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) (Z = B, Be) cluster cores. Dissolution of Rb(5)Zr(6)BCl(18) and K(5)Zr(6)BeCl(15) in an acetonitrile solution of Et(4)N(CN) led to the isolation of (Et(4)N)(5)[Zr(6)BCl(12)(CN)(6)] (1) and (Et(4)N)(5)[Zr(6)BeCl(12)(CN)(6)].2MeCN.2THF (2), respectively. The crystal structure of 1.1.5MeCN revealed the expected cyano-terminated cluster complex with a trans-N...N span of 11.73(3) Angstroms. Unfortunately, both Zr(6)ZCl(12)(CN)(6) 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 Zr(6)BCl(18) in the synthesis of expanded Prussian blue-type solids through reactions with Cr(CN)(6). The use of 2.2 M aqueous LiCl to stabilize the cluster during the reaction gave (Et(4)N)(2)[Zr(6)BCl(12)][Cr(CN)(6)]Cl.3H(2)O (3), while the use of 1 M acetic acid yielded (Et(4)N)(2)[Zr(6)BCl(12)][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 Zr(6)BCl(12) cores and Cr(CN)(6) 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.