Schiff Base Heterometallic Complexes and Their Potential Applications

A Schiff base ligand, H₂L, with two distinct compartments to accommodate a transition and an alkaline earth metal ion was used to synthesize two monometallic, [CuL-(H₂O)-(CH₃OH)] (<b>1</b>) and [NiL-(H₂O)] (<b>2</b>), and six heterometallic complexes, [CuCaL-(NO₃)₂] (<b>3</b>), [CuSrL-(NO₃)₂] (<b>4</b>), [CuBaL-(NO₃)₂]-(H₂O) (<b>5</b>), [NiCaL-(NO₃)₂] (<b>6</b>), [NiSrL-(NO₃)₂] (<b>7</b>), and [NiBaL-(NO₃)₂] (<b>8</b>), which were characterized by single crystal X-ray diffraction. Their potential as single-source precursors (SSPs) and their antibacterial properties were investigated. After annealing at 1000 °C in air for 1 h, the complexes (<b>3</b>), (<b>4</b>), (<b>7</b>), and (<b>8</b>) formed the following mixed metal oxides (MMOs): Ca₂CuO₃ for (<b>3</b>), CuSrO₂ and CuSr₂O₃ for (<b>4</b>), Ni_6.64Sr₉O₂₁ and Ni₂Sr₄O₉ for (<b>7</b>), and Ni₅Ba₆O₁₅ for (<b>8</b>). The mixture of two heterobimetallic complexes (<b>3</b>) and (<b>4</b>), (<b>3</b>) and (<b>7</b>), and (<b>4</b>) and (<b>6</b>) allowed the formation of MMOs containing three different metal ions, such as CuCa_1.50Sr_0.50O₃, CuCa_0.38Sr_0.62O₂, and CaCuSrO₃. The scanning electron microscopy (SEM) study revealed a sponge-like structure for all the obtained MMOs. The six heterobimetallic complexes showed good solubility in MeOH, DMF, and DMSO. With regard to the antibacterial properties, the protonated ligand and monometallic complex of copper-(II) showed a zone of inhibition (ZOI) that was twice the size of the tested heterobimetallic complexes.