The hydrothermal reaction of the versatile ligand 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (Hmtpo), and cobalt/nickel acetate afforded two isostructural Co(II) and Ni(II) frameworks [M(mtpo)2(H2O)]n (M = Co (1Co) or Ni (2Ni)). Both of them consist of heterochiral helical meshes fused together into a non-interpenetrated lvt topological network containing only planar four-coordinate nodes. The frameworks can be rationalized to a rare 6-c crs net if the water-donated hydrogen-bonds are considered. Two isomorphous complexes exhibit spin-canted antiferromagnetism, with the critical temperature Tc of ca. 3.0 K for 1Co and 19 K for 2Ni. The additional magnetic measurements (after the removal of guest molecules), IR, TGA and XRPD of the complexes were also discussed.
