An alternative method to access diverse N,N′-diquaternised-3,3′-biquinoxalinium “biquinoxen” dications

An alternative synthetic route for the design of N,N′-diquaternised-3,3′-biquinoxalinium “biquinoxen” dications is reported, involving oxidative radical coupling of dithionite reduced quinoxaline quaternary salts. Although the reaction is not regioselective, leading to relatively modest yields (up to 32%), the advantages of this new synthetic protocol lie in a simple potentially gram scale synthesis using inexpensive easily accessible reagents with no metal catalysts and no purification steps. Thus whereas the method reported previously to access the N,N′-dimethyl-3,3′-biquinoxalinium, “methylbiquinoxen” precursor gave higher yield than the new method reported here, this new method avoids the limitation of using scarce oxonium reagents. Overall, the new protocol is a robust synthetic strategy which offers new design possibilities

From the FeIII^{III}2_{2}Ln2_{2} Butterfly’s Perspective: the Magnetic Benefits and Challenges of Cooperativity within 3 d–4 f Based Coordination Clusters

The well-known oxo-centred Fe triangle is used to access the vast majority of [Fe$^{III}$$_{2}$Ln$_{2}$(μ$_{3}$-OR)$_{2}$L$_{2}$(O$_{2}$CR)$_{6}$] butterflies, since it provides a di-iron central body unit and carboxylate bridges to the wingtips, which are occupied by supplied Ln ions. The remaining coordination sites of the lanthanide are occupied by a multidentate ligand, which can also provide further bridging. This system provides a useful testbed for exploring multiple variations, for example changing the Ln, the bridging carboxylate and the nature of the chelating ligand. In this Review we discuss the tuning handles which can be used to steer the magnetic properties of Fe$^{III}$-4 f “butterfly” compounds. The majority of presented compounds were produced in the context of project A3 “Di- to tetranuclear compounds incorporating highly anisotropic paramagnetic metal ions” within the SFB/TRR88 “3MET”. These contain {Fe$^{III}$$_{2}$Ln$_{2}$} cores encapsulated in ligand shells which are easy to tune in a “test-bed” system. We identify the following advantages and variables in such systems: (i) the complexes are structurally simple usually with one crystallographically independent Fe$^{III}$ and Ln$^{III}$ respectively. This simplifies theory and anaylsis; (ii) choosing Fe allows $^{57}$Fe Mössbauer spectroscopy to be used as an additional technique which can give information about oxidation levels and spin states, local moments at the iron nuclei and spin-relaxation and, more importantly, about the anisotropy not only of the studied isotope, but also of elements interacting with this isotope; (iii) isostructural analogues with all the available (i. e. not Pm) 4 f ions can be synthesised, enabling a systematic survey of the influence of the 4 f ion on the electronic structure; (iv) this cluster type is obtained by reacting [Fe$^{III}$$_{3}$O(O$_{2}$CR)$_{6}$(L)$_{3}$](X) (X=anion, L=solvent such as H$_{2}$O, py) with an ethanolamine-based ligand L′ and lanthanide salts. This allows to study analogues of [Fe$^{III}$$_{2}$Ln$_{2}$(μ$_{3}$-OH)$_{2}$(L′)$_{2}$(O$_{2}$CR)$_{6}$] using the appropriate iron trinuclear starting materials. (v) the organic main ligand can be readily functionalised, facilitating a systematic investigation of the effect of organic substituents on the ligands on the magnetic properties of the complexes. We describe and discuss 34 {M$^{III}$$_{2}$Ln$_{2}$} (M=Fe or in one case Al) butterfly compounds which have been reported up to 2020. The analysis of these gives perspectives for designing new SMM systems with specific electronic and magnetic signature

Approaching the limit of CuII/CuImixed valency in a CuIBr2–N-methylquinoxalinium hybrid compound

A novel 1D hybrid salt (MQ)[CuBr2]∞ (MQ = N-methylquinoxalinium) is reported. Structural, spectroscopic and magnetic investigations reveal a minimal CuII doping of less than 0.1%. However it is not possible to distinguish CuI and CuII. The unusually close packing of the organic moieties and the dark brown colour of the crystals suggest a defect electronic structure

Synthesis and Supramolecular Structure of a (5-(3-(1H-tetrazol-5-yl)phenyl)-1H-tetrazole) Cobalt Complex

The reaction of CoCl2·6H2O with m-BDTH2 (1,3-benzeneditetrazol-5-yl) leads to [Co(C8H6N8)2(H2O)2(CH3CN)2]Cl2 (1). Both tetrazolic groups remain protonated existing in a 1H tautomeric form. A trifurcated chlorine atom and stacking interactions assemble compound 1 into a three-dimensional network

A fascinating multifaceted redox-active chelating ligand: introducing the N,N′-dimethyl-3,3′-biquinoxalinium “methylbiquinoxen” platform

To intimately combine a chelating ligand function with the numerous properties of a viologen-like redox-active centre would offer a rare possibility to design controllable multi-redox states, whose properties arise from strongly correlated phenomena between the organic ligand as well as with any metalloid coordinated centres. Such a concept previously proved to be feasible, however is not widely applicable owing to challenges in terms of synthesis, isolation, and aerial sensitivity of both the ligand and its metal complexes. Here we report the first stable example of such a redox-active molecule, N,N′-dimethyl-3,3′-biquinoxalinium2+/˙+/0 “methylbiquinoxen, MBqn2+/˙+/0”, which shows a rich redox chemistry and chelates a metal ion in the case of the metal complex [CdCl2(MBqn0)]. This goes beyond what is possible to achieve using viologens, which are limited by not providing chelation as well as having no accessible biradicaloid state, corresponding to the neutral direduced MBqn0 open-shell behaviour we observe here

A nickel(II) complex with an unsymmetrical tetradentate chelating ligand derived from pyridine-2,6-dicarbaldehyde and 2-aminothiophenol

[(2-{[6-(1,3-Benzo­thia­zol-2-yl)pyridin-2-yl]carbonyl­aza­nid­yl}phen­yl)sulf­anido]nickel(II), [Ni(C$_{19}$H$_{11}$N$_3$OS$_2$)], crystallizes in the centrosymmetric monoclinic space group $P2_1/n$ with one mol­ecule in the asymmetric unit. The expected ligand, a bis-Schiff base derived from pyridine-2,6-dicarbaldehyde and 2-amino­thio­phenol, had modified in situ in a both unexpected and unsymmetrical fashion. One arm had cyclized to form a benzo[$d$]thia­zol-2-yl functionality, while the imine linkage of the second arm had oxidized to an amide group. The geometry about the central Ni$^{II}$ atom is distorted square-planar N$_3$S. The mol­ecules form supra­molecular face-to-face dimers via rather strong π–π stacking inter­actions, with these dimers then linked into chains via pairwise C—H$\cdot\cdot\cdot$O inter­actions

A designed and potentially decadentate ligand for use in lanthanide(III) catalysed biomass transformations: targeting diastereoselective trans-4,5-diaminocyclopentenone derivatives

The goal of this study was to design a ligand system which can accommodate single lanthanide(III)-ions and investigate the properties of the resulting complexes. The complexes of all the accesible lanthanides and yttrium with the new ligand LH6 = N,N′-dimethyl-N,N′-ethylene-bis(5-bromo-3-(1H-benzimidazol-2-yl)hydrazineylidene)-2-hydroxybenzylamine) were obtained in high yield at room temperature under aerobic reaction conditions. The corresponding compounds were characterised using X-ray diffraction, FT-IR, elemental analysis and the optical properties of all complexes were investigated using UV-vis and fluorescence spectroscopy. The air stable complexes efficiently transform biomass furfural to trans-4,5-cyclopentenones in high yield

An undecanuclear ferrimagnetic Cu9Dy2 SMM achieved through ligand fine-tuning

We describe the concept of increasing the nuclearity of a previously reported high-spin Cu5Gd2 core using a “fine tuning” ligand approach. Thus two Cu9Ln2 coordination clusters, with Ln = Dy (1), Gd(2) were synthesized with the Gd compound having a ground spin state of 17/2 and the Dy analogue showing SMM behavior in zero field

Pseudopeptidic ligands: exploring the self-assembly of isopthaloylbisglycine (H2IBG) and divalent metal ions

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Tetranuclear CuII2DyIII2 coordination cluster as Suzuki (C–C) coupling reaction promoter

The air stable and high yielding tetranuclear coordination cluster [CuII2DyIII2L4(NO3)2(CH3CN)2]·2(CH3CN) promotes the Suzuki coupling reaction of phenylboronic acid with substituted aryl halides in environmentally benign conditions