Encapsulation of [Mn(bpy)3]2+ cations in 2D [Mn(dca)3]− sheet: Synthesis, X-ray structure and EPR study

The reaction of Mn(NO3)2 · 4H2O, 2,2′-bipyridine (bpy) and sodium dicyanamide (dca) in aqueous medium yielded the {[Mn(bpy)3][Mn(dca)3]2}n (1). The single-crystal X-ray analysis of 1 revealed that the anionic part of the complex, [Mn(dca)3]−, features infinite 2D sheets with a honeycomb-like porous structure having a void space of ca. 12 Å in which [Mn(bpy)3]2+ cations are encapsulated to yield a fascinating molecular assembly. MnII ions possess an octahedral geometry both in the anionic and cationic components of complex 1. In the anionic component, each MnII ion is bridged by three pairs of dicyanamide anions in an end-to-end fashion with two other MnII ions from adjacent [Mn(dca)3]− moieties. This type of linking propagates parallel to the bc crystallographic plane to form 2D sheets. [Mn(bpy)3]2+ is found to have somewhat “squeezed” upon encapsulation. No measurable magnetic interaction was evidenced through variable temperature magnetic susceptibility measurements. However, in addition to the broad g ≈ 2 resonance typical of magnetically diluted [Mn(bpy)3]2+ cations, EPR spectroscopy evidenced exchange narrowing of the [Mn(dca)3]− resonance at g ≈ 2 thus indicating operation of weak magnetic interactions extended over the whole 2D network through the dca− bridges.