Polyoxometalate-Assisted Assembly of Pearl-Chain-Like Cyanide-Bridged Single-Chain Magnets.

The introduction of Keggin-type POMs of [PMo 12 O 40 ] 3- or [SiW 12 O 40 ] 4- as counteranions into the Fe III -M II cyanometalate system afforded three chain complexes: [(Tp*)Fe(CN) 3 Ni(DMF) 4 ] 2 {[(Tp*)Fe(CN) 3 Ni(DMF) 3 (H 2 O)] 2 Ni(DMF) 4 }[PMo 12 O 40 ] 2 ·14DMF ( 1 , Tp*= hydridotris(3,5-dimethylpyrazol-1-yl)borate) and {[(Tp*)Fe(CN) 3 M(DMF) 3 (H 2 O)] 2 M(DMF) 4 }[SiW 12 O 40 ]·3DMF ( 2 , M = Ni II ; 3 , M = Co II ). Complex 1 contains both discrete cationic [Fe 2 Ni 2 ] 2+ squares and less-studied {Fe 2 Ni 3 } n pearl chains, namely 3,2-chains, while 2 and 3 consist of pure 3,2-chains due to the replacement of [PMo 12 O 40 ] 3- with [SiW 12 O 40 ] 4- bearing one more negative charge. Magnetic studies revealed that all of the complexes exhibit single-chain-magnet (SCM) behaviors with the effective thermal barriers of Δ τ1 / k B = 61.6 K (infinite regime) and Δ τ2 / k B = 36.5 K (finite regime) for 1 , Δ τ / k B = 46.9 K for 2 (finite), and Δ τ / k B = 30.6 K for 3 (finite). The POM moieties may play a pivotal role for the realization of this promising archetype of favoring SCM property: (1) the highly negatively charged POMs may facilitate the formation of the uncommon highly positive "pearl chain"; (2) the nanosized POMs necessarily led to the good isolation of the chains in the title complexes, and (3) the employment of POMs with different charges may regulate the resultant complexes in both structure and magnetism.