New trimethylhydrometallatranes, tris(2-hydroxypropyl)amine complexes with Ni^II, Zn^II, Cu^II, and Co^II salts of biologically active carboxylic acids (benzoic, cinnamic, salicylic, succinic), were synthesized. The structure of the tris(2-hydroxypropyl)amine complex with nickel(II) cinnamate was determined by single-crystal X-ray diff raction. Thermal stability of the synthesized tris(2-hydroxypropyl)amine complexes was compared with that of tris(2-hydroxyethyl)- amine complexes.