Synthesis and characterization of Prussian blue analogues incorporating the edge-bridged octahedral [Zr6BCl12]2+ cluster core

In attempts to produce a microporous magnet, two approaches were explored for expanding the Prussian blue structure type via incorporation of edge-bridged octahedral [Zr(6)ZCl(12)](2+) (Z = B, Be) cluster cores. Dissolution of Rb5Zr6BCl18 and K5Zr6BeCl15 in an acetonitrile solution of Et4N(CN) led to the isolation of (Et4N)(5)[Zr6BCl12(CN)(6)] (1) and (Et4N)(5)[Zr6BeCl12(CN)(6)](.)2MeCN(.)2THF (2), respectively. The crystal structure of 1(.)1.5MeCN revealed the expected cyano-terminated cluster complex with a trans-(NN)-N-... span of 11.73(3) angstrom. Unfortunately, both [Zr(6)ZCl(12)(CN)(6)](5-) clusters rapidly lose their cyanide ligands in aqueous solution making them ill-suited for solid-forming reactions with hydrated metal ions. Such outer-ligand exchange, however, allows the use of [Zr6BCl18](4-) in the synthesis of expanded Prussian blue-type solids through reactions with [Cr(CN)(6)](3-). The use of 2.2 M aqueous LiCl to stabilize the cluster during the reaction gave (Et4N)(2)[Zr6BCl12][Cr(CN)(6)]Cl(.)3H(2)O (3), while the use of 1 M acetic acid yielded (Et4N)(2)[Zr6BCl12][Cr(CN)(6)]Cl(.)2H(2)O(.)CH(3)CO(2)H (4). A Rietveld refinement against X-ray powder diffraction data collected for 3 confirmed the presence of a cubic Prussian blue framework structure, featuring alternating [Zr6BCl12](2+) cores and [Cr(CN)(6)](3-) anions. The temperature dependence of magnetization data obtained for 4 revealed activation of magnetic exchange interactions between the S = 1/2 cluster units and the S = 3/2 hexacyanochromate complexes below 10 K.