By employing hydrothermal method, six transition metal sulfates containing hydrazine (N2H4) have been obtained: [M(SO4)(2)(N2H5)(2)](n)(M = Mn(1), Co(2), Ni(3)) and [M(N2H4)SO4](n) (M = Mn(4), Co(5), Ni(6)). Their crystal structures and magnetic properties have been investigated experimentally and theoretically. Compounds 1-3 consist of one-dimensional sulfate bridged homometallic chains with protonated hydrazine molecule as terminal ligand, and compounds 4-6 are hydrazing-sulfate mixed bridged homometallic three-dimensional frameworks. Compounds 1-6 exhibit antiferromagnetic coupling between M2+ ions, but their magnetic properties differ at low temperatures because cri the different single-ion anisotropy and crystal structures. The magnetostructural correlations and the magnetic coupling mechanism are analyzed by density functional theory calculations (DFT).