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) center dot 4H(2)O, 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 angstrom in which [Mn(bPY)(3)](2+) cations are encapsulated to yield a fascinating molecular assembly. Mn-II ions possess an octahedral geometry both in the anionic and cationic components of complex 1. In the anionic component.. each Mn-II ion is bridged by three pairs of dicyanamide anions in an end-to-end fashion with two other Mn-II 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 approximate to 2 resonance typical of magnetically diluted [Mn(bPY)(3)](2+) cations, EPR spectroscopy evidenced exchange narrowing of the [Mn(dca)(3)](-) resonance at g approximate to 2 thus indicating operation of weak magnetic interactions extended over the whole 2D network through the dca(-) bridges. (c) 2007 Elsevier B.V. All rights reserved.