Several mononuclear N-4-macrocyclic Rh(III) hydrides were prepared and characterized in the solid state and in solution. H-1 NMR, IR, and UV data are reported. The complex {trans-(Cl)([14]aneN(4))RhH}(2)(ZnCl4) . dmso (1 . dmso) crystallizes in the triclinic system, space group P (1) over bar, in a unit cell of dimensions a = 10.680(3) Angstrom, b = 13.360(3) Angstrom, c = 14.277(4) Angstrom, alpha = 86.49(2)degrees, beta = 83.18(2)degrees, gamma = 66.64(2)degrees. The data refined to a final value of R = 0.070 and R(w), = 0.13 based on 2687 observed reflections. UV photolysis of chloride-free (H2O)L(1)RhH(2+) results in homolytic Rh-H bond cleavage. The rhodium(II) product, L(1)Rh(H2O)(2+), was characterized by ESR and UV spectroscopies. This species survives in acidic aqueous solution for over half an hour at room temperature. The photolysis of (H2O)L(1)RhH(2+) in the presence of O-2 produces the superoxorhodium(III) ion, trans-L(1)RhOO(2+).