Synthesis and characterization of a family of tetranuclear manganese(III) phosphonate complexes

Four tetranuclear manganese(III) complexes containing phosphonate ligands (RPO32-, R = Me, Et and n-Bu), [ Mn4O2(MePO3)(2)(O2CMe)(4)(bpy)(2)]center dot 4MeCOOH (1), [Mn4O2(EtPO3)(2)(O2CMe)(4)(bpy)(2)]center dot 7H(2)O (2), [Mn4O2(n-BuPO3)(2)(O2CMe)(4)(bpy)(2)]center dot 4H(2)O center dot(COOH)(2) ( 3) and [Mn4O2(MePO3)(2)(O2CPh)(4)(phen)(2)]center dot 4PhCOOH center dot 2MeCN (4), have been synthesized and characterized by IR spectroscopy, ESI-MS spectrometry, electrochemical analysis, magnetic measurements and TGA. The X-ray analysis shows that the four complexes all have one [Mn-4(mu(3)-O)(2)](8+) core with four coplanar Mn atoms disposed in an extended "butterfly-like'' arrangement and two O atoms triply bridging each "wing'', and the peripheral ligation is provided by four mu(2)-MeCO2- or four mu(2)-PhCO2-, two terminal bpy or phen (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline) groups at both ends of the molecule, and two bicapping mu(3)-phosphonate ligands, which each binds to three manganese centers above and below the plane. The cyclic voltammetry of 1 and 3 each displays four reduction and one oxidation processes, of which the four reduction processes are possibly attributed to the reduction of four Mn-III of the compounds to Mn-II. The ESI-MS data indicate that the family of complexes are stable in solution. Magnetic susceptibility measurements reveal that compounds 1 and 3 display antiferromagnetic interactions between the adjacent Mn-III ions mediated through the mu(3)-O, O-C-O and O-P-O bridges.