Redox Self-Equilibration in Molecular Vanadium Oxide Mixtures Enables Multi-Electron Storage.

Polyoxometalates (POMs) are ideal components for reversible multi-electron storage in energy technologies. To-date, most redox-applications employ only single, individual POM species, which limits the number of electrons that can be stored within a given potential window. Here, we report that spontaneous redox self-equilibration during cluster synthesis leads to the formation of two structurally related polyoxovanadates which subsequently aggregate into co-crystals.

SMM features of a large lanthanide family of butterfly CrIII2LnIII2 pivalate complexes (Ln = Gd, Tb, Dy, Ho, Er, Tm and Yb).

In this work we report the synthesis, structural characterization and magnetic properties of a family of butterfly complexes {CrLn} with Ln = Tb (4), Ho (5), Er (6), Tm (7) and Yb (8), extending the family of previously reported isostructural compounds with Gd (1), Dy (2) and Y (3). As in 1 and 2, an anti-ferromagnetic Cr(III)-Ln(III) exchange interaction is found. For oblate ions 4 and 5, SMM behavior with a purely Orbach relaxation mechanism is observed with thermal barriers of 38 cm (4) and 32 cm (5).

A combined theoretical and experimental approach to determine the right choice of co-ligand to impart spin crossover in Fe(II) complexes based on 1,3,4-oxadiazole ligands.

We present the synthesis of two new novel tetradentate ligands based on 1,3,4-oxadiazole, 2-(2-pyridyl)-5-[,-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole (LTetraPy-ODA) and 2-(2-phenyl)-5-[,-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole (LTetraPh-ODA). The ligands were used to prepare six mononuclear complexes [Fe(LTetraPy-ODA)(NCE)] (C1-C3) and [Fe(LTetraPh-ODA)(NCE)] (C4-C6) where E = S, Se or BH. In addition, the ligand LTetraPy-ODA was employed in the synthesis of a new di-nuclear complex [FeII2(LTetraPh)](ClO)·1 CHNO·1.

Quantification of the thermodynamic effects of the low-spin - high-spin interaction in molecular crystals of a mononuclear iron(II) spin crossover complex.

A method is proposed to estimate the energetic and entropic effects of spins of neighbouring molecules on the spin transition of a mononuclear spin crossover (SCO) complex in a molecular crystal. Density functional theory (DFT) methods have been used to model the SCO material [Fe(Lnpdtz)(NCS)] (Lnpdtz = 2-naphthyl-5-pyridyl-1,2,4-thiadiazole) exhibiting numerous π-π interactions using a 2D arrangement of 15 molecules. The modelling considers only the effects in the crystallographical plane with a particularly pronounced stacking but paves the way for future work with 3D arrangements which are computational much more costly.

Coupled reaction equilibria enable the light-driven formation of metal-functionalized molecular vanadium oxides.

The introduction of metal sites into molecular metal oxides, so-called polyoxometalates, is key for tuning their structure and reactivity. The complex mechanisms which govern metal-functionalization of polyoxometalates are still poorly understood. Here, we report a coupled set of light-dependent and light-independent reaction equilibria controlling the mono- and di-metal-functionalization of a prototype molecular vanadium oxide cluster.

Synergetic spin singlet-quintet switching and luminescence in mononuclear Fe(II) 1,3,4-oxadiazole tetradentate chelates with NCBH co-ligand.

We report the multi-step synthesis of the tetradentate 2-(naphthalen-2-yl)-5-[,-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole ligand (LTetra-ODA) along with its corresponding [Fe(LTetra-ODA)(NCBH)]·1.5CHOH (C1) complex, which is the first mononuclear 1,3,4-oxadiazole based Fe(II) spin crossover (SCO) complex, and its zinc analogue [Zn(LTetra-ODA)(NCBH)]·0.5HO (C2).

Interpenetration Phenomena via Anion Template Effects in Fe(II) and Co(II) Coordination Networks with a Bis-(1,2,4-triazole) Ligand.

Seven new coordination networks, [Fe(tbbt)](BF) (), [Co(tbbt)](BF) (), [Fe(tbbt)](ClO) (), [Co(tbbt)](ClO) (), [Fe(NCS)(tbbt)] (), [Co(NCS)(tbbt)] (), and [Fe(HO)(tbbt)]Br·2HO (), were synthesized with the linker 1,1'-(-2-butene-1,4-diyl)bis-1,2,4-triazole (tbbt) and structurally investigated. The structure of complexes - is composed of three interpenetrating, symmetry-related 3D networks. Each individual 3D network forms a primitive, nearly cubic lattice () with BF or ClO anions present in the interstitial spaces.

Structural insight into halide-coordinated [FeSXY] clusters (X, Y = Cl, Br, I) by XRD and Mössbauer spectroscopy.

Iron sulphur halide clusters [FeSBr] and [FeSXY] (X, Y = Cl, Br, I) were obtained in excellent yields (77 to 78%) and purity from [Fe(CO)], elemental sulphur, I and benzyltrimethylammonium (BTMA) iodide, bromide and chloride. Single crystals of (BTMA)[FeSBr] (1), (BTMA)[FeSBrCl] (2), (BTMA)[FeSClI] (3), and (BTMA)[FeSBrI] (4) were isostructural to the previously reported (BTMA)[FeSI] (5) (monoclinic, ). Instead of the chloride cubane cluster [FeSCl], we found the prismane-shaped cluster (BTMA)[FeSCl] (6) (1̄).

Experimental and theoretical investigations on three Dy single molecule magnets: structural and magneto-structural correlations.

The work in this report describes the syntheses, crystal structures, dc/ac magnetic behaviour, and theoretical calculations (both CASSCF and DFT) of three defect dicubane/planar butterfly type tetradysprosium(III) compounds of compositions [DyL(μ-OH)(carboxylate)(dmf)] (carboxylate = formate (1), acetate (2), propionate (3)), where HL = 2-(2-hydroxy-3-ethoxybenzylideneamino)phenol. In the butterfly type structures, two Dy centres (Dy) occupy the body positions while two other (Dy) units occupy the wing positions. SHAPE analyses reveal that the coordination geometries of the Dy and Dy centres, both octacoordinated, are triangular dodecahedron (TDD) and square antiprism (SAPR), respectively.

The Full d-d Redox Series of Mononuclear Manganese Complexes: Geometries and Electronic Structures of [Mn(dgpy)].

Although manganese ions exhibit a rich redox chemistry, redox processes are often accompanied by structural reorganization and a high propensity for ligand substitution, so that no complete structurally characterized manganese(II,III,IV) complex series without significant ligand sphere reorganization akin to the manganese(II,III,IV) oxides exists. We present here the series of pseudo-octahedral homoleptic manganese complexes [Mn(dgpy)] ( = 2-4) with the adaptable tridentate push-pull ligand 2,6-diguanidylpyridine (dgpy). Mn-N bond lengths and N-Mn-N bond angles change characteristically from = 2 to = 4, while the overall [MnN] coordination sphere is preserved.

SMM Behaviour of the Butterfly {Cr Dy } Pivalate Complex and Magneto-structurally Correlated Relaxation Thermal Barrier.

We are reporting the synthesis, single-crystal X-ray structure characterization, and magnetic property investigations of the pivalate butterfly {Cr Ln } complexes with Ln= Gd and Dy and the isostructural Y(III) sample. We found an anti-ferromagnetic Cr(III)-Ln(III) exchange interaction, which, as previously observed in related Cr(III)/Ln(III) systems, plays a key role in suppressing quantum tunnelling of magnetization and enhances the SMM performance in the Dy(III) complex. In fact, a pure Orbach relaxation mechanism, with absence of QT regime, is observed with a thermal barrier of 50 cm , leading to magnetization hysteresis opening, measured with a commercial magnetometer, up to 3.

Pronounced Magnetic Bistability in Highly Cooperative Mononuclear [Fe(L)(NCX)] Complexes.

Molecular materials that exhibit stimuli-responsive bistability are promising candidates for the development of molecular switches and sensors. We herein report on the coexistence of a wide thermal hysteretic spin crossover (SCO) effect and a thermally inducible metastable high-spin state at low temperatures achieved with the two new complexes [Fe(L)(NCX)] (X = S; Se), with L being (2-naphthyl-5-pyridyl-1,2,4-thiadiazole) and X = S () and Se (). Pronounced π-π-stacking of the aromatic side residues of the ligands enables strong intermolecular interactions, leading to abrupt SCO properties and broad magnetic hysteresis of 10 K for X = S and 58 K for X = Se.

Panchromatic Absorption and Oxidation of an Iron(II) Spin Crossover Complex.

In order to expand and exploit the useful properties of d-iron(II) and d-iron(III) complexes in potential magnetic, photophysical, or magnetooptical applications, crucial ligand-controlled parameters are the ligand field strength in a given coordination mode and the availability of suitable metal and ligand frontier orbitals for charge-transfer processes. The push-pull ligand 2,6-diguanidylpyridine (dgpy) features low-energy π* orbitals at the pyridine site and strongly electron-donating guanidinyl donors combined with the ability to form six-membered chelate rings for optimal metal-ligand orbital overlap. The electronic ground states of the pseudo-octahedral d- and d-complexes , , and as well as their charge-transfer (CT) and metal-centered (MC) excited states are probed by variable temperature UV/vis absorption, NMR, EPR, and Mössbauer spectroscopy, magnetic susceptibility measurements at variable temperature as well as quantum chemical calculations.

3d/4f Sandwich Complex Based on Metallacrowns.

A novel lanthanide double-decker complex with nickel metallacrowns (MCs) as coordinating ligands has been synthesized. In the 3d/4f metallacrown complex Tb[12-MC-4], the central lanthanide ion is sandwiched between two [12-MC-4] units, forming an almost ideal square-antiprismatic coordination sphere. The resulting zenithal angles at the central lanthanide ion are smaller than those for previously reported sandwich compounds.

Strongly Red-Emissive Molecular Ruby [Cr(bpmp)] Surpasses [Ru(bpy)].

Gaining chemical control over the thermodynamics and kinetics of photoexcited states is paramount to an efficient and sustainable utilization of photoactive transition metal complexes in a plethora of technologies. In contrast to energies of charge transfer states described by spatially separated orbitals, the energies of spin-flip states cannot straightforwardly be predicted as Pauli repulsion and the nephelauxetic effect play key roles. Guided by multireference quantum chemical calculations, we report a novel highly luminescent spin-flip emitter with a quantum chemically predicted blue-shifted luminescence.

Filling The Gap in The Metallacrown Family: The 9-MC-3 Chromium Metallacrown.

Invited for the cover of this issue is the group of Eva Rentschler at the Johannes Gutenberg University Mainz. The image depicts a puzzle that represents the metallacrown family with the gap for the chromium metallacrown complex. Read the full text of the article at 10.

Filling the Gap in the Metallacrown Family: The 9-MC-3 Chromium Metallacrown.

In this work, we report on a long-sought missing complex in the metallacrown family. We synthesized and characterized the novel chromium metallacrown (MC) complex {Cr (μ -piv) [9-MC -3](morph) }⋅MeOH (in which shi =salicyl hydroxamate, piv=pivalate, and morph=morpholine). The MC with a 9-MC-3 cavity of kinetically inert chromium(III) ions was synthesized by a solvothermal reaction.

Nickel(II) complexes based on L-amino-acid-derived ligands: synthesis, characterization and study of the role of the supramolecular structure in carbon dioxide capture.

The formation of the symmetrical μ-carbonate-bridged self-assembled trinuclear Ni complex Na{[Ni(LO)(HO)](μ-CO)} (LO is the carboxylate anion of a L-tyrosine derivative), involves atmospheric CO uptake. The asymmetric unit of the complex comprises an octahedral coordination for the Ni with two L-tyrosine-based ligands, a water molecule and one O atom of the carbonate bridge. The Ni-μ-CO core in this compound is the first reported of this kind according to the Cambridge Structural Database (CSD).

Vibrational properties of 1D- and 3D polynuclear spin crossover Fe(II) urea-triazoles polymer chains and quantification of intrachain cooperativity.

The vibrational dynamics of the iron centres in 1D and 3D spin crossover Fe(II) 4-alkyl-urea triazole chains have been investigated by synchrotron based nuclear inelastic scattering. For the 1D system, the partial density of phonon states has been modelled with density functional theory methods. Furthermore, spin dependent iron ligand distances and vibrational modes were obtained.

Combination of single-molecule magnet behaviour and luminescence properties in a new series of lanthanide complexes with tris(pyrazolyl)borate and oligo(β-diketonate) ligands.

A series of tris(pyrazolyl)borate mono-, di- and trinuclear complexes, [TpLn]X (Ln = Eu, Tb, Gd, Dy, X = various mono-, bis- and tris(β-diketonates) has been prepared. The Tb and Dy complexes are luminescent single molecular magnets (SMM) and exhibit luminescence quantum efficiencies up to 73% for the Tb and 4.4% for the Dy compounds.

A Vanadium(III) Complex with Blue and NIR-II Spin-Flip Luminescence in Solution.

Luminescence from Earth-abundant metal ions in solution at room temperature is a very challenging objective due to the intrinsically weak ligand field splitting of first-row transition metal ions, which leads to efficient nonradiative deactivation via metal-centered states. Only a handful of 3d metal complexes ( ≠ 10) show sizable luminescence at room temperature. Luminescence in the near-infrared spectral region is even more difficult to achieve as further nonradiative pathways come into play.

Spin Crossover and Long-Lived Excited States in a Reduced Molecular Ruby.

The chromium(III) complex [Cr (ddpd) ] (molecular ruby; ddpd=N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine) is reduced to the genuine chromium(II) complex [Cr (ddpd) ] with d electron configuration. This reduced molecular ruby represents one of the very few chromium(II) complexes showing spin crossover (SCO). The reversible SCO is gradual with T around room temperature.

First Cobalt(II) Spin Crossover Compound with NS-Donorset.

Herein we report the synthesis and characterization of a novel bis-tridentate 1,3,4-thiadiazole ligand ( = 2,5-bis[(2-pyridylmethyl)thio]methyl-1,3,4-thiadiazole). Two new mononuclear complexes of the type [M()](ClO) (with M = Fe () and Co ()) have been synthesized, containing the new ligand (). In both complexes the metal centers are coordinated by an NS-donorset and each of the two ligands is donating to the metal ion with just one of the tridentate pockets.

Phase Trapping in Multistep Spin Crossover Compound.

The dimeric motif is the smallest unit for two interacting spin centers allowing for systematic investigations of cooperative interactions. As spin transition compounds, dinuclear complexes are of particular interest, since they potentially reveal a two-step spin crossover (SCO), switching between the high spin-high spin [HS-HS], the high spin-low spin [HS-LS], and the low spin-low spin [LS-LS] states. Herein, we report the synthesis and characterization of six dinuclear iron(II) complexes [Fe(μ-)](BF) (), [Fe(μ-)](ClO) (), [Fe(μ-)](FCSO) (), [Fe(μ-)](BF) (), [Fe(μ-)](BF) (), and [Fe(μ-)](BF) (), based on the 1,3,4-thiadiazole bridging motif.

Structural characterization and magnetic property studies of a mixed-valence {CoCo} complex with a μ-oxo tetrahedral {Co} motif.

We have synthesized and structurally characterized a new mixed valence pentanuclear Co complex, bearing a rare μ4-O-tetrahedral CoII4 unit, by employing a pyridine-like Schiff base ligand. We have performed DC magnetic susceptibility and magnetization measurements over polycrystalline samples and chemical quantum computations in order to understand the exchange interaction pattern within Co(ii) sites and ground state magnetic anisotropy. This new complex shows an overall antiferromagnetic exchange interaction whose strength strongly depends on the local symmetry of Co(ii) sites.