The interaction of the PTA (PTA = 1,3,5-triaza-7-phosphaadamantane) ruthenium complex trans-[RuCl2(PTA)(4)] (trans-1) with visible light in chloroform and in water has been studied at room temperature. The complex trans-1 isomerizes to the cis isomer in CHCl3 with radiation of lambda > 416 nm (Phi(434) (nm) (CHCl3) = 0.13 +/- 0.01). The isomerization reaction is reversible as cis-1 is transformed into trans-1 with lambda = 367 nm (Phi(367) (nm) (CHCl3) = 0.25 +/- 0.02). Irradiation at lambda > 416 nm of a solution of trans-1 in water leads to the cis-isomer complex and to the aqua complex (OC-6-32)-[RuCl(H2O)(PTA)(4)]Cl (2Cl) by a photoisomerization and photoaquation reaction (Phi(434 nm) (D2O) = 0.27 +/- 0.02). The mole ratio of cis-1 to 2Cl is not dependent on the pH but on the concentration of the products in solution. Isomerization in water is not reversible even if only cis-1 is present in solution. Synthesis and characterization of (OC-6-32)-[RuCl(H2O)(PTA)(4)](CF3SO3) (2CF(3)SO(3)) are also presented.