A single-chain magnet (SCM) of [Mn(TBPP)(TCNE)]center dot 4m-PhCl2 (1), where TBPP2- = meso-tetra(4-biphenyl)porphyrinate; TCNE center dot- = tetracyanoethenide radical anion; m-PhCl2 = meta-dichlorobenzene, was prepared via suppression of interchain interactions. I has a one-dimensional alternating Mn-III(porphrin)-TCNE center dot- chain structure similar to those of a family of complexes reported by Miller and co-workers. From a comparison of the static magnetic properties of 1 with other Mn-III(porphyrin)-TCNE center dot- chains, a magneto-structural correlation between the intrachain magnetic exchange and both the dihedral angle between the mean plane on [Mn(TBPP)(TCNE)] and Mn-N equivalent to C was observed. The ac magnetic susceptibility data of 1 could be fit with the Arrhenius law, indicating that slow magnetic relaxation and ruling out three-dimensional long-range ordering and spin-glass-like behavior. The Cole-Cole plot for 1 was semicircular, verifying that it is an SCM. Therefore, 1 is an ideal single-chain magnet with significantly strong intrachain magnetic exchange interactions beyond the Ising limit.