Two compounds of [dmenH(2)(2+)][M-2(HCOO)(6)(2-)] (M = Mn-II and Co-II), synthesized using N,N'-dimethylethylenediammonium (dmenH(2) (2+)) as the template, possess anionic metal formate frameworks of a novel binodal 6-connected (4(12) center dot 6(3))(4(9) center dot 6(6)) topology. They are the first coordination examples of this unique network closely related to niccolite and colquiriite and exhibit 3D long-range antiferromagnetic ordering with small spin canting.