Reactions between the metal(II) salts [M(CH3CN)n](BF4)2 (M = Fe, n = 6; M = Mn, n = 4) and some organic anionic polynitriles were studied. With the pentacyanopropenide anion pcp− [pcp− = (NC)2CC(CN)C(CN)2−], were obtained, according to the experimental conditions, the new complexes [M(pcp)2(H2O)4] (1, M = Fe; 2, M = Mn) and [M(pcp)2] (3, M = Fe; 4 = Mn). Use of the hexacyano-3,4-diazahexadienediide anion [(NC)2CC(CN)NNC(CN)C(CN)22−] instead of pcp− did not afford polynitrile metal complexes but led to a new organic derivative 5, of formula C10N8H2. Crystallographic studies indicated that the isostructural compounds 1 and 2 involve discrete monomeric units with pcp ligands acting with a monodentate coordination mode and having the metal in a pseudooctahedral trans-MN2O4 environment; however, a rich hydrogen bond system gives rise to a 3D array. Complex 3, which presents metal in a pseudooctahedral MN6 environment, has a 3D structure arising from pcp ligands having an unprecedented μ3-coordination mode. Compound 5 is a bicyclic derivative with a pyrazolo[1,5-a]pyrimidine skeleton. In all derivatives, the organic part is essentially planar and involves a strongly delocalized π system. The magnetic properties of the inorganic complexes have been studied in the 2–300 K range. Fit of the magnetic data indicates high spin complexes with weak antiferromagnetic interactions in 2, 3 and 4 and the presence of a significant zero field splitting of the Fe(II) ion in 1.