Ferromagnetism in Cu II 4 and Co II 4 Complexes Derived from Metal‐Assisted Solvolysis of Di‐2,6‐(2‐pyridylcarbonyl)pyridine: Syntheses, Structures, and Magnetic Properties

Metal‐assisted solvolysis of di‐2,6‐(2‐pyridylcarbonyl)pyridine (pyCOpyCOpy, dpcp) by M(O 2 CMe) 2 · x H 2 O (M II = Cu II , Co II ) led to complex [Cu 4 {pyC(O) 2 pyC(O)(OEt)py}(O 2 CMe) 5 (EtOH) 2 ] ( 1 ), when the reaction was carried out in EtOH, and to complex [Co 4 {pyC(O)(OMe)pyC(O)(OMe)py} 2 (O 2 CMe) 2 (N 3 ) 2 ] ( 2 ), when the reaction was carried out in MeOH in the presence of azide anions. Complex 1 consists of four Cu II ions bridged by the hemiacetal‐ gem ‐diol form of the ligand, which is found in a μ 4 ‐η 2 :η 2 :η 2 :η 1 :η 1 :η 1 coordination mode. It exhibits ferromagnetic couplings among all nearest neighbors and antiferromagnetic next‐nearest‐neighbor interactions ( J 12 = J 1 = 48.0 cm –1 , J 23 = J 2 = 20.4 cm –1 , J 34 = J 3 = 16.9 cm –1 , J 24 = J 4 = –10.0 cm –1 , H = –2Σ J i J j spin Hamiltonian formalism), which stabilize an S = 1 ground state and an S = 2 state lying closely above it. Complex 2 consists of four Co II ions bridged by the bis(hemiacetal) form of the ligand, which is found in a μ 3 ‐η 2 :η 2 :η 1 :η 1 :η 1 coordination mode, and by μ 3 ‐azido ligands. It also exhibits ferromagnetic interactions due to the μ 3 –1,1,1 bridging mode of the azido ligands, which is known to promote ferromagnetic interactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)