Linking chiral clusters with molybdate building blocks:: From homochiral helical supramolecular arrays to coordination helices

The synthesis of four new oxo-centered Fe clusters (1a-c, 2) of the form [Fe-3(III)(mu(3)-O)(CH2=CHCOO)(6)] with acrylate as the bridging ligand gives rise to potentially intrinsically chiral oxo-centered {M-3} trimers that show a tendency to spontaneously resolve upon crystallization. For instance, 1a, [Fe-3(III)(mu(3)-O)(CH2=CHCOO)(6)(H2O)(3)](+), crystallizes in the chiral space group P3(1) as a chloride salt. Crystallization of 1b, [Fe-3(mu(3)-O)-(C2H3CO2)(6)(H2O)(3)]NO3 center dot 4.5H(2)O, from aqueous solution followed by recrystallization from acetonitrile also gives rise to spontaneous resolution to yield the homochiral salt [Fe-3(mu(3)-O)(C2H3CO2)(6)(H2O)(3)]NO3 center dot CH3CN of 1c (space group P2(1)2(1)2(1)). Furthermore, the reaction of 1a with hexamolybdate in acetonitrile gives the helical coordination polymer {[(Fe-3(mu(3)-O)L-6(H2O))(MoO4)(Fe-3(mu(3)-O)L-6(H2O)(2))]center dot 2CH(3)CN center dot H2O}(infinity). 2 (L: H2C=CHCOO), which crystallizes in the space group P2(1). The nature of the ligand geometry allows the formation of atropisomers in both the discrete (1a-c) and linked {Fe-3} clusters (2), which is described along with a magnetic analysis of 1a and 2.