Square planar Pd(II)/oximate complexes as 'metalloligands' for the directional assembly of 4f-metal ions: a new family of {LnPd} (Ln = lanthanide) clusters exhibiting slow magnetization relaxation.

A relatively unexplored approach in heterometallic chemistry of transition metals and lanthanides has been developed toward the controlled synthesis of a new family of linear heterotrinuclear Ln(III)-Pd(II)-Ln(III) complexes with the general formula [LnPd(pao)(NO)(MeOH)(HO)]·[Pd(pao)], where Ln = Dy (2), Gd (3), Er (4) and Yb (5). This strategy was based on the diamagnetic 'metalloligand' [Pd(pao)] (1), where pao is the anion of 2-pyridinealdoxime, containing two dangling oximate O-atoms which were to each other and available for binding with oxophilic lanthanide ions. Because of their -configuration, the [Pd(pao)] 'metalloligand' was able to direct the binding of two {Ln(NO)(MeOH)(HO)} units on opposite sites, thus yielding the reported trinuclear {Ln-Pd-Ln} clusters.

A Nanosized {Ni } Cluster with a 'Flying Saucer' Topology Exhibiting Slow Relaxation of Magnetisation Phenomena at Both 15 K and 1.3 K.

A high-nuclearity {Ni} complex (1) with a unique 'flying saucer' motif has been prepared from the organic chelate, α-methyl-2-pyridine-methanol (mpmH), in conjunction with bridging azido (N ) and peroxido (O ) ligands. Magnetic susceptibility measurements revealed the presence of both ferro- and antiferromagnetic exchange interactions between the metal centres in 1, and the stabilization of spin states with appreciable S values at two different temperature regimes. The end-on bridging azido and alkoxido groups are in all likelihood the ferromagnetic mediators, while the η:η:μ-bridging peroxides most likely promote the antiparallel alignment of the metals' spin vectors, yielding an overall non-zero spin ground state for the centrosymmetric compound 1.

Elevating the Performance of Heterometallic 3d/4f SMMs: The Role of Diamagnetic Co and Zn Ions in Magnetization Dynamics.

Recent advances in the synthesis of 3d/4f Single-Molecule Magnets (SMMs) have revealed the effective role of incorporating diamagnetic Co or Zn ions to enhance the magnetic properties of Ln ions. This concept highlights notable examples of Co/Ln and Zn/Ln SMMs documented in the recent literature, illustrating how the selection of various peripheral and/or bridging ligands can modulate the magnetic anisotropy of 4f metal ions, thereby increasing their energy barriers.

Peripheral site modification in a family of dinuclear [Dy(hynad)(NO)(sol)] single-molecule magnets bearing a {Dy(μ-OR)} diamond-shaped core and exhibiting dissimilar magnetic dynamics.

The first use of the organic chelate -hydroxy-1,8-naphthalimide (hynadH) in Dy chemistry has unveiled access to a synthetic 'playground' composed of four new dinuclear complexes, all of which possess the same planar {Dy(μ-OR)} diamond-shaped core, resulting from the bridging and chelating capacity of the hynad groups. The structural stability of the central {Dy} core has allowed for the modulation of the peripheral coordination sites of the metal ions, and specifically the NO/hynad ratio of capping groups, thus affording the compounds [Dy(hynad)(NO)(DMF)] (1), (MeN)[Dy(hynad)(NO)] (2), [Dy(hynad)(NO)(HO)] (3), and [Dy(hynad)(HO)] (4). Because of the chemical and structural modifications in the series 1-4, the Dy coordination polyhedra are also dissimilar, comprising the muffin (1 and 3), tetradecahedral (2), and spherical tricapped trigonal prismatic (4) geometries.

Slow Magnetization Relaxation in a Family of Triangular {Co Ln } Clusters: The Effect of Diamagnetic Co Ions on the Ln Magnetic Dynamics.

The first use of the Schiff base chelate N-naphthalidene-o-aminophenol (naphH ) in Co/Ln chemistry has afforded a family of isostructural [Co Ln (OMe) (naph) (O CMe) (MeOH) ] (Ln=Tb, Dy and Er) complexes, revealing a rare {Co Ln(μ -OMe)} triangular core composed of two diamagnetic Co ions and a 4f-ion with slightly distorted square antiprismatic geometry. Alternating current (ac) magnetic susceptibility studies revealed that {Co Dy}, and its magnetic diluted analogue {Co Dy Y }, behave as mononuclear single-molecule magnets (SMMs) with similar energy barriers for the magnetization reversal, U , of ~85-90 K. SMM properties were also detected for {Co Er}, with the compound exhibiting a U of 18.

A family of mono-, di-, and tetranuclear Dy complexes bearing the ligand 2,6-diacetylpyridine bis(picolinoylhydrazone) and exhibiting slow relaxation of magnetization.

The systematic investigation of the general reaction scheme Dy/X/LH, where X = Cl, CFSO, ClO, MeCO, and LH is the pocket-type ligand 2,6-diacetylpyridine bis(picolinoylhydrazone), resulting from the condensation of 2,6-diacetylpyridine with picolinic acid hydrazide, has led to a new family of mono-, di-, and tetranuclear metal complexes of the formulae [DyCl(LH)(MeOH)]Cl (1), [Dy(OSCF)(LH)(MeOH)(HO)](OSCF) (2), [Dy(LH)(MeOH)(HO)](ClO) (3), and [Dy(OH)(OCMe)(L)] (4), respectively. The organic chelate undergoes metal-assisted amide-iminol tautomerism and adopts the neutral zwitterionic, and single- and double-deprotonated forms, respectively, upon coordination with the metal center(s). Interestingly, the different forms of the ligand LH/LH/L act independently as penta-, hexa-, and heptadentate, either as single-chelating or chelating and bridging, thus yielding new Dy compounds of various nuclearities and different magnetic properties.

Further synthetic investigation of the general lanthanoid(iii) [Ln(iii)]/copper(ii)/pyridine-2,6-dimethanol/carboxylate reaction system: {CuLn} coordination clusters (Ln = Dy, Tb, Ho) and their yttrium(iii) analogue.

In addition to previously studied {CuGd}, {CuGd}, {CuLn} and {CuLn} coordination clusters (Ln = trivalent lanthanide) containing pdm or Hpdm ligands (Hpdm = pyridine-2,6-dimethanol) and ancillary carboxylate groups (RCO), the present work reports the synthesis and study of three new members of a fifth family of such complexes. Compounds [CuLnO(OMe)(NO)(OCCHBu)(pdm)(MeOH)] (Ln = Dy, 1; Ln = Tb, 2; Ln = Ho, 3) were prepared from the reaction of Ln(NO)·xHO (x = 5, 6), CuX·yHO (X = ClO, Cl, NO; y = 6, 2 and 3, respectively), Hpdm, BuCHCOH and EtN (2 : 2.5 : 2 : 1 : 9) in MeCN/MeOH.

4f-Metal Clusters Exhibiting Slow Relaxation of Magnetization: A {Dy} Complex with An Hourglass-like Metal Topology.

The reaction between Dy(NO)∙6HO 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)(HO)](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.

'Metal Complexes as Ligands' for the Synthesis of Coordination Polymers: A Mn Monomer as a Building Block for the Preparation of an Unprecedented 1-D {MnMn} Linear Chain.

A relatively unexplored synthetic route in redox-active Mn(II/III) coordination chemistry has been employed toward the preparation of a new mixed-valence Mn 1-D linear chain from the reaction of [Mn(sacb)] precursor with a Mn source, where sacbH is the Schiff base ligand -salicylidene-2-amino-5-chlorobenzoic acid. The mononuclear (PrNH)[Mn(sacb)] () compound was obtained in excellent yields (>85%) from the 1:2:3 reaction of Mn(OCMe)∙4HO, sacbH and PrNH, respectively. In , the two doubly deprotonated sacb ligands act as O,N,O-tridentate chelates, while the second carboxylate O atom of sacb is dangling and H-bonded to the PrNH countercation.

Experimental determination of single molecule toroic behaviour in a Dy single molecule magnet.

The enhancement of toroic motifs through coupling toroidal moments within molecular nanomagnets is a new, interesting and relevant approach for both fundamental research and potential quantum computation applications. We investigate a Dy8 molecular cluster and discover it has a antiferrotoroic ground state with slow magnetic relaxation. The experimental characterization of the magnetic anisotropy axes of each magnetic center and their exchange interactions represents a considerable challenge due to the non-magnetic nature of the toroidal motif.

Click chemistry as a route to the synthesis of structurally new and magnetically interesting coordination clusters: a {Ni} complex with a trapezoidal prismatic topology.

The synthesis of a new {Ni} cluster bearing tetrazolate- and azido-bridging ligands, and supported by chelating α-methyl-2-pyridine-methanol (mpmH) groups, is described herein. The reported compound has a unique trapezoidal prismatic topology, resulting from an unexpected in situ click reaction between the MeCN reaction solvent and the N ions under mild, room-temperature conditions. Such a click chemistry approach to the preparation of 0-D compounds is relatively unexplored and represents a fruitful strategy for the synthesis of new coordination clusters and molecule-based magnetic materials.

{Ni} Cubanes from enantiomerically pure 2-(1-hydroxyethyl)pyridine ligands: supramolecular chirality.

Homometallic {NiII4} cubane-like clusters with a rare chiral core have been prepared via the employment of enantiomerically pure 2-(1-hydroxyethyl)pyridine (Hmpm). Comparison with the achiral cubanes derived from the related 2-pyridinemethanol (Hpym) ligand reveals drastic structural changes as a consequence of the transfer of chirality from the ligands to the whole structure. Their magnetic properties have been related to the structural features of their cubane-type cores.

Rare "Janus"-faced single-molecule magnet exhibiting intramolecular ferromagnetic interactions.

A rare disk-like single-molecule magnet (SMM) exclusively bridged by end-on azides with a spin ground state of = 14 was prepared by the reaction of a divalent Fe precursor with MeSiN under basic conditions. AC magnetic susceptibility studies revealed unusual, "Janus"-faced SMM behavior for the dried and pristine forms of the compound attributed to solvation/de-solvation effects of the coordinated MeCN ligands which leads to alterations in the crystal field and symmetry of the metal ions. DFT calculations confirmed the ferromagnetic nature of the interactions between the Fe spin carriers with the zero-field splitting parameters = -0.

Organic chelate-free and azido-rich metal clusters and coordination polymers from the use of MeSiN: a new synthetic route to complexes with beautiful structures and diverse magnetic properties.

In this Feature Article, we highlight the feasibility of a new, recently developed approach towards the synthesis of high-spin molecules and single-molecule magnets (SMMs). The key to the preparation of such molecular compounds is the organic azide precursor Me3SiN3, which fosters the formation of 3d-metal azido clusters and coordination polymers without requiring the assistance of any organic chelating/bridging group. All the isolated compounds contain metallic cores which are surrounded by end-on bridging N3- groups.

Oximato-Based Ligands in 3 d/4 f-Metal Cluster Chemistry: A Family of {CuLn} Complexes with a "Propeller"-like Topology and Single-Molecule Magnetic Behavior.

The organic chelating and bridging ligands 9,10-phenanthrenedione-9-oxime (phenoxH) and 9,10-phenanthrenedione-9,10-dioxime (phendoxH) were synthesized and subsequently employed for the first time in heterometallic 3 d/4 f-metal cluster chemistry. The general reaction between CuCl·2HO, LnCl·6HO, phenoxH, and NEt in a 1:2:2:4 molar ratio, in a solvent mixture comprising MeCN and MeOH, afforded brown crystals of a new family of [CuLnCl(phenox)(MeOH)] clusters (Ln = Gd (1), Tb (2), Dy (3)) that possess an unprecedented [CuLn(μ-NO)] "propeller"-like core. Complexes 1-3 are the first {CuLn} clusters in which the outer Cu and the central Ln atoms are solely bridged by diatomic oximato bridges.

Increasing the nuclearity and spin ground state in a new family of ferromagnetically-coupled {Ni} disk-like complexes bearing exclusively end-on bridging azido ligands.

The synthesis of a new family of ferromagnetically-coupled {Ni} clusters counterbalanced by various [Ln(NO)] ions is herein described. The resulting compounds are organic chelate-free and the metal ions are exclusively bridged by end-on azido ligands to stabilize a beautiful disk-like topology reminiscent of the structure of the brucite mineral.

Heterometallic Cu/Ln cluster chemistry: ferromagnetically-coupled {CuLn} complexes exhibiting single-molecule magnetism and magnetocaloric properties.

A new family of {Cu4Ln2} (Ln = Gd, Tb and Dy) complexes bearing the gem-diol form of di-2-pyridyl ketone [(py)2CO] ligand is reported. Magnetic studies reveal the presence of predominant ferromagnetic exchange interactions between the metal ions. As a result, the hexanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present.

Structural and Magnetic Variations in a Family of Isoskeletal, Oximate-Bridged {Mn M } Complexes (M =Mn, Gd, Dy).

The self-assembly reaction of MnCl ⋅4H O, acenaphthenequinone dioxime (acndH ) and NEt has yielded an unprecedented, linear {Mn Mn } complex with an S=5 spin ground state and non-SMM behavior. The targeted replacement of the central Mn ion with Gd and Dy ions has successfully increased the S and turned on the SMM dynamics without affecting the core structure and the nature of the magnetic exchange interactions.

Transition Metal Single-Molecule Magnets: A {Mn} Nanosized Cluster with a Large Energy Barrier of ∼60 K and Magnetic Hysteresis at ∼5 K.

The first {Mn} cluster (1) has been prepared from carboxylate ions and the chelating/bridging ligand α-methyl-2-pyridine-methanol. Compound 1 possesses a unique nanosized structural topology with one of the largest energy barriers reported to-date for high-nuclearity 3d-metal clusters. Single-crystal magnetic hysteresis studies reveal the presence of hysteresis loops below 5 K, one of the highest temperatures below which molecular hysteresis has been observed for 3d-based SMMs.

Structural Diversities in Heterometallic Mn-Ca Cluster Chemistry from the Use of Salicylhydroxamic Acid: {MnCa}, {MnCa}, {MnCa}, and {MnCa} Complexes with Relevance to Both High- and Low-Valent States of the Oxygen-Evolving Complex.

One-pot reactions between the [MnO(OCPh)(py)] triangular precursors and either CaBr·xHO or CaCl·6HO, in the presence of salicylhydroxamic acid (shaH), have afforded the heterometallic complexes [MnCa(OCPh)(shi)(HO)(MeCO)] (1) and (pyH)[MnMnCaCl(OCPh)(shi)(py)] (2), respectively, in good yields. Further reactions but using a more flexible synthetic scheme comprising the Mn(NO)·4HO/Ca(NO)·4HO and Mn(OCPh)·2HO/Ca(ClO)·4HO "metal blends" and shaH, in the presence of external base NEt, led to the new complexes (NHEt)[MnMnCa(OEt)(shi)(EtOH)] (3) and (NHEt)[MnCa(CO)(shi)] (4), respectively. In all reported compounds, the anion of the tetradentate (N,O,O,O)-chelating/bridging ligand salicylhydroxime (shi), resulting from the in situ metal-ion-assisted amide-iminol tautomerism of shaH, was found to bridge both Mn and Ca atoms.

A family of 'windmill'-like {CuLn} complexes exhibiting single-molecule magnetism behavior and large magnetic entropy changes.

A family of nanosized {CuLn} clusters with a 'windmill'-like topology was prepared from the employment of 2,6-diacetylpyridine dioxime, in conjunction with bridging N, in 3d/4f-metal chemistry; the octadecanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present.

Large Energy Barrier and Magnetization Hysteresis at 5 K for a Symmetric {Dy} Complex with Spherical Tricapped Trigonal Prismatic Dy Ions.

The introduction of the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH) in 4f-metal chemistry has afforded a new dinuclear complex, [Dy(NO)(sacbH)(HO)(MeCN)] (1), with the metal ions adopting a rare spherical tricapped trigonal prismatic coordination geometry. The deprotonated phenoxido O atoms of the organic chelate occupy the axial triangular faces of the prism and were found to be very close to the main anisotropy axes of the two Dy ions. As a result, the {Dy} compound exhibits frequency- and temperature-dependent out-of-phase ac signals below ∼25 K in the absence of a static dc field, yielding an energy barrier of 109.

"Molecular Nanoclusters": A 2-nm-Sized {Mn} Cluster with a Spherical Structure.

The comproportionation reaction between Mn and Mn sources in the presence of 3,3-dimethylacrylic acid and azides has led to a new {Mn} molecular cluster with a spherical structure and dimensions of ∼2.2 nm, comparable in size to the smallest classical and magnetic nanoparticles.

Structural diversity in Ni(II) cluster chemistry: Ni5, Ni6, and {NiNa2}n complexes bearing the Schiff-base ligand N-naphthalidene-2-amino-5-chlorobenzoic acid.

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.