SYNTHESIS AND MAGNETIC-PROPERTIES OF NOVEL MALEATO-BRIDGED CYCLIC TETRANUCLEAR MANGANESE(II) COMPLEXES - CRYSTAL-STRUCTURE OF )(2)(BIPY)(8)](CLO4)(4)CENTER-DOT(MEOH)(2)(H2O)(2)

Novel cyclic tetranuclear manganese complexes with maleate dianions as bridging ligand, of formula [Mn-4(mu-C4H2O4)(2)(bipy)(8)](ClO4)(4) .( MeOH)(2)(H2O)(2) (1) and [Mn-4(mu-C4H2O4)(2)(phen)(8)](ClO4)(4) . H2O (2), have been prepared and characterized by elemental analysis, IR sp ectra, X-ray analysis and magnetic measurements. The crystal structure determination of complex 1 reveals that the cation [Mn-4(mu-maleate)( 2)(bipy)(8)](4+) has a centre of symmetry and the four manganese atoms are bridged by two maleate dianions, forming an unusual 16-membered m acrocyclic structure. Each manganese atom is coordinated in cis fashio n by two oxygen atoms of bridging maleate ligands and then by four nit rogen atoms from terminal bipyridine ligands, leading to a distorted o ctahedral geometry. The variable-temperature magnetic properties have been investigated in the range 1.4-300 K. The results show that the ma gnetic susceptibilities obey the Curie law and no magnetic exchange in teraction occurs between the carboxylato-bridged Mn-II ions.