Two new Mn(Ⅱ) coordination polymers, namely {[Mn₂(HL)(phen)₃(H₂O)₂]·7.5H₂O}_n (1) and [Mn₄(HL)₂(1, 4-bib)₃(H₂O)₂]_n (2), were synthesized under hydrothermal conditions by using Mn(Ⅱ) ions and 6-(3′, 4′-dicarboxylphenoxy)-1, 2, 4-benzenetricarboxylic acid (H₅L) in the presence of N-auxiliary ligands 1, 10-phenanthroline (phen) and 1, 4-bis(1H-imidazol-1-yl)benzene (1, 4-bib). The structures of coordination polymers 1 and 2 were characterized by infrared spectroscopy, single-crystal X-ray diffraction, thermogravimetric analysis, and powder X-ray diffraction. Single-crystal X-ray diffraction reveals that 1 has a 1D chain structure based on binuclear Mn(Ⅱ) units, while 2 features a (3, 8)-connected 3D network structure based on tetranuclear Mn(Ⅱ) units. Magnetic studies show that 1 and 2 exhibit antiferromagnetic interactions between manganese ions. 2 shows stronger antiferromagnetic interactions due to the shorter Mn…Mn distances within the tetranuclear manganese units.