The low spin Co(II) fragment with homoleptic 1,10-phenanthroline ligands: synthesis, structures, DFT investigations, and magnetic properties

Two complexes {Co(II)(phen)(3)]Co(III)(phen)(CN)(4)](2)}·phen·11H(2)O (1) and Co(II)(μ-CN)(2)(Co(III))(2)(phen)(4)(CN)(6)]·C(2)H(5)OH·2H(2)O (2) were synthesized with identical starting materials but with a different order of addition. Their crystal structures, spectroscopic analysis, DFT calculations, and investigations of their magnetic properties are reported herein. The X-ray diffraction studies reveal that complex 1 mainly consists of discrete Co(II)(phen)(3)](2+) cations and Co(III)(phen)(CN)(4)](-) anions, while complex 2 is dominantly comprised of discrete neutral V-shaped trinuclear units Co(II)(μ-CN)(2)(Co(III))(2)(phen)(4)(CN)(6)]. The first low-spin Co(II) fragment with homoleptic 1,10-phenanthroline ligands in 1 is observed at room temperature, owing to charge transfer from the neighboring anion via adventitious contacts and anion-π interactions. This is verified by structures, detailed theoretical analyses concerning frontier molecular orbital energy differences and Mulliken charge variations of the N atoms within the Co(II)N(6) sphere, and magnetism. Meanwhile, these kinds of supramolecular interactions are not found in complex 2, so it shows the ordinary magnetic behavior of the high-spin Co(II) ion. Our investigations highlight that for quantitative comprehension of spin-state energetic ordering in transition metal complexes, the supramolecular interactions must be taken into account in addition to classical ligand field theory. Moreover, we find that the Co(II)(phen)(3)](2+) dication is sensitive to its surroundings in the solid state, which is beneficial for magnetic adjustment for the further synthesis of tunable molecular magnets and spin crossover systems.