Synthesis and characterization of cyanide-bridged materials: From cluster-expanded Prussian blue analogues to single-molecule magnets

The work presented herein describes efforts to synthesize porous materials and magnetically-coupled transition metal-cyanide clusters, using the cubic framework of Prussian blue as a starting point.; In Chapter 2, a method for expanding the pores in crystalline frameworks is demonstrated with the substitution of face-capped octahedral [Re₆ Q₈(CN)₆]4− (Q = S, Se, Te) clusters into the Prussian blue structure. The clusters react in aqueous solution with Fe3+, Ga3+, and Cd2+ respectively, to precipitate M₄[Re₆Se₈(CN)₆] ₃·xH₂O, (M = Fe, Ga; Q = Se, Te) and [Cd₂(H₂O)₄][Re₆S₈(CN) ₆]·14H₂O. Incorporation of the larger Re₆ and Cd₂ clusters in the Prussian blue type framework leads to enhanced molecular sieve properties for these compounds.; Efforts to increase magnetic exchange coupling and introduce magnetic anisotropy in metal-cyanide clusters by substitution of MoIII for CrIII are presented in Chapter 3. In close parallel to reactions previously performed with [(Me₃tacn)Cr(CN)₃] (Me₃tacn = N,N′, N″-trimethyl-1,4,7-triazacyclononane), assembly reactions between [(Me₃tacn)Mo(CN)₃] and [Ni(H ₂O)₆]2+ or [(cyclam)Ni(H₂O) ₂]2+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) afford face-centered cubic [(Me₃tacn)₈Mo₈Ni ₆(CN)₂₄]12+ and linear [(Me₃tacn) ₂(cyclam)NiMo₂(CN)₆]2+ clusters, respectively. The magnetic properties of the linear cluster are consistent with the expected ferromagnetic coupling and an S = 4 ground state; additionally, fits to the magnetic data indicate the presence of axial zero-field splitting with a magnitude falling in the range |D| = 0.44–0.72 cm−1, and exchange coupling constants in the range J = 17.0–17.6 cm−1. These values represent significant increases over those displayed by the analogous CrIII-containing cluster.; Chapter 4 reports an attempt to prepare a VIII analogue of [(Me₃tacn)Cr(CN)₃], which results in oligomerization of cyanide to form [(Me₃tacn)₂V₂(CN) ₄(μ-C₄N₄)]. The conjugated pathway provided by the bridging ligand leads to strong antiferromagnetic coupling ( J = −112 cm−1) and an S = 0 ground state. Reduction of the complex generates the Class III mixed-valence anion [(Me₃tacn)₂V₂(CN)₄(μ-C ₄N₄)]1−, wherein resonance exchange induces strong ferromagnetic coupling to give a well-isolated S = 3/2 ground state.; Finally, the use of 1,3,5-triaminocyclohexane (tach) as a capping ligand in generating magnetic exchange-coupled metal-cyanide cages with accessible cavities is demonstrated in Chapter 5. Assembly reactions between [(tach)M(CN) ₃] (M = Fe, Co) and [M′ (H₂O)₆ ]2+ (M′ = Ni, Co) complexes in aqueous solution afford cubic [(tach)₄(H₂O)₁₂M ′₄M₄(CN)₁₂]8+ clusters stabilized by hydrogen bonding. Analogous to reactions previously performed with [(Me₃tacn)Cr(CN)₃], the reaction...