CrIII(NCMe)6]3+--a labile CrIII source enabling formation of Cr[M(CN)6] (M=V, Cr, Mn, Fe) Prussian blue-type magnetic materials

The kinetic inertness of the hexaaquachromium(III) (kH2O=2.4x10(-6) s(-1)) has led to challenges with respect to incorporating CrIII ions into Prussian blue-type materials; however, hexakis(acetonitrile)chromium(III) was shown to be substantially more labile (approximately 10(4) times) and enables a new synthetic route for the synthesis of these materials via nonaqueous solvents. The synthesis, spectroscopic, and physical properties of CrM(CN)6] (M=V, Cr, Mn, Fe) Prussian blue analogues synthesized from CrIII(NCMe)6]3+ and the corresponding MIII(CN)6]3- are described. All these compounds {(NEt4)0.02CrIIIVIII(CN)6]0.98(BF4)(0.08).0.10MeCN (1), CrIIICrIII(CN)6].0.16MeCN (2), CrIIIMnIII(CN)6].0.10MeCN (3), and (NEt4)0.04CrIII0.64CrIV0.40FeII(CN)6]0.40FeIII(CN)6]0.60(BF4)(0.16).1.02MeCN (4)} are ferrimagnets exhibiting cluster-glass behavior. Strong antiferromagnetic coupling was observed for M=V, Cr, and Mn with Weiss constants (theta) ranging from -132 to -524 K; and in 2, where the strongest coupling is observed (theta=-524 K), the highest Tc (110 K) value was observed. Weak antiferromagnetic coupling was observed for M=Fe (theta=-12 K) leading to the lowest Tc (3 K) value in this series. Weak coupling and the low Tc value observed in 4 were additionally contributed by the presence of both FeII(CN)6]4- and FeIII(CN)6]3- as confirmed by 57Fe-M?ssbauer spectroscopy.