New antimony-capped iron(II) and cobalt(III) clathrochelate precursors of the polytopic hybrid cage complexes: Synthesis, X-ray structures and electrochemistry

Cobalt complexes with hemilabile o-iminobenzoquinonate ligands: a novel example of redox-induced electron transfer

The tetracoordinated square-planar CoIII complex (imSQC(O)Ph)CoIII(APC(O)Ph) (1) bearing a radical anion and the closed-shell o-amidophenolate forms of the functionalized o-aminophenol H2LC(O)Ph were synthesized. The intermediate spin state (SCo = 1) CoIII center was found for compound 1. The cyclic voltammogram of derivative 1 contains two oxidative processes and one reductive redox process as well as an additional multi-electron wave at high negative potentials above -2 V, which can involve both the ligand and metal center. One-electron oxidation of 1 by silver triflate produces the [(imSQC(O)Ph)CoII(imQC(O)Ph)]OTf·2toluene (2) derivative with the trigonal prismatic coordination environment of the metal arising from the additional coordination of -C(O)Ph hemilabile groups. This is a first example of a trigonal prismatic coordination polyhedron in cobalt-based complexes featuring o-iminobenzoquinone ligands. The trigonal prismatic geometry achieved by the unique flexibility of the ligand allows metal-to-ligand redox-induced electron transfer (RIET). Chemical oxidation of complex 1 promotes the reduction of CoIII to CoII in compound 2 due to the redox-active nature of o-iminobenzoquinonate ligands. Remarkably, this is the first example of RIET in cobalt-based derivatives with this type of ligand. The oxidative states of the ligands and cobalt ion in both complexes were unequivocally established according to the X-ray data collection by using the utility of "metric oxidation state" (MOS). The spin states of the metal centers were unambiguously determined by density functional theory. The strong antiferromagnetic exchange via metal-ligand interactions is dominant in compounds 1 and 2, giving the doublet (S = 1/2) and triplet (S = 1) ground spin state, respectively.

Synthesis, X-ray structure and electrochemical properties of hybrid binuclear metallophthalocyaninate-capped tris-pyridineoximates

New antimony-capped iron and nickel(ii) tris-pyridineoximates easily underwent transmetallation with zirconium and hafnium(iv) phthalocyaninates giving metallophthalocyaninato-cross-linked complexes.

Preparation, X-ray Structures, Spectroscopic, and Redox Properties of Di- and Trinuclear Iron-Zirconium and Iron-Hafnium Porphyrinoclathrochelates

The first hybrid di- and trinuclear iron(II)-zirconium(IV) and iron(II)-hafnium(IV) macrobicyclic complexes with one or two apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using transmetalation reaction between n-butylboron-triethylantimony-capped or bis(triethylantimony)-capped iron(II) clathrochelate precursors and dichlorozirconium(IV)- or dichlorohafnium(IV)-5,10,15,20-tetraphenylporphyrins under mild conditions. New di- and trinuclear porphyrinoclathrochelates of general formula FeNx₃((Bn-Bu)(MTPP)) and FeNx₃(MTPP)₂ [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinato(2-); Nx = nioximo(2-)] were characterized by one-dimensional (¹H and ¹³C{¹H}) and two-dimensional (COSY and HSQC) NMR, high-resolution electrospray ionization mass spectrometry, UV-visible, and magnetic circular dichroism spectra, single-crystal X-ray diffraction experiments, as well as elemental analyses. Redox properties of all complexes were probed using electrochemical and spectroelectrochemical approaches. Electrochemical and spectroelectrochemical data suggestive of a very weak, if any, long-range electronic coupling between two porphyrin π-systems in FeNx₃(MTPP)₂ complexes. Density functional theory and time-dependent density functional theory calculations were used to correlate spectroscopic signatures and redox properties of new compounds with their electronic structures.

Insight into the electronic structure, optical properties, and redox behavior of the hybrid phthalocyaninoclathrochelates from experimental and density functional theory approaches

An insight into the electronic structure of several hafnium(IV), zirconium(IV), and lutetium(III) phthalocyaninoclathrochelates has been discussed on the basis of experimental UV-vis, MCD, electro- and spectroelectrochemical data as well as density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. On the basis of UV-vis and MCD spectroscopy as well as theoretical predictions, it was concluded that the electronic structure of the phthalocyninoclathrochelates can be described in the first approximation as a superposition of the weakly interacting phthalocyanine and clathrochelate substituents. Spectroelectrochemical data and DFT calculations clearly confirm that the highest occupied molecular orbital (HOMO) in all tested complexes is localized on the phthalocyanine ligand. X-ray crystallography on zirconium(IV) and earlier reported hafnium(IV) phthalocyaninoclathrochelate complexes revealed a slightly distorted phthalocyanine conformation with seven-coordinated metal center positioned ∼1 Å above macrocyclic cavity. The geometry of the encapsulated iron(II) ion in the clathrochelate fragment was found to be between trigonal-prismatic and trigonal-antiprismatic.