We report the monomeric complexes of magnesium and calcium of composition [M(THF)$_n${$\eta^2$-Ph₂P(Se)N(CMe₃)}₂] [M= Mg (3), n = 1 andM = Ca (4), n = 2)] and polymeric complexes of potassium and barium of composition [K(THF)₂{Ph₂P(Se)N(CMe₃)}]$_n$ (2) and [K(THF)Ba{Ph₂P(Se)N(CMe₃)}₃]$_n$(5) respectively. The potassium complex 2 was readily prepared by the reaction of potassium bis(trimethylsilyl)amide with phosphinoselenoic amide ligand (1) at ambient temperature. The calcium complex 4 was prepared by two synthetic routes: in the first method, commonly known as salt metathesis reaction, the potassium complex 2 was made to react with alkaline earth metal diiodide at room temperature to afford the corresponding calcium complex. The metal bis(trimethylsilyl)amides were made to react with protic ligand 1 in the second method to eliminate the volatile bis(trimethyl)silyl amine. The magnesium complex 3 and barium complex 5 were prepared only through the first method. Solid-state structures of all the new complexes were established by single crystal X-ray diffraction analysis. The smaller ionic radii of Mg²⁺ (0.72Å) and Ca²⁺ (0.99Å) ions form the monomeric complex, whereas the larger ions K⁺ (1.38Å) and Ba²⁺ (1.35Å) were found to form onedimensional polymeric complexes with monoanionic ligand 1. Compound 2 serves an example of magnesium complex with a Mg-Se direct bond.