1 1 METAL-COMPLEXES OF BIVALENT COBALT, NICKEL, COPPER, ZINC, AND CADMIUM WITH THE TRIPODAL LIGAND TRIS[2-(DIMETHYLAMINO)ETHYL]AMINE - THEIR STABILITIES AND THE X-RAY CRYSTAL-STRUCTURE OF ITS COPPER(II) COMPLEX SULFATE/

The complex formation by Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ with tris[2- (dimethylamino)ethyl]amine (N(CH(2)CH(2)NMe(2))(3), Me(6)tren) was inv estigated at 25 degrees and at an ionic strength of 1, using VIS spect roscopy and potentiometric measurements. The stability constants of th ese complexes are compared with those of tris(2-aminoethyl)amine (N(CH 2CH2NH2)(3), tren), obtained under the same conditions. The values of the constants for Me(6)tren are much lower than those for tren, due to the bulky Me substituents. The values of the constants can be correla ted with the ability of the individual metal ions to adopt coordinatio n number 5. This appears to be easier for Cu2+ and Co2+ than for Cd2and Zn2+ and is very difficult for Ni2+. The 1:1 complexes [ML(H2O)](2 +) are monoprotonic acids whose pK(s), values are similar or lower tha n those of the corresponding aquametal ions. The X-ray crystal structu re of the copper(II) complex [Cu(SO4)(Me(6)tren)].8H(2)O reveals penta coordination at the central ion. The UV/VIS spectra of the aqueous sol utions of the Co2+, Ni2+, and Cu2+ 1:1 complexes confirm that the same coordination number is present also in these complexes.