Crystal Structures and Solution Properties of Discrete Complexes Composed of Saddle-Distorted Molybdenum(V)-Dodecaphenylporphyrins and Keggin-Type Heteropolyoxometalates Linked by Direct Coordination

Nonplanar porphyrins: synthesis, properties, and unique functionalities

Porphyrins are variously substituted tetrapyrrolic macrocycles, with wide-ranging biological and chemical applications derived from metal chelation in the core and the 18π aromatic surface. Under suitable conditions, the porphyrin framework can deform significantly from regular planar shape, owing to steric overload on the porphyrin periphery or steric repulsion in the core, among other structure modulation strategies. Adopting this nonplanar porphyrin architecture allows guest molecules to interact directly with an exposed core, with guest-responsive and photoactive electronic states of the porphyrin allowing energy, information, atom and electron transfer within and between these species. This functionality can be incorporated and tuned by decoration of functional groups and electronic modifications, with individual deformation profiles adapted to specific key sensing and catalysis applications. Nonplanar porphyrins are assisting breakthroughs in molecular recognition, organo- and photoredox catalysis; simultaneously bio-inspired and distinctly synthetic, these molecules offer a new dimension in shape-responsive host-guest chemistry. In this review, we have summarized the synthetic methods and design aspects of nonplanar porphyrin formation, key properties, structure and functionality of the nonplanar aromatic framework, and the scope and utility of this emerging class towards outstanding scientific, industrial and environmental issues.

Porphyrins and Polyoxometalate Scaffolds

Polyoxometalates (POMs) can act as unique reservoirs for multiple electron transfers. As POMs display only weak absorption in the visible spectrum, they can be associated with chromophores such as porphyrins and porphyrin antennae. In this Minireview, the research dedicated to the combination of porphyrins and polyoxometalates is put in context and the state of the art identifying the challenges addressed in the optimization of hybrid materials for applications is detailed.

Discovery of a New Family of Polyoxometalate-Based Hybrids with Improved Catalytic Performances for Selective Sulfoxidation: The Synergy between Classic Heptamolybdate Anions and Complex Cations

A series of functional cation-regulated isopolymolybdate-based organic-inorganic hybrid compounds, Na₂H₂[Mo₄O₁₂(C₈H₁₇O₅N)₂]·10H₂O (1), Na₂[M(Bis-tris)(H₂O)]₂[Mo₇O₂₄]·10H₂O [M = Cu, 2; Ni, 3; Co, 4; Zn, 5; Bis-tris = 2,2-Bis(hydroxymethyl)-2,2',2″-nitrilotriethanol], and (NH₄)₂[M(Bis-tris)(H₂O)]₂[Mo₇O₂₄]·6H₂O (M = Zn, 6; Cu, 7), were synthesized and characterized toward advanced molecular catalyst design. Compound 1 is a covalently bonded adduct, and its self-assembly process can be probed by electrospray ionization mass spectrometry (ESI-MS). Compounds 2-7 are polyoxometalate (POM)-based hybrids containing classic heptamolybdate anions and complex cations with Bis-tris ligands. All of these compounds showed remarkable catalytic effects for selective sulfide oxidation. To the best of our knowledge, compound 5 presents the best catalytic activity so far among the reported hybrid materials with common easily synthesized small-molecule POM clusters and also exhibits outstanding reliability. The conclusion of the catalytic effect is drawn from the results that Zn-based compounds have better catalytic effects than other transition-metal-containing compounds and the compound constructed by Na⁺ has higher catalytic activity than that constructed by NH₄⁺. The mechanism studies show that the improvements of the catalytic performance are caused by the synergy between classic heptamolybdate anions and complex cations. ESI-MS data and UV-vis spectra revealed that the POM anions can form intermediate peroxomolybdenum units during catalytic reaction. Further, the combination of the substrate thioanisole with complex cations was characterized by NMR experiments and UV-vis spectra. Thus, a new synergistic mechanism of anions and cations is proposed in which the activated thioanisole is used as a nucleophile to attack the peroxomolybdenum bonds, and this provides a new strategy in the design of reliable POM-based catalysts.

Synthesis and structural, photophysical, electrochemical redox and axial ligation properties of highly electron deficient perchlorometalloporphyrins and selective CN− sensing by Co(ii) complexes

Synthesis and characterization of MTPP(NO₂)Cl₇ have been reported. Zn^II porphyrins exhibited higher Lewis acidity as compared to perbromoporphyrins. Co^II porphyrins were utilized for the selective rapid visual detection of cyanide ions.

Two novel bi-functional hybrid materials constructed from POMs and a Schiff base with excellent third-order NLO and catalytic properties

The first polyoxometalates modified by a porphyrin-resembling planar Schiff base have been successfully designed and synthesized under hydrothermal conditions. The third-order NLO responses indicated that they are excellent third-order NLO materials. Their catalytic performances are also investigated.

Two hybrid polyoxometalates constructed from Preyssler P5W30 clusters and Schiff base exhibiting interesting third-order NLO properties

Two novel inorganic–organic hybrid NLO materials constructed from Preyssler-type P₅W₃₀ cluster anions and Schiff-base have been isolated under hydrothermal conditions.

A molecular crown analogue templated by Keggin polyanions: synthesis, structure, and electrochemical and luminescent properties

A hybrid compound, [CuI 4(bpmb)4][PWVI 11WVO40] (1) (bpmb = 1,4-bis(pyrazol-1-ylmethyl)benzene), has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction analysis, infrared spectroscopy, elemental analyses and powder X-ray diffraction. In compound 1 crown-like [Cu4(bpmb)4]4+ macrocycles templated by Keggin-type [PWVI 11WVO40]4− polyanions (abbreviated PW12) exist. Supramolecular layers are formed by intermolecular hydrogen bonding interactions of discrete crown-like [Cu4(bpmb)4]4+ macrocycles and [PWVI 11WVO40]4− polyanions. The electrochemical and luminescence properties of compound 1 were investigated.

Hydrothermal synthesis, X-ray structure and DFT and magnetic studies of a (H2SiW12O40)2− based one-dimensional linear coordination polymer

In this paper, we report the synthesis and characterization of a novel POM-based inorganic–organic hybrid with an in situ transformation of pyridine-2,3-dicarboxylic acid into nicotinic acid and 2-hydroxynicotinic acid under hydrothermal conditions.

Control of the spatial arrangements of supramolecular networks based on saddle-distorted porphyrins by intermolecular hydrogen bonding

Supramolecular integration of a saddle-distorted zinc(II) porphyrin complex, which has hydroxyl groups at the para-position of the four meso-aryl groups, has been demonstrated on the basis of hydrogen bonding among the peripheral hydroxyl groups. The hydrogen-bonding patterns were controlled by the recrystallization solvents and additives, and particularly, addition of a bifunctional ligand such as 4,4'-bipyridine (bpy). The coordination of bpy to form dinuclear Zn(II)-porphyrin complexes causes a conformational difference: the dimeric complex with four hydroxyl groups is in an eclipsed form, however, a derivative without hydroxyl groups is in a staggered form due to the presence or absence of the intermolecular hydrogen bonding. In addition, the dimerization by the bpy coordination resulted in the expansion of the intermolecular space formed in the porphyrin networks, suggesting the potential to be applied for inclusion of guest molecules.

Synthesis, electrochemical and photophysical properties of covalently linked porphyrin-polyoxometalates

Two covalently linked porphyrin-polyoxometalate hybrids have been prepared: an Anderson-type hexamolybdate [N(C(4)H(9))(4)](3)[MnMo(6)O(18){(OCH(2))(3)CNHCO(ZnTPP)}(2)] with two pendant zinc(II)-tetraphenylporphyrins, and a Dawson-type vanadotungstate [N(C(4)H(9))(4)](5)H[P(2)V(3)W(15)O(59){(OCH(2))(3)CNHCO(ZnTPP)}] with one porphyrin. Electrochemical studies show independent redox processes for the organic and inorganic parts at usual potentials. Photophysical studies reveal an electron transfer from the excited porphyrin to the Dawson polyoxometalate, but not to the Anderson polyoxometalate. Time resolved absorption spectroscopy allows the identification of the electron transfer pathways and the determination of the time constants.

Undecaphenylcorroles

A first major study of undecaphenylcorrole (UPC) derivatives is presented. Three different Cu-UPC derivatives with different para substituents X (X = CF(3), H, CH(3)) on the β-aryl groups were synthesized via Suzuki-Miyaura coupling of Cu[Br(8)TPC] and the appropriate arylboronic acid. A single-crystal X-ray structure of the X = CF(3) complex revealed a distinctly saddled macrocycle conformation with adjacent pyrrole rings tilted by ~60-66° relative to one another (within the dipyrromethane units), which is somewhat higher than that observed for β-unsubstituted Cu-TPC derivatives but slightly lower than that observed for Cu[Br(8)TPC] (~70°) derivatives. Electrochemical and electronic absorption measurements afforded some of the first comparative insights into meso versus β substituent effects on the copper corrole core. The Soret maxima of the Cu-UPC complexes (~440-445 nm), however, are comparable to those of Cu[Br(8)TPC] derivatives and are considerably red-shifted relative to Cu-TPC derivatives. Para substituents on the β-phenyl groups were found to tune the redox potentials of copper corroles more effectively than those on meso-phenyl substituents, a somewhat surprising observation given that neither the HOMO nor LUMO has significant amplitudes at the β-pyrrolic positions.