Reaction of nitrated Ho_2O_3 with 1,10-phenanthroline in CH_3OH/H_2O results in a novel hydroxo bridged dinuclear Ho(III) complex [Ho_2(phen)_4(H_2O)_4(OH)_2] (phen)_2(NO_3)_4. Single crystal X-ray diffraction study shows that the title compound crystallizes in the triclinic space group P 1-bar (no. 2) with the cell dimensions; a = 1.1241(1) nm, b = 1.1439(1) nm, c = 1.4058 (1) nm, α = 93.989(7)°, β = 98.173(7)°, γ = 108.19(1)°, V = 1.6874(4) nm~3, Z = 1, D_c = 1. 737 g/cm~3, F(000) = 880, R_1 = 0.0499, wR_2 = 0.0858 for 5702 observed reflections [F_o~2 ≥ 2σ (F_o~2)] out of 7752 unique reflections. The compound consists of the centrosymmetric dinuclear [Ho_2(phen)_4(H_2O) _4(OH)_2]~(4+ complex cations, uncoordinated phen molecules and nitrate anions. The holmium atom coordinates to two phen ligands, two H_2O molecules and two hydroxo groups to form a [HoN_4O_4] square antiprism. An edge-shared bi-square-antiprism forms via the two bridging OH groups [d(Ho-N) = 0.2549～0.2565 nm, d(Ho-O_(H_2O) = 0.2356, 0.2366 nm, d(Ho-O_(OH)) = 0.2223, 0.2240 nm]. The complex cations and the uncoordinating phen molecules are assembled via hydrogen bonding and π -π stacking interactions into 2D layers parallel to (10 1-bar), between which the nitrate anions are sandwiched. The title compound behaves paramagnetically and obeys Curie-Weiss law X_m (T + 4.43) = 14. 72 cm~3·K·mol~(-1) between 5～300 K (X_m: magnetic susceptibility per mole Ho~(3+) ions). The effective magnetic moment at room temperature is 10.76 B. M., which is equal to the expected value for a free Ho~(3+) ion, suggesting no magnetic exchange within the dinuclear dinuclear cations.

Key words: HOLMIUM COMPLEX, DINUCLEAR COMPLEX, CRYSTAL STRUCTURE, MAGNETISM, PHENANTHROLINE P