Stepwise Crystallization:Illustrative Examples of the Use of Metalloligands [Cu6(mna)6]6-and [Ag6(Hmna)2(mna)4]4-(H2mna= 2-MercaptoNicotinic Acid) in the Formation of Heterometallic Two- and Three-DimensionalAssemblies with brucite, pcu, and sqlTopologies

Threenew inorganic coordination polymers, {[Mn(H2O)6][Mn2(H2O)6][(Cu6(mna)6]·6H2O}, 1, {[Mn4(OH)2(H2O)10][(Cu6(mna)6]·8H2O}, 2, and {[Mn2(H2O)5][Ag6(Hmna)2(mna)4]·20H2O}, 3, have been synthesized at room temperaturethrough a sequential crystallization route. In addition, we have alsoprepared and characterized the molecular precursor [Cu6(Hmna)6]. Compounds 1and 3have a two-dimensional structure, whereas 2has a three-dimensional structure. The formation of 2has been achieved by minor modification in the synthetic composition, suggesting the subtle relationship between the reactant compositionand the structure. The hexanuclear copper and silver cluster coreshave Cu···Cu and Ag···Ag distances closeto the sum of the van der Waals radii of Cu1+and Ag1+, respectively. The connectivity between [Cu6(mna)6]6-cluster units andMn2+ions gives rise to a bruciterelatedlayer in 1and a pcu-net in 2. The [Ag6(Hmna)2(mna)4]4-cluster in 3, on the other hand, formsa sql-net with Mn2+. Compound 1exhibits an interesting and reversible hydrochromic behavior, changing from pale yellow to red, on heating at 70 °C or treatment undera vacuum. Electron paramagnetic resonance studies indicate no changein the valence states, suggesting the color change could be due tochanges in the coordination environment only. The magnetic studiesindicate weak antiferromagnetic behavior. Proton conductivity studiesindicate moderate proton migrations in 1and 3. The present study clearly establishes sequential crystallizationas an important pathway for the synthesis of heterometallic coordinationpolymers. [ABSTRACT FROM AUTHOR]