Three complexes obtained by the reaction of Pr（Ⅲ） or Nd（Ⅲ） salts with 5-methyl-2-pyrazinecarboxylic acid（Hmpca） are structurally determined by single-crystal X-ray diffraction.Complex [Pr（mpca-）3（H2O）2]2·6H2O（1） is composed of dinuclear Pr（Ⅲ） units with two metal centers bridged by two anionic mpca-ligands in a κ^3O,O＇：O＇ bridging mode.Complexes [Pr（mpca-）3]n（2） and [Nd（mpca-）3]n（3） are isostructures,and they consist of polymeric chains based on Ln（Ⅲ） and mpca-ligands.Each pair of adjacent metal centers is linked by three mpca-molecules in a κ^3N,O：O bridging mode.
Two new transition metal compounds, [Mn（dpa）2（tmd）2]n （1, H2dpa = 4-hydroxy-phenyl-acetic acid, tmd = 4,4-trimethylenedipyridine） and [Co4（dpa）6（tmd）4（H2O）4]n·nH2O·nCl2 （2）, have been synthesized by hydrothermal synthesis. Compound 1 crystallizes in the monoclinic system, space group P21/n with a = 9.828（3）, b = 17.493（5）, c = 11.616（4）, β = 110.146（6）o, V = 1874.9（10）3, C42H42MnN4O6, Mr = 753.74, Z = 2, Dc = 1.335 g/cm3, μ = 0.406 mm-1, F（000） = 790, the final R = 0.1047 and wR = 0.2021 for 2698 observed reflections （I 〉 2σ（I））. Compound 2 crystallizes in the monoclinic system, space group P21/c with a = 11.7214（13）, b = 17.1582（19）, c = 24.625（3）, β = 103.055（3）o, V = 4824.4（9）3, C100H104Cl2Co4N8O23, Mr = 2094.55, Z = 2, Dc = 1.443 g/cm3, μ = 0.809 mm-1, F（000） = 2180, the final R = 0.0550 and wR = 0.0673 for 4104 observed reflections （I 〉 2σ（I））. These complexes were characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. The structural analyses show that the two compounds are both one-dimensional chain structures. However, compounds 1 and 2 form threedimensional supramolecular structures by hydrogen bonds, respectively.
