Synthesis, Characterization, and Electrochemistry of Heteroleptic Double-Decker Complexes of the Type Phthalocyaninato-Porphyrinato-Zirconium(IV) or -Hafnium(IV)

Abstract

The synthesis, spectroscopic characterization, and electrochemistry of 12 different neutral, singly and doubly oxidized heteroleptic double-decker complexes of the type [M^jPjjPc)]" where = 0, +1, or +2, M = Zr or Hf, P = the dianion of octaethylporphyrin (OEP) or tetraphenylporphyrin (TPP), and Pc = the dianion of phthalocyanine are reported. Each neutral compound was characterized by NMR, UV-visible, and IR spectroscopy while each oxidized or reduced compound was characterized by UV-visible and/or EPR spectroscopy. The neutral compounds all undergo two reversible ring-centered oxidations and two reversible ring-centered reductions.Comparison is made with data obtained for the corresponding actinide double-decker complexes containing Th(IV) or U(IV) central metal ions and correlations examined between £1/2 for all of the compounds and either the metal ionic radius or the absorbance band energy of the porphyrin Soret or phthalocyanine UV-band. The half-wave potentials depend upon the type of macrocycle. They also vary with the size of metal ion in the case of oxidation but not in reduction, where £1/2 values are relatively unaffected and shift by only 20-40 mV upon going from Hf(P)(Pc) to Th(P)(Pc) as compared to a much larger 220-280 mV shift between Em for the first oxidation of the same compounds.

Electrochemistry and spectroelectrochemistry of zirconium(IV) and hafnium(IV) phthalocyanines with b-diketone axial ligands

“…[40,41] Upon the first reduction at a potential of -1.10 V, the Soret band at 341 nm disappears along with the two strong visible bands at 680 and 692 nm while a new visible band at 985 nm appears. The band at 985 nm can be considered as a marker band for formation of the Pc π-anion radical [25,42] and this band is red-shifted by about 20 nm. The second reduction is also ring-centered and leads to formation of dianions ( Figure 5).…”

“…[15][16][17][18][19][20][21][22][23][24][25][26][27] Metallophthalocyanines in which the central atom has a valence of three or more are known to possess one or two out of plane axial ligands. [28][29][30][31] We recently reported the synthesis of zirconium and hafnium phthalocyanine complexes with various β-diketones and polyphenols which were made by replacing the two Cl -ions of the dichloro(phthalocyanine) complexes with organic ligands [17,23,24,27] and this was followed by a preliminary electrochemical study on some of these compounds.…”

Double-decker Yttrium(III) Complexes with Phthalocyaninato and Porphyrinato Ligands

“…A pale blue band containing a trace amount of the metal-free phthalocyanine H 2 (Pc) was developed, followed by a greenish-blue band which was collected and concentrated. The crude product was purified by recrystallization from a mixture of CHCl 3 …”

“…The sandwich-type double-decker complexes of phthalocyanines M(Pc) 2 (M = Ln, Th, U, Ti, Zr, Hf, Y, In, Sn) [1][2][3][4][5][6][7] and porphyrins M(Por) 2 (M = Ln, Th, U, Zr, Hf, Y) [2,3,[8][9][10][11][12][13] are well documented. Apart from their intrinsic interest, the chemistry of these compounds has been investigated with the goal of developing novel materials for practical applications based on the unique optical and electrical properties of these sandwich complexes.…”

“…Although a substantial number of such heteroleptic sandwich compounds have been synthesized recently, most of them are confined to lanthanide and group 4 transition metal complexes with unsubstituted phthalocyanine [14]. It has been reported that the electrochemical, spectroscopic and other physical properties of these double-decker complexes are related to the inter-ring distance in the molecule, which is determined by the ionic radius of the central metal ion and the strength of the metal-ligand bonds [3,[16][17][18][19]. Yttrium, which has a smaller ionic radius than the lanthanides (except Lu), also forms double-decker complexes, but examples are scarce.…”