Three new molecular compounds, [Ni5(bta)6(CO)4], I, [Ni9(bta)12(CO)6], II, [Ni9(bta)12(CO)6].2(C3H7NO), III, (bta = benzotriazole) were prepared employing solvothermal reactions. Of these, I have pentanuclear nickel, whereas II and III have nonanuclear nickel species. The structures are formed by the connectivity between the nickel and benzotriazole giving rise to the 5- and 9-membered nickel clusters. The structures are stabilised by extensive $\pi \ldots \pi$ and C-H$\ldots \pi$ interactions. Compound II and III are solvotamorphs as they have the same 9-membered nickel clusters and have different solvent molecules. To the best of our knowledge, the compounds I-III represent the first examples of the same transition element existing in two distinct coordination environment in this class of compounds. The studies reveal that compound I is reactive and could be an intermediate in the preparation of II and III. Thermal studies indicate that the compounds are stable upto 350°C and at higher temperatures (∼800°C) the compounds decompose into NiO.Magnetic studies reveal that II is anti-ferromagnetic.