The 2D coordination network (NH4)(2)[Ni-II(cyclam)](3)[Nb-IV(CN)(8)](2)center dot 21H(2)O (1.21H(2)O) was obtained on a cation-assisted synthetic pathway. The reaction between [Ni(cyclam)](2+) and [Nb(CN)(8)](4-) in the presence of excess of NH4Cl resulted in the formation of negatively charged coordination layers with the simultaneous incorporation of the NH4+ cations into the microporous channels of the structure. 1.21H(2)O network can be partly dehydrated in a single-crystal-to-single-crystal structural transformation to give (NH4)(2)[Ni-II(cyclam)](3)[Nb-IV(CN)(8)](2)center dot 14H(2)O (1.14H(2)O). The dehydration-induced structural changes, in particular the deformation of CN--bridges and the disruption of interlayer interactions, give rise to the solvatomagnetic effect. Fully hydrated 1.21H(2)O phase is a ferrimagnet with a critical temperature of magnetic ordering of 7.6 K and a narrow magnetization hysteresis loop, while 1.14H(2)O hydrate is an antiferromagnet with T-c = 7.2 K and metamagnetic transition at 6.3 kOe. Thanks to the presence of the NH4+ ions in the structure, the proton conductivity of similar to 4 X 10(-5) S cm(-1) (295 K, 100% relative humidity, RH) is observed with the activation energy of 0.80 eV.