AbstractLanthanum complex (phenH)2[La(NO3)5(phen)]×CH3OH (1, phen = phenanthroline) was synthesized and characterized by single-crystal X-ray diffraction. The title compound crystallizes in the monoclinic system, space group P21/c with a = 20.3040(3), b = 10.7091(1), c = 19.0771(2) Å, b= 102.090(1)°, V = 4056.07(8) Å3, Z = 4, Dc= 1.676 g/cm3, m = 1.142 mm-1, F(000) = 2056, the final R= 0.0346 and wR= 0.0793 for 9981 (Rint = 0.0358) independent reflections.The mononuclear complex 1 consists of four parts: two phenH+ cations formed by the protonation of phen, one complex anion [La(NO3)5(phen)]2-, and one solvent methanol molecule. The complex anion contains one phen and five nitrate ligands which both chelate the center La(III) ion, adopting a distorted twelve-coordinated icosahedral geometry. The cations, anion and solvent molecule are linked together by hydrogen bonds. One of the protonated phenanthrolines (phenH+) acting as cation connects to the anion via N–H···O hydrogen bond directly, and the other one links to the anion through an intermediate solvent CH3OH via N–H···O and O–H···O hydrogen bonds. By the plentiful additional weak C–H···O intermolecular hydrogen bonds, the compound molecules construct a two-dimensional layer structure.