Impacts of Alkali Metals on the Structures and Properties of Fe(III) Heterometallic Cyclobutane-1,1-dicarboxylate Complexes

Threenew Fe-III-M-I (M-I =Na, Rb, Cs) heterometallic two-dimensional (2D)-polymeric complexeswith cyclobutane-1,1-dicarboxylic acid anions were obtained. It wasshown that the configuration of the bischelate moieties influencesthe sign of the magnetic anisotropy. Three Fe-III-M-I heterometallic complexeswithanions of cyclobutane-1,1-dicarboxylic acid (H(2)cbdc) dianions[(MFe)-Fe-I(cbdc)(2)(H2O)(2)]( n ) (M-I = Na (1), Rb(2) or Cs (3)) were obtained, with the compoundsbeing two-dimensional (2D)-coordination polymers built of bischelatemoieties {Fe(cbdc)(2)(H2O)(2)}(-) bound with alkali metal ions. In 1, the two coordinatedwater molecules are in the cis-position, while in 2 and 3 they are in the trans-position. The DC magnetic data and ab initio calculations demonstrate that Fe3+ ionsin 1 possess a negative D value, whilethose in 2 and 3 have a positive D value. The easy-axis anisotropy found for 1 is a rare example for Fe3+ ions. A topological analysisof the compounds synthesized and a series of known mononuclear octahedrallycoordinated Fe3+ complexes (from Cambridge Structural Database)that are interconnected into a crystal structure by alkali metal cationsin a way similar to complexes 1-3 was carried out.