The complexes [H3O+.18-crown-6][W(CO)(5)Cl], (2) [H3O+.18-crown-6][W(CO)(4)Cl-3], (3) and [H2O.bis-aza-18-crown-6.(H+)(2)][W(CO)(4)Cl-3](2), (4) were synthesized from a mixture of W(CO)(6), HCl(g), H2O and either 18-crown-6 for 2 and 3 or bis-aza-18-crown-6 for 4, in toluene. Reaction conditions for [K+.18-crown-6][Cr(CO)(5)Cl], (1) were similar except that Cr(CO)(6) and KCl were used in place of W(CO)(6) and H2O, respectively. These reactions were promoted with the use of UV radiation and liquid clathrates were formed almost immediately upon reaction. X-ray crystal structures were deduced for each compound. Complex 1 crystallizes in the orthorhombic space group Pbnm with a = 7.432(1), b = 16.521(3), c = 19.508(2) Angstrom, and D-c = 1.48 g cm(-3) for Z = 4. Refinement based on 1277 observed reflections led to a final R value of 0.078. Complex 2 crystallizes in the rhombohedral space group R (3) over bar with a = 13.458(1), c = 10.769(1) Angstrom, and D-c = 1.77 g cm(-3) for Z = 3. Refinement based on 715 observed reflections led to a final R value of 0.014. Complex 3 crystallizes in the monoclinic space group C2/c with a = 22.411(2), b = 11.018(1), c = 16.340(2) Angstrom, beta = 114.34(1)degrees, and D-c = 1.24 g cm(-3) for Z = 4. Refinement based on 1966 observed reflections led to a final R value of 0.068. Complex 4 crystallizes in the triclinic space group P (1) over bar with a = 11.761(1), b = 12.096(1), c = 14.966(1) Angstrom, alpha = 107.88(1), beta = 91.19(1), gamma = 117.44(1)degrees, and D-c = 2.03 g cm(-3) for Z = 2. Refinement based on 3065 observed reflections led to a final R value of 0.054.