Synthesis, structural, thermal, and magnetic investigations of Co(II), Ni(II), and Mn(II) pyrophosphate chains

The reaction in water of cobalt(II), nickel(II) or manganese(II) chloride with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na 4P 2O 7) at low pH (∼2) afforded three isostructural pyrophosphate complexes of an unprecedented one-dimensional typology, namely, [M(phen)(H 2O)(H 2P 2O 7)] ·H 2O n with M = Co(1), Ni(2) and Mn(3). The di-hydrogen-pyrophosphate anion featured in these complexes adopts a rare bidentate/monodentate bridging mode leading to chain propagation. This unusual bridging pathway produces a metal-metal intra-chain separation of about 6.6-6.7 Å for 1-3, values much larger than the metal-metal distance across the classic bis-bidentate PPi in the parent homodinuclear complexes [Co(phen) 2] 2(μ-P 2O 7)·6MeOH (1a), [Ni(phen) 2] 2(H 2O)(μ-P 2O 7)·27H 2O (2a) and [Mn(phen) 2] 2(H 2O)(μ-P 2O 7)·13H 2O (3a), corresponding to ca. 4.9, 5.0 and 4.7 Å, respectively. Variable-temperature magnetic susceptibility measurements on polycrystalline samples of 1-3 revealed weak intrachain antiferromagnetic couplings [J = -0.93 (1), -1.88 (2) and -0.26 cm -1 (3)], consistent with previous data on the dinuclear complexes 1a-3a. © 2012 Elsevier B.V. All rights reserved.