4-Bromopyridine-Induced Chirality in Magnetic MII-[NbIV(CN)8]4– (M = Zn, Mn, Ni) Coordination Networks

Abstract

The introduction of 4-bromopyridine (4-Brpy) to a self-assembled MII-[NbIV(CN)8] (M = 3d metal ion) coordination system results in the formation of three-dimensional cyanido-bridged networks, {[MII(4-Brpy)4]2[NbIV(CN)8]}·nH2O (M = Zn, n = 1, 1; M = Mn, n = 0.5, 2; M = Ni, n = 2, 3). All these compounds are coordination frameworks composed of octahedral [MII(4-Brpy)4(μ-NC)2] complexes bonded to square antiprismatic [NbIV(CN)8]4– ions bearing four bridging and four terminal cyanides. 1 and 2 crystallize in the chiral I4122 space group as the mixture of two enantiomorphic forms, named 1(+)/1(−) and 2(+)/2(−), respectively. The chirality is here induced by the spatial arrangement of nonchiral but sterically expanded 4-Brpy ligands positioned around MII centers in the distorted square geometry, which gives two distinguishable types of coordination helices, A and B, along a 4-fold screw axis. The (+) forms contain left handed helices A, and right handed helices B, while the opposite helicity is presented in the...