Unexpected Supramolecular-Induced Redox Switching in Sandwich Gd Bisphthalocyaninate.

The redox state of the phthalocyanine in sandwich lanthanide complexes is crucial for their applications. In this work, we demonstrate that the cation-induced supramolecular assembly of crown-substituted phthalocyanine lanthanide complexes Ln[(15C5)4Pc]2 can be used to control the redox state of the ligand simultaneously with the coordination sphere of the central metal. We achieve unprecedented redox switching of phthalocyanine ligands in a double-decker Gd(III) complex, resulting from the intramolecular inclusion of potassium cations between the decks with simultaneous twisting of the ligands (the skew angle between them decreases from 44.61 to 0.21°). Such a structural change leads to an increase in the deck-to-deck distance and drastically facilitates ligand reduction. This process was shown to be anion-dependent: only potassium salts of weak acids (KOPiv and KOAc) induce intramolecular inclusion of cations with redox switching in contrast to salts of strong acids (KBr, KOPic, KSCN, and KPF6), where such a redox process does not occur. This breakthrough opens new avenues for controlling the electrochromic properties, of phthalocyanines, along with other properties, such as electrical conductivity, optics, etc.

Magnetic Anisotropy of Homo- and Heteronuclear Terbium(III) and Dysprosium(III) Trisphthalocyaninates Derived from Paramagnetic 1H-NMR Investigation.

1H-NMR spectroscopy of lanthanide complexes is a powerful tool for deriving spectral-structural correlations, which provide a clear link between the symmetry of the coordination environment of paramagnetic metal centers and their magnetic properties. In this work, we have first synthesized a series of homo- (M = M* = Dy) and heteronuclear (M ≠ M* = Dy/Y and Dy/Tb) triple-decker complexes [(BuO)8Pc]M[(BuO)8Pc]M*[(15C5)4Pc], where BuO- and 15C5- are, respectively, butoxy and 15-crown-5 substituents on phthalocyanine (Pc) ligands. We provide an algorithmic approach to assigning the 1H-NMR spectra of these complexes and extracting the axial component of the magnetic susceptibility tensor, χax. We show how this term is related to the nature of the lanthanide ion and the shape of its coordination polyhedron, providing an experimental basis for further theoretical interpretation of the revealed correlations.

Solvation-Induced Conformational Switching of Trisphthalocyanates for Control of Their Magnetic Properties.

Stabilization of different conformers of sandwich phthalocyaninates by changing the solvation environment has been demonstrated with the examples of new heteroleptic yttrium(III) and terbium(III) triple-decker complexes [(BuO)8Pc]M[(BuO)8Pc]M[(15C5)4Pc] (where M = Y or Tb, [(BuO)8Pc]2- = octa-n-butoxyphthalocyaninato ligand, and [(15C5)4Pc]2- = tetra-15-crown-5-phthalocyaninato ligand). To this end, we have performed a comprehensive crystallographic characterization of two solvates formed by the Y(III) complex with either toluene or dichloromethane. In the solvate with toluene, both pairs of Pc ligands are in staggered conformations, providing both metal cations with a square-antiprismatic environment. In contrast, in the solvate with dichloromethane, only one cation between the BuO- and 15C5-substituted ligands remains in a square-antiprismatic polyhedron, while the pair of BuO-substituted ligands switches to a gauche conformation. In both solvates, the staggered conformations are stabilized by weak interactions of peripheral substituents with solvent molecules. Detailed analysis of the 1H NMR spectra of the isostructural Tb(III) complex in aliphatic and aromatic solvents demonstrates that the stabilization of the corresponding conformations by solvation is also valid in the solution state, resulting in an increase in the axial component of the magnetic susceptibility tensor as the symmetry decreases from staggered to gauche. Thus, solvation-induced conformational switching of lanthanide trisphthalocyaninates can be used as a tool to control their magnetic properties.

Rare-earth based tetrapyrrolic sandwiches: chemistry, materials and applications.

The unique properties of natural tetrapyrrolic compounds have inspired the rapid growth of research interest in the design and synthesis of artificial porphyrinoids and their metal complexes as a basis of modern functional materials. A special role in the design of such materials is played by sandwich complexes formed by tetrapyrrolic macrocycles with rare earth elements, especially lanthanides. The development of synthetic approaches to the functionalization of tetrapyrrolic compounds and their rare earth complexes has facilitated the intensive development of new applications over the last decade. As a way of expanding the functionalities of rare earth complexes, sophisticated examples have been obtained, including mixed-ligand complexes, π-extended analogues, covalently linked and fused sandwiches, complexes with less-common tetrapyrrols, sandwiches with non-tetrapyrrolic macrocycles and even complexes containing up to six stacked ligands. This review intends to offer a general overview of the preparation of such sophisticated REE tetrapyrrolic sandwiches over the last decade as well as emphasizes the current challenges and perspectives of their application in areas such as single-molecule magnetism (SMM), organic field-effect transistors (OFET), conductive materials and nonlinear optics (NLO).

Nanostructured Aluminum Oxyhydroxide-A Prospective Support for Functional Porphyrin-Based Materials.

A method for the grafting of unsymmetrical A2BC-type 5,15-bis(4-butoxyphenyl)-10-(4-carboxyphenyl)-20-(phenanthrenoimidazolyl)-porphyrin onto the surface of nanostructured aluminum oxyhydroxide modified with a single SiO2 layer (NAOM) was successfully developed. A straightforward procedure towards surface modification of NAOM allowed us to prepare a new porphyrin-containing hybrid material. The obtained 3D heterostructure was extensively characterized using XPS, TEM and diffuse reflectance spectroscopy. Structural and morphological peculiarities of the inorganic support before and after the immobilization procedure were studied and discussed in detail. The stability of the material against leaching and the porphyrin immobilization ratio ca. 14% by weight were also revealed.

Tuning Photochemical and Photophysical Properties of P(V) Phthalocyanines.

The ability of P(V) phthalocyanines (Pcs) for efficient singlet oxygen (SO) generation was demonstrated for the first time by the example of unsubstituted and α- and ß-octabutoxy-substituted P(V)Pcs with hydroxy, methoxy and phenoxy ligands in the apical positions of the octahedral P centre. Variation of substituents in Pc ring and P(V) axial ligands allows careful tuning of photophysical and photochemical properties. Indeed, a combination of BuO groups in the ß-positions of the Pc ring and PhO groups as axial ligands provides significant SO generation quantum yields up to 90%; meanwhile, the values of SO generation quantum yields for others investigated compounds vary from 27 to 55%. All the complexes, except α-substituted P(V)Pc, demonstrate fluorescence with moderate quantum yields (10-16%). The introduction of electron-donating butoxy groups, especially in the α-position, increases the photostability of P(V)Pcs. Moreover, it has been shown in the example of ß-BuO-substituted P(V) that the photostability depends on the nature of axial ligands and increases in the next row: OPh < OMe < OH. The presence of oxy/hydroxy axial ligands on the P(V) atom makes it possible to switch the photochemical and photophysical properties of P(V)Pcs by changing the acidity of the media.

Site-Selective Solvation-Induced Conformational Switching of Heteroleptic Heteronuclear Tb(III) and Y(III) Trisphthalocyaninates for the Control of Their Magnetic Anisotropy.

In the present work, we report the synthesis of isomeric heteronuclear terbium(III) and yttrium(III) triple-decker phthalocyaninates [(BuO)8Pc]M[(BuO)8Pc]M*[(15C5)4Pc] (M = Tb, M* = Y or M = Y, M* = Tb, [(BuO)8Pc]2--octa-n-butoxyphthalocyaninato-ligand, [(15C5)4Pc]2--tetra-15-crown-5-phthalocyaninato-ligand). We show that these complexes undergo solvation-induced switching: the conformers in which both metal centers are in square-antiprismatic environments are stabilized in toluene, whereas in dichloromethane, the metal centers M and M* are in distorted prismatic and antiprismatic environments, respectively. This conclusion follows from the detailed analysis of lanthanide-induced shifts in 1H NMR spectra, which makes it possible to extract the axial component of the magnetic susceptibility tensor χaxTb and to show that this term is particularly sensitive to conformational switching when terbium(III) ion is placed in the switchable "M" site. This result provides a new tool for controlling the magnetic properties of lanthanide complexes with phthalocyanine ligands.

Octopus-Type Crown-Bisphthalocyaninate Anchor for Bottom-Up Assembly of Supramolecular Bilayers with Expanded Redox-Switching Capability.

Achievement of information storage at molecular level remains a pressing task in miniaturization of computing technology. One of the promising approaches for its practical realization is development of nanoscale molecular switching materials including redox-active systems. The present work demonstrates a concept of expansion of a number of available redox-states of self-assembled monolayers through supramolecular approach. For this, the authors synthesized an octopus-like heteroleptic terbium(III) bisphthalocyaninate bearing one ligand with eight thioacetate-terminated "tentacles" (octopus-Pc) and a ligand with four crown-ether moieties (H2 [(15C5)4 Pc]). It is shown that octopus-Pc forms stable monolayers on gold, where its face-on orientation allows for subsequent binding of crown-phthalocyanine molecules via potassium ion bridges. This chemistry is utilized to form a heterogeneous bilayer, in which a single molecule thick adlayer brings an additional redox-state to the system, thus expanding the multistability of the system as a whole. All four redox states available to this system exhibit characteristic absorbance in visible range, allowing for the switching to be easily read out using optical density measurements. The proposed approach can be used in wide range of switchable materials-single-molecule magnets, conductive, and optical devices, etc.

Substitution pattern in ruthenium octa-n-butoxyphthalocyanine complexes influence their reactivity in N-H carbene insertions.

Ruthenium phthalocyanine complexes bearing n-OBu substituents in the peripheral or non-peripheral positions are efficient catalysts for the selective double or single carbene insertion to the amine N-H bonds. This complementary reactivity of two Ru complexes can be used for the synthesis of asymmetric tertiary amines and diamines bearing different substituents and has been demonstrated by two examples of readily available primary amines using different carbene precursors in successive reactions.

Switchable Nanozyme Activity of Porphyrins Intercalated in Layered Gadolinium Hydroxide.

In this study, organo-inorganic nanohybrids LHGd-MTSPP with enzyme-like activity were prepared by in situ intercalation of anionic 5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin and its complexes with Zn(II) and Pd(II) (MTSPP, M = 2H, Zn(II) and Pd(II)) into gadolinium layered hydroxide (LHGd). The combination of powder XRD, CHNS analysis, FT-IR, EDX, and TG confirmed the layered structure of the reaction products. The basal interplanar distances in LHGd-MTSPP samples were 22.3-22.6 Å, corresponding to the size of an intercalated tetrapyrrole molecule. According to SEM data, LHGd-MTSPP hybrids consisted of individual lamellar nanoparticles 20-50 nm in thickness. The enzyme-like activity of individual constituents, LHGd-Cl and sulfoporphyrins TSPP, ZnTSPP and PdTSPP, and hybrid LHGd-MTSPP materials, was studied by chemiluminescence analysis using the ABAP/luminol system in phosphate buffer solution. All the individual porphyrins exhibited dose-dependent antioxidant properties with respect to alkylperoxyl radicals at pH 7.4. The intercalation of free base TSPP porphyrin into the LHGd preserved the radical scavenging properties of the product. Conversely, in LHGd-MTSPP samples containing Zn(II) and Pd(II) complexes, the antioxidant properties of the porphyrins changed to dose-dependent prooxidant activity. Thus, an efficient approach to the design and synthesis of advanced LHGd-MTSPP materials with switchable enzyme-like activity was developed.

Redox-Triggered Switching of Conformational State in Triple-Decker Lanthanide Phthalocyaninates.

Double- and triple-decker lanthanide phthalocyaninates exhibit unique physical-chemical properties, particularly single-molecule magnetism. Among other factors, the magnetic properties of these sandwiches depend on their conformational state, which is determined via the skew angle of the phthalocyanine ligands. Thus, in the present work we report the comprehensive conformational study of substituted terbium(III) and yttrium(III) trisphthalocyaninates in solution depending on the substituents at the periphery of molecules, redox-states and nature of solvents. Conjunction of UV-vis-NIR spectroscopy and quantum-chemical calculations within simplified time-dependent DFT in Tamm-Dancoff approximation provided the spectroscopic signatures of staggered and gauche conformations of trisphthalocyaninates. Altogether, it allowed us to demonstrate that the butoxy-substituted complex behaves as a molecular switcher with controllable conformational state, while the crown-substituted triple-decker complex maintains a staggered conformation regardless of external factors. The analysis of noncovalent interactions within the reduced density gradient approach allowed to shed light on the nature of factors stabilizing certain conformers.

Low-Symmetry Phthalocyanines Bearing Carboxy-Groups: Synthesis, Spectroscopic and Quantum-Chemical Characterization.

The synthesis and characterization of A3B-type phthalocyanines, ZnPc1-4, bearing bulky 2,6-diisopropylphenoxy-groups or chlorine atoms on isoindoline units "A" and either one or two carboxylic anchors on isoindoline unit "B" are reported. A comparison of molecular modelling with the conventional time dependent-density functional theory (TD-DFT) approach and its simplified sTD-DFT approximation provides further evidence that the latter method accurately reproduces the key trends in the spectral properties, providing colossal savings in computer time for quite large molecules. This demonstrates that it is a valuable tool for guiding the rational design of new phthalocyanines for practical applications.

Structure Determination of Binuclear Triple-Decker Phthalocyaninato Complexes by NMR via Paramagnetic Shifts Analysis Using Symmetry Peculiarities.

The detailed knowledge about the structure of multinuclear paramagnetic lanthanide complexes for the targeted design of these compounds with special magnetic, sensory, optical and electronic properties is a very important task. At the same time, establishing the structure of such multinuclear paramagnetic lanthanide complexes in solution, using NMR is a difficult task, since several paramagnetic centers act simultaneously on the resulting chemical shift of a particular nucleus. In this paper, we have demonstrated the possibility of molecular structure determination in solution on the example of binuclear triple-decker lanthanide(III) complexes with tetra-15-crown-5-phthalocyanine Ln2[(15C5)4Pc]3 {where Ln = Tb (1) and Dy (2)} by quantitative analysis of the pseudo-contact lanthanide-induced shifts (LIS). The symmetry of complexes was used for the simplification of the calculation of pseudo-contact shifts on the base of the expression for the magnetic susceptibility tensor in the arbitrary oriented magnetic axis system. Good agreement between the calculated and experimental shifts in the 1H NMR spectra indicates the similarity of the structure for the complexes 1 and 2 in solution of CDCl3 and the structure in the crystalline phase, found from the data of the X-ray structural study of the similar complex Lu2[(15C5)4Pc]3. The described approach can be useful for LIS analysis of other polynuclear symmetric lanthanide complexes.

Switchable Aromaticity of Phthalocyanine via Reversible Nucleophilic Aromatic Addition to an Electron-Deficient Phosphorus(V) Complex.

Reversible nucleophilic addition to a phthalocyanine core was observed for the first time for the electron-deficient cationic phosphorus(V) complex [PcP(OMe)2]+, whose reaction with KOH afforded a highly distorted nonaromatic adduct bearing an OH group at one of the α-pyrrolic carbon atoms. This adduct was characterized by single-crystal X-ray diffraction, ESI HRMS, and NMR, and UV-vis spectroscopy, together with quantum-chemical modeling. The acidic treatment of this adduct restored aromaticity and recovered the starting cationic complex. The reversible aromaticity breakage resulted in dramatic changes in the photophysical properties of the studied complex, which could pave the way to novel switchable Pc-based compounds and materials.

Porphyrinylphosphonate-Based Metal-Organic Framework: Tuning Proton Conductivity by Ligand Design.

A novel metal-organic framework [Zn3 (Ni-H2 TPPP)(Ni-H4 TPPP)(Ni-H5 TPPP)⋅7(CH3 )2 NH2 ⋅DMF⋅7 H2 O] (where Ni-Hx TPPP (x=2,4,5) are partially deprotonated [5,10,15,20-tetrakis(3-(phosphonatophenyl)-porphyrinato(2-))]nickel(II) species), IPCE-2Ni, with outstanding proton conductivity (1.0×10-2  S cm-1 at 75 °C and 95 % relative humidity) has been obtained. The high concentration of free phosphonate groups and compensating dimethylammonium cations bound by hydrogen bonds in the unique crystal structure of IPCE-2Ni is a key factor responsible for the observed high proton conductivity, which is one order of magnitude higher than for the corresponding MOF based on 5,10,15,20-tetrakis(4-(phosphonatophenyl)porphyrinato(2-))]nickel(II) IPCE-1Ni and comparable with that of leaders among MOFs.

Cation-Induced Dimerization of Crown-Substituted Gallium Phthalocyanine by Complexing with Alkali Metals: The Crucial Role of a Central Metal.

The single-crystal X-ray diffraction characterization of cation-induced supramolecular assembly of the gallium(III) tetra(15-crown-5)phthalocyaninate [(HO)Ga(15C5)4Pc] (1Ga) is reported. The structures of two crystalline dimers, {[(1Ga)2Rb4]4+(iNic-)4}·10CDCl3 and {[(2Ga)2Rb4]4+(OH-)2(Piv-)2}·16CDCl3 (2Ga-[(Piv)Ga(15C5)4Pc]), as well as UV-vis and NMR studies of the soluble supramolecular dimers formed by 1Ga and K+, Rb+, and Cs+ salts are provided. In contrast to the previously reported aluminum complex where the Al-O-Al bond was formed, no µ-oxo bridge was observed between the gallium atoms in the supramolecular dimers under similar conditions, despite the fact that aluminum and gallium belong to the same group of the periodic table. The detailed investigation of the cation-induced dimers of 1Ga confirms the uniformity of their structure for all large alkali cations, where two molecules of crown-substituted gallium phthalocyaninate are 4-fold bound by K+, Rb+, or Cs+. The gallium(III) coordination sphere is labile, and the nature of the solvent during supramolecular dimerization has an effect on the axial ligand exchange: Piv- in nonpolar CHCl3 replaces the initial OH- in 1Ga, while such a process is not observed in CHCl3/CH3OH media.

Heteroleptic Crown-Substituted Tris(phthalocyaninates) as Dynamic Supramolecular Scaffolds with Switchable Rotational States and Tunable Magnetic Properties.

Herein we report single-crystal X-ray diffraction characterization and complementary solution studies of supramolecular interaction between potassium salts and heteroleptic homo- and heteronuclear triple-decker crown phthalocyaninates [(15C5)4Pc]M*[(15C5)4Pc]M(Pc) or [M*,M], where M* and M = Y and/or Tb. Our results evidence that, in contrast to the previously studied crown-substituted phthalocyanines, the interaction of K+ cations with [M*,M] does not induce their intermolecular aggregation. Instead, the cations reversibly intercalate between the crown-substituted phthalocyanine ligands, resulting in switching of the coordination polyhedron of the metal center M* from square-antiprismatic to square-prismatic. In the case of terbium(III) complexes, such a switching alters their magnetic properties, which can be read-out by 1H NMR spectroscopy. For [Tb*,Y], such a switching causes an almost 25% increase in the axial component of the magnetic susceptibility tensor. Even though the polyhedron of the paramagnetic center in [Y*,Tb] is not switched, minor structural perturbations associated with the overall reorganization of the receptor also cause smaller, but nevertheless appreciable, growth of the axial anisotropy. The observed effects render the studied complexes as molecular switches with tunable magnetic properties.

Ion-Driven Self-Assembly of Lanthanide Bis-phthalocyaninates into Conductive Quasi-MOF Nanowires: an Approach toward Easily Recyclable Organic Electronics.

Controlled self-assembly and rapid disintegration of supramolecular nanowires is potentially useful for ecology-friendly organic electronics. Herein, a novel method exploiting the binding between crown-substituted double-decker lanthanide phthalocyaninates (ML2, M = Lu, Ce, Tb) and K+ ions is applied for the one-step fabrication of macroscopically long conductive one-dimensional quasi-metal-organic frameworks. Their properties are controlled by the size of the lanthanide ion guiding the assembly through either intra- or intermolecular interactions. A LuL2 linker with a small interdeck distance yields fully conjugated intermolecular-bonded K+-LuL2 nanowires with a thickness of 10-50 nm, a length of up to 50 µm, and a conductivity of up to 11.4 S cm-1, the highest among them being reported for phthalocyanine assemblies. The large size of CeL2 and TbL2 leads to the formation of mixed intra- and intermolecular K+-ML2 phases with poor electric properties. A field-assisted method is developed to deposit aligned conductive K+-LuL2 assemblies on solids. The solid-supported nanowires can be disintegrated into starting components in a good aprotic solvent for further recycling.

Spin Crossover in Nickel(II) Tetraphenylporphyrinate via Forced Axial Coordination at the Air/Water Interface.

Coordination-induced spin crossover (CISCO) in nickel(II) porphyrinates is an intriguing phenomenon that is interesting from both fundamental and practical standpoints. However, in most cases, realization of this effect requires extensive synthetic protocols or extreme concentrations of extra-ligands. Herein we show that CISCO effect can be prompted for the commonly available nickel(II) tetraphenylporphyrinate, NiTPP, upon deposition of this complex at the air/water interface together with a ruthenium(II) phthalocyaninate, CRPcRu(pyz)2, bearing two axial pyrazine ligands. The latter was used as a molecular guiderail to align Ni···Ru···Ni metal centers for pyrazine coordination upon lateral compression of the system, which helps bring the two macrocycles closer together and forces the formation of Ni-pyz bonds. The fact of Ni(II) porphyrinate switching from low- to high-spin state upon acquiring additional ligands can be conveniently observed in situ via reflection-absorption UV-vis spectroscopy. The reversible nature of this interaction allows for dissociation of Ni-pyz bonds, and thus, change of nickel cation spin state, upon expansion of the monolayer.

Long-Sought Redox Isomerization of the Europium(III/II) Complex Achieved by Molecular Reorientation at the Interface.

Redox isomerism, that is, the change of a metal cation valence state in organic complexes, can find promising applications in multistable molecular switches for various molecular electronic devices. However, despite a large number of studies devoted to such processes in organic complexes of multivalent lanthanides, redox-isomeric transformations were never observed for europium. In the present work, we demonstrate the unique case of redox isomerization of Eu(III)/Eu(II) complexes on the example of Eu double-decker octa-n-butoxyphthalocyaninate (Eu[(BuO)8Pc]2) under ambient conditions (air and room temperature). It is shown that assumption of the face-on orientation on the aqueous subphase surface, in which two of each phthalocyanine decks in Eu[(BuO)8Pc]2 are located in different media (air and water), leads to the intramolecular electron transfer that results in the formation of a divalent Eu(II) cation in the complex. Lateral compression of the thus-formed monolayer results in the reorientation of bisphthalocyaninate to the edge-on state, in which the ligands can be considered identical, and occurrence of the reverse redox-isomeric transformation into the complex with a trivalent Eu cation. Both redox-isomeric states were directly observed by X-ray absorption near-edge structure spectroscopy in ultrathin films formed under different conditions.