Magnetocaloric efficiency tuning through solvent-triggered 3D to 2D interconversion in holmium(III)-based dynamic MOFs.

The neutral holmium(III) oxalate octadecahydrate {[Ho(ox)(HO)]·12HO} of mixed hexagonal/decagonal (6·10) 3D net topology shows important changes in the magnetocaloric efficiency upon dehydration/rehydration by heating and water vapor exposition to give the holmium(III) oxalate decahydrate {[Ho(ox)(HO)]·4HO} of hexagonal (6) 2D net topology through the intermediacy of the elusive amorphous anhydrous compound {Ho(ox)}.

Enantiomeric Complexes Based on Ruthenium(III) and 2,2'-Biimidazole: X-ray Structure and Magnetic Properties.

We have prepared and characterized two Ru(III) compounds based on the 2,2'-biimidazole (Hbiim) ligand, namely, a single complex of formula cis-[RuCl(Hbiim)]Cl·4HO () and a racemic mixture of formula {cis-[RuCl(Hbiim)]Cl}·4HO (), which contains 50% of Ru(III) complex . Both compounds crystallize in the monoclinic system with space groups 2 and 2 for and , respectively. These complexes exhibit the metal ion bonded to four nitrogen atoms from two Hbiim molecules and two chloride ions, which balance part of the positive charges in a distorted octahedral geometry.

pH-Switching of the luminescent, redox, and magnetic properties in a spin crossover cobalt(ii) molecular nanomagnet.

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 {[Co(HL)][Co(HL)L]}(ClO)·9HO (1) and [CoL]·5HO (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.

Lipoic Acid-Functionalized Hexanuclear Manganese(III) Nanomagnets Suitable for Surface Grafting.

Highly anisotropic single-molecule magnets (SMMs) have attracted much interest in the field of molecular magnetism because of their spin features and potential technological applications. Additionally, a great effort has been devoted to the functionalization of such molecule-based systems which are made with ligands containing functional groups suitable to connect SMMs to junction devices or to perform their grafting on surfaces of different substrates. We have synthesized and characterized two lipoic acid-functionalized and oxime-based Mn(III) compounds, of formula [Mn(μ-O)(HN-sao)(lip)(MeOH)][Mn(μ-O)(HN-sao)(cnph)(MeOH)]}·10MeOH () and [Mn(μ-O)(HN-sao)(lip)(EtOH)]·EtOH·2HO () [HN-saoH = salicylamidoxime, lip = lipoate anion, cnph = 2-cyanophenolate anion].

Trinuclear Cobalt(II) Triple Helicate with a Multidentate Bithiazolebis(oxamate) Ligand as a Supramolecular Nanomagnet.

The cobalt(II)-mediated self-assembly of the potentially tris(chelating) ,'-2,2'-(4,4'-bithiazole)bis(oxamate) (dabtzox) ligand gives a new metal-organic supramolecular nanomagnet of formula KCo(dabtzox)·8HO·MeOH () featuring a unique linear triple-stranded trinuclear structure of the helicate type.

A rare isostructural series of 3d-4f cyanido-bridged heterometallic squares obtained by assembling [Fe{HB(pz)}(CN)] and Ln ions: synthesis, X-ray structure and cryomagnetic study.

A new series of cyanido-bridged {FeLn} neutral molecular squares of general formula [Fe{HB(pz)}(CN)(μ-CN)Ln(NO)(pyim)(PhPO)]·2CHCN [Ln = Ce (1), Pr (2), Nd (3), Gd (4), Tb (5), Dy (6) and Er (7); {HB(pz)} = hydrotris(pyrazolyl)borate, pyim = 2-(1-imidazol-2-yl)pyridine and PhPO = triphenylphosphine oxide] were obtained by reacting the low-spin [Fe{HB(pz)}(CN)] species with the preformed [Ln(pyim)(NO)(pyim)(PhPO)] complex anions (generated by mixing the nitrate salt of each Ln(III) ion with pyim and PhPO molecules). Single-crystal X-ray diffraction studies show that 1-7 are isostructural compounds that crystallize in the triclinic 1̄ space group. Their crystal structures consist of centrosymmetric cyanido-bridged {FeLn} molecular squares where two [Fe{HB(pz)}(CN)] units adopt bis-monodentate coordination modes towards two [Ln(pyim)(NO)(pyim)(PhPO)] moieties.

Holmium(III) Single-Ion Magnet for Cryomagnetic Refrigeration Based on an MRI Contrast Agent Derivative.

The coexistence of field-induced blockage of the magnetization and significant magnetocaloric effects in the low-temperature region occurs in a mononuclear holmium(III) diethylenetriamine-,,',″,″-pentaacetate complex, whose gadolinium(III) analogue is a commercial MRI contrast agent. Both properties make it a suitable candidate for cryogenic magnetic refrigeration, thus enlarging the variety of applications of this simple class of multifunctional molecular nanomagnets.

Ferro- and Antiferromagnetic Interactions in Oxalato-Centered Inverse Hexanuclear and Chain Copper(II) Complexes with Pyrazole Derivatives.

Two novel copper(II) complexes of formulas {[Cu(4-Hmpz)][Cu(4-Hmpz)(µ-ox-,::)(ClO)]} () and {[Cu(3,4,5-Htmpz)][Cu(3,4,5-Htmpz)(µ-ox-,::)(HO)(ClO)][Cu(3,4,5-Htmpz)(µ-ox-,:,)]}(ClO)·6HO () have been obtained by using 4-methyl-1-pyrazole (4-Hmpz) and 3,4,5-trimethyl-1-pyrazole (3,4,5-Htmpz) as terminal ligands and oxalate (ox) as the polyatomic inverse coordination center. The crystal structure of consists of perchlorate counteranions and cationic copper(II) chains with alternating bis(pyrazole)(µ-,::-oxalato)copper(II) and tetrakis(pyrazole)copper(II) fragments. The crystal structure of is made up of perchlorate counteranions and cationic centrosymmetric hexanuclear complexes where an inner tetrakis(pyrazole)(µ-,:,-oxalato)dicopper(II) entity and two outer mononuclear tetrakis(pyrazole)copper(II) units are linked through two mononuclear aquabis(pyrazole)(µ-,::-oxalato)copper(II) units.

Field-induced slow magnetic relaxation and magnetocaloric effects in an oxalato-bridged gadolinium(iii)-based 2D MOF.

The coexistence of field-induced slow magnetic relaxation and moderately large magnetocaloric efficiency in the supra-Kelvin temperature region occurs in the 2D compound [Gd(ox)(HO)]·4nHO (1), a feature that can be exploited in the proof-of-concept design of a new class of slow-relaxing magnetic materials for cryogenic magnetic refrigeration.

Electroswitching of the single-molecule magnet behaviour in an octahedral spin crossover cobalt(ii) complex with a redox-active pyridinediimine ligand.

Thermal-assisted spin crossover and field-induced slow magnetic relaxation coexist in the solid state for the mononuclear cobalt(ii) complex with the non-innocent 2,6-bis(N-4-methoxyphenylformimidoyl)pyridine ligand. One-electron oxidation of the paramagnetic low-spin Co ion (S = 1/2) to the diamagnetic low-spin Co ion (S = 0) leads to the electroswitching of the slow magnetic relaxation in acetonitrile solution.

On the magneto-structural role of the coordinating anion in oxamato-bridged copper(ii) derivatives.

We herein present the synthesis, spectroscopic analysis, description of the crystal structures and magnetic properties of four new complexes of the formula [{Cu(opba)(HO)}{Cu(dmphen)(SCN)}]·dmf (1), [{Cu(opba)}{Cu(dmphen)Cl}]·1.5dmf·2.5dmso (2), [{Cu(opba)}{Cu(dmphen)Br}]·dmf·2.

Field-induced slow relaxation of magnetisation in an anionic heterotetranuclear [ZnRe] system.

The compound (NBu4)4[ZnII{ReIVCl4(μ-ox)}3] (1) [NBu4+ = tetra-n-butylammonium cation and ox2- = oxalate dianion] is the first example of an oxalato-bridged ZnII system coordinated to a 5d metal ion that exhibits slow relaxation of magnetisation.

Spin Crossover in Double Salts Containing Six- and Four-Coordinate Cobalt(II) Ions.

The preparation and spectroscopic and structural characterization of three cobalt(II) complexes of formulas [Co(tppz)](dca) (1), [Co(tppz)][Co(NCS)]·MeOH (2), and [Co(tppz)][Co(NCO)]·2HO (3) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and dca = dicyanamide] are reported here. Compounds 1-3 have in common the presence of the cationic [Co(tppz)] entity where each mer-tridentate tppz ligand coordinates to the cobalt(II) ion equatorially through two pyridyl donors and axially via the pyrazine, completing the six-coordination. The electroneutrality is achieved by the organic dca group (1) and the anionic tetrakis(thiocyanato-κN)cobaltate(II) (2) and tetrakis(cyanato-κN)cobaltate(II) (3) complexes.

Mass effect on the equienergetic high-spin/low-spin states of spin-crossover in 4,4'-bipyridine-bridged iron(II) polymeric compounds: synthesis, structure, and magnetic, Mössbauer, and theoretical studies.

The suitability of the system [Fe(4,4'-bipy)(H(2)O)(2)(NCX)(2)].(4,4'-bipy), where 4,4'-bipy stands for 4,4'-bipyridine and X = S (1) and Se (2), as a precursor for the synthesis of new polymeric spin-crossover compounds has been studied. The reaction of 1 or 2 with bt (2,2'-bithiazoline) afforded the polymeric compounds of formula [Fe(4,4'-bipy)(bt)(NCX)(2)] (X = S (3), Se (4)).

Light- and thermal-induced spin crossover in [Fe(abpt)2(N(CN)2)2]. Synthesis, structure, magnetic properties, and high-spin<-->low spin relaxation studies.

[Fe(abpt)2(N(CN)2)2] (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) represents the first example of an iron(II) spin-crossover compound containing dicyanamide ligand, [N(CN)(2)](-), as a counterion. It shows an incomplete two-step spin transition with around 37% of HS molecules trapped in the low-temperature region when standard cooling or warming modes, i.e.