Series of 2D Heterometallic Coordination Polymers Based on Ruthenium(III) Oxalate Building Units: Synthesis, Structure, and Catalytic and Magnetic Properties

A series of 2D ruthenium-based coordination
polymers with hcb-hexagonal
topology, {[K­(18-crown-6)]3[MII3(H2O)4{Ru­(ox)3}3]}n (MII = Mn (1), Fe (2), Co (3), Cu (4), Zn (5)), has been synthesized through self-assembly reaction. All compounds
are isostructural frameworks that crystallize in the monoclinic space
group C2/c. The crystal packing
consists of a 2D honeycomb-like anionic mixed-metal framework intercalated
by [K­(18-crown-6)]+ cationic template. Dehydration processes
take place in the range 40–200 °C exhibiting two phase
transitions. However, the spontaneous rehydration occurs at room temperature.
Both hydrated and dehydrated compounds were tested as Lewis acids
heterogeneous catalysts in the acetalyzation of benzaldehyde achieving
high yields with the possibility to be recovered and reused. All the
investigated materials do not show any long-range magnetic ordering
down to 2 K. However, the Fe-based compound 2 presents
a magnetic irreversibility in the ZFC-FC magnetization data below
5 K, which suggest a spin-glass-like behavior, characterized also
by short-range ferromagnetic correlations. The coercive field increases
as the temperature is lowered below 5 K, reaching a value of 1 kOe
at 2 K. Alternating current measurements obtained at different frequencies
confirm the freezing process that shows weak frequency dependence,
being characteristic of a system exhibiting competing magnetic interactions.