Nanostructures as the Substrate for Single-Molecule Magnet Deposition

Anchoringsingle-molecule magnets (SMMs) on the surface of nanostructures is gaining particular interest in the field of molecular magnetism. The accurate organization of SMMs on low-dimensional substrates enables controlled interactions and the possibility of individual molecules' manipulation, paving the route for a broad range of nanotechnological applications. In this comprehensive review article, the most studied types of SMMs are presented, and the quantum-mechanical origin of their magnetic behavior is described. The nanostructured matrices were grouped and characterized to outline to the reader their relevance for subsequent compounding with SMMs. Particular attention was paid to the fact that this process must be carried out in such a way as to preserve the initial functionality and properties of the molecules. Therefore, the work also includes a discussion of issues concerning both the methods of synthesis of the systems in question as well as advanced measurement techniques of the resulting complexes. A great deal of attention was also focused on the issue of surface-molecule interaction, which can affect the magnetic properties of SMMs, causing molecular crystal field distortion or magnetic anisotropy modification, which affects quantum tunneling or magnetic hysteresis, respectively. In our opinion, the analysis of the literature carried out in this way will greatly help the reader to design SMM-nanostructure systems.

Negative Tone Metallic Organic Resists with Improved Sensitivity for Plasma Etching: Implications for Silicon Nanostructure Fabrication and Photomask Production

Metal-organic materials such as [NH₂(CH₂-CH=CH₂)₂][Cr₇NiF₈(Pivalate)₁₆] can act as negative tone resists for electron beam lithography (EBL) with high-resolution patterning of sub-40 nanometer pitch while exhibiting ultrahigh dry etch selectivities >100:1 and giving line dose exposures >11,000 pC/cm. It is clear that the resist sensitivity is too low to be used to manufacture the latest nanoscale photomasks that are suitable for extreme ultraviolet lithography. Therefore, the focus of this work here is to improve the sensitivity of this resist while maintaining its resolution and dry etch selectivity. Using our latest Monte Carlo simulation called Excalibur, we predict that the sensitivity would increase by a factor of 1.4 when the nickel atom is substituted by a cadmium atom. EBL studies showed an excellent agreement with the simulation, and plasma etching studies demonstrated that this did not affect the dry etch performance of the resist which remains very good with a selectively of ca. 99:1 for the etching of silicon at these resolutions with a low sensitivity of 7995 pC/cm.

Gold(i) bridged dimeric and trimeric heterometallic {Cr7Ni}-based qubit systems and their characterization

Gold(i) bridged dimeric and trimeric structures of a ground state spin S = 1/2 heterometallic {Cr₇Ni} wheel have been prepared and studied by continuous wave (CW) and pulsed wave EPR spectrometry. The {Cr₇Ni} relaxation time constants (T₁ and T_m) show rates matching well with previous observations. Four pulse Double Electron Resonance (DEER) studies suggest presence of more than one conformations. Small Angle X-ray Scattering (SAXS) in conjunction with Molecular Dynamic (MD) Simulations were performed to look at the possible conformations in solution. In line with DEER results, simulation data further indicated more flexible molecular geometry in solution than the one in solid state.

Experimental Evidence of the Coexistence of Proper Magnetic and Structural Incommensurability on the [CH3NH3][Ni(COOH)3] Compound

The present work is dedicated to characterization of the structural phase transition and incommensurate magnetic structure of the [CH₃NH₃][Ni(COOH)₃] (1) perovskite-like metal-organic compound. The structural and magnetic characterization has been performed through variable-temperature single-crystal and powder neutron diffraction. Compound 1 crystallizes in the orthorhombic Pnma space group at room temperature. Below 84 K, a new phase has been observed. The occurrence of new reflections, which can be indexed with a wavevector along the c axis [q = 0.1426(2)c*], suggests the occurrence of an incommensurately modulated crystal structure. The structure was determined using the superspace group formalism on the Pnma(00γ)0s0 space group. This incommensurate phase remains unchanged with a decrease of the temperature up to the base temperature (ca. 2 K). Moreover, the magnetic susceptibility data, collected under zero-field-cooled and field-cooled conditions at different applied magnetic fields, show that compound 1 exhibits antiferromagnetic behavior below 34 K. In the current paper, we have confirmed that compound 1 presents the coexistence of nuclear and proper magnetic incommensurability below T_N.

Using SMILES strings for the description of chemical connectivity in the Crystallography Open Database

Computer descriptions of chemical molecular connectivity are necessary for searching chemical databases and for predicting chemical properties from molecular structure. In this article, the ongoing work to describe the chemical connectivity of entries contained in the Crystallography Open Database (COD) in SMILES format is reported. This collection of SMILES is publicly available for chemical (substructure) search or for any other purpose on an open-access basis, as is the COD itself. The conventions that have been followed for the representation of compounds that do not fit into the valence bond theory are outlined for the most frequently found cases. The procedure for getting the SMILES out of the CIF files starts with checking whether the atoms in the asymmetric unit are a chemically acceptable image of the compound. When they are not (molecule in a symmetry element, disorder, polymeric species,etc.), the previously published cif_molecule program is used to get such image in many cases. The program package Open Babel is then applied to get SMILES strings from the CIF files (either those directly taken from the COD or those produced by cif_molecule when applicable). The results are then checked and/or fixed by a human editor, in a computer-aided task that at present still consumes a great deal of human time. Even if the procedure still needs to be improved to make it more automatic (and hence faster), it has already yielded more than 160,000 curated chemical structures and the purpose of this article is to announce the existence of this work to the chemical community as well as to spread the use of its results.

Syntheses, structures and magnetic properties of tetranuclear cubane-type and heptanuclear wheel-type nickel(ii) complexes with 3-methoxysalicylic acid derivatives

Three mono- and multi-nuclear Ni(ii) compounds were synthesised and investigated.

Filling the gap between the quantum and classical worlds of nanoscale magnetism: giant molecular aggregates based on paramagnetic 3d metal ions

In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term "giant clusters" is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.

Making hybrid [n]-rotaxanes as supramolecular arrays of molecular electron spin qubits

Quantum information processing (QIP) would require that the individual units involved--qubits--communicate to other qubits while retaining their identity. In many ways this resembles the way supramolecular chemistry brings together individual molecules into interlocked structures, where the assembly has one identity but where the individual components are still recognizable. Here a fully modular supramolecular strategy has been to link hybrid organic-inorganic [2]- and [3]-rotaxanes into still larger [4]-, [5]- and [7]-rotaxanes. The ring components are heterometallic octanuclear [Cr7NiF8(O2C(t)Bu)16](-) coordination cages and the thread components template the formation of the ring about the organic axle, and are further functionalized to act as a ligand, which leads to large supramolecular arrays of these heterometallic rings. As the rings have been proposed as qubits for QIP, the strategy provides a possible route towards scalable molecular electron spin devices for QIP. Double electron-electron resonance experiments demonstrate inter-qubit interactions suitable for mediating two-qubit quantum logic gates.

Solvothermal synthesis of discrete cages and extended networks comprising {Cr(iii)3O(O2CR)3(oxime)3}2− (R = H, CH3, C(CH3)3, C14H9) building blocks

We present the solvothermal synthesis, structural and magnetic characterisation of a family of Cr(iii) cages and extended networks comprising {Cr(iii)₃O(O₂CR₁)₃(R₂-sao)}²⁻ (R₁ = H, CH₃, C(CH₃)₃, C₁₄H₉; R₂ = Me, Ph, ^tBu, C₁₀H₆) building blocks.

Synthesis and reactions of N-heterocycle functionalised variants of heterometallic {Cr7Ni} rings

Here we present a series of linked cage complexes of functionalised variants of the octametallic ring {Cr₇Ni} with the general formula [ⁿPr₂NH₂][Cr₇NiF₈(O₂C^tBu)₁₅(O₂CR)], where HO₂CR is a N-heterocycle containing carboxylic acid.

Supramolecular aggregates of single-molecule magnets: exchange-biased quantum tunneling of magnetization in a rectangular [Mn3]4 tetramer

Exchange-biased QTM within a magnetically-supramolecular tetramer of Mn₃ single-molecule magnets with spin S = 6 has been analyzed.

The syntheses and properties of four magnetically-supramolecular oligomers of triangular Mn₃ units are reported: dimeric [Mn₆O₂(O₂CMe)₈(CH₃OH)₂(pdpd)₂] (3) and [Mn₆O₂(O₂CMe)₈(py)₂(pdpd)₂](ClO₄)₂ (4), and tetrameric [Mn₁₂O₄(O₂CR)₁₂(pdpd)₆](ClO₄)₄ (R = Me (5), ^tBu (6)). They were all obtained employing 3-phenyl-1,5-di(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH₂), either in direct synthesis reactions involving oxidation of Mn^II salts or in metathesis reactions with the preformed complex [Mn₃O(O₂CMe)₆(py)₃](ClO₄) (1); complex 6 was then obtained by carboxylate substitution on complex 5. Complexes 3 and 4 contain two [MnIII2Mn^II(μ₃-O)]⁶⁺ and [MnIII3(μ₃-O)]⁷⁺ units, respectively, linked by two pdpd^2– groups. Complexes 5 and 6 contain four [MnIII3(μ₃-O)]⁷⁺ units linked by six pdpd^2– groups into a rectangular tetramer [MnIII3]₄. Solid-state dc magnetic susceptibility studies showed that the Mn₃ subunits in 3 and 4 have a ground-state spin of S = 3/2 and S = 2, respectively, while the Mn₃ subunits in 5 and 6 possess an S = 6 ground state. Complexes 5 and 6 exhibit frequency-dependent out-of-phase (χ′′_M) ac susceptibility signals indicating 5 and 6 to be tetramers of Mn₃ single-molecule magnets (SMMs). High-frequency EPR studies of a microcrystalline powder sample of 5·2CH₂Cl₂ provided precise spin Hamiltonian parameters of D = –0.33 cm^–1, |E| = 0.03 cm^–1, B04 = –8.0 × 10^–5 cm^–1, and g = 2.0. Magnetization vs. dc field sweeps on a single crystal of 5·xCH₂Cl₂ gave hysteresis loops below 1 K that exhibit exchange-biased quantum tunneling of magnetization (QTM) steps with a bias field of 0.19 T. Simulation of the loops determined that each Mn₃ unit is exchange-coupled to the two neighbors linked to it by the pdpd^2– linkers, with an antiferromagnetic inter-Mn₃ exchange interaction of J/k_B = –0.011 K (Ĥ = –2Jŝ_i·ŝ_j convention). The work demonstrates a rational approach to synthesizing magnetically-supramolecular aggregates of SMMs as potential multi-qubit systems for quantum computing.

Heterometallic Rings: Their Physics and use as Supramolecular Building Blocks

An enormous family of heterometallic rings has been made. The first were Cr7 M rings where M = Ni(II), Zn(II), Mn(II), and rings have been made with as many as fourteen metal centers in the cyclic structure. They are bridged externally by carboxylates, and internally by fluorides or a penta-deprotonated polyol. The size of the rings is controlled through templates which have included a range of ammonium or imidazolium ions, alkali metals and coordination compounds. The rings can be functionalized to act as ligands, and incorporated into hybrid organic-inorganic rotaxanes and into molecules containing up to 200 metal centers. Physical studies reported include: magnetic measurements, inelastic neutron scattering (including single crystal measurements), electron paramagnetic resonance spectroscopy (including measurements of phase memory times), NMR spectroscopy (both solution and solid state), and polarized neutron diffraction. The rings are hence ideal for understanding magnetism in elegant exchange-coupled systems.

Enlarging the ring by incorporating a phosphonate coligand: from the cyclic hexanuclear to octanuclear dysprosium clusters

Solvothermal reaction of a double pyrazinyl hydrazone ligand EDDC(2-) with Dy(OAc)3 results in a cyclic hexanuclear cluster [Dy6(EDDC)2(OAc)14(H2O)2]·MeOH·2H2O (). The addition of 1-naphthylphosphonate to the reaction mixture expands the ring size with the formation of a cyclic octanuclear cluster [Dy8(EDDC)4(O3PC10H7)4(OAc)8(H2O)4]·12H2O (). The latter shows slow magnetization relaxation below 12 K, characteristic of single molecule magnet behavior.

A hybrid organic–inorganic molecular daisy chain

A hybrid daisy-chain has been made, involving an organic thread for an inorganic ring, where the organic thread for the ring also acts as a ligand for a second ring. The ring contains six chromium(iii) and two zinc(ii) ions, and two isomers of the rings are found in the daisy-chain.

Metal distribution and disorder in the crystal structure of [NH2Et2][Cr7MF8(tBuCO2)16] wheel molecules forM= Mn, Fe, Co, Ni, Cu, Zn and Cd

The homometallic wheel compound [Cr8F8(O2CCMe3)16] formed with fluorine and pivalic acid ligands can be modified by introducing in the synthesis process a divalent cationMcapable of octahedral coordination instead of one of the trivalent Cr centres in the ring. Heterometallic mono-anionic species [Cr7MF8(O2CCMe3)16]−can form diethylammonium salts and be crystallized from ethylacetate solution as compounds with the general formula [NH2Et2][Cr7MF8(tBuCO2)16][C4H8O2]0.5forM= Mn, Fe, Co, Ni, Cu, Zn and Cd. Their structures are isomorphous, belonging to the space groupP21/c. The study has determined the degree of order for the individualMheterometal over the possible metal positions of the ring in the crystal structure by modelling based on X-ray diffraction data. The model took into account disorder intert-butyl groups of the pivalate ligands and in the position and orientation of the ethylacetate solvent molecule. The heterometal turned out to be partly ordered in the crystal structure.