Molecule-based Magnets Research Articles

What role has organic chemistry played in the development of molecule-based magnets?

Contributions of organic chemistry to the interdisciplinary science of molecule-based magnets are discussed in reference to transition metal coordination chemistry carried out successfully by Olivier Kahn and other scientists. Typical organic molecules have closed-shell structures and therefore organic compounds are usually diamagnetic. Organic chemists had to start with the design and construction of more-or-less stable open-shell organic molecules. Only then it became possible to study how to let their electron spins exchange-couple strongly by means of spin delocalization and polarization within a molecule and among molecules. Non-Kekulé π-systems were chosen to make the triplet carbene species to interact ferromagnetically. Approaches by means of synthetic organic chemistry proved effective. Magnetic susceptibility measurements revealed that such tetracarbene and nonacarbene have ground S=4 and S=9 states, respectively. Thus, the open-shell hydrocarbon molecules have been shown to have higher magnetic moments than those of S=5/2 Fe(III) and S=7/2 Gd(III) ions. Stable aminoxyl radicals played various roles in generating organic ferromagnets by controlling the exchange coupling between molecules in crystal, or by forming the metal/aminoxyl radical hybrid systems that were made on the basis of the supramolecular approaches and led to a number of ferro- and ferrimagnets. Metal/pyridylcarbene hybrid systems generated photochemically not only revealed the mode of the exchange coupling between the spins of metal d-orbital and those residing in organic π-orbital, but also suggested the route to novel photoresponsive magnetic materials. Most of the organic and metal/organic magnets discussed in the 80s and early 90s were trying to mimic conventional magnets by molecular materials. It is only after the advent of the single-molecule magnets when molecule-based magnets became molecular materials in their own right in the area of nano-science. Here again, novel organic molecules are used as useful, functional ligands for making single ion magnets and single chain magnets.

Update 1 of: Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets

Update 1 of: Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets

Magnetoelastic coupling in [Ru2(O2CMe)4]3[Cr(CN)6] molecule-based magnet

Infrared and Raman vibrational spectroscopies were employed to explore the lattice dynamics of [Ru${}_{2}$(O${}_{2}$CMe)${}_{4}$]${}_{3}$[Cr(CN)${}_{6}$] through the field- and temperature-driven magnetic transitions. The high field work reveals systematic changes in the C$\ensuremath{\equiv}$N stretching mode and Cr-containing phonons as the system is driven away from the antiferromagnetic state. The magnetic intersublattice coalescence transition at ${B}_{c}\ensuremath{\simeq}0.08$ T, on the contrary, is purely magnetic and takes place with no lattice involvement. The variable temperature spectroscopy affirms overall [Cr(CN)${}_{6}$]${}^{3\ensuremath{-}}$ flexibility along with stronger intermolecular interactions at low temperature. Based on a displacement pattern analysis, we discuss the local lattice distortions in terms of an adaptable chromium environment. These findings provide deeper understanding of spin-lattice coupling in [Ru${}_{2}$(O${}_{2}$CMe)${}_{4}$]${}_{3}$[Cr(CN)${}_{6}$] and may be useful in the development of technologically important molecule-based magnets.

Neutron-diffraction evidence for the ferrimagnetic ground state of a molecule-based magnet with weakly coupled sublattices

The diruthenium compound [Ru2(O2CMe)4]3[Cr(CN)6] contains two weakly coupled, ferrimagnetically ordered sublattices occupying the same volume. Due to the weak, antiferromagnetic dipolar interaction Kc ≈ 5 × 10−3 meV between sublattices, a small magnetic field Hc ∼ Kc/μB ≈ 800 Oe aligns the sublattice moments. Powder neutron-diffraction measurements on a deuterated sample confirm an earlier prediction that the sublattice moments are restricted by the anisotropy of the diruthenium ‘paddle-wheels’ to the cubic diagonals. Those measurements also suggest that quantum corrections to the ground state are significant.

Publisher’s Note: “Magnetic diagnostics using the third-harmonic magnetic response for a molecule-based magnet networked by a single chiral ligand” [J. Appl. Phys. 111, 103914 (2012)

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Single-wall carbon nanotube interactions with copper-oxamato building block of molecule-based magnets probed by resonance Raman spectroscopy

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.

Enhanced Magnetic Hardness in a Nanoscale Metal-Organic Hybrid Ferrimagnet

A new layered metal-organic hybrid compound, namely, [Co(3)(μ(3 -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 Co(3) (μ(3)-OH), with the cavities filled with the PO(3) groups. The interlayer space is occupied by the 3-bromothienyl groups of BTP(2-). The bulk sample of compound 1 experiences a long-range ferromagnetic ordering below 30.5 K, with a coercivity (H(c)) 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.

Magnetic diagnostics using the third-harmonic magnetic response for a molecule-based magnet networked by a single chiral ligand

We investigated complex magnetic domain formation on a chiral molecule-based magnet, [Cr(CN)6][Mn(R)-pnH(H2O)](H2O) (termed as R-GN), whose two-dimensional molecular network was constructed with the help of a single-handed chiral ligand ((R)-pn). There, the first- and third-harmonic magnetic responses (M1ω and M3ω) against the ac magnetic field were observed, and magnetic hysteresis in ac field of a few Oe was discussed in terms of Rayleigh loop. The diagnostics of this magnetic hysteresis clarified the complex process of magnetic domain formation against a change in temperature. For R-GN, it was reported that a giant M3ω (termed #4 in this paper) appeared just above the so-called “magnetic ordering temperature (TC).” In the present study, three M3ω responses (#1-3) were newly observed on the lower-temperature side of #4, and the ac field dependencies for all of #1-#4 were investigated. #1 also accompanied the giant M3ω, which suggests that a significant degree of magnetic fluctuation surviving below TC. This glassy behavior below TC is an attractive new phenomenon in molecule-based magnets with a single-handed chiral ligand. #2 and #3 exhibited magnetic ordering and the formation of a small magnetic domain, respectively. The M3ω responses of #1-3 were suppressed with increasing the amplitude of ac field, and the corresponding magnetic hysteresis was a normal Rayleigh loop accompanying the out-of-phase of the M1ω response. The M3ω response of #4 without the out-of-phase of M1ω was, however, enhanced with increasing the amplitude of ac field, and #4 represented a large magnetic hysteresis in the paramagnetic region, intrinsically different from those of #1-#3.

Tailoring magnetic properties of electrodeposited thin films of the molecule-based magnet Cr5.5(CN)12 11.5H2O.

This paper reports on molecular-based magnetic thin films of Prussian blue analogues (PBA) with high critical temperatures composed of mixed-valence chromium cyanides. The thin films of PBA were synthesized by means of electrodeposition technique. Morphology and magnetic study are presented in a function of electrochemical deposition conditions. We present the electrochemical methods as a promising and effective tool for preparing molecular-based magnetic thin films of Prussian blue analogue.

Dimensionality Selection in a Molecule-Based Magnet

Gaining control of the building blocks of magnetic materials and thereby achieving particular characteristics will make possible the design and growth of bespoke magnetic devices. While progress in the synthesis of molecular materials, and especially coordination polymers, represents a significant step towards this goal, the ability to tune the magnetic interactions within a particular framework remains in its infancy. Here we demonstrate a chemical method which achieves dimensionality selection via preferential inhibition of the magnetic exchange in an S=1/2 antiferromagnet along one crystal direction, switching the system from being quasi-two- to quasi-one-dimensional while effectively maintaining the nearest-neighbor coupling strength.

First magnets based on thiocyanato-bridges

2-D NCS-bridged {3d-4d} molecule-based magnets, formed by reaction of [Mo(III)(NCS)(6)](3-) with either Ni(II) or Co(II) complexes, have been found to exhibit magnetic ordering with T(C) = 39 K for {Co(3)Mo(2)} while {Ni(3)Mo(2)} has a non-magnetic ground state as a result of exact compensation by the individual sub-lattices.

Cyano-bridged terbium(iii)–chromium(iii) bimetallic quasi-one-dimensional assembly exhibiting long-range magnetic ordering

A new cyano-bridged Tb(III)-Cr(III) heterometallic complex [Tb(H(2)O)(2)(DMF)(4){Cr(CN)(6)}]·H(2)O (DMF = dimethylformamide) (1), assembled from paramagnetic hexacyanochromium(III) [Cr(CN)(6)](3-) building block and highly anisotropic terbium(III) ion has been prepared and structurally and magnetically characterized. Complex 1 shows one-dimensional (1D) zig-zag chain-like structural motif which is further extended into three-dimensional network through hydrogen-bonding interactions. The long-range magnetic ordering observed in complex 1, which is possibly due to interchain magnetic dipolar interactions, illuminates that this complex is a molecule-based magnet with critical temperature of about 5 K. This higher critical temperature among those of Ln(III)-Cr(III) heterometallic complexes exhibiting long-range magnetic ordering is probably due to the introduction of highly anisotropic terbium(III) ion.

Frontier and perspectives in molecule-based quantum magnets

Frontier and perspectives in molecule-based quantum magnets

The structure and magnetic properties of molecule-based magnet nanoparticles K x V y [Cr(CN)6] z .nH2O

We have synthesized K x V y [Cr(CN)6] z . n H 2 O molecule-based magnet nanoparticles belonging to the Prussian blue (PB) family of compounds. The synthesized samples were characterized by infrared spectroscopy (IR), Raman spectroscopy, UV–Vis spectroscopy, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The crystal structure was refined from the x-ray powder diffraction profile by the Rietveld method. The samples are cubic, Fm3m space group with lattice parameter a=1.045 nm. The magnetic properties are determined from thermal variation of the magnetization and hysteresis loop. The most interesting result is the successful preparation of K x V y [Cr(CN)6] z . n H 2 O crystal Prussian blue nanomaterial which had Curie temperature (T c ) approaching room temperature.

Family of molecule-based magnets withMIIμ4-TCNE sheets

Family of molecule-based magnets with<i>M</i>^IIμ₄-TCNE sheets

ChemInform Abstract: Framework‐Structured Weak Ferromagnets

AbstractReview: 273 refs.

Magneto‐Optical Properties of Electrodeposited Thin Films of the Molecule‐Based Magnet Cr5.5(CN)12·11.5H2O

Electrodeposited thin films of the molecule-based magnet Cr5.5(CN)12·11.5H2O exhibit a magneto-optical Kerr effect (MOKE) with large coercive fields at 200 K. As the thickness of the films is reduced to the nanometer scale, the particle size decreases and the magneto-optical hysteresis becomes relatively large.

Spectroscopic study of (two-dimensional) molecule-based magnets: [MII(TCNE)(NCMe)2][SbF6] (M = Fe, Mn, Ni)

The M-[TCNE] (M = 3d metal; TCNE = tetracyanoethylene) system is one of the most interesting classes of molecule-based magnets, exhibiting a plethora of compositions and structures (inorganic polymer chains, 2D layers, 3D networks, and amorphous solids) with a wide range of magnetic ordering temperatures (up to 400 K). A systematic study of vibrational (both infrared and, for the first time, Raman) properties of the family of new TCNE-based magnets of M(II)(TCNE) (NCMe)(2)[SbF(6)] [M = Mn, Fe, Ni] composition is discussed in conjunction with their magnetic behavior and newly reso-lved crystal structures. The vibrational properties of the isolated TCNE(●-) anion in the paramagnetic Bu(4)N [TCNE(●-)] salt and recently characterized 2D layered magnet Fe(II)(TCNE)(NCMe)(2)[FeCl(4)] are also reported for comparison. Additionally, a linear correlation between ν(C=C) (a(g)) frequency of the TCNE ligand and its formal charge Z (the spin density on the π* orbital), Z = [1571 - ν(C=C) (a(g))]/154.5 [e], is presented. It is shown that monitoring Z by Raman spectroscopy is of great use in providing information that allows understanding the peculiarity of the superexchange interaction in M-[TCNE] magnets and establishing the structure-magnetic properties correlations in this class of magnetic material.

Thin films of molecule-based charge transfer complex cobalt tetracyanoethylene: In situ X-ray photoemission study

Thin films of molecule-based charge transfer magnet, cobalt tetracyanoethylene [Co(TCNE) x , x ~ 2] consisting of the transition metal Co, and an organic molecule viz . tetracyanoethylene (TCNE) have been deposited by using physical vapor deposition method under ultra-high vacuum conditions at room temperature. X-ray photoelectron spectroscopy (XPS) technique has been used extensively to investigate the electronic properties of the Co(TCNE) x thin films. The XPS measurements show that the prepared Co(TCNE) x films are clean, and oxygen free. The stoichiometries of the films, based on atomic sensitive factors, are obtained, and yields a ~ 1:2 ratio between metal Co and TCNE for all films. Interestingly, the positive shift of binding energy position for Co(2p), and negative shifts for C(1s) and N(1s) peaks suggest a charge-transfer from Co to TCNE, and cobalt is assigned to its Co(II) valence state. In the valence band investigation, the highest occupied molecular orbital (HOMO) of Co(TCNE) x is found to be at ~ 2.4 eV with respect to the Fermi level, and it is derived either from the TCNE − singly occupied molecular orbital (SOMO) or Co(3d) states. The peaks located at ~ 6.8 eV and ~ 8.8 eV are due to TCNE derived electronic states. The obtained core level and valence band results of Co(TCNE) x , films are compared with those of V(TCNE) x thin film magnet: a well known system of M(TCNE) x type of organic magnet, and important points regarding their electronic properties have been brought out.

An invitation to molecular magnetism.

Molecular magnetism is a new and extremely fascinating field on the borders of chemistry, physics and materials science. The design and synthesis of molecule-based magnets requires the chemist to exert considerable control over the molecules to arrange them appropriately. It also demands the development of new theories to explain the complex magneto-structural behaviour of these intriguing solids. Molecular magnetism is still at a very early stage of development. The main challenge is to increase the strength of the magnetic interactions between spin carriers so the resulting materials can be usable at room temperature. However molecular magnets exhibit true potential to become multifunctional materials. They show some considerable advantages over conventional magnets: optical transparency, chemical sensitivity and low weight to name just a few. The following article is not a complete review of the field. Its aim is rather to show how beautiful and versatile magnetic molecular solids can be, and to encourage the in-depth study of the subject.