Two new coordination chain compounds based on octacyanoniobate-(IV) are reported: {[Mn-II(bpy)(H2O)(2)](2)[Nb-IV(CN)(8)]center dot 5H(2)O}(n) (1) and {[Mn-II(bpy)(H2O)(2)][Mn-II(bpy)(2)][Nb-IV(CN)(8)]center dot 5H(2)O}(n) (2) (bpy = 2,2'-bipyridine). Both have the topology of vertex-sharing CN-bridged squares. The Mn2Nb2 units are mutually parallel in 1 and perpendicular in 2. The antiferromagnetic intrachain interactions between the MnII and Nb-IV centers in 1 and 2, typical for Mn-II-[Nb-IV(CN)(8)] family of compounds, lead to ferrimagnetic ground state of each single chain. Both compounds show bulk ferrimagnetic ordering below their critical temperatures (T-c) of 6.4 K in 1 and 4.7 K in 2. Such a behavior is due to the ferromagnetic interchain interactions, assured by the pi-pi contacts between the 2,2'-bipyridine rings and by the hydrogen bonds between the terminal cyanide ligands of the [Nb-IV(CN)(8)]-building blocks and coordination/crystallization water molecules. 1 and 2 are rare examples of ferrimagnets promoted by interchain ferromagnetic exchange, and the T-c of 1 is one of the highest among similar 1-D coordination polymers.