Cyanide-Bridged Iron−Copper Molecular Squares with Doublet and Quintet Spin Ground States

Abstract

Reactions of [FeII(CN)2(bpy)2] and [FeIII(CN)2(bpy)2](PF6) with [CuII(bpy)(CH3OH)2](PF6)2 in methanol yielded cyanide-bridged cyclic tetranuclear complexes of [FeII 2CuII 2(μ-CN)4(bpy)6](PF6)4·2H2O·4CHCl3 (1) and [FeIII 2CuII 2(μ-CN)4(bpy)6](PF6)6·4CH3CN·2CHCl3 (2), respectively. In the squares of 1 and 2, the Fe2+/3+ (low-spin) and Cu2+ ions are alternately bridged by the cyanide ions, the carbon atoms of which coordinate to the iron ions. Variable-temperature magnetic susceptibility studies of complexes revealed that the Cu2+ ions in 1 are magnetically isolated. In the square of 2, the adjacent Fe3+ and Cu2+ ions were ferromagnetically coupled through the cyanide bridges with a J 1 value of +6.3(1) cm-1 and the weaker antiferromagnetic interactions between the orthogonal Fe3+···Fe3+ and Cu2+···Cu2+ pairs are operative (J 2 = −3.1(1) cm-1). The propagation of the ferromagnetic interaction in 2 can be understood by the orthogonal magnetic orbitals of the low-spin Fe3+ (dπ) and Cu2+ (dσ) ions. Cyclic voltammograms of the squares have been recorded and discussed. Crystal data for 1: triclinic space group P1̄, a = 14.491(4) Å, b = 15.312(4) Å, c = 12.959(3) Å, α = 91.38(2)°, β = 109.56(2)°, γ = 65.41(2)°, Z = 1. Crystal data for 2: triclinic space group P1̄, a = 14.472(9) Å, b = 15.310(6) Å, c = 12.523(5) Å, α = 102.58(3)°, β = 107.19(4)°, γ = 75.08(4)°, Z = 1.

Cyanide‐Bridged Molecular Squares – The Building Units of Prussian Blue

“…The first reported example was presented by the Oshio group, [13] in which an Fe 4 square could be tuned to display SCO behavior. Previous studies on the [Fe 2 M 2 (μ-CN) 4 -(bpy) 8 ] n+ molecular squares (M = late-first-row transition metal ion) [10] led to diamagnetic clusters when Fe II ions were used; however, by replacing bpy with tris(2-pyridylmethyl)amine (tpa), the ligand-field strength on the Fe II centers could be weakened, and the resulting ferrous square, [Fe II 4 (μ-CN) 4 (bpy) 4 Figure 6}, showed a two-step spin transition. Single-crystal X-ray diffraction data collected at 100 K led to the elucidation of a structure in which all four Fe II centers had very similar bond lengths, within the range 1.958-1.976 Å, characteristic of LS Fe II ions.…”

“…[8] Since then, there have been many reports of similar structures, both homo-and heterometallic, constructed from both transition metal and closed shell metal ions. This review is concerned primarily with open-shell transition metal ion square complexes.…”

Syntheses, Structures, and Electrochemical and Magnetic Properties of Rectangular Heterobimetallic Clusters Based on Tricyanometallic Building Blocks

“…[21] The Fe 2+ /Fe 3+ redox waves of complexes 5-7 (-0.36 to -0.18 V) are less negative than that of the same reduction process for their precursors 1-3 (-0.78 to -0.82 V), which could be attributed to the higher molecular charge, as well as the lower electron density on the Fe 3+ ion in 5-7. [22] The mixed valence species with grid + is perhaps an interesting precursor for further studies in molecular electronics, such as quantum dot cellular automata. [23] …”

Nuclearity Controlled Cyanide‐Bridged Bimetallic CrIII–MnII Compounds: Synthesis, Crystal Structures, Magnetic Properties and Theoretical Calculations

“…[16][17][18][19][20][21][22][23] The possibilities offered by this type of precursors in preparative chemistry and the relevant parameters to be taken into account are summarized in Scheme 1. One can see there how the nature, denticity and charge of L are crucial parameters given the possibility of supramolecular interactions (case of aromatic L groups), the control of the stereochemistry (fac-or mer-arrangement of the three cyanide groups when L is a tridentate ligand) or the selective complexation (L being a bridging ligand in addition to the cyanide groups).…”