Valence-Tautomeric Metal–Organic Nanoparticles

Two-Dimensional Polymer Networks Locking on Inorganic Nanoparticles

Two-dimensional polymers (2DPs), single-layer networks of covalently linked monomers, show perspectives as membranes and in electronics. However, 2D polymerization of monomers in orthogonal directions limited the formation of 2DPs on nanoparticles (NPs) with high surface curvatures. Here we propose a high-curvature 2D polymerization to form a single-layer 2DP network as a non-contacting ligand on the surface of NPs for their stabilization and functionalization. The high-curvature 2D polymerization of amphiphilic Gemini monomers was conducted in situ on surfaces of NPs with various sizes, shapes, and materials, forming highly cross-linked 2DPs. Selective etching of core-shell NPs led to 2DPs as a non-contact ligand of yolk-shell structures with excellent shape retention and high NP-surface accessibility. In addition, by copolymerization, the 2DP ligands can covalently link to other functional molecules. This work promotes the development of 2DPs on NPs for their functional modification.

A Convenient DFT-Based Strategy for Predicting Transition Temperatures of Valence Tautomeric Molecular Switches

The ability to identify promising candidate switchable molecules computationally, prior to synthesis, represents a considerable advance in the development of switchable molecular materials. Even more useful would be the possibility of predicting the switching temperature. Cobalt-dioxolene complexes can exhibit thermally induced valence tautomeric switching between low-spin Co^III-catecholate and high-spin Co^II-semiquinonate forms, where the half-temperature (T_1/2) is the temperature at which there are equal amounts of the two tautomers. We report the first simple computational strategy for accurately predicting T_1/2 values for valence tautomeric complexes. Dispersion-corrected density functional theory (DFT) methods have been applied to the [Co(dbdiox)(dbsq)(N₂L)] (dbdiox/dbsq^•- = 3,5-di-tert-butyldioxolene/semiquinonate; N₂L = diimine) family of valence tautomeric complexes, including the newly reported [Co(dbdiox)(dbsq)(MeO-bpy)] (1) (MeO-bpy = 4,4'-dimethoxy-2,2'-bipyridine). The DFT strategy has been thoroughly benchmarked to experimental data, affording highly accurate spin-distributions and an excellent energy match between experimental and calculated spin-states. Detailed orbital analysis of the [Co(dbdiox)(dbsq)(N₂L)] complexes has revealed that the diimine ligand tunes the T_1/2 value primarily through π-acceptance. We have established an excellent correlation between experimental T_1/2(toluene) values for [Co(dbdiox)(dbsq)(N₂L)] complexes and the calculated lowest unoccupied molecular orbital energy of the corresponding diimine ligand. The model affords accurate T_1/2(toluene) values for [Co(dbdiox)(dbsq)(N₂L)] complexes, with an average error of only 3.7%. This quantitative and simple DFT strategy allows experimentalists to not only rapidly identify proposed VT complexes but also predict the transition temperature. This study lays the groundwork for future in silico screening of candidate switchable molecules prior to experimental investigation, with associated time, cost, and environmental benefits.

One-Step Synthesis of Spin Crossover Nanoparticles Using Flow Chemistry and Supercritical CO2

Switchable materials are increasingly considered for implementation in devices or multifunctional composites leading to a strong need in terms of reliable synthetic productions of well-defined objects. Here, an innovative and robust template-free continuous process was developed to synthesize nanoparticles of a switchable coordination polymer, including the use of supercritical CO₂ , aiming at both quenching the particle growth and drying the powder. This all-in-one process offers a 12-fold size reduction in a few minutes while maintaining the switching properties of the selected spin crossover coordination polymer.

A new water-insoluble coordination polymer as efficient dye adsorbent and olefin epoxidation catalyst

A new water-insoluble bi-metallic coordination polymer was simply prepared via polymerization-precipitation of molybdenum complex building blocks with Zn²⁺ cation. The linker was a di-carboxylic acid consisting of two coordination sites i.e. N,O and COO^- suitable for coordinating to MoO₂ unit and Zn²⁺, respectively. Characterization of the prepared coordination polymer was carried out with various physicochemical methods which confirmed the proposed structure. The prepared coordination polymer preferentially adsorbed methylene blue (more than 92% of methylene blue after 2 min) relative to methyl orange and can be reused at least four times without any loss of adsorption efficiency. The adsorption process of both dyes followed the pseudo-second order kinetic equation. Additionally, the obtained coordination polymer catalyzed epoxidation of olefins with tert-butylhydroperoxide (TBHP) quantitatively with excellent selectivity (>99%) under mild reaction conditions.

Synthesis of Coordination Polymer Nanoparticles using Self-Assembled Block Copolymers as Template

Nowadays there is a high demand in specialized functional materials, for example, for applications as sensors in biomedicine. For the realization of such applications, nanostructures and the integration in a composite matrix are indispensable. Coordination polymers and networks, for example, with spin crossover properties, are a highly promising family of switchable materials in which the switching process can be triggered by various external stimuli. An overview over different strategies for the synthesis of nanoparticles of such systems is given. A special focus is set on the use of block copolymer micelles as templates for the synthesis of nanocomposites. The block copolymer defines the final size and shape of the nanoparticle core. Additionally it allows a further functionalization of the obtained nanoparticles by variation of the polymer blocks and an easy deposition of the composite material on surfaces.

Phthalocyanine-based coordination polymer nanoparticles for enhanced photodynamic therapy

In the photodynamic therapy (PDT) of cancer, zinc phthalocyanine (ZnPc) as a photosensitizer possesses superior photosensitive properties. However, the therapeutic effect of ZnPc in PDT is limited due to its aggregation, low solubility and poor selectivity. In this study, charge-reversal phthalocyanine-based coordination polymer nanoparticles (PCPN) are developed for improving the curative effect of ZnPc. Tetra(4-carboxyphenoxy)-phthalocyaninatozinc(ii) (TPZnPc) is coordinated with the zinc ion to form the core of PCPN, which is coated with a lipid bilayer by self-assembly (PCPNs@Lip). TPZnPc molecules in the core of PCPN are in the monomeric state and can generate cytotoxic singlet oxygen (¹O₂) efficiently, which solves the solubility and aggregation problems of ZnPc. Meanwhile, 1,2-dicarboxylic-cyclohexane anhydride modified lysyl-cholesterol (DLC) is functionalized on the surface of PCPN (PCPNs@Lip/DLC), endowing PCPN with a charge-reversal ability which could be triggered by a mildly acidic tumor microenvironment. PCPNs@Lip/DLC is proved to enhance tumor cellular uptake and generate more intracellular ¹O₂ after irradiation. As confirmed by in vitro and in vivo studies, PCPNs@Lip/DLC remarkably increases the PDT effect. All these results demonstrate that PCPNs@Lip/DLC is a promising nanoplatform for the application of ZnPc in effective PDT.

Photodegradable Coordination Polymer Particles for Light-Controlled Cargo Release

Stimuli-responsive coordination polymer particles (CPPs) show great promise for encapsulating and releasing cargos due to their unique and highly tailorable structures and properties. In particular, photoresponsive CPPs have received enormous interest, as noninvasive light can be spatially and temporally controlled, resulting in great safety and efficiency. In this work, we report the design and synthesis of novel photodegradable CPPs by infinite coordination polymerization of Zn2+ and a photocleavable organic linker containing o-nitrobenzyl derivatives. We further demonstrate that these novel photodegradable CPPs are able to efficiently encapsulate cargos and are applicable for on-command drug release upon low-power UV light irradiation (5.78 mW/cm2). Because light is a highly desirable remote-trigger and can be used externally, we expect that these photodegradable CPPs can provide a unique platform for controlled cargo release.

Influence of Intermolecular Interactions on Valence Tautomeric Behaviors in Two Polymorphic Dinuclear Cobalt Complexes

Two polymorphic structures have been well determined in a valence tautomeric (VT) dinuclear cobalt complex. These polymorphs showed distinct thermal- and photomagnetic behavior, and are thus ideal for studying the "pure" intermolecular factors to VT transitions. In polymorph 1A, the VT cations are arranged head-to-waist with their neighbors and exhibit weak π⋅⋅⋅π interactions, resulting in a gradual and incomplete thermal VT transition. In contrast, the cations in polymorph 1B are arranged head-to-tail and exhibit relatively strong π⋅⋅⋅π interactions, leading to an abrupt and complete thermal VT transition with adjustable hysteresis loop at around room temperature. The VT process for both polymorphs can be induced by light, but the light-excited state of 1B⋅2H₂ O has a higher thermal relaxation temperature than that of 1A⋅3H₂ O.

Carriers for the tunable release of therapeutics: etymological classification and examples

Introduction Physiological processes at the molecular level take place at precise spatiotemporal scales, which vary from tissue to tissue and from one patient to another, implying the need for carriers that enable tunable release of therapeutics. Areas covered Classification of all drug release to intrinsic and extrinsic is proposed, followed by the etymological clarification of the term 'tunable' and its distinction from the term 'tailorable'. Tunability is defined as analogous to tuning a guitar string or a radio receiver to the right frequency using a single knob. It implies changing a structural parameter along a continuous quantitative scale and correlating it numerically with the release kinetics. Examples of tunable, tailorable and environmentally responsive carriers are given, along with the parameters used to achieve these levels of control. Expert opinion Interdependence of multiple variables defining the carrier microstructure obstructs the attempts to elucidate parameters that allow for the independent tuning of release kinetics. Learning from the tunability of nanostructured materials and superstructured metamaterials can be a fruitful source of inspiration in the quest for the new generation of tunable release carriers. The greater intersection of traditional materials sciences and pharmacokinetic perspectives could foster the development of more sophisticated mechanisms for tunable release.

Magnetism and variable temperature and pressure crystal structures of a linear oligonuclear cobalt bis-semiquinonate

The crystal structure of the first oligomeric cobalt dioxolene complex, Co₃(3,5-DBSQ)₂(^tBuCOO)₄(NEt₃)₂, 1, where DBSQ is 3,5-di-tert-butyl-semiquinonate, has been studied at various temperatures between 20 and 200 K.

Incorporation of Fe3O4 nanoparticles into organometallic coordination polymers by nanoparticle surface modification

Surface-modified Fe(3)O(4) nanoparticles (NPs) can be obtained by substituting [(eta(5)-semiquinone)Mn(CO)(3)] for oleylamine surface protecting groups. The resulting NP can function as a nucleus or template to generate crystalline coordination polymers that contain superparamagnetic Fe(3)O(4) NPs. Hybridized magnetic properties can be obtained by introducing paramagnetic metal nodes, such as Mn(2+), into the polymers (see picture).

Metal-organic spheres as functional systems for guest encapsulation

Music of the spheres: Infinite coordination polymerization of Zn(2+) ions and a multitopic ligand produces metal-organic micro- and nanospheres that can be used as functional matrices. The spheres can encapsulate combinations of active substances, such as organic dyes, magnetic nanoparticles, or luminescent quantum dots (see image), which results in spheres that are luminescent in the blue, green, and red regions of the spectrum.

Modular synthesis of functional nanoscale coordination polymers

The coordination-directed assembly of metal ions and organic bridging ligands has afforded a variety of bulk-scale hybrid materials with promising characteristics for a number of practical applications, such as gas storage and heterogeneous catalysis. Recently, so-called coordination polymers have emerged as a new class of hybrid nanomaterials. Herein, we highlight advances in the syntheses of both amorphous and crystalline nanoscale coordination polymers. We also illustrate how scaling down these materials to the nano-regime has enabled their use in a broad range of applications including catalysis, spin-crossover, templating, biosensing, biomedical imaging, and anticancer drug delivery. These results underscore the exciting opportunities of developing next-generation functional nanomaterials based on molecular components.