Linear Tetranickel String Complexes with Mixed Supported Ligands and Mixed‐Valence Units [Ni 2 ] 3+ : Synthesis, Crystal Structure, and Magnetic Studies

The synthesis, crystal structures, and magnetic properties of linear tetranickel string complexes supported by mixed 2‐(α‐pyridylamino)‐1,8‐naphthyridine (Hpyany) and N ‐( p ‐tolylsulfonyl)dipyridyldiamine (H 2 tsdpda) ligands are reported. In comparing the crystal structure of [Ni 4 (pyany) 2 (tsdpda) 2 Cl] ( 1 ) with that of [Ni 4 (pyany) 2 (tsdpda) 2 Cl(H 2 O)](PF 6 ) ( 2 ), the one‐electron‐reduced compound 1 displays shorter Ni(3)–Ni(4) (ca. 2.28 Å) and longer Ni(3)–N (ca. 2.02 Å) bond lengths. Similar trends have also been observed for axial NCS – ‐substituted derivatives [Ni 4 (pyany) 2 (tsdpda) 2 (NCS)] ( 3 ) and [Ni 4 (pyany) 2 (tsdpda) 2 (NCS) 2 ] ( 4 ). These structural variations indicate the formation of a mixed‐valence [Ni 2 ] 3+ unit and a three‐electron, two‐center Ni(4)–Ni(3) σ bond. Magnetic measurements of 2 and 4 show that both terminal Ni(1) and Ni(4) ions are in the high‐spin states ( S = 1) and are antiferromagnetically coupled. The one‐electron‐reduced complexes 1 and 3 , however, exhibit a delocalized mixed‐valence [Ni 2 ] 3+ unit ( S = 3 / 2 ), which is antiferromagnetically coupled with the terminal high‐spin Ni II ion.