Tuning the Valence of the Cerium Center in (Na)phthalocyaninato and Porphyrinato Cerium Double-Deckers by Changing the Nature of the Tetrapyrrole Ligands

Abstract

A series of 7 cerium double-decker complexes with various tetrapyrrole ligands including porphyrinates, phthalocyaninates, and 2,3-naphthalocyaninates have been prepared by previously described methodologies and characterized with elemental analysis and a range of spectroscopic methods. The molecular structures of two heteroleptic [(na)phthalocyaninato](porphyrinato) complexes have also been determined by X-ray diffraction analysis which exhibit a slightly distorted square antiprismatic geometry with two domed ligands. Having a range of tetrapyrrole ligands with very different electronic properties, these compounds have been systematically investigated for the effects of ligands on the valence of the cerium center. On the basis of the spectroscopic (UV-vis, near-IR, IR, and Raman), electrochemical, and structural data of these compounds and compared with those of the other rare earth(III) counterparts reported earlier, it has been found that the cerium center adopts an intermediate valence in these complexes. It assumes a virtually trivalent state in cerium bis(tetra-tert-butylnaphthalocyaninate) as a result of the two electron rich naphthalocyaninato ligands, which facilitate the delocalization of electron from the ligands to the metal center. For the rest of the cerium double-deckers, the cerium center is predominantly tetravalent. The valences (3.59-3.68) have been quantified according to their L(III)-edge X-ray absorption near-edge structure (XANES) profiles.

Orientation-Induced Redox Isomerism in Planar Supramolecular Systems

“…15,31−35 The coexistence of cerium complexes with tetrapyrrole ligands in two neutral forms (two redox isomers) that differ by the valent state of the cerium atom (III/IV) and the corresponding charge of the ligands was described earlier. 15,34,35 Unusual physicochemical and electrochemical properties of cerium bis [tetra (15 crown 5) phthalocyaninate] (Ce [(15C5) 4 Pc] 2 ; Figure 1) in comparison with other rare earth element complexes have been described recently in solution, Langmuir monolayers and Langmuir−Blodgett (LB) films. 34,36 In particular, changes in the UV−visible spectra of Ce [(15C5) 4 Pc] 2 monolayers that can be hypothetically attributed to IET were observed.…”

“…14 Moreover, the ability of the metal ion in such complexes to change its valent state can be tuned by the introduction of peripheral substituents of different nature into phthalocyanine ring. 15 Substituents can also drastically affect the electrochemical and optical properties of the materials based on these compounds. For example, the introduction of crown ethers into phthalo cyanine leads to novel efficient photorefractive materials and components of nonlinear optics.…”

A Macrocyclic Chelator That Selectively Binds Ln4+ over Ln3+ by a Factor of 1029

“…[55][56] Molecular cerium compounds are usually stabilized in the 4+ formal oxidation state by halides 57 and hard, oxygen donor ligands such as alkoxides [58][59][60][61][62][63][64][65][66][67] and acetylacetonates. [68][69] Many "non-classical" tetravalent cerium molecules have also been prepared, including organometallic compounds, [70][71][72] amide, 65,70,[73][74][75][76][77][78] porphyrins [79][80][81][82][83] and a variety of other multidentate N-donor ligands. [84][85][86][87][88][89][90][91] Among these, the lanthanide sandwich molecule cerocene, (C8H8)2Ce, [92][93][94][95][96][97][98][99][100]…”

Synthesis and magnetic properties of cerium macrocyclic complexes with tetramethyldibenzotetraaza[14]annulene, tmtaaH2

“…[9][10][11][12][13][14] In addition, the diamagnetic complexes Zr(cot) 2 , Zr(porph) 2 and Zr(pc) 2 with a d 0 electronic configuration are known. 11, 15-20 50 70 The binary f-transition metal complexes of cot 2-, porph 2-and pc 2-are known only for cerium, [21][22][23][24][25] but Ce(tmtaa) 2 is unknown. These complexes are of considerable interest since deductions about their electronic structure implied by their stoichiometry have been questioned.…”

“…These complexes are of considerable interest since deductions about their electronic structure implied by their stoichiometry have been questioned. 23,26 For example, the electronic structure of cerocene, Ce(cot) 2 27 Complexes of the phthalocyanato ligand, Ce(pc) 2 , have been suggested to be examples of this "valence ambiguity". 23,24 These long known and largely ignored complexes have therefore become the focus of intensive studies that are concerned with the question of exchange coupling between electrons in f-orbitals and therefore their role in covalent bonding.…”