| Description |
Of the many different classes of molecule-based magnets (MBMs) none are better understood or studied than Prussian blue (PB) and its analogues. Even though this field is centuries old there still remain many interesting aspects about Prussian blue analogues (PBAs) left to be discovered. The work described within details an in depth investigation into magnetically ordered non-Prussian blue structured Mn(II) PBAs. The reaction of the alkali metal cyanides with Mn(II) salts (e.g., Mn(O2CMe)2) formed a material of composition A2Mnn[Mnn(CN)6] (A = K, Rb, Cs) and Na2Mnn[Mnn(CN)6]^2H2O which was dehydrated to form Na2Mnn[Mnn(CN)6]. While the Cs analogue exhibited the typical face centered cubic (fcc) structure expected for Prussian blue structured materials; the K, Rb, and hydrated Na analogues have monoclinic unit cells. Even further reduced from the fcc unit cell is the dehydrated Na analogue which has a hexagonal unit cell. The linearity of the Mn-N^c bonds increases as the size of the alkali metal cation increases [142.4° (Na+) > 148.8° (K+) > 153.3° (Rb+) > 165.3° (Na+^2H2O) > 180° (Cs+)] which directly effects the magnetic ordering temperature, Tc [59 K (Na+) > 41 K (K+) > 34.6 K (Rb+) > 30 K (Na+^2H2O) > 21 K (Cs+)]. Currently, the structure of the material which resulted from the reaction of LiCN^DMF and Mn(O2CMe)2 has not been solved hindering further conclusions about this material. The reaction of tetraethylammonium cyanide and Mn(II) salts yielded a new PBA of [Et4N]2 MnII3 (CN) 8 composition that exhibited an unprecedented layered two-dimensional (2-D) structure with both octahedral and tetrahedral Mn(II) sites. Due to negligible intralayer coupling, [NEt4]2[Mn3(CN)8] orders as a ferrimagnet at 25 K with a coercive field and remnant magnetization of 1140 Oe and 22,800 emuOe/mol, respectively. When the reaction is carried out in methanol a material of [Et4N]Mn''3(CN)7 composition formed in which the 2-D layers, similar to that observed for [Et4N]2Mn''3(CN)8, are bridged through the tetrahedral sites forming an extraordinary threedimensional (3-D) bridged layered structure. [NEt4]Mn3(CN)7 orders as an antiferromagnetic and is the first Prussian blue analogue possessing an antiferromagnetic ground state lacking both a coercive field and remanant magnetization. The reaction of tetramethylammonium cyanide with Mn(O2CMe)2 yielded [NMe4]3Mn5(CN)13 which is the first material to incorporate a pentacyanomanganate ion. Thermal decomposition of either [Et4N]2MnII3(CN)8, [Et4N]MnII3(CN)7, or [NMe4]3Mn5(CN)13 led to the formation of a material of MnII(CN)2 composition which possess an interpenetrating sphalerite-type 3-D framework similar to that of Mn"[Mn"(CN)4]. |
