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The electronic interactions between the [Cu(opba)]2− anions (where opba is orthophenylenebis (oxamato)) and single-wall carbon nanotubes (SWCNTs) were investigated by resonance Raman spectroscopy. The opba can form molecular magnets, and the interactions of opba with SWCNTs can produce materials with very different magnetic/electronic properties. It is observed that the electronic interaction shows a dependence on the SWCNT diameter independent of whether they are metallic or semiconducting, although the interaction is stronger for metallic tubes. The interaction also is dependent on the amount of complex that is probably adsorbed on the carbon surface of the SWCNTs. Some charge transfer can be also occurring between the metallic complex and the SWCNTs. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Tunnel junction-based molecular devices (TJMDs) are highly promising for realizing futuristic electronics and spintronics devices for advanced logic and memory operations. Under this approach, ~2.5 nm molecular device elements bridge across the ~2-nm thick insulator of a tunnel junction along the exposed side edge(s). This paper details the efforts and insights for producing a variety of TJMDs by resolving multiple device fabrication and characterization issues. This study specifically discusses (i) compatibility between tunnel junction test bed and molecular solutions, (ii) optimization of the exposed side edge profile and insulator thickness for enhancing the probability of molecular bridging, (iii) effect of fabrication process-induced mechanical stresses, and (iv) minimizing electrical bias-induced instability after the device fabrication. This research will benefit other researchers interested in producing TJMDs efficiently. TJMD approach offers an open platform to test virtually any combination of magnetic and nonmagnetic electrodes, and promising molecules such as single molecular magnets, porphyrin, DNA, and molecular complexes. [ABSTRACT FROM AUTHOR]

A comprehensive study of the magnetocaloric effect (MCE) in the Mn2-[Nb(CN)8] molecular magnet with a two-step magnetic sponge behavior is reported. The structural transformations provoked by dehydration bring about an increase in the magnetic ordering temperature ( Tc) from 43 K through to 68 K and up to 98 K. All three phases are soft isotropic ferrimagnets. The change in magnetic entropy in the partially and fully dehydrated phases is smaller than that in the 'as synthesized' form by a factor of 0.6. The field dependence of MCE at Tc is consistent with the values of the critical exponents derived from the magnetization data. [ABSTRACT FROM AUTHOR]

A new layered metal-organic hybrid compound, namely, [Co3(μ3-OH)2(BTP)2] ( 1; BTP=4-(3-bromothienyl)phosphonate), is reported. The inorganic layer can be viewed as a pseudo-Kagomé lattice composed of corner-sharing irregular triangles of Co3(μ3-OH), with the cavities filled with the PO3 groups. The interlayer space is occupied by the 3-bromothienyl groups of BTP2−. The bulk sample of compound 1 experiences a long-range ferromagnetic ordering below 30.5 K, with a coercivity ( Hc) of 5.04 kOe at 5 K. A systematic study on the size-dependent magnetic coercivity of 1 reveals that the coercivity of 1 increases with reduced particle size from the micrometer to the nanometer scale. When the particle size is about 50-200 nm, the coercivity reaches 24.2 kOe at 5 K. The results demonstrate that compound 1 can vary from a soft magnet to one of the hardest molecule-based magnets, simply by reducing the particle size to nanoscale region. [ABSTRACT FROM AUTHOR]

Three new cyanido-bridged heterometallic ReNi and ReCu one-dimensional systems were synthesized and extensively characterized both structurally and magnetically. Single-crystal X-ray diffraction analysis revealed that these compounds display a common topology, with chains composed of alternating [ReCl(CN)] and [M(cyclam)] (M = Ni in 1, Cu in 2) or [Cu( N,N′-dimethylcyclam)] (in 3) building units. Two different chain orientations with a tilt angle of ca. 51° to 55° are present in the crystal packing of these compounds. The magnetic susceptibility measurements suggest the presence of intrachain ferromagnetic interactions between the S = 3/2 Re centers and the 3d metal ions: S = 1 Ni or S = 1/2 Cu. At low temperature, a three-dimensional ordered magnetic phase induced by interchain antiferromagnetic interactions (antiferromagnetic for 1 and 2; canted antiferromagnetic for 3) is detected for the three compounds. [ABSTRACT FROM AUTHOR]

Abstract: We propose and analyze a novel scheme to realize the large Kerr nonlinearity via electromagnetically induced transparency (EIT) in molecular magnets. This scheme uses two magnetic fields to induce spin coherence. We obtain the analytical expressions of linear susceptibility, self-Kerr, cross-Kerr susceptibility, phase shift and absorption coefficients. Last, we investigate the nonlinear dynamics of the weak field, and show that the dark and bright microwave soliton can form in the magnetic medium. [Copyright &y& Elsevier]

Effects of magnetic frustration in the model of nine-membered antiferromagnetic s = 3/2 molecular spin ring are investigated. We use a Heisenberg spin model with nearest-neighbor interactions, single-ion anisotropy and with tunable bond defect leading to continuously varying topology: from closed to open ring. In order to identify a frustrated phase we calculate the full energy spectrum of the model and a number of thermodynamic quantities at low temperature. The calculations are performed by means of numerically exact methods: quantum transfer matrix and exact diagonalization. It is shown that total and local magnetizations, nearest-neighbor spin correlations and spin fluctuations can serve as consistent frustration signatures. Magnetizations and spin-spin correlations are reduced in the frustrated phase whereas fluctuations and correlations of fluctuations increase. The ground state in a frustrated phase is a m = 1/2 doublet and in the non-frustrated phase a m = 3/2 doublet. In the system studied bipartiteness is not opposite to frustration as there are regions in the parameter space for which the system is neither bipartite nor frustrated. [ABSTRACT FROM AUTHOR]

We built new hybrid devices consisting of chemical vapor deposition (CVD) grown carbon nanotube (CNT) transistors, decorated with TbPc2 (Pc = phthalocyanine) rare-earth based single-molecule magnets (SMMs). The drafting was achieved by tailoring supramolecular p-p interactions between CNTs and SMMs. The magnetoresistance hysteresis loop measurements revealed steep steps, which we can relate to the magnetization reversal of individual SMMs. Indeed, we established that the electronic transport properties of these devices depend strongly on the relative magnetization orientations of the grafted SMMs. The SMMs are playing the role of localized spin polarizer and analyzer on the CNT electronic conducting channel. As a result, we measured magneto-resistance ratios up to several hundred percent. We used this spin valve effect to confirm the strong uniaxial anisotropy and the superparamagnetic blocking temperature (TB ∼ 1 K) of isolated TbPc2 SMMs. For the first time, the strength of exchange interaction between the different SMMs of the molecular spin valve geometry could be determined. Our results introduce a new design for operable molecular spintronic devices using the quantum effects of individual SMMs. [ABSTRACT FROM AUTHOR]

We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compounds (TPP = meso-tetraphenylporphyrinato, TCNE = tetracyanoethylene), based on Density Functional Theory (DFT) methods, in order to interpret the magnetic ordering in these prototypic systems. We compare and contrast the results of broken-symmetry DFT calculations for extended systems, with periodic boundary conditions, and for finite systems, magnetic dimers modeling the actual molecular magnets. By varying systematically the main angles, we are able to determine the geometry dependence of the exchange interaction. Structure-properties correlations in these charge-transfer salts reveal the determinant role of the Mn-(N≡C) bond angle on the strength of the ferrimagnetic coupling between the S = 2 spin located on the Mn-porphyrin donor and the S = 1/2 spin positioned on the cyanocarbon acceptor. When the Mn-(N≡C) angle is decreased, the intrachain magnetic coupling strengthens, correlated with the increase in the $$ d_{{z^{2} }} - \pi * $$ orbital overlap. The exchange coupling constants resulting from DFT calculations of extended systems, with periodic boundary conditions, were found to be consistent with those obtained for the dimers, but systematically smaller. The exchange constants vary strongly with the functional used, hybrid functionals such as B3LYP leading to results that better correlate with the experimental mean-field critical temperatures. The coupling constant varies significantly with the type of broken-symmetry approach, depending on the overlap between magnetic orbitals, but weakly on the basis set once polarization effects are included. The electronic structure calculations for the extended systems provide a density of states consistent with the energy spectrum of the corresponding dimer, allowing for an intuitive explanation of the intrachain ferrimagnetic ordering. [ABSTRACT FROM AUTHOR]

The structures of a number of neutral high-spin, triangular carbon and silicon systems were studied and their stabilities were predicted using the density functional theory methods (B3LYP functional with the 6-311++G** and 6-311+G** basis sets). The calculated spin-spin coupling constants have high positive values, thus indicating strong ferromagnetic interactions in the title systems. [ABSTRACT FROM AUTHOR]

In this work, we elucidate the role of various microscopic interactions in high spin molecular nanomagnets. Starting from an effective spin Hamiltonian, we explain the origin and the importance of each coupling. We give special attention to exchange and dipole-dipole interactions between molecular magnets in a cubic lattice. The dispersion relation and magnetization behaviors are analyzed in the quantum magnons formalism taking into account the experimental reality and using common parameters values. [ABSTRACT FROM AUTHOR]

Abstract: The impressive potential of the metallosupramolecular approach in designing new functional magnetic materials constitutes a great scientific challenge for the chemical research community that requires an interdisciplinary collaboration. New fundamental concepts and future applications in nanoscience and nanotechnology will emerge from the study of magnetism as a supramolecular function in metallosupramolecular chemistry. Our recent work on the rich supramolecular coordination chemistry of a novel family of aromatic polyoxalamide (APOXA) ligands with first-row transition metal ions has allowed us to move one step further in the rational design of metallosupramolecular assemblies of increasing structural and magnetic complexity. Thus, we have taken advantage of the new developments of metallosupramolecular chemistry and, in particular, the molecular-programmed self-assembly methods that exploit the coordination preferences of paramagnetic metal ions and suitable designed polytopic ligands. The resulting self-assembled di- and trinuclear metallacyclic complexes with APOXA ligands, either metallacyclophanes or metallacryptands, are indeed ideal model systems for the study of the electron exchange mechanism between paramagnetic metal centers through extended π-conjugated aromatic bridges. So, the influence of different factors such as the topology and conformation of the bridging ligand or the electronic configuration and magnetic anisotropy of the metal ion have been investigated in a systematic way. These oligonuclear metallacyclic complexes can be important in the development of a new class of molecular magnetic devices, such as molecular magnetic wires (MMWs) and switches (MMSs), which are major goals in the field of molecular electronics and spintronics. On the other hand, because of their metal binding capacity through the outer carbonyl-oxygen atoms of the oxamato groups, they can further be used as ligands, referred to as metal–organic ligands (MOLs), toward either coordinatively unsaturated metal complexes or fully solvated metal ions. This well-known “complex-as-ligand” approach affords a wide variety of high-nuclearity metal–organic clusters (MOCs) and high-dimensionality metal–organic polymers (MOPs). The judicious choice of the oligonuclear MOL, ranging from mono- to di- and trinuclear species, has allowed us to control the overall structure and magnetic properties of the final oxamato-bridged multidimensional (nD, n =0–3) MOCs and MOPs. The intercrossing between short- (nanoscopic) and long-range (macroscopic) magnetic behavior has been investigated in this unique family of oxamato-bridged metallosupramolecular magnetic materials expanding the examples of low-dimensional, single-molecule (SMMs) and single-chain (SCMs) magnets and high-dimensional, open-framework magnets (OFMs), which are brand-new targets in the field of molecular magnetism and materials science. [Copyright &y& Elsevier]

Abstract: We consider theoretically a resonant interaction of crystals of molecular magnets with an electromagnetic wave. The influence of the wave polarization on an arising magnetization is discussed. The calculations are provided for the cases of exact resonance and the common relaxation time approaching. Our numerical estimations show the effect can be experimentally detected. [Copyright &y& Elsevier]

Abstract: With the advent of molecular magnets the quest for suitable high density magnetic storage materials has fuelled further research in this area. Here in this report, we present a detailed mechanistic investigation of thermal decomposition of cyclopentadienyl cobalt [CoCp(CO)2] precursor where Cp is the cyclopentadienyl moiety. The reaction revealed the formation of cobalt nanoparticles (Co-NPs) through an isolable reaction intermediate characterized as a Single Chain Magnet (SCM), [Co(Cp)2]2CoCl4 (1). The SQUID magnetic measurements showed the presence of very strong antiferromagnetic interactions between Co2+ ions. The zero-field cooled (ZFC) and field cooled (FC) magnetization curves branch out below 5K and there is evidence for frequency dependent complex susceptibility along with a maximum observed around 2.5K. The optical studies indicated that the Co2+ d-d transition is influenced by the polarity of the solvents. The cobalt nanoparticles (Co-NPs) were obtained, either directly from 1 or from its precursor. They are spherical in shape with a mean size 15nm, have fcc crystal structure and were found to be ferromagnetic at room temperature. [Copyright &y& Elsevier]

Single crystals of the new cationic chromene, 7-methyl-3,3-diphenyl-3 H-pyrano[3,2- f-quinolinium iodide (CHNO)I (1), were synthesized. The crystal structure of the new compound was studied, and quantum chemical calculation for the open and closed forms were carried out. The bifunctional compounds containing mono- and bimetallic 3d metal (tris)oxalates with the chromenium cation, (CHNO)[Cr(CO)] · 4HO (2) and (CHNO)[CrMn(CO)] · HO (3), were prepared. Compound 1 is paramagnetic due to low-lying thermally excited states of the chromene molecules. At low temperatures (∼2 K), the paramagnetic states are frozen, and the compound becomes diamagnetic. Compound 2 is paramagnetic and its magnetic properties are determined mainly by the Cr ions and the thermally induced paramagnetic states of the chromene molecules. At high temperatures, the magnetic moment of compound 3 consists of the contributions of the paramagnetic Cr and Mn ions and the thermally induced paramagnetic states of chromenes. At low temperatures (2-3 K), the thermally induced magnetism of organic molecules is frozen, and the magnetically ordered (and, probably, spin-glass) state is observed in the two-dimensional network of metal oxalates ( T = 3 K in the zero magnetic field). The UV irradiation leads to an increase in the magnetic moment of the compound in the paramagnetic region due to the generation of radiation defects. [ABSTRACT FROM AUTHOR]

Abstract: The magnetoelastic instability in nanostructured ring-shaped Ising-like spin 1/2 model has been investigated by using the exact diagonalization method. It is found that there exists two critical anisotropy parameters and () in the phase diagram. As the anisotropy parameter , the magnetoelastic transition from dimerized phase to uniform phase is a first order transition with an increase of the lattice spring constant. While for , the transition is continuous. Another critical value divides the different lattice distortion behavior as the anisotropy is strengthened. [Copyright &y& Elsevier]

Abstract: We extend previous transport calculations performed on a single-electron transistor (SET) based upon a semiconductor quantum dot (QD) doped with a single Mn ion (which behaves as a quantum nanomagnet) by calculating the stationary fluctuations of the current, or shot noise, of hole transport through the SET. Our results show that the zero-frequency shot noise is determined by the magnetic state of the QD. In particular, we find super-Poissonian noise in a region of bias and gate voltages where the competing dynamics between slow and fast channels results in bunching. [Copyright &y& Elsevier]

Polynuclear complexes are an important class of inorganic functional materials and are of interest particularly for their applications in molecular magnets. Multidentate chelating ligands play an important role in the design and syntheses of polynuclear metal clusters. A novel linear tetranuclear CoII cluster, namely bis{μ3-( E)-2-[(2-oxidobenzylidene)amino]phenolato}bis{μ2-( E)-2-[(2-oxidobenzylidene)amino]phenolato}bis(1,10-phenanthroline)tetracobalt(II), [Co4(C14H11NO2)4(C12H8N2)2], was prepared under solvothermal conditions through a mixed-ligand synthetic strategy. The structure was determined by X-ray single-crystal diffraction and bulk purity was confirmed by powder X-ray diffraction. The complex molecule has a centrosymmetric tetranuclear chain-like structure and the four CoII ions are located in two different coordination environments. The CoII ions at the ends of the chain are in a slightly distorted octahedral geometry, while the two inner CoII ions are in five-coordinate distorted trigonal bipyramidal environments. A magnetic study reveals ferromagnetic CoII...CoII exchange interactions for the complex. [ABSTRACT FROM AUTHOR]

A theoretical investigation of spin wave dynamics and scattering at a molecular junction between two Heisenberg ferromagnets is presented. The model system consists of two ferromagnetic ultrathin films with equal thickness of three atomic layers, joined together by a magnetic molecule. No electronic effects are considered, but local changes in the magnetic exchange field are assumed to be dominant. The mathematical framework of the matching method is used with nearest neighbor magnetic exchange interactions, to analyze both the spin fluctuation dynamics and the spin wave scattering phenomena at the junction boundary. The coherent reflection and transmission probabilities and the conductance of spin waves incident from the interior of the films onto the boundary are calculated in accordance with the Landauer–Büttiker formalism, and numerical results are presented for representative sets of system parameters for a large range of scattering frequencies. The scattered spectra show interesting sharp features, with associated Fano resonances, as a function of scattering frequencies, system parameters, and spin wave incidence angle. Moreover, a frequency selective conductance of the spin waves via Fano resonances can be obtained by an appropriate choice of the spin wave incident angle and system parameters. [ABSTRACT FROM AUTHOR]

Abstract: In this work we show that commonly neglected fluctuations of the net total spin of a molecular nanomagnet strongly modified its tunneling properties and provide a scenario to explain some discrepancies between theory and experiment. Starting off from an effective spin Hamiltonian, we study the quantum tunneling of the magnetization of molecular nanomagnets in the regime where the giant-spin approximation is breaking down. This study is done using an instanton description of the tunneling path. The instanton is calculated considering its coupling to quantum fluctuations. [Copyright &y& Elsevier]

Abstract: Inelastic neutron scattering has been used to determine the microscopic Hamiltonian describing two high-spin variants of the high-anisotropy Mn6 nanomagnet. The energy spectrum of both systems is characterized by the presence of several excited total-spin multiplets partially overlapping the S =12 ground multiplet. This implies that the relaxation processes of these molecules are different from those occurring in prototype giant-spin nanomagnets. In particular, we show that both the height of the energy barrier and resonant tunnelling processes are greatly influenced by low-lying excited total-spin multiplets. [Copyright &y& Elsevier]

Abstract: Energy level diagrams have been determined for two molecular clusters, K12[(VO)3(SbW9O33)2]·15H2O and K12[(VO)3(BiW9O33)2]·29H2O, by low-temperature heat capacity measurements down to 85mK under magnetic field strengths up to 9T. Both compounds exhibit a broad heat capacity peak dependent upon the magnetic field, which can be explained by the thermal excitation in the magnetic energy levels. A detailed analysis based on the numerical calculation reveals that the spin–spin interaction between the V4+ ions includes a Dzyaloshinskii–Moriya interaction. [Copyright &y& Elsevier]

Abstract: The effect of UV light on Weiss temperature and ESR spectra in 1-isopropyl-3, 3, 5′, 6′-tetramethylspiro[indolin-2,2′-[2H]pyrano[3,2-b]pyridinium] tris(oxalato)chromate (III) (Sp3Cr(C2O4)3) has been found. Additional line has been observed in the ESR spectra of irradiated samples in “strong” magnetic fields of ~15kOe. The analysis of angular dependences of the ESR spectra allowed a contribution of Cr3+ ions to magnetic properties of Sp3Cr(C2O4)3 to be determined. The zero-field splitting parameters D=0.619cm−1, E=0.024cm−1 were derived from the experimental data. The parameters were typical for Cr3+ in the chromium oxalate. Weiss temperature changed sign from 25 to −25K under UV irradiation. The value of Weiss temperature and its changing cannot be explained by exchange interaction, dipole–dipole interaction or the effect of crystal field. The existence of Weiss temperature is explained by the changes in amount and spin of paramagnetic particles. The change is due to thermoactivated redistribution of electrons between chromium ions and spiropyrane molecules. Light-induced transfer of electrons is also explaining the change in sign of Weiss temperature under UV irradiation. [Copyright &y& Elsevier]

Abstract: The relative stability of [Cr n (OCH3)2 n (CH3COO) n ] depending on the number n of its interior groups (n =4, 6, 8, 10, 12 and 14) has been studied by means of Hartree–Fock (HF) and Density Functional Theory (DFT) calculations. The calculation schemes employ atom-centered localized basis orbitals. As the first step, the structures of the molecules were optimized by means of quantum-chemistry and molecular mechanics approaches. All the molecules were found to have a lower energy in the anti-ferromagnetic state than in the ferromagnetic one; the total energy per one coordination section E tot/n was calculated for further discussions. The relative stability of [Cr n (OCH3)2 n (CH3COO) n ] molecules for different n, as estimated by the DFT, correlates with a structural rule, which allows the prediction of the relative stability of different ‘wheel’-type compounds by using a simple formula. This study demonstrates that computational chemistry can be useful for theoretical forecasting of new stable molecules of the ‘wheel’-type. This approach can be used for the rational design of molecular systems possessing magnetic properties. [Copyright &y& Elsevier]

Abstract: Systematic studies of magnetic critical exponents in local moment molecular magnets can be made by combining three different types of measurement; zero-field precession, longitudinal relaxation and the frequency shift in transverse field. Systems have been studied with 1D, 2D and 3D structures, having both simple and non-collinear magnetic interactions and the measurements have included investigation of the effect of chirality on the critical spin fluctuations. In the case of the model Heisenberg antiferromagnetic 1D chain Heisenberg antiferromagnetic quantum critical fluctuations suppress magnetic ordering and TCNQ radical ion salts can provide some excellent examples of this model. In particular, DEOCC–TCNQF4 behaves as a nearly ideal case with no ordering seen down to 20mK even though the intrachain exchange interaction is 110K. In contrast the DMTzNC–TCNQ compound orders at 1.5K, but still shows evidence for significant residual quantum fluctuations in its ordered state in the form of a large suppression of the magnitude of the ordered part of the magnetic moment. From analysis of the characteristic field dependent muon relaxation behaviour as a function of temperature above the transition, the nature of the spin fluctuations is found to change as the transition is approached, suggesting a crossover either to 2D diffusion or to 1D ballistic motion. [Copyright &y& Elsevier]

Abstract: Metal ion coordination in metallo-supramolecular assemblies offers the opportunity to fabricate and study devices and materials that are equally important for fundamental research and new technologies. Metal ions embedded in a specific ligand field offer diverse thermodynamic, kinetic, chemical, physical and structural properties that make these systems promising candidates for active components in functional materials. In particular, dynamic coordination polymers offer exciting opportunities to provide materials with responsive properties. In addition, this approach allows to incorporate the well known properties of metal complexes in polymeric architectures. This review highlights the improvements and the possible applications based on metallo-supramolecular systems with an emphasis on materials science. Examples for new materials such as molecular magnets, coordination polymers as carrier package as well as molecular electronics are featured in this article. [Copyright &y& Elsevier]

The authors theoretically investigate the formation of ultraslow dark and bright solitons via four-wave mixing (FWM) in a crystal of molecular magnets in the presence of a uniform d.c. magnetic field, where two strong continuous wave pump electromagnetic fields and a weak-pulsed probe electromagnetic field produce a pulsed FWM electromagnetic field. By solving the Maxwell–Schrödinger equations under the slowly varying envelope approximation and rotating-wave approximations, we demonstrate that both the weak-pulsed probe and FWM electromagnetic fields can evolve into dark and bright solitons with the same shape and the same ultraslow group velocity. [ABSTRACT FROM AUTHOR]

A common feature of many organic-based molecular magnets is that inter-molecular magnetic interactions are extremely weak compared to intra-molecular ones. As a result a bulk sample can be described in terms of independent individual molecular magnets made up of a cluster of a small finite number of coupled magnetic spins. Because of the large value of individual spins of several molecular magnetic compounds it turns out that such systems can be described to very high accuracy, at sufficiently high temperatures, by a classical Heisenberg spin model. Only for sufficiently low temperatures need one incorporate the quantum character of the spins. In this work we focus on the exact classical spin dynamics of small nanoscale molecular magnetic clusters of classical Heisenberg spins. The present study permits us to obtain analytical solutions for the time-dependent spin-spin autocorrelation function for certain clusters of classical Heisenberg spins coupled through exchange interaction. This study underscores the potential utility of a classical spin treatment of nanoscale magnetic clusters and provides results useful to interpret data obtained from experiments. • Classical Heisenberg description of finite clusters of coupled magnetic spins. • Model for organic-based molecular magnets with high spin values. • Model assumes all spins are equally coupled to each other. • Exact spin dynamics and time-dependent spin autocorrelation function is obtained. • Mathematical method applies to spin systems with special interaction scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coordination chemistry of transition metal hexacyanometallates. • Electronic structure of transition metal hexacyanometallates. • Structural diversity of transition metal hexacyanometallates. • Functional properties of transition metal hexacyanometallates. • Coordination controlled dimensionality in transition metal hexacyanometallates. The coordination chemistry of transition metal hexacyanometallates is a field of continuous advances and emerging applications. In the last three decades, relevant progress has been achieved on the understanding of the crystal and electronic structures of these materials, including those compositions resulting from non-conventional preparative routes. In this review, we summarize such advances at the time that provide a comprehensive overview of the structure-properties relationship. Since an improvement of the functionality of a given material is facilitated when its crystal and electronic structures are known, we provide guidelines on how to understand and predict the properties of these coordination polymers. In this family of materials, the extended 3D framework is usually formed by interconnected ⋅⋅⋅-T-N≡C-M-C≡N-T-⋅⋅⋅ chains. When these chains have a linear geometry, the formed solids crystallize either with a cubic or pseudocubic unit cell, and these coordination polymers are known as Prussian blue analogs. In the last years, deviations from such regularity have been observed for an increasing number of T metals, where the N end of the CN– ligand forms a bifurcated coordination bonding with two T metal centers. Other less common coordination modes at the N end have been also documented and are herein considered. Since the first documented report on this family of coordination polymers (in 1704), a search of published documents, using Science Finder and Google Scholar under the keywords of Prussian blue and transition metal hexacyanometallates, produces above four thousand outputs, mainly scientific papers. But these papers mostly deal with potential applications, and only a small fraction of them includes structural studies in the context of coordination chemistry. This review is structured in three blocks of sections. Initially, the crystal and electronic structures are discussed, then, the related physical properties are analyzed, and finally, their implications on the applications, with the focus on the structure-properties relationship are discussed. The accompanying Supplementary Data file has been conceived as a source of useful structural information, which together with the main document will help the readers to understand better these compounds and devise new and promising applications. [ABSTRACT FROM AUTHOR]

Abstract: Thin films of the metal organic molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)2), (C24H36N2O4Cu, Cu(II)), deposited on ferromagnetic Co(111) at 40 K, exhibit a finite electron spin polarization. The spin polarization magnitude and sign for Cu(CNdpm)2 deposited on Co(111) is coverage dependent, but deviates from the mean field expectations for a simple paramagnet on a ferromagnetic substrate. The spin asymmetry is seen to favor select molecular orbitals, consistent with the predicted single molecule density of states. The overlayer polarization observed indicates a strong influence of the ferromagnetic Co(111) substrate and some extra-molecular magnetic coupling. [Copyright &y& Elsevier]

Abstract: The effects of vacuum ultraviolet radiation on the adsorbed copper center molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)2), (C24H36N2O4Cu, Cu(II)) was studied by photoemission spectroscopy. Changes in the ultraviolet photoemission spectra (UPS) of Cu(CNdpm)2, adsorbed on Co(111), indicate that the ultraviolet radiation leads to decomposition of Cu(CNdpm)2 and this decomposition is initially dominated by loss of peripheral hydrogen. [Copyright &y& Elsevier]

Abstract: We model the magnetic behavior of spin frustrated trinuclear clusters in the region of field induced crossover of the levels. The emphasis is made on a competitive role of the antisymmetric (AS) exchange and static structural distortions as well as on the consequences of the dynamic pseudo-Jahn–Teller (JT) instability. We employ the three-spin model for the cluster anion present in (V15 cluster) and analyze the role of different components of AS in the half step magnetization. Both types of deformations (static and dynamic) are shown to be competitive with the AS exchange and tend to reduce the magnetic anisotropy caused by AS. [Copyright &y& Elsevier]

Abstract: We propose a theoretical study of the magnetic behavior of spin frustrated trinuclear clusters in the region of the field induced crossover of the levels which are crucial for the description of the static magnetization and dynamic behavior in a sweeping field. The emphasis is made on a competitive role of the antisymmetric (AS) exchange and static structural distortions of the metal center network as well as on the consequences of the dynamic pseudo Jahn–Teller (JT) instability that is closely related to spin frustration. The structural conformations are shown to be controlled by the magnetic field in the anticrossing region (magnetoelastic coupling). We employ the three-spin model for the cluster anion present in (V15 cluster) and analyze the role of different components of AS exchange in the shape of the magnetic susceptibility vs field. Both types of deformations (static and dynamic) are shown to be competitive to the AS exchange and tend to reduce the magnetic anisotropy caused by the AS exchange. [Copyright &y& Elsevier]

The crystal structures and electronic and magnetic properties of conducting molecular magnets developed by our group are reviewed from the viewpoints of our two current strategies for increasing the efficiency of the π–d interaction. (EDTDM)2FeBr4 is composed of quasi-one-dimensional donor sheets sandwiched between magnetic anion sheets. The ground state of the donor layer changes from the insulator state to the metallic state by the application of pressure. When it is near to the insulator–metal phase boundary pressure, the magnetic order of the anion spins considerably affects the transport properties of the donor layer. The crystal structure of (EDO–TTFBr2)2FeX4 (X = Cl, Br) is characterized by strong intermolecular halogen–halogen contacts between the organic donor and FeX4 anion molecules. The presence of the magnetic order of the Fe3+ spins and relatively high magnetic order transition temperature proves the role of the halogen–halogen contacts as exchange interaction paths. [ABSTRACT FROM AUTHOR]

Abstract: Metal ion induced self-assembly of polytopic ligands can be employed to make macromolecular assemblies in solution. This new class of coordination polymers has recently attracted increasing interest. By carefully adjusting the boundary conditions of self-assembly it is possible to form soluble macromolecular assemblies in solution. For this, the binding constants between metal ions and ligands have to be of the appropriate strength. If the interaction is too weak, macromolecular species will not form, but if it is too strong, precipitation may occur. Intermediate binding constants imply a facile exchange of ligands, that is, soluble coordination polymers are generally dynamic equilibrium systems. Through the design of the ligands, the choice of the metal ions and through the pH, ionic strength, temperature and other experimental parameters it is possible to define a window of opportunity where soluble coordination polymers exist. However, the dynamic nature poses a great challenge for characterization because structure and property depend on the external conditions. Besides the value-adding properties of transition metal ions such as electrochemical, magnetic, optical and reactive parameters these polymers add a dynamic component to an already rich spectrum of polymer properties. The dynamic nature makes them unique for fundamental research to address questions concerning self-assembly thermodynamics and kinetics. Additionally, these polymers provide an enormous potential for the development of stimuli-responsive and intelligent materials. [Copyright &y& Elsevier]

Abstract: Intercalation of an organic photochromic molecule into layered magnetic systems has a possibility to provide multifunctional properties such as photomagnetism. In order to build up photosensitive multifunctional magnets, organic–inorganic hybrid systems coupled with photochromic diarylethene ion (DAE) and layered ferromagnets such as cobalt layered hydroxides (LDHs) and layered perovskite-type copper halides were synthesized. In the case of cobalt LDHs with DAE, Co4(OH)7(DAE)0.5·3H2O, the remarkable enhancement of the Curie temperature from 9 to 20K was realized by substituting the open form of DAE with the closed form of DAE as intercalated molecule because of the delocalized π electrons in the closed form of DAE. By UV irradiation at 313nm, Co4(OH)7(DAE)0.5·3H2O shows the photoisomerization of DAE from the open form to the closed one in the solid state, which induces the enhancement of the Curie temperature. In the case of layered perovskite-type copper chlorides with a diarylethene cation (DAE)CuCl4 with the open form of DAE, this shows the antiferromagnetic transition at T N =3K, while (DAE)CuCl4 with the closed form of DAE shows no magnetic phase transition above 2K. [Copyright &y& Elsevier]

Abstract: The photo-induced charge transfer in four series of Prussian blue (PB) analogues was studied from photoacoustic spectra. In cobalticyanides the observed signals were assigned to a metal-to-ligand charge transfer, which appears as a shoulder below 450nm, and to d–d transitions for Co(II), Ni(II) and Cu(II) complex salts. No evidence of metal-to-metal charge transfer was observed for this series, which is probably due to the high stability of low spin cobalt(III) in the hexacyanide complex. Photoacoustic spectra for ferricyanides are broad bands, which result particularly intense up to 750nm. Such features were attributed to the overlapping of contributions from metal-to-ligand (<600nm) and metal-to-metal charge transfer transitions, with probably also a minor contribution from d–d transitions in the outer metal. The spectra for the ferrocyanides series are dominated by the metal-to-ligand charge transfer band below 550nm, approximately 100nm above this transition in cobalticyanides. Within the studied solids, the most intense and broad metal-to-metal charge transfer bands were found for a series of low spin Co(III) high spin Co(II) hexacyanoferrates(II,III) and with similar features also for ferric ferrocyanide (Prussian blue), assigned to Fe(II)→Co(III) and Fe(II)→Fe(III) photo-induced transition, respectively. The first of these transitions requires of more energetic photons to be observed, its maximum falls at 580nm while for Prussian blue it is found at 670nm. Prussian blue analogues are usually obtained as nanometric size particles and many of them have a microporous structure. The role of surface atoms on the observed charge transfer bands in the studied series of compounds is also discussed. [Copyright &y& Elsevier]

Abstract: In this article, we analyze the interplay between the antisymmetric (AS) exchange interaction and Jahn–Teller (JT) vibronic coupling in spin-frustrated systems with triangular units. AS exchange in these systems creates a strong first order magnetic anisotropy related to the orbitally degenerate frustrated ground state that is analyzed for the unique structure of the cluster anion present in (V15 cluster) exhibiting layers of different magnetization. Spin-frustration inherently related to the orbital degeneracy creates a structural instability that is shown to be competitive to the AS exchange. The vibronic pseudo JT coupling arising from the modulation of the exchange interaction by the double degenerate molecular vibrations is shown to reduce AS exchange giving rise to a restoration of magnetization quenched by AS exchange. This leads to an essential reduction of the magnetic anisotropy in spin-frustrated triangular clusters so that in the limit of strong JT coupling the isotropic exchange model becomes adequate. [Copyright &y& Elsevier]

Abstract: The crystal structures and magnetic properties of two new salts containing polymeric dicyanamidocuprate(II) anions are reported. Subtle changes in cation templation effects, crystallization conditions, and the coordination geometry of the metal center result in dramatic changes in the structure of the anionic framework. We report that the (PPh4)Cu(dca)3H2O [dca=dicyanamide, ] salt contains singly bridged μ1,5-dca chains that are linked into a two-dimensional network through coordinated water molecules. Replacement of one of the cation phenyl groups with a butyl group results in the formation of the (PPh3Bu)2Cu(dca)4 salt, which contains doubly bridged μ1,5-dca chains. Only negligibly weak magnetic interactions were observed in both compounds. [Copyright &y& Elsevier]

Abstract: We report on the studies of the influence of hydrostatic pressure (up to 1.2GPa) on dynamic electronic structure phenomena in 3d transition metal coordination compounds by Mössbauer and magnetic susceptibility measurements. We present examples of mononuclear spin crossover compounds of iron(II) and chromium(II), dinuclear complexes of iron(II) exhibiting coexistence of intramolecular antiferromagnetic coupling and thermal spin crossover, 1D, 2D and 3D spin crossover coordination polymers of iron(II), a valence tautomeric system of cobalt(II) showing thermal transition from a high-spin [CoII(semiquinone)] to a low-spin [CoIII(catecholate)] species on lowering the temperature, a photo-magnetically active Prussian blue-type system with temperature- and pressure-induced electron transfer, and finally an iron–TCNE compound with ferromagnetic interaction. [Copyright &y& Elsevier]

Abstract: In the present work, we address the determination of the electronic structure of a monolayer of Mn12 clusters, grafted on Au(111) substrate by a suitable functionalization, by means of X-ray absorption and resonant valence band photoemission (RESPES) spectroscopies taken across the Mn 2p–3d absorption edge. The absorption edge of the Mn12 monolayer is compared with that – reported in literature – of bulk Mn12, showing that the deposition procedure does not significantly affect the intimate nature of the Mn12 cluster. Quantitative comparison between RESPES spectra data allow us to extract the Mn 3d density of states from the Mn12-monolayer valence band spectrum, which is dominated by the Au 5d states. The shape of the experimentally obtained valence band DOS is in good agreement with the theoretical DOS, obtained by first-principle LDA+ U calculations, confirming the importance of correlation effects in the determination of the electronic properties of the Mn12 cluster. [Copyright &y& Elsevier]

Abstract: Heterometallic molecular chromium wheels are fascinating new magnetic materials. We reexamine the available experimental susceptibility data on MCr7 wheels in terms of a simple isotropic Heisenberg Hamiltonian for M=Fe, Ni, Cu, and Zn and find in that FeCr7 needs to be described with an iron–chromium exchange that is different from all other cases. In a second step we model the behavior of the proton spin lattice relaxation rate as a function of applied magnetic field for low temperatures as it is measured in nuclear magnetic resonance (NMR) experiments. It appears that CuCr7 and NiCr7 show an unexpectedly reduced relaxation rate at certain level crossings. [Copyright &y& Elsevier]

Abstract: Density functional self-consistent spin-polarized calculations with the discrete variational method were performed to investigate the electronic structure, magnetic and hyperfine properties of the single molecule magnet [Fe8O2(OH)12(tacn)6]+8 (shortly named Fe8). Magnetic moments, total spin, density of states, charge and spin density contour maps are obtained. The average moment and net charge per Fe site are about 4.2 μ B and +2.5e, respectively. The total magnetic moment of 20 μ B is obtained which is in accordance with experimental results. The anisotropy of Fe8 is investigated from the charge and spin density distribution. The hyperfine magnetic field and isomer shift for different Fe ions are also studied by comparing with the Mössbauer spectrum. [Copyright &y& Elsevier]