Solution studies (pH and 1 H NMR titrations) on Zn 2 + complexes 1 and 2 derived from N',N'',N'''-tris(3-aminopropyl)amine L1 and N',N'',N'''-tris(3-dimethyl-aminopropyl)amine L2 revealed that the presence of the hydrophobic (methyl) groups attached to the tripodal ligand side arms decreased the pK a of Zn-bound water molecule from 9.99 for 1 to 8.01 for 2, respectively. The X-ray diffraction studies have established the structures [L1Zn](ClO 4 ) 2 1 and [L1Zn(DETP)](ClO 4 ) 3, DETP - =O,O-diethyl thiophospate. Compound 1 consists of a monomeric cation and ClO 4 - counter ions. The coordination geometry of the Zn(II) centers may be described as distorted tetrahedral. Whereas in compound 3 the zinc atom adopts the slightly distorted trigonal-bipyramidal coordination geometry with the three primary nitrogen's on the basal plane and the tertiary nitrogen and the oxygen of DETP - at the apex. The hydroxo complexes [ZnL(OH)] + species showed slight catalytic activity in the hydrolysis of the phosphotriester 2,4-dinitrophenyl diethyl phosphate.