A block single-crystal was obtained using a diffusion method with a concentrated acetone-water(vol. 1/1) solution of [Ru(phen)(3)]Cl-2. 6H(2)O (phen = 1,10-phenanthroline) and a concentrated aqueous solution of K-3[Cr(CN)(6)], without evaporating solvents. The crystal was identified as a double-complex salt including two acetone and fourteen solvent water molecules, [Ru(phen)(3)](2)[Cr(CN)(6)]Cl .2(CH3)(2)CO . 14H(2)O (1). Measurement of the X-ray diffraction pattern of the double-complex salt was performed using an X-ray diffractometer with an Imaging-Flare (IP) Weissenberg camera. 1 crystallizes in the triclinic space group P (1) over bar, with a = 13.930(5) Angstrom, b = 14.783(5) Angstrom, c = 11.137(6) Angstrom, alpha = 89.87(4)degrees, beta = 107.47(3)degrees gamma = 96.68(3)degrees, and Z = 2. The crystal structure is very different from that of [Ru(bpy)(3)](2)[Cr(CN)(6)]Cl . 8H(2)O (2) (bpy = 2,2 ' -bipyridine), which could be obtained using the same procedure and crystallizes in the monoclinic space group C2, with a = 22.414(2) Angstrom, b = 13.7686(15) Angstrom, c = 22.207(2) Angstrom, beta = 90.713(8)degrees, and Z = 4. The distance between the central-metal ions of ruthenium(II) and chromium(III) complexes in [Ru(phen)(3)](2)[Cr(CN)(6)]Cl .2(CH3)(2)CO . 14H(2)O (7.170 Angstrom) is shorter than that in [Ru(bPY)(3)](2)[Cr(CN)(6)]Cl . 8H(2)O (9.173 Angstrom) by about 2 Angstrom, while the rate of energy transfer from the (MLCT)-M-3 state of [Ru(N-N)(3)](2+) to the E-2(g) state of [Cr(CN)(6)](3-) in the former salt (9.5 x 10(5) s(-1)) is far slower than that in the latter one (6.0 x 10(6) s(-1)) at 77 K. These results indicate that the energy-transfer rate strongly depends, not upon the distance between central metal ions, rather, upon the mutual relative orientation between the donor and the acceptor complexes in double-complex salts.