K2Mn3O(OH)(VO4)(V2O7) with Sawtooth Chains of Multivalent Manganese Triangular Trimer Units: Magnetic Susceptibility Shrouding a Long-Range Antiferromagnetic Order of Ferromagnetic Triangles.

ortho-Pyrovanadate (or ortho-diorthovanadate) K2Mn23+Mn2+O(OH)(VO4)(V2O7) synthesized hydrothermally crystallizes in the orthorhombic space group Pnma with a = 17.9155(5), b = 5.8940(2), c = 10.9971(3) Å, V = 1161.23(6) Å3, and Z = 4. Its crystal structure features linear chains of edge-sharing Mn3+O6 octahedra with every second pair of Mn3+O6 octahedra condensed with a Mn2+O6 octahedron on one side of a chain in a sawtooth pattern so that each sawtooth chain consists of a triangular trimer. These sawtooth chains, running parallel to the b axis and linked by the VO4 and V2O7 groups, form a framework with channels populated by K atoms. The new compound is a structural analogue of the mineral zoisite Ca2Al3O(OH)(SiO4)(Si2O7), showing a striking example of very different chemical compositions. K2Mn3O(OH)(VO4)(V2O7) undergoes a phase transition into an ordered antiferromagnetic (AFM) state at TN = 14.4 K, which was detected by high-frequency electron spin resonance as well as by both specific heat Cp and Fisher's specific heat d(χT)/dT measurements. However, this phase transition was not detected by magnetic susceptibility measurements. The origin of this puzzling observation was resolved by evaluating the spin exchanges of K2Mn3O(OH)(VO4)(V2O7), which revealed that each triangular trimer is a ferromagnetically coupled cluster, and the observed ordering involves an AFM ordering between the ferromagnetic (FM) clusters. This ordering is shrouded in magnetic susceptibility measurements due to the susceptibility contributions from the individual FM triangular trimers even below TN. We showed that the magnetic susceptibility of K2Mn3O(OH)(VO4)(V2O7) between ∼30 K and room temperature is satisfactorily described by an AFM chain made up of ferromagnetically coupled triangular clusters, as described by a few spin-exchange parameters.

(Na,Li)3(Cl,OH)[Cu3OAl(PO4)3]: a first salt-inclusion aluminophosphate oxocuprate with a new type of crystal structure.

The synthesis and characterization of a first salt-inclusion aluminophosphate oxocuprate, (Na,Li)3(Cl,OH)[Cu3OAl(PO4)3], obtained as single crystals, is reported. A novel phase, with a strongly pseudo-orthorhombic structure, is described as a monoclinic crystal structure established by the study of a pseudomerohedric microtwin. It was investigated using scanning electron microscopy, microprobe analysis and low-temperature X-ray diffraction. The composite crystal structure represents an original framework assembled from Cu-centered polyhedra, AlO6 octahedra and PO4 tetrahedra with channels, which incorporate the Na/Li salt component [(Na,Li)3(Cl,OH)]2+ that ensures electroneutrality of the compound. Layers of strongly corrugated chains of Cu-centered octahedra with shared edges and linked by PO4 tetrahedra are shown to be topologically identical with the layers also built from Cu-centered polyhedra and AsO4/VO4 tetrahedra forming the crystal structure of a fumarolic mineral aleutite, (M0.5Cl)[Cu5O2(AsO4)(VO4)] [Siidra et al. (2019). MinMag, 83, 847-853]. `Sawtooth chains' and pairs of Cu-centered octahedra inherent in the title structure may be of interest in solid-state physics, engaging studies in the field of low-dimensional and frustrated magnetism.

First crystal structure of an Fe(III) anionic complex based on a pyruvic acid thiosemicarbazone ligand with Li+: synthesis, features of magnetic behavior and theoretical analysis.

The iron(III) anionic complex based on a pyruvic acid thiosemicarbazone ligand with the lithium cation Li[FeIII(thpy)2]·3H2O (1) has been synthesized and characterized by FTIR spectroscopy, powder and single crystal X-ray diffraction, direct current magnetic susceptibility measurements, and 57Fe Mössbauer spectroscopy. Moreover, the molecular structure of the [Fe(thpy)2]- anion has been determined for the first time. The [Fe(thpy)2]- units in the triclinic P1̄ lattice of 1 are assembled into layers parallel to the bc plane. The Li+ cations and water molecules are located between the layers and the structure is stabilized by hydrogen bonding. The [Fe(thpy)2]- anions form interconnected dimer pairs through hydrogen bonds and short contacts with Fe⋯Fe separation of 6.7861(4) Å. According to dc magnetic measurements, compound 1 demonstrates an incipient spin-crossover transition from the LS (S = 1/2) to the HS (S = 5/2) state above 250 K. The Bleaney-Bowers equation for a model of an isolated LS dimer with a mean-field correction was applied to fit the experimental data of magnetic susceptibility dependence on temperature in the temperature range of 2-250 K. The intra-dimer J1 = -1.79(1) K and inter-dimer J2 = -0.24(3) K antiferromagnetic coupling constants were defined. The analysis of the 57Fe Mössbauer spectra at 80 K and 296 K confirms the presence of the shortened distances between the iron nuclei. Moreover, the influence of the lithium cation on the stabilization of the LS state was shown for the [Fe(thpy)2]- anion. BS-DFT calculations for the optimized structure of two isolated [Fe(thpy)2]- anions also correctly predict a weak exchange J1(calc) = -0.92 K. DFT calculations revealed the OPBE (GGA-type) functional that correctly predicts the spin-crossover transition for the iron(III) thpy compounds. Besides, the effect of the N2O4, N2S2O2, and N2Se2O2 coordination environments on the energy stabilization of the LS state of iron(III) anionic thpy complexes was noted as well.

[MII(H2dapsc)]-[Cr(CN)6] (M = Mn, Co) Chain and Trimer Complexes: Synthesis, Crystal Structure, Non-Covalent Interactions and Magnetic Properties.

Four new heterometallic complexes combining [MII(H2dapsc)]2+ cations with the chelating H2dapsc {2,6-diacetylpyridine-bis(semicarbazone)} Schiff base ligand and [Cr(CN)6]3- anion were synthesized: {[MII(H2dapsc)]CrIII(CN)6K(H2O)2.5(EtOH)0.5}n·1.2n(H2O), M = Mn (1) and Co (2), {[Mn(H2dapsc)]2Cr(CN)6(H2O)2}Cl·H2O (3) and {[Co(H2dapsc)]2Cr(CN)6(H2O)2}Cl·2EtOH·3H2O (4). In all the compounds, M(II) centers are seven-coordinated by N3O2 atoms of H2dapsc in the equatorial plane and N or O atoms of two apical -CN/water ligands. Crystals 1 and 2 are isostructural and contain infinite negatively charged chains of alternating [MII(H2dapsc)]2+ and [CrIII(CN)6]3- units linked by CN-bridges. Compounds 3 and 4 consist of centrosymmetric positively charged trimers in which two [MII(H2dapsc)]2+ cations are bound through one [CrIII(CN)6]3- anion. All structures are regulated by π-stacking of coplanar H2dapsc moieties as well as by an extensive net of hydrogen bonding. Adjacent chains in 1 and 2 interact also by coordination bonds via a pair of K+ ions. The compounds containing MnII (1, 3) and CoII (2, 4) show a significant difference in magnetic properties. The ac magnetic measurements revealed that complexes 1 and 3 behave as a spin glass and a field-induced single-molecule magnet, respectively, while 2 and 4 do not exhibit slow magnetic relaxation in zero and non-zero dc fields. The relationship between magnetic properties and non-covalent interactions in the structures 1-4 was traced.

A Novel Mineral-like Copper Phosphate Chloride with a Disordered Guest Structure: Crystal Chemistry and Magnetic Properties.

Novel copper phosphate chloride has been obtained under middle-temperature hydrothermal conditions. Its crystal structure was established based on the low-temperature X-ray diffraction data: Na2Li0.75(Cs,K)0.5[Cu5(PO4)4Cl]·3.5(H2O,OH), sp. gr. C2/m, a = 19.3951(8) Å, b = 9.7627(3) Å, c = 9.7383(4) Å, ß = 99.329(4)°, T = 150 K, MoKα (λ = 0.71073 Å), R = 0.049. The crystal structure includes tetrameric copper clusters as the main building blocks, which are built of four CuO4Cl pyramids sharing apical Cl vertices. The clusters are combined through phosphate groups and additional copper-centered polyhedra to form two mostly ordered periodic layers. Between the layers and inside the framework channels, alkali ions, H2O molecules, or OH groups are statistically distributed. Na2Li0.75(Cs,K)0.5[Cu5(PO4)4Cl]·3.5(H2O,OH) is a synthetic modification of a sampleite-polymorph of the lavendulan mineral group and represents a new member in a mero-plesiotype series of copper phosphates and arsenates, for which the crystal structures contain two-periodic [Cu4X(TO4)4]∞ modules (T = As, P; X = Cl, O). Magnetically, this phase exhibits the phase transition at TC = 6.5 K, below which it possesses a weak ferromagnetic moment.

A Series of Novel Pentagonal-Bipyramidal Erbium(III) Complexes with Acyclic Chelating N3O2 Schiff-Base Ligands: Synthesis, Structure, and Magnetism.

A series of six seven-coordinate pentagonal-bipyramidal (PBP) erbium complexes, with acyclic pentadentate [N3O2] Schiff-base ligands, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) [H2DAPMBH], or 2,6-diacethylpyridine bis(salicylhydrazone) [H4DAPS], and various apical ligands in different charge states were synthesized: [Er(DAPMBH)(C2H5OH)Cl] (1); [Er(DAPMBH)(H2O)Cl]·2C2H5OH (2); [Er(DAPMBH)(CH3OH)Cl] (3); [Er(DAPMBH)(CH3OH)(N3)] (4); [(Et3H)N]+[Er(H2DAPS)Cl2]- (5); and [(Et3H)N]+[Y0.95Er0.05(H2DAPS)Cl2]- (6). The physicochemical properties, crystal structures, and the DC and AC magnetic properties of 1-6 were studied. The AC magnetic measurements revealed that most of Compounds 1-6 are field-induced single-molecule magnets, with estimated magnetization energy barriers, Ueff ≈ 16-28 K. The experimental study of the magnetic properties was complemented by theoretical analysis based on ab initio and crystal field calculations. An experimental and theoretical study of the magnetism of 1-6 shows the subtle impact of the type and charge state of the axial ligands on the SMM properties of these complexes.

Abrupt Spin-State Switching in Mn(III) Complexes with BPh4 Anion: Effect of Halide Substituents on Crystal Structure and Magnetic Properties.

Three tetraphenylborates of mononuclear Mn(III) cation complexes with hexadentate ligands, the products of the reaction between a N,N'-bis(3-aminopropyl)ethylenediamine and salicylaldehydes with the different haloid substitutions at the 5 or 3,5 positions, have been synthesized: [Mn(5-F-sal-N-1,5,8,12)]BPh4 (1), [Mn(3,5-diCl-sal-N-1,5,8,12)]BPh4 (2) and [Mn(3,5-Br,Cl-sal-N-1,5,8,12)]BPh4 (3). Their crystal structure, dielectric constant (ϵ) and magnetic properties have been studied. Ligand substituents have a dramatic effect on the structure and magnetic properties of the complexes. With decreasing temperature, the complex (1) shows a gradual spin crossover from the high-spin state (HS) to the HS:LS intermediate phase, followed by an abrupt transition to the low-spin state (LS) without changing the crystal symmetry. The complexes 2 and 3 are isostructural, but have fundamentally different properties. Complex 2 demonstrates two structural phase transitions related to sharp spin crossovers from the HS to the HS:LS intermediate phase at 137 K and from the intermediate phase to the LS at 87 K, while complex 3 exhibits only one spin transition from the HS to the HS:LS intermediate phase at 83 K.

Crystal structure and thermodynamic properties of dinickel diphosphate dihydrate Ni2(H2O)2[P2O7].

Single crystals of dinickel diphosphate dihydrate, Ni2(H2O)2[P2O7], have been synthesized by a hydrothermal method. Its structure was refined in the monoclinic P21/n space group (unit cell parameters a = 6.2517(1) Å, b = 13.7892(3) Å, c = 7.2894(2) Å, ß = 94.507(2)°, V = 626.45(2) Å3, and Z = 4) based on low-temperature X-ray diffraction data until R- 0.016. Corrugated chains of NiO5(H2O) octahedra sharing edges are aligned in the [101[combining macron]] direction. They are linked into a three-dimensional framework through diphosphate groups and hydrogen bonds. A detailed crystal chemical analysis of the family Me2(H2O)2[X2O7] revealed correlations between the unit-cell parameters of the isotypic transition metal phosphates and arsenates, their structural features and the sizes of structure forming cations. Despite the isolation of the cis and trans edge-sharing infinite zigzag chains of Ni-centered octahedra from each other no pronounced low dimensionality is seen in the magnetic response of Ni2(H2O)2[P2O7]. The magnetic susceptibility χ evidences a short range correlation maximum at Tmax = 11.9 K accompanied by the onset of long-range magnetic order at TN = 9.4 K. Below TN, the title compound exhibits the features of an archetype three-dimensional easy-axis antiferromagnet which experiences a sequence of spin-flop and spin-flip phase transitions. Basing on specific heat Cp and magnetization M studies, the magnetic phase diagram of Ni2(H2O)2[P2O7] has been established.

Magnetism, Conductivity and Spin-Spin Interactions in Layered Hybrid Structure of Anionic Radicals [Ni(dmit)2] Alternated by Iron(III) Spin-Crossover Complex [Fe(III)(3-OMe-Sal2trien)] and Ferric Moiety Precursors.

In this study, crystals of the hybrid layered structure, combined with Fe(III) Spin-Crossover (SCO) complexes with metal-dithiolate anionic radicals, and the precursors with nitrate and iodine counterions, are obtained and characterized. [Fe(III)(3-OMe-Sal2trien)][Ni(dmit)2] (1), [Fe(III)(3-OMe-Sal2trien)]NO3·H2O (2), [Fe(III)(3-OMe-Sal2trien)]I (3) (3-OMe-Sal2trien = hexadentate N4O2 Schiff base is the product of the condensation of triethylenetetramine with 3-methoxysalicylaldehyde; H2dmit = 2-thioxo-1,3-dithiole-4,5-dithiol). Bulk SCO transition was not achieved in the range 2.0-350 K for all three compounds. Alternatively, the hybrid system (1) exhibited irreversible segregation into the spatial fractions of Low-Spin (LS) and High-Spin (HS) phases of the ferric moiety, induced by thermal cycling. Fractioning was studied using both SQUID and EPR methods. Magnetic properties of the LS and HS phases were analyzed in the framework of cooperative interactions with anionic sublattice: Anion radical layers Ni(dmit)2 (1), and H-bonded chains with NO3 and I (2,3). LS phase of (1) exhibited unusual quasi-two-dimensional conductivity related to the Arrhenius mechanism in the anion radical layers, ρ||c = 2 × 105 Ohm·cm and ρ⟂c = 7 × 102 Ohm·cm at 293 K. Ground spin state of the insulating HS phase was distinctive by ferromagnetically coupled spin pairs of HS Fe3+, S = 5/2, and metal-dithiolate radicals, S = 1/2.

The first pentagonal-bipyramidal vanadium(III) complexes with a Schiff-base N3O2 pentadentate ligand: synthesis, structure and magnetic properties.

A series of three mononuclear pentagonal-bipyramidal V(iii) complexes with the equatorial pentadentate N3O2 ligand (2,6-diacethylpyridinebis(benzoylhydrazone), H2DAPBH) in the different charge states (H2DAPBH0, HDAPBH1-, DAPBH2-) and various apical ligands (Cl-, CH3OH, SCN-) were synthesized and characterized structurally and magnetically: [V(H2DAPBH)Cl2]Cl·C2H5OH (1), [V(HDAPBH)(NCS)2]·0.5CH3CN·0.5CH3OH (2) and [V(DAPBH)(CH3OH)2]Cl·CH3OH (3). All three complexes reveal paramagnetic behavior, resulting from isolated S = 1 spins with positive zero-field splitting energy expected for the high-spin ground state of the V3+ (3d2) ion in a PBP coordination. Detailed high-field EPR measurements for compound 3 show that its magnetic properties are best described by using the spin Hamiltonian with the positive ZFS energy (D = +4.1 cm-1) and pronounced dimer-like antiferromagnetic spin coupling (J = -1.1 cm-1). Theoretical analysis based on superexchange calculations reveals that the long-range spin coupling between distant V3+ ions (8.65 Å) is mediated through π-stacking contacts between the planar DAPBH2- ligands of two neighboring [V(DAPBH)(CH3OH)2]+ complexes.

Novel K/Mn phosphate hydrates, K2Mn3(H2O)2[P2O7]2 and KMn(H2O)2[Al2(PO4)3]: hydrothermal synthesis and crystal chemistry.

Two novel K/Mn phosphate hydrates, namely, dipotassium trimanganese dipyrophosphate dihydrate, K2Mn3(H2O)2[P2O7]2, (I), and potassium manganese dialuminium triphosphate dihydrate, KMn(H2O)2[Al2(PO4)3], (II), were obtained in the form of single crystals during a single hydrothermal synthesis experiment. Their crystal structures were studied by X-ray diffraction. Both new compounds are members of the morphotropic series of phosphates with the following formulae: A2M3(H2O)2[P2O7]2, where A = K, NH4, Rb or Na and M = Mn, Fe, Co or Ni, and AM2+(H2O)2[M3+2(PO4)3], where A = Cs, Rb, K, NH4 or (H3O); M2+ = Mn, Fe, Co or Ni; and M3+ = Al, Ga or Fe. A detailed crystal chemical analysis revealed correlations between the unit-cell parameters of the members of the series, their structural features and the sizes of the cations. It has been shown that a mixed type anionic framework is formed in (II) by aluminophosphate [(AlO2)2(PO4)2]∞ layers, with a cationic topology similar to the Si/Al-topology of the crystal structures of feldspars. A study of the magnetic susceptibility of (II) demonstrates a paramagnetic behaviour of the compound.

Slow Magnetic Relaxation, Antiferromagnetic Ordering, and Metamagnetism in MnII (H2 dapsc)-FeIII (CN)6 Chain Complex with Highly Anisotropic Fe-CN-Mn Spin Coupling.

Reactions of [Mn(H2 dapsc)Cl2 ]⋅H2 O (dapsc=2,6- diacetylpyridine bis(semicarbazone)) with K3 [Fe(CN)6 ] and (PPh4 )3 [Fe(CN)6 ] lead to the formation of the chain polymeric complex {[Mn(H2 dapsc)][Fe(CN)6 ][K(H2 O)3.5 ]}n ⋅1.5n H2 O (1) and the discrete pentanuclear complex {[Mn(H2 dapsc)]3 [Fe(CN)6 ]2 (H2 O)2 }⋅4 CH3 OH⋅3.4 H2 O (2), respectively. In the crystal structure of 1 the high-spin [MnII (H2 dapsc)]2+ cations and low-spin hexacyanoferrate(III) anions are assembled into alternating heterometallic cyano-bridged chains. The K+ ions are located between the chains and are coordinated by oxygen atoms of the H2 dapsc ligand and water molecules. The magnetic structure of 1 is built from ferrimagnetic chains, which are antiferromagnetically coupled. The complex exhibits metamagnetism and frequency-dependent ac magnetic susceptibility, indicating single-chain magnetic behavior with a Mydosh-parameter φ=0.12 and an effective energy barrier (Ueff /kB ) of 36.0 K with τ0 =2.34×10-11  s for the spin relaxation. Detailed theoretical analysis showed highly anisotropic intra-chain spin coupling between [FeIII (CN)6 ]3- and [MnII (H2 dapsc)]2+ units resulting from orbital degeneracy and unquenched orbital momentum of [FeIII (CN)6 ]3- complexes. The origin of the metamagnetic transition is discussed in terms of strong magnetic anisotropy and weak AF interchain spin coupling.

Spin-crossover behavior of neutral iron(iii) complexes with salicylaldehyde thio-, seleno- and semicarbazone ligands: experiment and theoretical analysis.

The iron(iii) complex [Fe(Hsemsal)(semsal)]·3H2O (1) (H2semsal - salicylaldehyde semicarbazone) has been synthesized and characterized by powder and single crystal X-ray diffraction, and magnetic susceptibility measurements. Crystal structure analysis showed that the complex forms neat stacks stabilized by hydrogen-bonding through water molecules and π-π interactions between phenolate rings of ligands. The complex does not exhibit spin-crossover phenomena and remains in the high-spin state down to 2 K. DFT calculations were performed for a series of neutral Fe(iii) complexes, and the influence of the N2S2O2, N2Se2O2 and N2O4 coordination environment on the spin transition in these complexes was traced. The effect of substituents in the benzene ring of salicylaldehyde on the stabilization of the HS or LS states in complexes of this type was analyzed.

Insights into the influence of ethylene group orientation on the iron(iii) spin state in the spin crossover complex [FeIII(Sal2-trien)].

The DFT calculations of the spin crossover complex [FeIII(Sal2-trien)]+ (1) with the following classification of conformers of 1 were performed. The study shows that rearrangements of ethylene group orientation in a coordinated ligand lead to the stabilization of the high-spin or low-spin iron(iii) state.

Static Modulation Wave of Arrays of Halogen Interactions Transduced to a Hierarchy of Nanoscale Change Stimuli of Crystalline Rotors Dynamics.

Here we present a study where what can be seen as a static modulation wave encompassing four successive arrays of interacting iodine atoms in crystalline 1,4-Bis((4'-(iodoethynyl)phenyl) ethynyl)bicyclo[2,2,2]octane rotors changes the structure from one-half molecule to three-and-a-half molecules in the asymmetric unit below a phase transition at 105 K. The remarkable finding is that the total 1H spin-lattice relaxation rate, T1-1, of unprecedented complexity to date in molecular rotors, is the weighted sum of the relaxation rates of the four contributing rotors relaxation rates, each with distinguishable exchange frequencies reflecting Arrhenius parameters with different activation barriers ( Ea) and attempt frequencies (τo-1). This allows us to show in tandem with rotor-environment interaction energy calculations how the dynamics of molecular rotors are able to decode structural information from their surroundings with remarkable nanoscale precision.

Synthesis, Structure, and Magnetic Properties of 1D {[MnIII(CN)6][MnII(dapsc)]}n Coordination Polymers: Origin of Unconventional Single-Chain Magnet Behavior.

Two one-dimensional cyano-bridged coordination polymers, namely, {[MnII(dapsc)][MnIII(CN)6][K(H2O)2.75(MeOH)0.5]}n·0.5n(H2O) (I) and {[MnII(dapsc)][MnIII(CN)6][K(H2O)2(MeOH)2]}n (II), based on alternating high-spin MnII(dapsc) (dapsc = 2,6-diacetylpyridine bis(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of I with an energy barrier of Ueff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the MnIII-CN-MnII spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [MnIII(CN)6]3-. The prospects of [MnIII(CN)6]3- complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.

The Conducting Spin-Crossover Compound Combining Fe(II) Cation Complex with TCNQ in a Fractional Reduction State.

The radical anion salt [Fe{HC(pz)3}2](TCNQ)3 demonstrates conductivity and spin-crossover (SCO) transition associated with Fe(II) complex cation subsystem. It was synthesized and structurally characterized at temperatures 100, 300, 400, and 450 K. The compound demonstrates unusual for 7,7,8,8,-tetracyanoquinodimethane (TCNQ)-based salts quasi-two-dimensional conductivity. Pronounced changes of the in-plane direct-current resistivity and intensity of the electron paramagnetic resonance (EPR) signal, originated from TCNQ subsystem, precede the SCO transition at the midpoint T* = 445 K. The boltzmannian growth of the total magnetic response and structural changes in the vicinity of T* uniquely show that half [Fe{HC(pz)3}2] cations exist in high-spin state. Robust broadening of the EPR signal triggered by the SCO transition is interpreted in terms of cross relaxation between the TCNQ and Fe(II) spin subsystems.

meso-Phenyltetrabenzotriazaporphyrin based double-decker lanthanide(III) complexes: synthesis, structure, spectral properties and electrochemistry.

A series of half-sandwich and sandwich-type lanthanide(III) complexes have been prepared using tetrabenzotriazaporphyrin ligands. Reaction of 27-phenyl-29H,31H-tetrabenzo[b,g,l,q][5,10,15]-triazaporphyrin (PhTBTAPH2, 1) with salts [LnX3]·nH2O (Ln = Eu (a), Lu (b); X = OAc, acac) afforded the single- and homoleptic double-deckers (PhTBTAP)LnOAc (2) and (PhTBTAP)2Ln (3) respectively. Heteroleptic double-decker compounds (PhTBTAP)LnPc (4a,b) were obtained upon interaction of 1 with the corresponding Ln mono(phthalocyaninates). An unexpected formation of partially and completely dephenylated co-products 5 and 6 has been detected in the synthesis of sandwich 3, while the possibility of the dearylation of the half-sandwich compound 2 has been demonstrated as well. A more predictable yet firstly observed formation of the triple-decker compound (PhTBTAP)3Eu2 (7) has also been found. Structural studies of 3 supported by 1H NMR spectra, XRD analysis and DFT theoretical calculations reveal that the Eu complex 3a is formed as a single isomer, while the lutetium compound 3b represents an inseparable mixture of two rotational isomers with virtually identical spectral characteristics. The double-decker compounds 3 and 4 reveal intrinsic UV-Vis/NIR absorption as well as peculiar electrochromic behavior. The heteroleptic derivatives 4 generally show intermediate spectral and electrochemical properties with respect to their homoleptic relatives.

Superconducting fluctuations in organic molecular metals enhanced by Mott criticality.

Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-T(c) cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above T(c). By studying alloys of quasi-two-dimensional organic molecular metals in the κ-(BEDT-TTF)2X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all.