(ClO4)2, by X-ray crystallography at room temperature and by EPR spectroscopy between 4 and 300 K. In the perchlorate salt the CuN6 octahedron shows essentially tetragonal, static elongation between 4 and 300 K. The nitrate salt undergoes a phase transition at ~120 K; below 120 K Cu(tach)22+ is statically distorted; immediately above 120 K Cu(tach)22+ dynamically oscillates between two and, at higher temperatures, between all three possible, tetragonal elongations of the CuN6 octahedron. The degree of elongation (Jahn-Teller radius RJT) was estimated from the observed temperature factors of Cu(tach)2(NO3)2 and Ni(tach)2(NO3)2 by two methods. Both methods, namely semirigid body analysis of the entire complex cation M(tach)22+ and analysis of differences in thermal motion between Cu, Ni and N, lead essentially to the same value for RJT (0.33 Å). Furthermore both RJT and the average Cu-N distance d0 were found to be equal within experimental error for dynamically distorted Cu(tach)2(NO3)2 and statically distorted Cu(tach)2(ClO4)2. Further values of RJT and values of EJT (the stabilization energy gained by Jahn-Teller distortion) were obtained from literature data on CuN6 complexes with six chemically equivalent ligand atoms (Cu(en)32+, Cu(bpy)32+, Cu(phen)32+, Cu(N02)64-) Comparison of all data yields strikingly similar RJT(=0.32±0.03 Å) and EJT (=0.20±0.02 μm-1)-This suggests that consideration of the local CuN6 fragment alone (cluster model) provides an adequate description of the Jahn-Teller effect in octahedral Cu(II) complexed to six chemically equivalent nitrogen ligand atoms. © 1979, American Chemical Society. All rights reserved.