Tetra-MnIII-Containing 30-Tungsto-4-phosphate, [MnIII4(H2O)2(P2W15O56)2]12–: Synthesis, Structure, XPS, Magnetism, and Electrochemical Study

Reaction of the mixed-valent Mn 12 -acetato complex [Mn III 8 Mn IV 4 O 12 (CH 3 COO) 16 (H 2 O) 4 ] with the trilacunary Wells-Dawson-type heteropolytungstate [P 2 W 15 O 56 ] 12– in acidic acetate solution (pH 1.1) resulted in the tetra-Mn III -containing polyanion [Mn III 4 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 12– ( 1 ). Single-crystal XRD on Na 12 [Mn III 4 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ]·84H 2 O ( 1a ) revealed that four Mn III ions form a rhombic Mn 4 O 16 core encapsulated by two [P 2 W 15 O 56 ] 12– units. X-ray photoelectron spectroscopy (XPS) data confirm the +3 oxidation state of the four manganese ions in 1 . Magnetic measurements from 1.8−300 K in a 100 Oe magnetic field allowed for the extraction of full fitting parameters from the susceptibility data for 1 . The negative J a value ( J a = −2.16 ± 0.08 K, J b = 3.24 ± 1.73 K, g = 2.35 ± 0.040, and ρ = 0.34 ± 0.03) suggests a dominant antiferromagnetic spin exchange interaction between the four Mn III ions, with the positive J b being an accompanying result of J a . Electrochemical studies revealed a reversible Mn IV /Mn III redox couple in 1 at the +0.80 to +1.1 V potential region with E 1/2 = +0.907 V.