Structural and magnetic studies of two-dimensional solvent-free manganeseII complexes prepared via ligand exchange...

Systematic investigation of the ligand exchange reactions between manganese(II) acetate and benzoic acid under solvothermal conditions led to the isolation of crystalline complexes {Mn5(OC(O)CH3)6(OC(O)C6H5)4}(infinity) ( 1) and {Mn5(OC(O)CH3)4(OC(O)C6H5)6}}(infinity) ( 2) in high (i.e., >90%) yields. The complexes are characterized structurally as 2-D honeycomb-like sheets comprised of edge-shared Mn 12 loops with some noteworthy differences as follows. First, buckling of the 2-D sheet in 1 is not observed for 2, presumably as a consequence of additional intersheet phenyl groups in the latter. Second, complex 1 is comprised of only six-coordinate MnII, while 2 has both pseudo-octahedral and distorted trigonal bipyramidal coordinate metal ions. Third, while complex 2 exhibits pi-stacking interactions with intersheet phenyl-phenyl contacts of 3.285 and 3.369 A, 1 exhibits no such bonding. Antiferromagnetic exchange is observed with Weiss constants (theta) of -28 and -56 K and Neel temperatures of 2.2 and 8.2 K for complexes 1 and 2, respectively. The paramagnetic transition at higher temperatures for complex 2 may be attributed to pi-pi exchange through phenyl groups in adjacent layers. Preliminary gas sorption studies (76 K) indidate preferential adsorption of H2 versus N2 for complex 1 only.