A family of five 1D Re IV Ln III [Ln III = Dy, Tb, Gd] complexes based on derivatives of (3,4- and 3,5-)pyridinedicarboxylic acid has been prepared and characterised. The Re IV Dy III -based family members exhibit field-induced slow magnetic relaxation.

The design and synthesis of molecule-based multifunctional magnetic materials (MMMs) with desired chemical (e.g., host-guest, catalytic, acid-base, or redox) and physical (e.g., optical, magnetothermal, proton, or electron conducting) properties, in addition to magnetism, constitute a major goal in coordination chemistry. A deep knowledge of the metal-ligand self-assembly and metalloligand design approaches is essential for achieving the synergy that elevates classical molecular magnets and nanomagnets into the realm of MMMs. This review chronicles the journey of the versatile oxalato-type ligand family—including oxalate (ox), oxamate (oxa), oxamidate (oxm), dithiooxalate (dto), and tetrathiooxalate (tto)—in building homo- and heterometallic polynuclear complexes (PCs) and coordination polymers (CPs). These systems incorporate paramagnetic transition (nd, n = 3–5) and rare-earth (4f, 5f) metal ions, alongside diamagnetic alkaline or alkaline-earth ones, to construct MMMs ranging from discrete metal-organic clusters (MOCs) to extended metal-organic frameworks (MOFs). Ultimately, this review demonstrates how the foundational principles of magnetochemistry, established with this versatile ligand family, are now providing a robust blueprint for tackling the great challenges of the third millennium: designing advanced materials for quantum information processing, sustainable catalysis, selective molecular biosensing, diagnostic imaging, cryomagnetic refrigeration, water remediation, and chemical decontamination.

The design and the synthesis of molecule-based crystalline salts made up of simple cationic and/or anionic building blocks with multiple, occasionally stimulus-responsive, chemical (host–guest, catalytic, acid–base, or redox) and physical (optical, magnetic, or conducting) properties constitute two major goals in inorganic, organic, organometallic, and coordination chemistries. A deep knowledge of the basic features of molecular and supramolecular interactions that occur in the solid state is needed to progress along these tasks to obtain new advanced multifunctional materials. Inspired by the outstanding research of several groups on magnetic molecular salts from the mid-1970s to the present day, this review offers a personal portrayal of the history of molecular magnetism and molecular electronics and its current evolution toward molecular spintronics and quantum computing. We focus on the well-known families of molecular salts based on paramagnetic tetrathiafulvalenium/tetraselenafulvalenium or tetracyanoethenide/tetracyanoquinodimethanide organic radicals, cyclopentadienide/cyclooctatetraenide metallocenium complexes, and polyhalide/polycyanide, porphyrin/phthalocyanine, oxalate/dithiooxalate, or dithiolene/dithiolate metal complexes with first-, second-, or third-row transition metal (nd, n = 3–5) and lanthanide (4f) ions. This old but evergreen class of magnetic molecular salts provides illustrative “textbook” examples of advanced multifunctional materials such as molecular magnets and conductors, molecular magnetic conductors, molecular nanomagnets, and molecular quantum bits with potential nanotechnological applications in quantum information storage and processing.

Two tetranuclear complexes were obtained by a self-assembly process employing di-2-pyridyl ketone ((py)2CO), benzoate and M(NO3)2 (M = Co and Ni). The compounds [M4{(py)2C(OH)O}4(O2CPh)4], where {(py)2C(OH)O}− is the monoanion of the gem-diol form of (py)2CO, were characterized through single-crystal X-ray diffraction and magnetic measurements. Structural analysis revealed that both complexes possess a [M4O4] cubane-like core. A two-J model and magnetic anisotropy were employed to analyze the magnetic properties of both compounds. These studies indicate the presence of dominant ferromagnetic interactions within both tetranuclear cores. DFT and CASSCF/NEVPT2 calculations were also performed to support the fitting of experimental magnetic data.

The copper(II) complexes {Na4(H2O)8[Cu2(acriba)2(H2O)2]}n·4nH2O (1) and (Bu4N)4[Cu2(acriba)2]·5H2O (2) [H4acriba = N,N'-3,6-acridinebis(oxamic acid) and Bu4N+ = tetra-n-butylammonium cation] have been synthesized and characterized. Their crystal structures revealed the occurrence of [Cu2(acriba)2(H2O)2]4- (1) and [Cu2(acriba)2]4- (2) units of the [3,3] metallacyclophane-type which are built by two acridine linkers connected by two N-Cu-N bonds. The electroneutrality in 1 is achieved by their coordination to hydrated sodium(I) cations to afford a heterobimetallic sheet-like polymer, whereas that in 2 is ensured by bulky organic Bu4N+ cations to yield well-separated discrete dicopper(II) complexes. The spectrophotometric study of the catalytic activity of 1 and the related complex [Na6Cu2(mpyba)2Cl2(H2O)8]·7H2O (3) [H4mpyba = N,N'-2,6-pyridinebis(oxamic acid)] towards the oxidation of phenolic derivatives in aqueous solution showed a remarkable catalytic performance only for the hydroquinone with a better catalytic role in the case of 1. This superior catalytic behavior may be explained by the higher Lewis acidity of the Cu(II) ions derived from the inherent electronic delocalization of the extended aromatic acridine fragment compared to the pyridine one. The magnetic properties of 1 and 2 show weak intramolecular ferromagnetic interactions within their metallacyclophane units [J = +1.83 (1) and +1.72 cm-1 (2); H = -JSCu1·SCu2 where SCu1 = SCu2 = 1/2], their nature and magnitude being substantiated by theoretical calculations. These two examples illustrate the ability of the acridine moieties to mediate ferromagnetic interactions between copper(II) ions through the very long -Namidate-C-C-C-N-C-C-C-Namidate- exchange pathway in the context of the spin polarization mechanism.

Four homodinuclear triple mesocates of general formula (PPh4)2[M2(H2mpba)3]& sdot;2DMSO & sdot;4H2O (M = Co(II) (1), Ni(II) (2), Mn(II) (3) and Fe(II) (4), H4mpba = N,N'-1,3-phenylenebis(oxamic acid), PPh4+ = tetraphenylphosphonium and DMSO = dimethyl sulfoxide) have been synthesized. Their crystal structures were determined by single-crystal X-ray diffraction. 1-4 are isostructural dinuclear compounds that crystallize in the space group C2/ c with very close unit cell metrics, having in common the presence of [M2(H2mpba)3]2- mesocate entities whose charge is balanced by PPh4+ cations. Each metal ion in 1-4 is surrounded by six oxygen atoms from three bidentate monoprotonated oxamate groups in a somewhat distorted octahedral surrounding. The H2mpba2ligands in 1-4 exhibit the bis-bidentate coordination mode, each monoprotonated oxamate fragment acting as a bidentate donor toward a metal ion through the amide-oxygen and one of the two carboxylate oxygen atoms. The values of the intramolecular metal-metal separation cover the range 6.10-6.74 & Aring;. Hydrogen bonds between the mesocates lead to a zigzag-shaped supramolecular chain. Variable-temperature magnetic susceptibility data were carried out for 1-4 in the temperature range 4.0-300 K. A very weak ferromagnetic interaction between the metal center is observed for 3. In contrast, it is most likely masked by the zero-field splitting effects in the case of 1, 2, and 4. Although antibacterial activity against Escherichia coli (ATCC 25922) was observed only for 1 (MIC = 32 mu g/mL), all four complexes showed antibacterial activity against Staphylococcus aureus (ATCC 6538) with MIC values of 32 mu g/mL (1 and 3) and 64 mu g/mL (2 and 4). The antibacterial properties against S. aureus were demonstrated by complexes with Mn(II) and Fe(II), with MBC of 64 (3) and 128 mu g/mL (4), which leads to a possible investigation of the mechanism of these compounds against Gram-positive bacteria.

The search for appropriate structural correlations in molecule-based crystalline salts is of paramount importance to obtain new advanced multifuctional materials with higher performance in nanoscience and nanotechnology. In this article, we focus on the structural features and bonding interactions in the related family of optical- and electroactive molecular salts of anionic mononuclear bis(dithiooxalato)nickel(II), palladium(II), platinum(II), copper(II), copper(III), and zinc(II) complexes with several uni- and divalent, either inorganic or organic countercations. Steric and/or electronic effects of the metal ion and the inorganic or organic countercation determine the molecular structure and conformation of the resulting bis(dithiooxalato)metalate complex anion in the solid state, concerning both the metal coordination environment and the ligand skeleton, twisting and folding along this family of molecular salts.

A unique series of spin-crossover cobalt( ii )-pyridine-2,6-dimine molecular nanomagnets as prototypes of molecular spin quantum transitors and capacitors exhibiting a dual metal- and ligand-centred multielectron redox behaviour is reported.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Spin-crossover (SCO) and single-ion magnets (SIMs), or their mixed SCO-SIM derivatives, are a convenient solution in the evolution from molecular magnetism toward molecular spintronics and quantum computing. Herein, we report on the current trends and future directions on the use of mononuclear six-coordinate CoII SCO-SIM complexes with potential opto-, electro-, or chemo-active 2,6-pyridinediimine (PDI)- and 2,2′:6′,2′-terpyridine (TERPY)-type ligands as archetypical examples of multifunctional and multiresponsive magnetic devices for applications in molecular spintronics and quantum computing technologies. This unique class of spin-crossover cobalt(II) molecular nanomagnets is particularly well suited for addressing and scaling on different supports, like metal molecular junctions or carbon nanomaterials (CNMs) and metal–organic frameworks (MOFs) or metal-covalent organic frameworks (MCOFs), in order to measure the single-molecule electron transport and quantum coherence properties, which are two major challenges in single-molecule spintronics (SMS) and quantum information processing (QIP).

Coexistence of tunable spin-crossover and field-dependent single-molecule magnet behaviours in cobalt( ii )-pyridine-2,6-diiminephenyl complexes.

New trinuclear Ni(ii) complex exhibiting intratrimer both weak ferro- and antiferromagnetic interactions resulting from the strict orthogonality between the magnetic orbitals, and a combination of spin delocalisation and spin polarisation mechanisms.

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A new mixed-valence one-dimensional coordination polymer of formula {[CoII(MeOH)2][(μ-NC)2CoIII(dmphen)(CN)2]2}n·2nH2O (1) was obtained by reacting the Ph4P[CoII(dmphen)(CN)3] metalloligand (dmphen = 2,9-dimethyl-1,10-phenanthroline and Ph4P+ = tetraphenylphosphonium ion) with cobalt(II) acetate tetrahydrate. The structural analysis shows the formation of a neutral 4,2-ribbon-like chain of vertex-sharing cyanido-bridged {CoIII2CoII2} squares in which the metalloligand underwent an oxidation process and a reorganization to form {CoIII(dmphen)(CN)4}− linkers that coordinate to the [CoII(MeOH)2]2+ units through single cyanido ligands. Both cobalt(II) and Co(III) cations are six-coordinated in distorted octahedral environments. The shortest intrachain distance between the paramagnetic cobalt(II) ions is 7.36 Å, a value which is shorter than the shortest interchain one (10.36 Å). Variable-temperature (1.9–300 K) static (dc) magnetic measurements for 1 indicate the occurrence of magnetically isolated high-spin cobalt(II) ions with a D value of +67.0 cm−1. Dynamic alternating current (ac) magnetic measurements between 2.0–13 K reveal that 1 exhibits slow magnetic relaxation under non-zero applied dc fields, being thus a new example of field-induced SIM with easy-plane magnetic anisotropy. Theoretical calculations by CASSCF/NEVPT2 on 1 support the results from magnetometry. The relaxation of the magnetization occurs in the ground state under external dc fields through a two-phonon Raman process and one intra-Kramers mechanism.

The partial lossof crystallization water molecules inthe gadolinium(III)-nickel(II)dithiooxalate dodecahydrate [Gd2Ni3(dto)(6)(H2O)(10)]& BULL;12H(2)O (1) to yield the dihydrate derivative [Gd2Ni3(dto)(6)(H2O)(10)]& BULL;2H(2)O (2) provokes significant and reversible changesin the spin relaxation dynamics. This unique single-crystal-to-single-crystaltransformation emerges as a new route toward solvatoswitchable single-moleculemagnets for molecular spintronics and quantum computing. A unique single-crystal-to-single-crystal transformationin heteropentanuclear gadolinium(III)-nickel(II) dithiooxalate hydratesemerges as a new route toward solvatoswitchable single-molecule magnetsfor molecular spintronics and quantum computing.

The ability of mononuclear first-row transition metal complexes as dynamic molecular systems to perform selective functions under the control of an external stimulus that appropriately tunes their properties may greatly impact several domains of molecular nanoscience and nanotechnology. This study focuses on two mononuclear octahedral cobalt(ii) complexes of formula {[CoII(HL)2][CoII(HL)L]}(ClO4)3·9H2O (1) and [CoIIL2]·5H2O (2) [HL = 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine], isolated as a mixed protonated/hemiprotonated cationic salt or a deprotonated neutral species. This pair of pH isomers constitutes a remarkable example of a dynamic molecular system exhibiting reversible changes in luminescence, redox, and magnetic (spin crossover and spin dynamics) properties as a result of ligand deprotonation, either in solution or solid state. In this last case, the thermal-assisted spin transition coexists with the field-induced magnetisation blockage of "faster" or "slower" relaxing low-spin CoII ions in 1 or 2, respectively. In addition, pH-reversible control of the acid-base equilibrium among dicationic protonated, cationic hemiprotonated, and neutral deprotonated forms in solution enhances luminescence in the UV region. Besides, the reversibility of the one-electron oxidation of the paramagnetic low-spin CoII into the diamagnetic low-spin CoIII ion is partially lost and completely restored by pH decreasing and increasing. The fine-tuning of the optical, redox, and magnetic properties in this novel class of pH-responsive, spin crossover molecular nanomagnets offers fascinating possibilities for advanced multifunctional and multiresponsive magnetic devices for molecular spintronics and quantum computing such as pH-effect spin quantum transformers.

The cyanido-bridged square-like molecules with d/f metal ions occupying the corners of the square are considered molecular models of the Prussian Blue Analogues (PBAs) because they reproduce one face of their 3D face-centered cubic structure, being called low-dimensional PBAs. Such highly regular complexes provide unique insights into the short-range magnetic exchange interaction between the metal ions of PBAs and exhibit magnetic properties which are not found for PBAs. This review focuses on the preparative routes and magneto-structural characterization of d- d(d ')/d-f tetranuclears with a square-like topology generating rich families of molecular switches and nanomagnets. Relevant examples that provided a better comprehension of the magnetic behavior of PBAs, including subtle chemical factors that interfere in the photo-and thermally induced electron transfer are reviewed herein. A special attention is paid to the design of d-f cyanido-bridged squares, less numerous compared to the d-d/d ' ones, that proved to be suitable model compounds for the theoretical treatment of the magnetic exchange interaction between d and f spin carriers across the cyanide ligand. The square-shaped PBAs represent a very active area of research that is enriched yearly with new examples with potential for the development of molecular-scaled electronic devices.

A reaction between CoCl2 and L3-(CO2-)2 (2 : 1 stoichiometry) in CH3OH affords a discrete complex [CoII4-{L3-(CO2-)2}2(μ3-OCH3)2(CH3OH)2(H2O)2Cl2] (1) [L3-(CO2-)2 = 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)]. The structure of 1 reveals two terminal mononuclear CoII{L3-(CO2-)2}Cl units connected by a dimeric CoII2(μ3-OCH3)2(CH3OH)2(H2O) unit present in the centre through two methoxo (μ3-OCH3)- and two carboxylate (μ-1,1-OCO-) bridges affording a tetranuclear coordination cluster of Co(II) with a defective dicubane topology. In 1, Co1 (terminal) has distorted octahedral CoIIN2O3Cl and the central Co2 has CoIIO6 coordination. Such coordination arrangements afford the observed topology. Variable-temperature magnetic studies reveal anti-ferromagnetic coupling in 1. Three magnetic exchange interactions (one anti-ferromagnetic and two ferromagnetic: J1 = +3.3 cm-1 (Co⋯Co 3.176 Å; μ-1,1-OCO- and μ3-OCH3 bridges), J2 = -2.5 cm-1 (Co⋯Co 3.228 Å; μ-1-OCO- and μ3-OCH3 bridges) and J3 = +10.6 cm-1 (Co⋯Co 3.084 Å; two μ3-OCH3 bridges)) have been identified, with the inclusion of the orbital reduction parameter (α = Aκ = 1.38), spin-orbit coupling (λ = -158 cm-1) and axial distortion (energy gap Δ = -975 cm-1 between singlet and doublet levels), rationalized by density functional theory (DFT) calculations.

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)2](ClO4)2∙4H2O (1) and [Ni(terpyepy)2](ClO4)2 MeOH (2) [terpyCOOH = 4′-carboxyl-2,2′:6′,2″-terpyridine and terpyepy = 4′-[(2-pyridin-4-yl)ethynyl]-2,2′:6′,2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel–nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9–200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χMT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to −6.0 (1) and −4.7 cm−1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0–5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.