Hydrothermal reaction of 1,2,4-benzenetricarboxylic acid, and MnCl24H2O with 1,10-phenanthroline gave the title complex, [Mn(phen)(m-phth)]n, which crystallizes in the monoclinic system, space group P2/c with a=0.83582(3) nm, b=1.04246(4) nm, c=1.87777(7) nm, =100.314(2), V=1.60968(10) nm3, Z=4, and the final R=0.0576, wR=0.1294. In the complex, each Mn(II) ion is coordinated to four O atoms of carboxylate groups and two N atoms of phen. Isophthalate was generated in situ through the loss of one carboxylate group of 1,2,4-benzenetricarboxylic acid under the hydrothermal condition. Each isophthalate is bound to three manganese atoms through O atoms of carboxylate in bridging and chelating fashion, affording manganese(II) pairs that are linked by the isophthalate group to yield a zig-zag chain along the c-axis. Hydrothermal reaction of 1,2,4-benzenetricarboxylic acid, and MnCl24H2O with 1,10-phenanthroline gave the title complex, [Mn (phen) (m-phth)] n, which crystallizes in the monoclinic system, space group P2 / c with a = 0.83582 (3) nm, b = 1.04246 (4) nm, c = 1.87777 (7) nm, = 100.314 (2), V = 1.60968 (10) nm3, wR = 0.1294. In the complex, each Mn (II) ion is coordinated to four O atoms of carboxylate groups and two N atoms of phen. Isophthalate was generated in situ through the loss of one carboxylate group of 1,2,4-benzenetricarboxylic acid Each isophthalate is bound to three manganese atoms through O atoms of carboxylate in bridging and chelating fashion, affording manganese (II) pairs that are linked by the isophthalate group to yield a zig-zag chain along the c-axis .