Interactions of nicotinic or isonicotinic acid N-oxides (N-nicOH and N-inicOH, respectively) with 3 d metal (II) perchlorates in ethanol-triethyl orthoformate lead, in most cases, to partial substitution of perchlorate with nicotinate (N-nicO) or isonicotinate(N-inicO) N-oxide anionic groups. These reactions led to the isolation of the following new metal complexes: Ni(N-inicOH) 3(ClO 4) 2·3H 2O: the only true adduct of the series, apparently polynuclear, with both unidentate terminal and bidentate bridging N-inicOH, bridging O 2ClO 2 ligands, ionic ClO 4 − and lattice water. Complexes with exclusively anionic ligands of the type ▪ (ClO 4) (MMn, Cu for LN-nicO; MCu for LN-inicO), with both terminal and bridging L, ionic and unidentate coordinated perchlorate, and aqua ligands. The rest of the complexes are of the mixed ligand type, i.e.: [H 2O) 2(O 3ClO)M(N-nic) 2M(N-nicOH)(OH 2) 2] (ClO 4) (MCo, Ni), with bridging N-nicO, terminal N-nicOH,-OClO 3 and aqua ligands, and ionic ClO 4 −; M 4(N-inicOH) (N-inicO) 5 (ClO 4) 3. 4H 2O (MMn, Co, Zn), polynuclear with exclusively bridging organic ligands, terminal aqua and bidentate perchlorato groups, and ionic ClO 4 −; and, Zn 4(N-nicOH)N-nicO) 5(ClO 4) 3. 10H 2O, probably tetrameric, with four bridging and one terminal N-nicO groups, and terminal N-nicOH, aqua and =O 2ClO 2 ligands, as well as ionic ClO 4 −. With the exception of the latter complex, which is hexacoordinated, the new metal complexes appear to be pentacoordinated. The likely structural types proposed for these compounds were based on the overall spectral and magnetic evidence obtained.