Synthesis, structure and spectroelectrochemistry of hybrid metal(iv)phthalocyaninato-capped 3d-metal pyrazoloximates as prospective precursors of stimuli-induced (responsive) single-molecule magnets, logic gates and qubits

Abstract

Title hybrid iron(II)- and cobalt(III)-centered complexes were prepared in moderate yields using the template reactions of 3-acetylpyrazoloxime as a chelating ligand synthon with a Lewis-acidic zirconium or hafnium(IV) phthalocyaninate on the corresponding 3d-metal ion as a matrix. Formation of the cobalt(III)-centered complexes is observed due to the oxidation of Co²⁺ cations of the initial cobalt(II) salt. Thus obtained binuclear chloride H-bonded iron(II) and cobalt(III) compounds were characterized using elemental analysis, ¹H and ¹³C {¹H} NMR, MALDI-TOF mass, ⁵⁷Fe Mössbauer (for iron compounds) and UV-vis spectra, and by single-crystal X-ray diffraction (XRD). Their redox properties were studied by cyclic (CV) and differential pulse voltammetry methods, and using spectroelectrochemical experiments. Their encapsulated 3d-metal ions with the electronic d⁶ configuration are located almost in the center of MN₆-coordination polyhedra, the geometry of which is more closer to a trigonal antiprism (TAP, the distortion angle φ = 60°) than to a trigonal prism (TP, φ = 0°) with φ ∼ 40°. Fe^II–N distances fall in the range 1.913(6)–1.965(7) Å, while the Co^III–N bond lengths are from 1.890(8) to 1.935(8) Å. The geometry of M^IVO₃N₄-coordination polyhedra of their capping metal(IV) ions is intermediate between a capped TAP and a capped TP. In the molecules of Zr^IVM^IIIM^IIM^IIZr^IV-pentanuclear intracomplexes, (HS)Fe^III–N and (LS)Co^III–N distances in their two semiclathrochelate fragments fall in the ranges 1.915(10)–1.980(12) Å and 1.886(13)–1.930(13) Å, respectively, and the geometry of MN₆-coordination polyhedra is closer to a TAP (values of φ are higher than 30°). The geometry of MN₆-polyhedra of the HS cross-linking metal(II) ions between them is close to a TAP (values of φ are higher than 50°). All the obtained binuclear hybrid complexes exhibit very similar electrochemical patterns. Their CVs contain quasi-reversible or irreversible three reduction and three oxidation waves. The potentials of electrochemical reductions, assigned to the Pc-localized redox processes, are close to each other. The first of them is a quasi-reversible process attributed to the Pc-based one-electron reduction, while the first oxidation wave was assigned to the metal-centered M^2+/3+ redox couples. The spectroelectrochemical data confirmed an assignment of the aforementioned electrochemical processes.