1,1‘-Ferrocenedicarboxylate-Bridged Redox-Active Organotin and -tellurium-Containing 16-Membered Macrocycles: Synthesis, Structure, and Electrochemistry

Ferrocene-Derived Palladium(II)-Based Metallosupramolecular Structures: Synthesis, Guest Interaction, and Stimulus-Responsiveness Studies

Using ferrocene-based ligand systems, a series of heterobimetallic architectures of the general formula [Pd_mL_n]^x+ were designed with the aim of installing an opening and closing mechanism that would allow the release and binding of guest molecules. Palladium complex formation was achieved through coordination to pyridyl groups, and using 2-, 3-, and 4-pyridyl derivatives provided access to defined PdL, PdL₂, and Pd₂L₄ structures, respectively. The supramolecular complexes were characterized using nuclear magnetic resonance (NMR) and infrared spectroscopy, mass spectrometry, and elemental analysis, and for some examples density functional theory calculations and single-crystal X-ray diffraction analysis. ¹H NMR spectroscopy was used to investigate disassembly and reassembly of the metallosupramolecular structures. The former was induced by cleavage of the relatively labile Pd-N_pyridyl bonds with the introduction of the competing ligands N,N'-dimethylaminopyridine (DMAP) and Cl^- (using tetrabutylammonium chloride) to yield [Pd(DMAP)₄]²⁺ and [PdCl₄]^2-, respectively. The process was found to be reversible for several of the heterodimetallic compounds, with the addition of H⁺ or Ag⁺ triggering complex reassembly. Guest binding studies with several architectures revealed interactions with the anionic guests p-toluenesulfonate and octyl sulfate, but not with neutral molecules. Furthermore, the release of guests was reversibly induced with Cl^- ions as a stimulus.

Better Together: Functional Heterobimetallic Macrocyclic and Cage-like Assemblies

Metallosupramolecular chemistry has attracted the interest of generations of researches due to the versatile properties and functionalities of oligonuclear coordination complexes. Quite a number of different discrete cages were investigated, mostly consisting of only one type of ligand and one type of metal cation. Looking for ever more complex structures, heterobimetallic complexes became more and more attractive, as they give access to new structural motifs and functions. In the last years substantial success has been made in the design and synthesis of cages consisting of more than one type of metal cations, and a rapidly growing number of functional materials has appeared in the literature. This Minireview describes recent developments in the field of discrete heterometallic macrocycles and cages focusing on functional materials that have been used as host‐systems or as magnetic, photo‐active, redox‐active, and even catalytically active materials.

Organotellurium compounds: an overview of synthetic methodologies

In wake of emerging applications of organotellurium compounds in biological and material science avenues, the current review describes their key synthetic methodologies while focusing the synthesis of organotellurium compounds through five ligand-to-metal linkages including carbon; carbon-oxygen; carbon-nitrogen; carbon-metal; carbon-sulfur to tellurium. In all of these linkages whether tellurium links with ligands through a complicated or simple pathways, it is often governed through electrophilic substitution reactions. The present study encompasses these major synthetic routes so as to acquire comprehensive understanding of synthetic organotellurium compounds.

Dy(III)-Based Metal-Organic Framework as a Fluorescent Probe for Highly Selective Detection of Picric Acid in Aqueous Medium

A dysprosium metal-organic framework, {[Dy(μ₂-FcDCA)_1.5(MeOH)(H₂O)]·0.5H₂O}_n (1), where FcDCA = 1,1'-ferrocene dicarboxylic acid, was prepared by slow-diffusion technique at room temperature. The crystal structure analysis of 1 by single-crystal X-ray diffraction reveals different binding modes of FcDCA linkers coordinated with Dy(III) metal ions, which forms continuous porous two-dimensional (2D) infinite framework. The resulting 2D layers are linked by π···π interactions to build three-dimensional (3D) supramolecular framework. Observably, this thermally stable 3D architecture was topologically simplified as a three-connected uninodal net with fes topology. Furthermore, the practical applicability of 1 was investigated as a fluorescence sensor for the sensitive detection of picric acid in aqueous medium with an impressive detection limit of 0.71 μM with quenching constant (K_SV) quantified to be 8.55 × 10⁴ M^-1. The distinguished selectivity in the presence of other nitroaromatics suggests the possible incorporation of 1 in real-world futuristic diagnostic kits. Additionally, the electrochemical behavior of 1 exhibits reversible in nature attributed to the ferrocene/ferrocenium cation.

Heterobimetallic (FeII/PtII)-Based Supramolecular Coordination Complexes Using 1,1'-Ferrocene Dicarboxylate: Self-Assembly and Interaction with Carbon Dots

The synthesis and characterization of a new pyrazine-based ditopic organoplatinum(II) complex having a bite angle of 180° is reported. The facile and efficient syntheses are described of three discrete neutral Fe(II)/Pt(II) heterobimetallic SCCs with Pt(II) acceptor clips of different binding angles, 0, 120, and 180°. These new SCCs were characterized by multinuclear NMR and mass spectrometry. Electrochemical response of these ferrocene containing self-assembled ensembles was studied using cyclic voltammetry. The diplatinum acceptor organometallic clips significantly quench the fluorescence of highly emitting carbon quantum dots (CD), while the self-assembled macrocycles tend to nullify the quenching effect of the organometallic clips. Interestingly, the inefficient quenching of CD fluorescence by these SCCs was found to be directly related to the angular disposition of the binding sites in the Pt(II) based organometallic clips.

Novel mono- and bimetallic organotin(iv) compounds as potential linkers for coordination polymers

Organotin(iv) compounds might be used as linkers for building coordination polymers as suggested by the isolation of [{2-(OCH)C₆H₄}Me₂SnO(O)CC₅H₄N-4]ZnTPP.

Selenium– and tellurium–halogen reagents

Selenium and tellurium form binary halides in which the chalcogen can be in formal oxidation states (IV), (II) or (I). They are versatile reagents for the preparation of a wide range of inorganic and organic selenium and tellurium compounds taking advantage of the reactivity of the chalcogen–halogen bond. With the exception of the tetrafluorides, the tetrahalides are either commercially available or readily prepared. On the other hand, the low-valent species, EX2 (E = Se, Te; X = Cl, Br) and E2X2 (E = Se, Te; X = Cl, Br) are unstable with respect to disproportionation and must be used as in situ reagents. Organoselenium and tellurium halides are well-known in oxidation states (IV) and (II), as exemplified by REX3, R2EX2 and REX (R = alkyl, aryl; E = Se, Te; X = F, Cl, Br, I); mixed-valent (IV/II) compounds of the type RTeX2TeR are also known. This chapter surveys the availability and/or preparative methods for these widely used reagents followed by examples of their applications in synthetic inorganic and organic selenium and tellurium chemistry. For both the binary halides and their organic derivatives, the discussion is subdivided according to the formal oxidation state of the chalcogen.

Variation of the Molecular Conformation, Shape, and Cavity Size in Dinuclear Metalla-Macrocycles Containing Hetero-Ditopic Dithiocarbamate-Carboxylate Ligands from a Homologous Series of N-Substituted Amino Acids

A homologous series of dithiocarbamate ligands derived from N-substituted amino acids was reacted with different diorganotin dichlorides to give 18 diorganotin complexes. Spectroscopic and mass spectrometric analysis evidenced the formation of assemblies with six-coordinate tin atoms embedded in skewed-trapezoidal bipyramidal coordination environments of composition C₂SnS₂O₂. Single-crystal X-ray diffraction analysis for three of the compounds revealed a one-dimensional polymeric structure for the complex with the ligand derived from 5-aminopentanoic acid, which through further intermolecular Sn···O interactions generated an overall two-dimensional coordination polymer containing 40-membered hexanuclear tin macrocycles. On the contrary, the ligands derived from 6-aminohexanoic and 8-aminooctanoic acid provided the expected 22- and 26-membered dinuclear macrocyclic structures. Density functional theory calculations for a representative series of macrocyclic complexes of composition [Me₂SnLx]₂ with Lx = ¯S₂CN(Me)-(CH₂)_x-COO¯ (x = 3-12) enabled a detailed analysis of the variations in the molecular conformation, shape, and cavity size of the macrocycles in dependence of the aliphatic spacer. Because of odd-even effects, the difunctional ligands can adopt either a curved or a twisted-pincer shape, while the SnS_xO_4-x (x = 0-4) moieties can act either as linear or angular tectons with varying connectivity angles.

Electrochemical evidence of intramolecular electronic communication in Zr and Hf phthalocyanines bearing ferrocene-containing β-diketonato axial ligands: structure of [PcHf(FcCOCHCOC6H5)2]

The series of zirconium(IV) and hafnium(IV) phthalocyanine complexes [PcM(FcCOCHCOR)2] (Pc = phthalocyaninato; M = Zr; R = CF3 (1), CH3 (2), C6H5 (3), Fc ((C5H5)Fe(C5H4), 4), as well as M = Hf ; R = CF3 (5), CH3 (6), C6H5 (7), and Fc (8)) were synthesized. A single-crystal X-ray diffraction analysis of the structure of [PcHf(FcCOCHCOC6H5)2], 7 (Z = 2, space group P1), showed the two axial β-diketonato ligands were orientated in such a way that the ferrocenyl groups were positioned diagonally opposite each other. From the structural determination of 7 it was clear that these complexes have a distorted D4h symmetry at the coordination site of the metal centers, which explains a splitting of the UV-vis Q band into Qx and Qy components with 3 ≤ Δλ(max,Q) ≤ 10 nm. Cyclic and square wave voltammetric studies in CH2Cl2/[N((n)Bu)4][B(C6F5)4] allowed observation of at least three phthalocyaninato macrocycle-based redox couples as well as all (i.e., two or four) well-resolved ferrocenyl couples in 1-8. For M = Zr and R = Fc, formal reduction potentials of the four ferrocenyl groups were found to be E°' = 296, 386, 538, and 687 mV versus free ferrocene. Spectroelectrochemical evidence, UV-vis Q-band maximum wavelengths, and HOMO-LUMO energy gaps as expressed by ΔE°'I-III = ΔE°'wave I - ΔE°'wave III were mutually consistent, indicating that the first phthalocyaninato ring-based oxidation occurs before ferrocenyl oxidations take place. The potential for each redox process was found to be dependent on the sum of β-diketonato R-group group electronegativities, ΣχR. Mathematical relationships for the dependency of E°' on ΣχR for all four observed ring-based redox processes as well as for the ferrocenyl-based redox processes were determined. This allowed prediction of potentials for redox processes that fall outside the workable potential window of the solvent. No significant differences were found between the corresponding redox potentials of zirconium and hafnium analogues bearing the same axial ligands.

Tellurium: an element with great biological potency and potential

Tellurium has long appeared as a nearly 'forgotten' element in Biology, with most studies focusing on tellurite, tellurate and a handful of organic tellurides. During the last decade, several discoveries have fuelled a renewed interest in this element. Bioincorporation of telluromethionine provides a new approach to add heavy atoms to selected sites in proteins. Cadmium telluride (CdTe) nanoparticles are fluorescent and may be used as quantum dots in imaging and diagnosis. The antibiotic properties of tellurite, long known yet almost forgotten, have attracted renewed interest, especially since the biochemical mechanisms of tellurium cytotoxicity are beginning to emerge. The close chemical relationship between tellurium and sulfur also transcends into in vitro and in vivo situations and provides new impetus for the development of enzyme inhibitors and redox modulators, some of which may be of interest in the field of antibiotics and anticancer drug design.

Heterobimetallic metal-complex assemblies constructed from the flexible arm-like ligand 1,1'-bis[(3-pyridylamino)carbonyl]ferrocene: structural versatility in the solid state

The bidentate ferrocenyl sandwich molecule 1,1'-bis[(3-pyridylamino)carbonyl]ferrocene (3-BPFA) has been employed as an organometallic ligand in reactions with a series of transition metal salts to construct heterobimetallic architectures. X-ray crystallographic characterization reveals that the crystal packing of free ligand 3-BPFA induces spontaneous resolution of helical chains via intermolecular hydrogen bonds. By combining the flexibility from the arm-like molecule (3-BPFA) with the variation of the coordination property from different metal ions and/or the different counteranions, five different types of architectures are prepared: one octahedral coordination cage (copper(II) complex 1); two discrete pseudocapsules for combination of chlorine anions (nickel(II) complex 2 and cobalt(II) complex 3); two dimers with metal-metal interactions (silver(I) complexes 4 and 5); one macrocyclic complex (mercury(II) complex 6); and five two-dimensional mixed-metal-organic frameworks (M'-MOFs) (zinc(II), cadmium(II), and mercury(II) complexes 7-11). The structures of all complexes are characterized in detail by IR, elementary analysis, and single-crystal X-ray diffraction analysis. The factors inducing the structure variation among the complexes are discussed by taking account of the coordination geometry of different metal ions, the span angle between the two "arms", and the coordination mode of the 3-BPFA ligand.