A family of four Ln(III) complexes has been synthesized with the general formula Ln
(NO
)
(L)
(S) (Ln = Gd, Tb, Er, and S = H
O;
,
and
, respectively/Ln = Dy, S = MeOH, complex
), where HL is the ...flexible ditopic ligand
'-(1-(pyridin-2-yl)ethylidene)pyridine-2-carbohydrazide. The structures of isostructural MeOH/H
O solvates of these complexes were determined by single-crystal X-ray diffraction. The two Ln
ions are doubly bridged by the deprotonated oxygen atoms of two "head-to-head" 2.21011 (Harris notation) L¯ ligands, forming a central, nearly rhombic {Ln
(μ-OR)
}
core. Two bidentate chelating nitrato groups complete a sphenocoronal 10-coordination at one metal ion, while two bidentate chelating nitrato groups and one solvent molecule (H
O or MeOH) complete a spherical capped square antiprismatic 9-coordination at the other. The structures are critically compared with those of other, previously reported metal complexes of HL or L¯. The IR spectra of
-
are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The f-f transitions in the solid-state (diffuse reflectance) spectra of the Tb(III), Dy(III), and Er(III) complexes have been fully assigned in the UV/Vis and near-IR regions. Magnetic susceptibility studies in the 1.85-300 K range reveal the presence of weak, intramolecular Gd
∙∙∙Gd
antiferromagnetic exchange interactions in
/
= -0.020(6) K based on the spin Hamiltonian
= -2
(
∙
) and probably weak antiferromagnetic Ln
∙∙∙Ln
exchange interactions in
-
. Ac susceptibility measurements in zero dc field do not show frequency dependent out-of-phase signals, and this experimental fact is discussed for
in terms of the magnetic anisotropy axis for each Dy
center and the oblate electron density of this metal ion. Complexes
and
are Single-Molecule Magnets (SMMs) and this behavior is optimally observed under external dc fields of 600 and 1000 Oe, respectively. The magnetization relaxation pathways are discussed and a satisfactory fit of the temperature and field dependencies of the relaxation time
was achieved considering a model that employs Raman, direct, and Orbach relaxation mechanisms.
The unique properties of graphene, transition-metal dichalcogenides and other two-dimensional (2D) materials have boosted interest in layered coordination solids. In particular, 2D materials that ...behave as both conductors and magnets could find applications in quantum magnetoelectronics and spintronics. Here, we report the synthesis of CrCl2(pyrazine)2, an air-stable layered solid, by reaction of CrCl2 with pyrazine (pyz). This compound displays a ferrimagnetic order below ∼55 K, reflecting the presence of strong magnetic interactions. Electrical conductivity measurements demonstrate that CrCl2(pyz)2 reaches a conductivity of 32 mS cm–1 at room temperature, which operates through a 2D hopping-based transport mechanism. These properties are induced by the redox-activity of the pyrazine ligand, which leads to a smearing of the Cr 3d and pyrazine π states. We suggest that the combination of redox-active ligands and reducing paramagnetic metal ions represents a general approach towards tuneable 2D materials that consist of charge-neutral layers and exhibit both long-range magnetic order and high electronic conductivity.
The reaction between Dy(NO
)
∙6H
O and the bulky Schiff base ligand,
-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH
), in the presence of the organic base NEt
has led to crystallization and ...structural, spectroscopic and magnetic characterization of a new heptanuclear Dy
(OH)
(OMe)
(NO
)
(nacb)
(nacbH)
(MeOH)(H
O)
(NO
)
(
) compound in ~40% yield. Complex
has a unique hourglass-like metal topology, among all previously reported {Dy
} clusters, comprising two distorted {Dy
(μ
-OH)
(μ
-OMe)}
cubanes that share a common metal vertex (Dy2). Peripheral ligation about the metal core is provided by the carboxylate groups of four η
:η
:η
:μ single-deprotonated nacbH
and two η
:η
:η
:η
:μ
fully-deprotonated nacb
ligands. Complex
is the first structurally characterized 4f-metal complex bearing the chelating/bridging ligand nacbH
at any protonation level. Magnetic susceptibility studies revealed that
exhibits slow relaxation of magnetization at a zero external dc field, albeit with a small energy barrier of ~5 K for the magnetization reversal, most likely due to the very fast quantum-tunneling process. The combined results are a promising start to further explore the reactivity of nacbH
upon all lanthanide ions and the systematic use of this chelate ligand as a route to new 4f-metal cluster compounds with beautiful structures and interesting magnetic dynamics.
Abstract
Electronic synergy between metal ions and organic linkers is a key to engineering molecule-based materials with a high electrical conductivity and, ultimately, metallicity. To enhance ...conductivity in metal-organic solids, chemists aim to bring the electrochemical potentials of the constituent metal ions and bridging organic ligands closer in a quest to obtain metal-
d
and ligand-
π
admixed frontier bands. Herein, we demonstrate the critical role of the metal ion in tuning the electronic ground state of such materials. While VCl
2
(pyrazine)
2
is an electrical insulator, TiCl
2
(pyrazine)
2
displays the highest room-temperature electronic conductivity (5.3 S cm
–1
) for any metal-organic solid involving octahedrally coordinated metal ions. Notably, TiCl
2
(pyrazine)
2
exhibits Pauli paramagnetism consistent with the specific heat, supporting the existence of a Fermi liquid state (i.e., a correlated metal). This result widens perspectives for designing molecule-based systems with strong metal-ligand covalency and electronic correlations.
The initial employment of the fluorescent bridging ligand N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2) in metal cluster chemistry has led to new Ni12 (1) and Ni5 (2) clusters with wheel-like ...and molecular-chain topologies, respectively. The doubly-deprotonated nacb(2-) ligands were found to adopt four different coordination modes within 1 and 2. The nature of the ligand has also allowed unexpected organic transformations to occur and ferromagnetic and emission behaviors to emerge. The combined work demonstrates the ability of some "ligands-with-benefits" to yield beautiful structures with exciting topologies and interesting physicochemical properties.
The employment of the fluorescent bridging and chelating ligand N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2) in Ni(II) cluster chemistry has led to a series of pentanuclear and hexanuclear ...compounds with different structural motifs, magnetic and optical properties, as well as an interesting 1-D coordination polymer. Synthetic parameters such as the inorganic anion present in the NiX2 starting materials (X = ClO4(-) or Cl(-)), the reaction solvent and the nature of the organic base employed for the deprotonation of nacbH2 were proved to be structure-directing components. Undoubtedly, the reported results demonstrate the rich coordination chemistry of nacbH2 in the presence of Ni(II) metal ions and the ability of this chelate to adopt a variety of different modes, thus fostering the formation of high-nuclearity molecules with many physical properties.
Three structurally and magnetically different tetranuclear Ni(II) complexes have been isolated and magnetically characterized, emphasizing the effect of the reaction solvent and organic ligand ...substitution on the chemical identity of cluster compounds.
There has been a renaissance in the interdisciplinary field of Molecular Magnetism since ~2000, due to the discovery of the impressive properties and potential applications of d- and f-metal ...Single-Molecule Magnets (SMMs) and Single-Ion Magnets (SIMs) or Monometallic Single-Molecule Magnets. One of the consequences of this discovery has been an explosive growth in synthetic molecular inorganic and organometallic chemistry. In SMM and SIM chemistry, inorganic and organic ligands play a decisive role, sometimes equally important to that of the magnetic metal ion(s). In SMM chemistry, bridging ligands that propagate strong ferromagnetic exchange interactions between the metal ions resulting in large spin ground states, well isolated from excited states, are preferable; however, antiferromagnetic coupling can also lead to SMM behavior. In SIM chemistry, ligands that create a strong axial crystal field are highly desirable for metal ions with oblate electron density, e.g., TbIII and DyIII, whereas equatorial crystal fields lead to SMM behavior in complexes based on metal ions with prolate electron density, e.g., ErIII. In this review, we have attempted to highlight the use of few, efficient ligands in the chemistry of transition-metal SMMs and SIMs, through selected examples. The content of the review is purely chemical and it is assumed that the reader has a good knowledge of synthetic, structural and physical inorganic chemistry, as well as of the properties of SIMs and SMMs and the techniques of their study. The ligands that will be discussed are the azide ion, the cyanido group, the tris(trimethylsilyl)methanide, the cyclopentanienido group, soft (based on the Hard-Soft Acid-Base model) ligands, metallacrowns combined with click chemistry, deprotonated aliphatic diols, and the family of 2-pyridyl ketoximes, including some of its elaborate derivatives. The rationale behind the selection of the ligands will be emphasized.
The self-assembly reaction between NiI2, benzoic acid (PhCO2H) and the Schiff base chelate, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in the presence of the organic base triethylamine ...(NEt3), has resulted in the isolation and the structural, spectroscopic, and physicochemical characterization of the dodecanuclear Ni12I2(OH)6(O2CPh)5(nacb)5(H2O)4(MeCN)4I (1) cluster compound in ~30% yield. Complex 1 has a cage-like conformation, comprising twelve distorted, octahedral NiII ions that are bridged by five μ3-OH−, one μ-OH−, an I− in 55% occupancy, five PhCO2− groups (under the η1:η1:μ, η1:η2:μ3 and η2:η2:μ4 modes), and the naphthoxido and carboxylato O-atoms of five doubly deprotonated nacb2− groups. The overall {Ni12} cluster exhibits a nanosized structure with a diameter of ~2.5 nm and its metallic core can be conveniently described as a series of nine edge- or vertex-sharing {Ni3} triangular subunits. Complex 1 is the highest nuclearity coordination compound bearing the nacbH2 chelate, and a rare example of polynuclear NiII complex containing coordinating I− ions. Direct current (DC) magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the NiII ions, while photophysical studies of 1 in the solid-state showed a cyan-to-green centered emission at 520 nm, upon maximum excitation at 380 nm. The reported results demonstrate the rich coordination chemistry of the deprotonated nacb2− chelate in the presence of NiII metal ions, and the ability of this ligand to adopt a variety of different bridging modes, thus fostering the formation of high-nuclearity molecules with rare, nanosized dimensions and interesting physical (i.e., magnetic and optical) properties.
Magnets derived from inorganic materials (e.g., oxides, rare-earth-based, and intermetallic compounds) are key components of modern technological applications. Despite considerable success in a broad ...range of applications, these inorganic magnets suffer several drawbacks, including energetically expensive fabrication, limited availability of certain constituent elements, high density, and poor scope for chemical tunability. A promising design strategy for next-generation magnets relies on the versatile coordination chemistry of abundant metal ions and inexpensive organic ligands. Following this approach, we report the general, simple, and efficient synthesis of lightweight, molecule-based magnets by postsynthetic reduction of preassembled coordination networks that incorporate chromium metal ions and pyrazine building blocks. The resulting metal-organic ferrimagnets feature critical temperatures up to 242°C and a 7500-oersted room-temperature coercivity.
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