1,721,027 research outputs found
Spin crossover in iron(II) complexes of 3,5-di(2-pyridyl)-1,2,4-triazoles and 3,5-di(2-pyridyl)-1,2,4-triazolates
No full textThe iron coordination chemistry of 3,5-di(2-pyridyl)-1,2,4-triazoles and 3,5-di(2-pyridyl)-1,2,4-triazolates is reviewed. This includes both mononuclear and dinuclear complexes, and both iron(II) and iron(III) oxidation states. The main focus is on the synthesis, structure and magnetic properties of these complexes
Two dicobalt(iii) complexes of triazolate-containing [2+2] Schiff-base macrocycles coordinate thiocyanate ions via the sulfur atom
No full textHighly unusual S-coordination modes are observed for the four axial thiocyanate co-ligands in two structurally characterised dicobalt(III) [2+2] triazolate-based macrocyclic complexes
Nano-magnetic materials: spin crossover compounds vs. single molecule magnets vs. single chain magnets
No full textBrief introductions to spin crossover (SCO), single molecule magnetism (SMM) and single chain magnetism (SCM) are provided. Each section is illustrated by selected examples that have contributed significantly to the development of these fields, including recent efforts to produce materials (films, attachment to surfaces etc.). The advantages and disadvantages of each class of magnetically interesting compound are considered, along with the key challenges that remain to be overcome before such compounds can be used commercially as nanocomponents. This invited perspective article is intended to be easily comprehensible to non-specialists in the field
Surface-based molecular self-assembly: Langmuir-Blodgett films of amphiphilic Ln(III) complexes
No full textThe unique photophysical properties of the Ln(III) series has led to significant research efforts being directed towards their application in sensors. However, for “real-life” applications, these sensors should ideally be immobilised onto surfaces without loss of function. The Langmuir-Blodgett (LB) technique offers a promising method in which to achieve such immobilisation. This mini-review focuses on synthetic strategies for film formation, the effect that film formation has on the physical properties of the Ln(III) amphiphile, and concludes with examples of Ln(III) LB films being used as sensors
Colorimetric ‘naked eye’ sensing of anions using a thiosemicarbazide receptor: a case study of recognition through hydrogen bonding versus deprotonation
No full textThe thiosemicarbazide receptors 1 and 2, containing three N–H donors (including a thiourea motif), have been synthesized and studied for their anion binding abilities. The recognition of 1 and 2 with various anions [AcO?, F?, H2PO4?, SO42? and OH? for 1; OAc? and F? for 2] as their tetrabutylammonium salts was studied spectroscopically in CH3CN and EtOH. Significant changes were observed in the UV–vis absorption spectra of 1 which was red-shifted in both solvents when titrated with these anions. A dramatic colour change from yellow to red was also clearly observed. In contrast, the absorption changes for 2 were smaller with a colour change from colourless to yellow. These changes were determined to be due to deprotonation of the central N–H moiety (belonging to the thiourea) and not due to hydrogen bonding of these anions to the receptors. This was confirmed using single crystal X-ray crystallography, as crystals of 1 grown with TBAAc were found to correspond to the deprotonated structure 3
Lanthanides: supramolecular chemistry
No full textIn this chapter, some of the most recent examples of the use of lanthanide ions in the formation of functional supramolecular complexes and self-assemblies are detailed. The examples focus mainly on the use of the lanthanides to direct the synthesis of complex structures published within the last few years, in the form of mononuclear or polynuclear complexes, where the physical properties of the lanthanides, such as their luminescent and magnetic properties, have been exploited to form functional supramolecular assemblies, e.g., luminescent-based sensors or single molecule magnets (SMMs). The use of the lanthanides to direct the formation of complex self-assembly architectures is an area of research that is rapidly growing in the field of lanthanide-based supramolecular chemistry, where the coordination requirements of the lanthanides when coupled with ligand design can give rise to the formation of highly novel and structurally complex species
Alkylations ofN4-(4-Pyridyl)-3,5-di(2-pyridyl)-1,2,4-triazole: first observation of room-temperature rearrangement of anN4-substituted triazole to the N1 analogue
No full textAttempts to use alkylation to introduce a positive charge at the nitrogen atom of the 4-pyridyl ring in the bis(bidentate) triazole ligand N-4-(4-pyridyl)-3,5-di(2-pyridy1)-1,2,4-triazole (pydpt) were made to ascertain what effect a strongly electron-withdrawing group would have on the magnetic properties of any subsequent iron(II) complexes. Alkylation of pydpt under relatively mild conditions led in some cases to unexpected rearrangement products. Specifically, when benzyl bromide is used as the alkylating agent, and the reaction is carried out in refluxing acetonitrile, the N-4 substituent moves to the NI position. However, when the same reaction is performed in dichloromethane at room temperature, the rearrangement does not occur and the desired product containing an alkylated N4 substituent is obtained. Heating a pure sample of N-4-Bzpydpt center dot 3r to reflux in MeCN resulted in clean conversion to N-1-Bzpydpt center dot Br. This is consistent with AP-Bzpydpf Br being the kinetic product whereas N-1-Bzpydpt.Br is the thermodynamic product. When methyl iodide is used as the alkylating agent, the N-4 to N-1 rearrangement occurs even at room temperature, and at reflux pydpt is doubly alkylated. The observation of the lowest reported temperatures for an N-4 to N-1 rearrangement is due to this particular rearrangement involving nucleophilic aromatic substitution: a possible mechanism for this transformation is suggested
Fluorescenttren-based 4-amino-1,8-naphthalimide sensor for Cu(II) based on the use of the (fluorophore–spacer–receptor) photoinduced electron transfer (PET) principle
No full textThe design, synthesis and photophysical evaluation of a new chemosensor for copper [Cu(II)] is described based on the use of a functionalised 1,8-naphthlimide structure substituted at the 4-position with a tris(2-aminomethyl)amine-based (tren) ligand as a receptor for Cu(II). The sensor 1 functions as a classical photoinduced electron transfer sensor for protons, where the 4-amino-1,8-naphthalimide emission, occurring in the green part of the electromagnetic spectrum, is reversibly switched ‘ON–OFF’. A screen of various groups I and II as well as d-metal ions showed that only in the case of Cu(II), in buffered 100 mM NaCl solution, was the emission of 1 modulated, being quenched by ca. 80% upon addition of one equivalent of CuCl2 in buffered solution. The emission was, however, reversibly switched back ON, by the addition of either EDTA or glutathione. While only small changes occurred in the ground state, analysis of the changes in the emission spectra at various pH values showed that Cu(II) was detected through the formation of either a 2:1 or a 1:1 (ligand to metal) stoichiometry. The overall changes in the emission spectra of 1 as a function of H+ and Cu(II) can also be described as a molecular-level logic gate operation, corresponding to a two-input INHIBIT function
The effect of the 4-amino functionality on the photophysical and DNA binding properties of alkyl-pyridinium derived 1,8-naphthalimides
No full textThe synthesis and characterisation of two cationic pyridinium based 4-amino-1,8-naphthalimide derivatives ( and ) are described and compared to those of compound . The photophysical properties of and are shown to vary greatly with the solvent polarity and H-bonding ability. The dimethylamino substitution in results in a weak quantum yield of fluorescence emission due to faster non-radiative deactivation of the excited singlet state than that seen for . As with , the fluorescence of was found to be enhanced in its 1:1 complex with 5'-adenosine-monophosphate (5'-AMP) while it was partially quenched in its complex with 5'-guanosine-monophosphate (5'-GMP). In contrast, the fluorescence of was enhanced ('switched on') in the presence of both adenine and guanine rich sequences. Linear and circular dichroism studies showed that each of , and binds to double-stranded DNA by intercalation. However, and do not show the preference for AT-rich DNA observed for . Comparative fluorescence studies with double stranded DNA show that the emission of was 16 times enhanced in its DNA bound form, suggesting potential use of this structure as a spectroscopic probe for studying nucleic acid structure
Hydrogen bonding interactions and supramolecular networks of pyridine-aryl based thiosemicarbazides and their Zn(ii) complexes
No full textThe synthesis of five pyridyl derived thiosemicarbazides, 1–5, is presented. All five were formed in a single step from 2-hydrazinopyridine with commercially available isothiocyanates using microwave assisted synthesis. Compounds 1–4 were structurally characterised by single crystal diffraction analysis, and showed extended supramolecular hydrogen bonding arrays. Furthermore, the Zn(II) complexes 6 and 7 have been prepared using ligands 1 and 5, and structurally characterised, again showing elegant assemblies of metal-supramolecular structures with solvent accessible channels, demonstrating that these building units are excellent candidates for use in supramolecular chemistry and crystal engineering
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