Structure and magnetism of heptanuclear complexes formed on encapsulation of hexacyanoferrate(II) with the Mn(II) and Ni(II) complexes of 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane

The reaction of [Mn(dmptacn)OH₂]²⁺ and [Ni(dmptacn)OH₂]²⁺ (dmptacn = 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane) with each cyano ligand on ferricyanide results in the assembly of heteropolynuclear cations around the cyanometalate core and reduction of Fe^III to Fe^II. In [{Mn(dmptacn)CN}₆Fe] [CIO₄]₈·5H₂O (1) and [{Ni(dmptacn)-CN}₆Fe] [CIO₄]₈·7H₂O (2), ferrocyanide is encapsulated by either six Mn^II or Ni^II dmptacn moieties. These same products are obtained when ferrocyanide salts are used in the synthesis instead of ferricyanide. A binuclear complex, [{Mn(dmptacn)}₂CN][CIO₄]₃ (3), has also been formed from KCN and [Mn(dmptacn)OH₂]²⁺. For both Mn^II and Ni^II, the use of the pentadentate dmptacn ligand facilitates the formation of discrete cations in preference to networks or polymeric structures. 1 crystallizes in the trigonal space group R3̄ (No. 148) with a = 30.073(3) Å, c = 13.303-(4)Å, and Z = 3 and is composed of heptanuclear [{Mn(dmptacn)CN}₆Fe]⁸⁺ cations whose charge is balanced by perchlorate counteranions. Weak H-bonding interactions between neighboring heptanuclear cations and some perchlorate counterions generate an infinite 1D chain of alternating [{Mn(dmptacn)CN}₆Fe]⁸⁺ and CIO₄^- ions running along the c-axis. Complex 3 crystallizes in the orthorhombic space group Pbcn (No. 60) with a = 16.225(3) Å, b = 16.320(2) Å, c = 18.052(3) Å, and Z = 8 and is composed of binuclear [{Mn(dmptacn)}₂CN]³⁺ cations in which the cyano-bridged Mn^II centers are in a distorted trigonal prismatic geometry. Variable temperature magnetic susceptibility measurements have revealed the presence of a weak ferromagnetic interaction between the paramagnetic Mn^II centers in 1, mediated either by the -NC-Fe-CN- bridging units or by Mn-NH⋯;CIO₄^-⋯NH-Mn intercluster pathways.