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

Abstract The reaction in water of cobalt(II), nickel(II) or manganese(II) chloride with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na 4 P 2 O 7 ) at low pH (∼2) afforded three isostructural pyrophosphate complexes of an unprecedented one-dimensional typology, namely, {[M(phen)(H 2 O)(H 2 P 2 O 7 )]·H 2 O} 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 A 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 2 O 7 )}·6MeOH ( 1a ), {[Ni(phen) 2 ] 2 (H 2 O)(μ-P 2 O 7 )}·27H 2 O ( 2a ) and {[Mn(phen) 2 ] 2 (H 2 O)(μ-P 2 O 7 )}·13H 2 O ( 3a ), corresponding to ca . 4.9, 5.0 and 4.7 A, 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 .