Diverse alkali metal thioselenophosphinates, M[SeSPR2] (M = Li, Na, K, Rb, and Cs; R = alkyl, aryl, aralkyl, and hetaralkyl), have been synthesized in 78–94 % yields by means of a one-pot multicomponent reaction between secondary phosphanes, sulfur, selenium, and alkali metal hydroxides under mild conditions (room temperature, –50 °C, 0.5 h, EtOH). The molecular and electronic structure of the [SeSPPh2]– anion and its coordination behavior towards Li+, Na+, and K+ cations have been investigated at the B3LYP level of theory. The alkylation of the alkali metal thioselenophosphinates with various organic halides proceeds regiosecifically at the selenium center to form Se–organyl thioselenophosphinates, R2P(S)SeR′ (R′ = Me, Et, Bn, allyl, propargyl), in 78–96 % yields. By the action of molecular iodine, the alkali metal thioselenophosphinates instantly (room temperature, ca. 1 s, 1,4-dioxane) undergo selective Se–Se oxidative coupling to afford the corresponding diselenides, R2P(S)SeSe(S)PR2, in 81–92 % yields. The alkali metal thioselenophosphinates are readily converted into the corresponding ammonium derivatives. Square-planar NiII complexes, Ni[SeSPR2]2 (R = Ph, CH2CH2Ph), have been prepared in 68–81 % yield by the treatment of sodium thioselenophosphinates, Na[SeSPR2], with NiBr2 at room temperature (EtOH/CH2Cl2, 10 min).