CADMIUM(II) COMPLEXATION BY A SERIES OF TRIAZACYCLOALKANES ([X]ANEN(3), X=9-12) - AN EQUILIBRIUM AND STRUCTURAL STUDY

The complexation of Cd(II) by a series of triazacycloalkanes, ([x]aneN (3), x = 9-12), has been studied in 0.10 mol dm(-3) KNO3 aqueous solut ion at 298.2+/-0.1 K. Stability constants (beta(CdL)) for the complexe s decrease in magnitude with increasing number of atoms in the ligand ring, and are several orders of magnitude smaller than corresponding b eta(ZnL) values. Two complexes [Cd-2([9]aneN(3))(2)(mu-Cl)(2)Cl-2] (1) and [Cd-2([11]aneN(3))(2)a(mu-Cl)(2)Br-2] (2) were synthesized, and t he structures determined by X-ray crystallography. Complex 1 crystalli zes in the triclinic space group P1, with a = 7.657(2), b = 7.741(2), c = 17.750(2) Angstrom, alpha = 90.13(3), beta = 94.65(3), gamma = 90. 76(3)degrees and V = 1048.5(5) Angstrom(3) for Z = 2. Complex 2 crysta llizes in the monoclinic space group P2(1)/c with a = 8.144(2), b = 8. 469(2), c = 18.480(4) Angstrom, beta = 97.62(3)degrees and V = 1263.3( 6) Angstrom(3) for Z = 2. Both structures contain bridging di-mu-chlor o groups separating six-coordinate Cd(II). Each Cd(II) is also bonded to a tridentate ligand and Cl (structure 1) or Br (structure 2).