Coordination compounds of benzotriazole and related ligands

The coordination chemistry of benzotriazole towards several transition metal compounds has been studied. Unpon reaction of neutral benzotriazole (BTAH) with metal compounds under varying conditions, both neutral (BTAH) ligands and anionic, deprotonated ligands (BTA−) may be coordinated to the metal. The compounds have the general formula M(BTAH)nXm, with M = Cu, Zn, Cd, Hg, Pd, Ti, Sn, n = 1, 2, 3, 4, X = Cl, Br and m = 2 or 4. Similar compounds of formula Cu(ligand)nX2 (X = Cl, Br; n = 1, 2) with 5-nitrobenzotriazole and N-methylbenzotriazole, were obtained. Compounds with anionic BTA have the formulae: Cu(BTA)Cl, Cu(BTA)1.5(BF4)0.5, Cu(BTA)2, Hg(BTA)2, Cu(phen)2(BTA)2, Hg(BTA)(CH3), Si(BTA)(CH3)3, Mn(BTA)(CO)5. In addition some mixed compounds were isolated, i.e. Cu2(BTA)2(BTAH)(NO3)2, Cu2(BTA)(BTAH)(SO4) and Ni(BTAH)(BTA)(BF4). Structures of the compounds have been proposed based on infrared and far-infrared spectroscopy, ligand field and UV spectroscopy, EPR spectroscopy, conductivity data and NMR spectroscopy. The most common mode of bonding for neutral, monodentate benzotriazole to metal ions seems to involve N(3) in BTAH (this is named N(1) in BTA). In the case of bidentate binding, it is not clear whether N(1)N(2) or N(1)N(3) bidentate bridging occurs. Spectral measurements are unable to distinguish between these modes. Tridentate binding of salt-like structures seems likely for Cu(BTA)2 and Hg(BTA)2, and might be present in a few other compounds such as Cu(BTA)Cl. Due to the insoluble nature of most of the compounds, polymeric structures using BTA and BTAH as bridging ligands seem to occur most frequently. Such structures are discussed in relation to the corrosion-inhibiting properties of benzotriazole.