Deprotonated 3-(4-nitrophenyl)-1-phenyltriazene N-oxide reacts with YCl3 center dot 6H(2)O and LnCl(3)center dot 6H(2)O (Ln = Eu, Ho, Yb) to give the monoclinic chelate complexes [Y{O2N(C6H4)NNN(O)Ph}(4)](Et3NH)center dot H2O (1) (Ph = C6H5; Et = C2H5) and [Ln(III){O2N(C6H4)NNN(O)Ph}(4)](Et3NH)center dot H2O center dot{CH3OH*} {Ln(III) = Eu (2), Ho (3), Yb* (4), in which the metal centers present a square antiprismatic configuration. As already observed for hydrated ammonium complexes of triazene-oxides ligands with (C6H4)-NO2 groups, multiple, effective O center dot center dot center dot H and N center dot center dot center dot H interactions hold the species in supramolecular 3D assemblies. The optical and the luminescent properties of the triazene-oxide europium complex 2 are also presented and fully discussed. (C) 2010 Elsevier B.V. All rights reserved.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)