SYNTHESIS, STRUCTURE AND MAGNETIC-PROPERTIES OF THE FIRST 2-DIMENSIONAL INFINITE SHEET-LIKE MIXED-VALENCE MANGANESE(II,III) COMPLEX WITH BRIDGING SALICYLATE AND PYRIDINE-2-CARBOXYLATE LIGANDS

A two-dimensional infinite sheet-like mixed-valence manganese (II,III) complex [{Na2Mn4(sal)(4)(pyca)(4)-(MeOH)(2)}(n)]. 2nH(2)O (H(2)sal = salicyclic acid and Hpyca = pyridine-2-carboxylic acid) has been prepa red and characterized by X-ray crystallography and magnetic measuremen ts. The structure consists of a [Mn-4(sal)(4)(pyca)(4)(MeOH)(2)](2n-)( n) anion, 2nNa(+) cations and 2n non-coordinated H2O. In every [Mn-4(s al)(4)(pyca)(4)(MeOH)(2)](2-) unit there are two six-co-ordinate M(III ) [Mn(1) and Mn(2)] located at symmetry centres, and two six-co-ordina te Mn-II [Mn(3) and Mn(3')]. Atoms Mn(1) and Mn(3) [or Mn(2) and Mn(3) ] are connected by a salicylate (pyridine carboxylate) carboxylate in a syn-anti configuration, while Mn(3) and Mn(3') are bridged by two ox ygen atoms of two pyridine carboxylates. The Na+ cation is six-co-ordi nated, having contacts with six oxygens of carboxylate groups of Mn(1) , Mn(2) and Mn(3) polyhedral units. The magnetic behaviour of the comp lex in the temperature range 1.4-300 K has been interpreted in terms o f a dimer unit [Mn-2(II)(pyca)(2)] and two manganese(III) polyhedral u nits assuming the Mn-III to obey a Curie-Weiss law, and the values obt ained for J, g and theta were -0.98 cm(-1), 2.00 and -5.66 K(-3.93 cm( -1)), respectively.