## 3 Results and Discussion
### Characterization of Metal Complexes  
Physical properties of all the synthesized compounds are presented in Table 4. The synthesized metal complexes were prepared in good yield (65-87%), insoluble in ethanol, methanol, chloroform and other common organic solvents but easily soluble in DMSO and DMF. Metal complexes were characterized with mass, Fourier-transform infrared (FT-IR) and Ultraviolet-visible (UV-Visible) spectroscopies. Since the cobalt is paramagnetic in nature the \(\mathrm{\SIUnitSymbolMicro}\)\(\mathrm{n}\)-NMR technique was not performed. The molar conductance values of the complexes in DMSO (10\({}^{-3}\) M solutions) were calculated at room temperature using \(\Lambda_{\mathrm{m}}=\frac{\kappa}{2}\) equation; where C is the concentration of the solutions (mol/L) and \(\kappa\) is  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Compounds** & **Band Position (nm)** & **Assignment** \\ \hline \multirow{2}{*}{\(\mathbf{L_{1}}\)} & 260 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 350 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\ \hline \multirow{2}{*}{\(\mathbf{L_{2}}\)} & 300 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 390 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\ \hline \multirow{2}{*}{\(\mathbf{L_{3}}\)} & 310 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 290 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 320 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\ \hline \multirow{2}{*}{\(\mathbf{L_{5}}\)} & 290 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 370 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\ \hline \multirow{2}{*}{\(\mathbf{L_{6}}\)} & 340 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 310 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 350 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\  & 600 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{1}\) \\  & 690 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{2}\) \\ \hline \multirow{2}{*}{\(\mathbf{CoL_{2}}\)} & 280 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 410 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\  & 610 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{1}\) \\  & 680 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{2}\) \\ \hline \multirow{2}{*}{\(\mathbf{CoL_{3}}\)} & 280 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 370 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\  & 600 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{1}\) \\  & 680 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{2}\) \\ \hline \multirow{2}{*}{\(\mathbf{CoL_{4}}\)} & 290 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 350 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\  & 610 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{1}\) \\  & 690 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{2}\) \\ \hline \multirow{2}{*}{\(\mathbf{CoL_{5}}\)} & 260 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 310 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\  & 590 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{1}\) \\  & 660 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{2}\) \\ \hline \multirow{2}{*}{\(\mathbf{CoL_{6}}\)} & 270 & \(\pi\)\(\rightarrow\)\(\pi^{\star}\) \\  & 390 & \(\mathrm{n}\)\(\rightarrow\)\(\mathrm{p}^{\star}\) \\  & 605 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{1}\) \\  & 680 & \({}^{4}\)A\({}_{1}\)\(\rightarrow\)\({}^{4}\)B\({}_{2}\) \\ \hline \hlinethe measured conductivity. Measurements were performed to establish the charge of the complexes. The molar conductivity of the metal complexes lies in the range of 10-22 (\(\Omega^{-1}\) mol\({}^{-1}\) cm\({}^{2}\)), indicating that all the complexes were non-electrolytes. In metal complexes with NO\({}_{2}\) groups (**CoL\({}_{1}\)** and **CoL\({}_{4}\)**), the NO\({}_{2}\) group can coordinate to the metal center in various ways e.g., via the nitrogen (nitro), oxygen (nitrito), both oxygens (nitrito-\(O\),\(O^{\prime}\)) and via nitrogen and oxygen (bridging nitro) [25; 26; 27].