A novel, two-dimensional organic/inorganic coordinate polymers, Mn-2(H2O)[O2C(CH2)(4)CO2](2), was synthesized as single crystals by the hydrothermal reaction of MnCl2 with adipic acid in the presence of base and characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermal analysis, and SQUID magnetic measurement. It crystallized in the monoclinic space group C2/c(No. 15), with a = 21.671(2) Angstrom, b = 7.6023(7) Angstrom, c = 9.1452(9) Angstrom , beta = 108.849(7) Angstrom, Z = 4. The rifle compound presents a structure constituted by the stacking along [100] of MnO6 layers interleaved with adipate ions. The novel feature of the anionic layer is that it contains close-packed trans alkyl chains residing in an extended framework. Magnetization measurement shows this compound is antiferromagnetic below 15 K.