High Nuclearity Antimonato‐Polyoxovanadate Cluster {V15Sb6O42} as a Synthon for the Solvothermal in situ Generation of α‐ and β‐{V14Sb8O42} Isomers

New heteroatom polyoxovanadates (POVs) were synthesized by applying a water‐soluble high‐nuclearity cluster as new synthon. The [V₁₅Sb₆O₄₂]^6? cluster shell exhibiting D₃ symmetry was in situ transformed into completely different cluster shells, namely, the α‐[V₁₄Sb₈O₄₂]^4? isomer with D_2d and the β‐[V₁₄Sb₈O₄₂]^4? isomer with D_2h symmetry. The solvothermal reaction of {Ni(en)₃}₃[V₁₅Sb₆O₄₂(H₂O)_x] ? 15 H₂O (x=0 or 1; en=ethylenediamine) in water led to the crystallization of [{Ni(en)₂}₂V₁₄Sb₈O₄₂] ? 5.5 H₂O containing the β‐isomer. The addition of [Ni(phen)₃](ClO₄)₂ ? 0.5 H₂O (phen=1,10‐phenanthroline) to the reaction slurry gave the new compound {Ni(phen)₃}₂[V₁₄Sb₈O₄₂] ? phen ? 12 H₂O with the α‐isomer. Both transformation reactions are complex due the change of symmetry, the chemical composition, and rearrangement of the VO₅ square pyramids and Sb₂O₅ handle‐like moieties.     

Supramolecular Recognition Influences Magnetism in [X@HVIV8VV14O54]6− Self‐Assemblies with Symmetry‐Breaking Guest Anions

Mixed‐valence polyoxovanadates(IV/V) have emerged as one of the most intricate class of supramolecular all‐inorganic host species, able to encapsulate a wide variety of smaller guest templates during their self‐assembly formation process. As showcased herein, the incorporation of guests, though governed solely by ultra‐weak electrostatic and van der Waals interactions, can cause drastic effects on the electronic and magnetic characteristics of the shell complex of the polyoxovanadate. We address the question of methodology for the magnetochemical analysis of virtually isostructural {V^IV/V₂₂O₅₄}‐type polyoxoanions of D_2d symmetry enclosing diamagnetic VO₂F₂^? (C_2v), SCN^? (C_∞v), or ClO₄^? (T_d) template anions. These induce different polarization effects related to differences in their geometric structures, symmetry, ion radii, and valence shells, eventually resulting in a supramolecular modulation of magnetic exchange between the V(3d) electrons that are partly delocalized over the {V₂₂O₅₄} shells. We also include the synthesis and characterization of the novel [V^VO₂F₂@HV^IV₈V^V₁₄O₅₄]^6? system that comprises the rarely encountered discrete difluorovanadate anion as a quasi‐isolated guest species.     

A novel oxovanadate structural type – Synthesis,single crystal structure and magnetic properties of a mixed-valence polyoxovanadate formed by {V17O40(Cl)} and {V15O36(Cl)} clusters

A novel polyoxovanadate structural type, with an average nuclearity of V₁₆, formed by a mixture of two different polyoxovananadates: {V₁₅O₃₆(Cl)} and{V₁₇O₄₀(Cl)} has been synthesized and characterized. The title compound, formulated as [Ni(phen)₃]₂{[V₁₅O₃₆(Cl)]_0.5[V₁₇O₄₀(Cl)]_0.5} · H₂O (1) (phen = 1,10′-phenanthroline), presents two different polyoxovanadate architectures: {V₁₅O₃₆(Cl)} and {V₁₇O₄₀(Cl)}, with the last one representing a new framework type in polyoxovanadate chemistry. Here, we present the synthesis of this novel polyoxovanadate under hydrothermal conditions and its characterization by IR and XPS spectroscopies, elemental and thermogravimetric analysis, redox titration, magnetic measurements and single-crystal X-ray diffraction.     

pH-Dependent Assembly of Two Novel Organic–inorganic Hybrids Based on Vanadoantimonate Clusters

Two novel organic–inorganic hybrid vanadoantimonate compounds, [Zn₂(dien)₃][{Zn(dien)}₂V₁₆Sb₄O₄₂(H₂O)]·4H₂O (1) and [Zn(dien)₂]₂ [{Zn(dien)}₂(V₁₄Sb₈O₄₂)₂(H₂O)]·4H₂O (2) (dien = Diethylenetriamine), have been synthesized hydrothermally at different pH value, and structurally characterized by elemental analyses, FT-IR, XPS, TGA and single crystal X-ray diffraction analysis. Compound 1 is composed of the rare [V₁₆Sb₄O₄₂]⁸⁻ cluster covalently linked by two [Zn(dien)]²⁺ coordination cations to yield a novel one-dimensional linear chain. Compound 2 exhibits a one-dimensional zigzag chain constructed from the [V₁₄Sb₈O₄₂]⁴⁻ cluster and [Zn(dien)]²⁺ coordination polymer. The two examples represent the first one-dimensional assemblies based on vanadoantimonate cluster and the metal–organic complex moieties.     

New Perspectives for Old Clusters: Anderson–Evans Anions as Building Blocks of Large Polyoxometalate Frameworks in a Series of Heterometallic 3 d–4 f Species

A series of nine [Sb₇W₃₆O₁₃₃Ln₃M₂(OAc)(H₂O)₈]^17? heterometallic anions ( Ln₃M₂ ; Ln=La–Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs‐type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW₉O₃₃} capping unit formed by a planar {MW₆O₂₄} fragment to which three {WO₂} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ?‐Keggin cluster. It is shown, for the first time, that classical Anderson–Evans {MW₆O₂₄} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk‐shaped species is also revealed. The Ln₃M₂ anions possess chirality owing to a {Sb₄O₄} cluster being encapsulated in left‐ or right‐handed orientations. Their ability to self‐associate in blackberry‐type vesicles in solution has been assessed for the Ce₃Co₂ derivative.     

Ba3MIIITiMVO9 (MIII = Fe,Ga, Y,Lu; MV = Nb,Ta, Sb) perovskite oxides: Synthesis,structure and dielectric properties

We describe the synthesis, structures and dielectric properties of new perovskite oxides of the formula, Ba₃M^IIITiM^VO₉, for M^III = Fe, Ga, Y, Lu and M^V = Nb, Ta, Sb. While M^V = Nb and Ta oxides adopt disordered/partially ordered 3C perovskite structures where M^III/Ti/M^V metal-oxygen octahedra are corner-connected, the M^V = Sb oxides show a distinct preference for the 6H structure, where Sb^V/Ti^IV metal-oxygen octahedra share a common face forming (Sb,Ti)O₉ dimers that are corner-connected to the M^IIIO₆ octahedra. The preference of antimony oxides (Sb^V:4d¹⁰) for the 6H structure – which arises from a special Sb^V–O chemical bonding that tends to avoid linear Sb–O–Sb linkages unlike Nb^V/Ta^V:d⁰ atoms which prefer ～180° Nb/Ta–O–Nb/Ta linkages – is consistent with the crystal chemistry of M^V–O oxides in general. The dielectric properties reveal a significant difference among M^III members. All the oxides with the 3C structure excepting those with M^III = Fe show a normal low loss dielectric behaviour with ε = 20–60 in the temperature range 50–400 °C; the M^III = Fe members with this structure (M^V = Nb, Ta) display a relaxor-like ferroelectric behaviour with large ε values at frequencies ≤1 MHz (50–500 °C).     

Time‐Resolved Assembly of Cluster‐in‐Cluster {Ag12}‐in‐{W76} Polyoxometalates under Supramolecular Control

We report the time‐resolved supramolecular assembly of a series of nanoscale polyoxometalate clusters (from the same one‐pot reaction) of the form: [H_(10+m)Ag₁₈Cl(Te₃W₃₈O₁₃₄)₂]_n, where n=1 and m=0 for compound 1 (after 4 days), n=2 and m=3 for compound 2 (after 10 days), and n=∞ and m=5 for compound 3 (after 14 days). The reaction is based upon the self‐organization of two {Te₃W₃₈} units around a single chloride template and the formation of a {Ag₁₂} cluster, giving a {Ag₁₂}‐in‐{W₇₆} cluster‐in‐cluster in compound 1 , which further aggregates to cluster compounds 2 and 3 by supramolecular Ag‐POM interactions. The proposed mechanism for the formation of the clusters has been studied by ESI‐MS. Further, control experiments demonstrate the crucial role that TeO₃^2?, Cl^?, and Ag⁺ play in the self‐assembly of compounds 1 – 3 .     

Controlling Nucleation and Crystal Growth of a Distinct Polyoxovanadate Cluster: An In Situ Energy Dispersive X‐ray Diffraction Study under Solvothermal Conditions

The formation of the antimonato polyoxovanadates [V₁₄Sb₈(C₆H₁₅N₃)₄O₄₂(H₂O)] ? 4H₂O ( 1 ), (C₆H₁₇N₃)₂[V₁₅Sb₆(C₆H₁₅N₃)₂O₄₂(H₂O)] ? 2.5H₂O ( 2 ), {C₆H₁₅N₃}₄[V₁₆Sb₄O₄₂] 2H₂O ( 3 ) (C₆H₁₅N₃=1‐(2‐aminoethyl)piperazine, AEP) has been studied under solvothermal conditions by using in situ energy dispersive X‐ray diffraction (EDRXD). The syntheses were performed with an identical ratio for Sb₂O₃ and NH₄VO₃. If the reactions slurries are not stirred during the solvothermal reaction and by applying 70–75 % amine concentration, the products contain all three compounds, whereas 3 is observed at 80 %. Under stirring conditions, variation of the concentration of AEP led to crystallization of the three different compounds at distinct concentrations, that is, 1 is formed at 75 %, 1 and 2 between 75 and 80 % and 3 at 80 %. At an amine concentration of 77.5 %, first reflections of 2 occurred and at later stages, compound 1 started to crystallize. The sample with the lowest number of V^IV species was formed at the lowest amine concentration, whereas crystallization of 3 required the highest concentration. The formation of the compounds occurred without crystalline intermediates and/or precursors. With increasing reaction temperature, the incubation time was significantly reduced.     

Unprecedented High‐Nuclear Transition‐Metal‐Cluster‐Substituted Heteropolyoxoniobates: Synthesis by {V8} Ring Insertion into the POM Matrix and Antitumor Activities

Reactions of hexaniobate with vanadate in the presence of Ni²⁺, Zn²⁺, or Cu²⁺ have furnished three high‐nuclear vanadium cluster‐substituted heteropolyoxoniobates (HPNs): {Ni(en)₃}₅H{V^VNb₈V^IV₈O₄₄} ? 9 H₂O ( 1 ), (H₂en)Na₂[{Zn(en)₂(Hen)}{Zn(en)₂(H₂O)}₂{PNb₈V^IV₈O₄₄}] ? 11 H₂O ( 2 ), and Na{Cu(en)₂}₃{[Cu(en)₂]₂[PNb₈V^IV₈O₄₄]} ? 11 H₂O ( 3 ) (en=1,2‐diaminoethane). Their structures have been determined and characterized by single‐crystal X‐ray diffraction analysis, thermogravimetric analysis (TGA), and elemental analysis. Structural analysis has revealed that compounds 1 – 3 contain similar {V₈}‐substituted [X^VNb₈V^IV₈O₄₄]^11? (X=P, V) clusters, obtained by inserting a {V₈} ring into tetravacant HPN [XNb₈O₃₆]^27?. To the best of our knowledge, compounds 1 – 3 represent the first high‐nuclear vanadium cluster‐substituted HPNs, and compound 1 is the largest vanadoniobate cluster yet obtained in HPN chemistry. Nickel and zinc cations have been introduced into HPNs for the first time, which might promise a more diverse set of structures in this family. Antitumor studies have indicated that compounds 1 and 2 exhibit high activity against human gastric cancer SGC‐7901 cells, SC‐1680 cells, and MG‐63 cells.     

[M3V18O42(H2O)12(XO4)]⋅24 H2O (M=Fe,Co; X=V,S): Metal Oxide Based Framework Materials Composed of Polyoxovanadate Clusters

New framework materials composed of well-defined vanadium oxide clusters were prepared by low-temperature reactions and characterized by X-ray crystal structure analysis. The structures of these solids contain {V₁₈O₄₂} cages linked into two interpenetrating three-dimensional networks by bridging {M(H₂O)₄} groups (M=Fe^II, Co^II; see picture).     

Following the Reaction of Heteroanions inside a {W18O56} Polyoxometalate Nanocage by NMR Spectroscopy and Mass Spectrometry

By incorporating phosphorus(III)‐based anions into a polyoxometalate cage, a new type of tungsten‐based unconventional Dawson‐like cluster, [W₁₈O₅₆(HP^IIIO₃)₂(H₂O)₂]^8?, was isolated, in which the reaction of the two phosphite anions [HPO₃]^2? within the {W₁₈O₅₆} cage could be followed spectroscopically. As well as full X‐ray crystallographic analysis, we studied the reactivity of the cluster using both solution‐state NMR spectroscopy and mass spectrometry. These techniques show that the cluster undergoes a structural rearrangement in solution whereby the {HPO₃} moieties dimerize to form a weakly interacting (O₃PH???HPO₃) moiety. In the crystalline state the cluster exhibits a thermally triggered oxidation of the two P^III template moieties to form P^V centers (phosphite to phosphate), commensurate with the transformation of the cage into a Wells–Dawson {W₁₈O₅₄} cluster.     

{[CuSn5Sb3]2−}2: A Dimer of Inhomogeneous Superatoms

Reaction of the binary Zintl anion (Sn₂Sb₂)^2? with the β‐diketiminato complex [LCu(NCMe)] (L=nacnac=[(N(C₆H₃ⁱPr₂‐2,6)C(Me))₂CH]^?) in ethylenediamine or DMF affords the ternary cluster dimer {[CuSn₅Sb₃]^2?}₂ ( 1 ) as its [K(crypt‐222)]⁺ salt. The chemical formulation of 1 is supported by energy‐dispersive X‐ray spectroscopy (EDX) and quantum chemical calculations. Each monomeric part of the dimer represents a trimetallic “[CuSn₅Sb₃]^2?” cluster, with an architecture in between a tricapped trigonal prism and a capped square antiprism. As shown by quantum chemical investigations, the presence of Sb atoms and, in particular, of Cu atoms in the cluster skeleton makes the monomeric unit behave like an inhomogeneous superatom, which clearly prefers to dimerize, thereby producing a relatively short, yet virtually non‐bonding Cu???Cu distance.     

Syntheses,structures, and magnetism of {V15M6O42(OH)6(Cl)} (M = Si,Ge)

Two [V₁₅M₆(OH)₆O₄₂(Cl)]^7? (M = Si for 1, Ge for 2) cluster anions with protonated amines as counterions have been synthesized under hydrothermal conditions and characterized by FT-IR, energy dispersive spectroscopy, XPS, powder X-ray diffraction, thermogravimetric analysis (TGA), elemental analysis, and single-crystal X-ray analyses. Both compounds consist of {V₁₅M₆O₄₂(OH)₆(Cl)} (M = Si for 1, Ge for 2), which are derived from {V₁₈O₄₂} by substitution of three {VO₅} square pyramids with three {Si₂O₅(OH)₂/Ge₂O₅(OH)₂} units. It represents the first example of cage-like polyoxovanadates (POVs) containing three (Si/Ge)₂O₅(OH)₂ units. There are extensive hydrogen bonding interactions between POVs and organoamines in 1 and 2. Compound 1 presents a close-packed layer aggregate, while 2 exhibits the packing of six-membered rings with a 1-D channel. Magnetism measurements demonstrate the presence of strong antiferromagnetic interaction between V^IV centers in 1.     

Hydrothermal synthesis and crystal structure of a 1-D compound constructed from molybdovanadate clusters [V2Mo6O26]6− and copper complexes

A 1-D organic–inorganic hybrid compound, {Cu(en)₂}[V₂Mo₆O₂₆{Cu(en)₂}₂] · 4H₂O [en = ethylenediamine] (1), was hydrothermally synthesized and characterized by IR, UV spectroscopy, TG/DTA analyses, and single crystal X-ray diffraction. The X-ray crystallography analysis reveals an infinitely extended 1-D chain constructed from a molybdovanadate cluster [V₂Mo₆O₂₆]^6? as a building unit, two copper(II) complex fragments, {Cu(en)₂}²⁺, as attached groups and a copper(II) fragment, {Cu(en)₂}²⁺, as a bridging group. Each chain links to adjacent chains through weaker secondary Cu–O interactions forming an interesting 3-D supramolecular architecture.     

Theoretical study of isomerism in protonated forms of N2O,NPO, and P2O

The geometric parameters of the isomers HN₂O⁺, HPNO⁺, and HP₂O⁺ were calculated by the nonempirical SCF/3-21G* method and their relative energies were determined with consideration of the electronic correlation in the MP3/DEHD + PS approximation. According to the calculations, protonation of N₂O, PNO, and P₂O molecules should preferably take place at the oxygen atom. Isomers with a quasilinear NNO and PNO backbone are most advantageous in HN₂O⁺ and HPNO⁺, and cyclic isomers are 60 and 30 kcal/mole less stable, respectively. On the contrary, the cyclic form is more stable for HPO ₂ ⁺ (by 10 kcal/mole). The bond at the attacked atom usually weakens (breaks) and the neighboring (opposite) bonds are strengthened in protonation. Protonation of P₂O stabilizes the cyclic isomer by 15 kcal/mole more strongly than the "open" isomer, resulting in inversion of their position on the energy scale. In the case of N₂O and PNO, the relative position of the cyclic and basic isomers virtually does not change, but the linear NPO isomer is destabliized. The stability of the cyclic isomers in comparison to the "open" isomers increases on substitution of N atoms by P atoms in both molecules of N₂O, PNO, and P₂O and in their ions HN₂O⁺, HPNO⁺, and HP₂O⁺. This tendency probably holds in subsequent transition to As and Sb atoms.Institute of New Chemical Problems, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 126–134, January, 1992.     

Layered polyoxovanadate V15: from structure to highly anisotropic magnetism§

Abstract

In this article, we give a short overview of the theoretical background and properties of the unique polyoxovanadate K₆[V^IV₁₅As₆O₄₂(H₂O)]·8H₂O (abbreviated V₁₅) containing a cluster of the fifteen V^IV ions and exhibiting layers of different magnetizations. Analysis of the magnetic and spectroscopic properties of this fascinating system constitutes a distinct trend in the study of complex nanoscopic polyoxometalates. V₁₅ cluster exhibits strong magnetic anisotropy closely related to the unquenched orbital angular momentum in the degenerate ground state. The degeneracy is interrelated with the spin frustration in V₁₅ which gives rise to a variety of interesting phenomena observed in this polyoxovanadate. We summarize the studies of the isotropic and antisymmetric exchange interaction and analyze its manifestations in magnetic properties, electron paramagnetic resonance, and inelastic neutron scattering spectra as well as in the spin-phonon relaxation in V₁₅. We briefly discuss also a long coherence time (Rabi oscillations) first discovered in molecular magnets due to which the V₁₅ cluster proved to be a prerequisite for the use of molecular magnets in quantum computing.     

The Missing Link in Low Nuclearity Pure Polyoxovanadate Clusters: Preliminary Synthesis and Structural Analysis of a New {V16} Cluster and Related Products

Two new metastable polyoxovanadate-based cluster compounds have been isolated and crystallographically characterized with nuclearities of {V₁₆} (1) and {V₁₈} (2). The {V₁₆} cluster represents a new framework type and incorporates two protons into the cluster framework whereas the {V₁₈} framework has been previously characterised, and the oxidation states of the {V₁₈} cluster can be assigned as {V^IV ₁₅V^V ₃}. Compound K₁₀[H₂V₁₆O₃₈]13H₂O (1) crystallizes in the monoclinic space group P2₁/c, a=12.12820(10), b=38.2302(3), c=12.35400(10) Å, =115.0470(10)°, V=5189.43(7) ų, D _c=2.624 gcm^–3. 10086 unique reflection and 702 refined parameters were used in structure refinement. R1=0.039, R2=0.109 (all data). From the same preparation the new compound K₁₁[V₁₈O₄₂(SO₄)]20H₂O (2) was also isolated and crystallographically characterized. Compound 2 crystallizes in the monoclinic space group P2₁/n, a=12.7854(3), b=20.2812(5), c=13.2386(4) Å, =115.3400(10)°, V=3102.53(14) ų, D _c=2.650 gcm^–3. 7115 unique reflections and 462 refined parameters were used in structure refinement. R1=0.046, R2=0.121 (all data).     

A New Molybdophosphate Constructed From {Mo<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>O<Subscript>4</Subscript>(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>}<Superscript>2+</Superscript> and 1-Hydroxyethylidenediphosphonate

A new molybdophosphate (NH₄)₈{Mo₂^VO₄[(Mo₂^VIO₆)CH₃C(O)(PO₃)₂]₂}·14H₂O (1), has been synthesized by the reaction of {Mo₂^VO₄(H₂O)₆}²⁺ fragments with 1-hydroxyethylidenediphosphonate (hedp HOC(CH₃)(PO₃H₂)₂), and it is characterized by ³¹P NMR, IR, UV, element analysis, TG and single-crystal X-ray analysis. The structure analysis reveals that the polyoxoanion can be described as two {(Mo₂^VIO₆)(CH₃C(O)(PO₃)₂} units connected by a {Mo₂^VO₄}²⁺ moiety. In the structure, the six Mo atoms are arranged into a new “W-shaped” structure, which represents a new kind of molybdophosphate.     

The first di-cadmium-substituted vanadoarsenate derived from α-{As8V14O42} shell

Two di-cadmium-substituted vanadoarsenates, [Cd(enMe)₃]₂{α-[(enMe)₂Cd₂As₈V₁₂O₄₀(0.5H₂O)]}·5.5H₂O (1, enMe=1,2-diaminopropane) and [Cd(enMe)₂]₂{β-[(enMe)₂Cd₂As₈V₁₂O₄₀(0.5H₂O)]} (2), were hydrothermally synthesized and characterized by elemental analyses, IR, TGA, UV-Vis, XRD, magnetic measurements and single crystal structural analyses. Crystal data for 1: monoclinic, P2(1)/c, a=15.040(9) Å, b=20.288(12) Å, c=27.873(17) Å, β=98.046(8)°, V=8421.3(19) Å³, Z=4; for 2: monoclinic, P2(1)/n, a=12.753(3) Å, b=19.334(5) Å, c=14.310(3) Å, β=99.984(3)°, V=3475.1(14) Å³, Z=2. X-ray diffraction analyses reveal that compounds 1 and 2 exhibit isolated and one-dimensional inorganic-organic hybrid structures, respectively. The former is the first di-cadmium-substituted vanadoarsenate derived from α-{As₈V₁₄O₄₂} shell, while the latter is another kind of di-cadmium-substituted vanadoarsenate derived from β-{As₈V₁₄O₄₂} shell. Variable temperature susceptibility measurements demonstrate the presence of antiferromagnetic interactions between V^IV cations in 1 and 2.     

Untersuchungen zur Darstellung von [CpxSb{M(CO)5}2] (Cpx = Cp,Cp*; M = Cr,W)

Investigations of the Synthesis of [Cp^xSb{M(CO)₅}₂] (Cp^x = Cp, Cp*; M = Cr, W) The reaction of CpSbCl₂ with [Na₂{Cr₂(CO)₁₀}] leads to the chlorostibinidene complex [ClSb{Cr(CO)₅}₂(thf)] ( 1 ), whereas the reaction of CpSbCl₂ with [Na₂{W₂(CO)₁₀}] results in the formation of the complexes [ClSb{W(CO)₅}₃] ( 2 ), [Na(thf)][Cl₂Sb{W(CO)₅}₂] ( 3 ), [ClSb{W(CO)₅}₂(thf)] ( 4 ) and [Sb₂{W(CO)₅}₃] ( 5 ). The stibinidene complex [CpSb{Cr(CO)₅}₂] ( 6 ) is obtained by the reaction of [ClSb{Cr(CO)₅}₂] with NaCp, while its Cp* analogue [Cp*Sb{Cr(CO)₅}₂] ( 7 ) is formed via the metathesis of Cp*SbCl₂ with [Na₂{Cr₂(CO)₁₀}]. The products 2 , 3 , 4 and 7 are additionally characterised by X‐ray structure analyses.