The compounds [K(18-crown-6)](3)[Ir(Se-4)3] (1), [K(2.2.2-cryptand)](3)[Ir(Se-4)(3)]. C6H5CH3 (2), and [K(18-crown-6)(DMF)(2)] [Ir(NCCH3)(2)(Se-4)(2)] (3) (DMF = dimethylformamide) have been prepared from the reaction of [Ir(NCCH3)(2)(COE)(2)][BF4] (COE = cyclooctene) with polyselenide anions in acetonitrile/DMF. Analogous reactions utilizing [Rh(NCCH3)(2)(COE)(2)][BF4] as a Rh source produce homologues of the Ir complexes; these have been characterized by Se-77 NMR spectroscopy. [NH4](3)[Ir(S-6)(3)]. H2O . 0.5CH(3)CH(2)OH (4) has been synthesized from the reaction of IrCl3 . nH(2)O with aqueous (NH4)(2)Sm. In the structure of [K(18-crown-6)](3)[Ir(Se-4)(3)] (1) the Ir(III) center is chelated by three Se-4(2-) Ligands to form a distorted octahedral anion. The structure contains a disordered racemate of the Delta lambda lambda and Lambda lambda lambda conformers. The K+ cations are pulled out of the planes of the crowns and interact with Se atoms of the [Ir(S-4)(3)](3-) anion. [K(2.2.2-cryptand)](3)[Ir(Se-4)(3)]. C6H5CH3 (2) possesses no short K...Se interactions; here the [Ir(Se-4)(3)](3-) anion crystallizes as the Delta lambda delta/Lambda delta lambda racemate. In the crystal structure of [K(18-crown-6)(DMF)(2)][Ir(NCCH3)(2)(Se-4)(2)] (3), the K+ cation is coordinated by an 18-crown-6 ligand and two DMF molecules and the anion comprises an octahedral Ir(III) center bound by two chelating Se-4(2-) chains and two trans acetonitrile groups. The [Ir(Se-4)(3)](3-) and [Rh(Se-4)(3)](3-) anions undergo conformational transformations as a function of temperature, as observed by Se-77 MMR spectroscopy. The thermodynamics of these transformations are : [Ir(Se-4)(3)](3-), Delta H = 2.5(5) kcal mol(-1), Delta S = 11.5(2.2) eu; [Rh(Se-4)(3)](3-), Delta H = 5.2(7) kcal mol(-1), Delta S = 24.7(3.0) eu.