Synthesis, Crystal Structure, and Magnetic Properties of Hexanuclear $[\{MnL_2\}_4\{Nb(CN)_8\}_2]$ and Nonanuclear $[\{MnL_2\}_6\{Nb(CN)_8\}_3]$ Heterometallic Clusters (L = bpy, phen)

Abstract

A hexanuclear cyano-bridged $\{Mn^{II}_4Nb^{IV}_2\}$ cluster (1) bearing 2,2'-bipyridine (bpy) as the blocking ligand at manganese is obtained from the reaction of cis-$[MnCl_2(bpy)_2]$ and $K_4[Nb(CN)_8]$. When the blocking ligand is 1,10-phenanthroline (phen), a nonanuclear cluster $\{Mn^{II}_6Nb^{IV}_3\}$ (2) is obtained. The structure of $[\{Mn(bpy)_2\}_4\{Nb(CN)_8\}_2]$ has been solved by single-crystal X-ray crystallography, whereas the phen derivative has been confirmed by means of he structure analysis of the corresponding $W^{IV}$ analogue $[\{Mn(phen)_2\}_6\{W(CN)_8\}_3(H_2O)_2]$. Magnetic measurements revealed S = 9 and 27/2 spin ground states for these aggregates as a result of antiferromagnetic Nb-Mn interaction with $J_{Nb-Mn} = -18.1 cm^{-1}$ (1) and $-13.6 cm^{-1}$ (2)