Synthesis, Structural, Thermal and Magnetic Characterization of a Pyrophosphato‐Bridged Cobalt(II) Complex

The reaction in water of Co II sulfate heptahydrate with 1,10‐phenanthroline (phen) and sodium pyrophosphate (Na 4 P 2 O 7 ) in a 2:4:1 stoichiometric ratio resulted in the crystallization of a neutral dinuclear Co II complex, {[Co(phen) 2 ] 2 (μ‐P 2 O 7 )} · 6MeOH ( 1 ), as revealed by a single‐crystal X‐ray diffraction study. The bridging pyrophosphato ligand between the two [Co(phen) 2 ] 2+ units in a bis(bidentate) coordination mode places the adjacent metal centers at 4.857 Å distance, and its conformation gives rise to intramolecular π–π stacking interaction between adjacent phen ligands. Indeed, intermolecular π–π stacking interactions between phen ligands from adjacent dinuclear complexes create a supramolecular 2D network in 1 . Magnetic susceptibility measurements on a polycrystalline sample of 1 in the temperature range 1.9–295 K are typical of an overall antiferromagnetic coupling with a maximum of the magnetic susceptibility at 3.0 K. The analysis of the magnetic data in the whole temperature range allows the determination of the value of the intramolecular magnetic coupling ( J = –1.23 cm –1 ). The ability of the pyrophosphato ligand to mediate magnetic interactions between different first‐row transition‐metal ions when adopting the bis(bidentate) bridging mode is analyzed and discussed in the light of the small number of magneto‐structural reports on this type of compound, bearing in mind the number of unpaired electrons and type of magnetic orbitals on each metal center. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)