New complexes of 2-(2'-hydroxy-5'-methylphenyl)-benzotriazole (Hhmbt), [Zn(hmbt)(2)(H2O)(2)], [Zn(hmbt)(OAc)(H2O)(2)], [Pd(hmbt)(H2O)Cl], [Pd(hmbt)(2)], [M(PPh3)(hmbt)Cl], [M(L)(hmbt)]Cl (M(II) = Pd, Pt; L = bpy, phen), [Ag-2(hmbt)(2)], [Ag(phen)(hmbt)], [Ag(PPh3)(hmbt)], [Rh(hmbt)(2)(H2O)(2)]Cl, [Ru(hmbt)(2) (H2O)(2)], [Ru(PPh3)(hmbt)(2)Cl] and cis-[MoO2(hmbt)(2)] have been synthesized. They have been structurally and spectroscopically characterized on the basis of elemental analysis, IR, NMR (H-1, C-13, P-31), UV-vis. and ESI-mass spectroscopy, thermal and molar conductivity measurements. 2-(2'-Hydroxy-5'-methylphenyl)benzotriazole behaves as a mononegative bidentate through the deprotonated phenolic oxygen and imine nitrogen atoms. The reported complexes have been tested against human breast cancer (MDA-MB231) and human ovarian cancer (OVCAR-8) cell lines. The complexes, [Ag(hmpbt)(PPh3)], [Rh(hmbt)(2)(H2O)(2)]Cl, [Pt(phen)(hmbt)]Cl and [Pd(phen)(hmbt)]Cl exhibit the highest growth inhibitory activity with mean IC50 values 1.37, 7.52, 5.24 and 4.85 mu M (MDA-MB231) and 1.75, 8.50, 3.00 and 2.99 mu M (OVACAR-8), respectively. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.