We report the monomeric complexes of magnesium and calcium of composition [M(THF)n{η 2-Ph2P(Se)N(CMe3)}2] [M = Mg (3), n = 1 and M = 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 1in the second method to eliminate the volatile bis(trimethyl)silyl amine. The magnesium complex 3and 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+ (0.72 Å) and Ca2+ (0.99 Å) ions form the monomeric complex, whereas the larger ions K+ (1.38 Å) and Ba2+ (1.35 Å) were found to form one-dimensional polymeric complexes with monoanionic ligand 1. Compound 2 serves an example of magnesium complex with a Mg-Se direct bond. © 2014 Indian Academy of Sciences.