Two-dimensional transition-metal coordination polymers (2)(infinity)[MCl2(bpy)] (M = Fe, Co, Ni; Co/Ni, bpy = 4, 4'-bipyridine) have been synthesized in superheated water solutions. The hydrothermal routes resulted in four compounds (2)(infinity)[FeCl2(bpy)](I), (2)(infinity)[CoCl2(bpy)](II), (2)(infinity)[NiCl2(bpy)](III), and (2)(infinity)[(Co/Ni)Cl-2(bpy)](IV). Compounds I-IV are isostructural and belong to orthorhombic crystal system, spate group Cmmm (No. 65). Crystal data for I: a = 11.929(2) Angstrom, b = 11.447(2) Angstrom, c = 3.638(1) Angstrom, V = 496.77(18) Angstrom(3), Z = 2 Crystal data for II: a 11.993(2) Angstrom, b = 11.374(2) Angstrom, c = 3.611(1) Angstrom, V = 492.57(18) Angstrom(3), Z = 2. The structure is a noninterpenetrating two-dimensional network containing transition-metal centers octahedrally coordinated by four bridging chlorine and two bpy ligands at trans positions. The adjacent bpy ligands within a single layer are parallel to each other at a distance of 3.6 Angstrom. Spontaneous antiferromagnetic ordering was found in all compounds from the magnetic susceptibility chi(T) measurements under low fields. The transition temperatures are 10.0, 5.0, 8.5, and 7.5 K, for I, II, III, and IV, respectively. The mu(eff) values yielded from fitting the high temperature chi(T) indicate the high spin states of metal ions. In addition, a metamagnetic transition was observed in the field-dependent magnetization measurement for all four compounds. The magnetic properties observed in this system are attributed to the ferromagnetic intrachain M-M exchange interaction through the Cl-2 bridges along the c axis and the antiferromagnetic interchain interaction between the M ions. TGA studies indicate that all four compounds are thermally stable with an on-set temperature of weight loss greater than 400 degrees C.