Pentanuclear Heterometallic {Mn^III₂Ln₃} (Ln = Gd, Dy, Tb, Ho) Assemblies in an Open-Book Type Structural Topology: Appearance of Slow Relaxation of Magnetization in the Dy(III) and Ho(III) Analogues

The reaction of Ln­(III) nitrate and Mn­(ClO₄)₂·6H₂O salts in the presence of a multidentate sterically unencumbered ligand, (<i>E</i>)-2,2′-(2-hydroxy-3-((2-hydroxyphenylimino)­methyl)-5-methylbenzylazanediyl)­diethanol (<b>LH</b>_<b>4</b>) leads to the isolation of four isostructural pentanuclear hetereometallic complexes [Mn^III₂Gd₃(LH)₄(NO₃)­(HOCH₃)]­ClO₄·NO₃ (<b>1</b>), [Mn^III₂Dy₃(LH)₄(NO₃)­(HOCH₃)]­ClO₄·NO₃ (<b>2</b>), [Mn^III₂Tb₃(LH)₄(NO₃)­(HOCH₃)]­ClO₄·NO₃ (<b>3</b>), and [Mn^III₂Ho₃(LH)₄(NO₃)­(HOCH₃)]­ClO₄·NO₃ (<b>4</b>) with an open-book type structural topology. <b>1</b>–<b>4</b> are dicationic and crystallize in the achiral space group, <i>P</i>2₁/<i>n</i>. A total of four triply deprotonated ligands, [LH]^3–, are involved in holding the pentameric metal framework, {Mn^III₂Ln₃}. In these complexes both the lanthanide and the manganese­(III) ions are doubly bridged, involving phenolate or ethoxide oxygen atoms. The magnetochemical analysis reveals the presence of global antiferromagnetic interactions among the spin centers at low temperatures in all the four compounds. AC susceptibility measurements show the presence of temperature dependent out-of-phase <i>ac</i> signal for compounds <b>2</b> and <b>4</b> indicating an SMM behavior

Supramolecular Organization and Magnetic Properties of Mesogen-Hybridized Mixed-Valent Manganese Single Molecule Magnets [Mn^III₈Mn^IV₄O₁₂(L_{<i>x</i>,<i>y</i>,<i>z</i>‑CB})₁₆­(H₂O)₄]

Single molecule magnets (SMM) may be considered for the construction of future integrated nanodevices, provided however that some degree of ordering is imparted to these molecules (surfaces nanostructuration). Combining such nanoobjects with liquid-crystalline orderings to control their assembly and to potentially address them individually therefore appears as one promising strategy. Four mesomorphic, mixed-valent [Mn^III₈Mn^IV₄O₁₂­(L_{<i>x</i>,<i>y</i>,<i>z</i>‑CB})₁₆​­(H₂O)₄] SMM, differing in the number of liquid-crystalline promoters, (L_{<i>x</i>,<i>y</i>,<i>z</i>‑CB}), were synthesized, and their self-organizing and magnetic properties were investigated. The influence of the peripheral modifications, and precisely how supramolecular ordering and magnetic properties may be affected by the evolution of the proto-mesogenic cyanobiphenyl-based ligands substitution pattern, was explored. Small-angle X-ray scattering studies revealed that all of the hybridized clusters self-organize into room-temperature bilayer smectic phases, mandated by the specific mesogenic functionalization and that the polymetallic cores are further organized according to a short-range pseudo-2D lattice with hexagonal and/or square symmetry. All mesomorphous hybridized dodecamanganese complexes still behave as SMM: they exhibit blocking of the magnetization at about 2.6 K as evidenced by the occurrence of frequency-dependent out-of-phase ac susceptibility signals as well as an opening of the hysteresis cycle with coercive fields varying between 0.13 and 0.6 T, depending on the surface ligands topology. Comparison of the magnetic properties within this series reveals intricate correlations between the structural features of the mesomorphous molecule magnet (i.e., symmetry of the ligands substitution patterns, molecular conformation, average intercluster distances, and respective inclination) with respect to the relative proportion of slow- and fast-relaxing species and the absolute values of the coercive fields

Assembly, Disassembly, and Reassembly: Conversion of Homometallic Coordination Networks into Mixed Metal–Organic Frameworks

A strategy for the conversion of homometallic coordination networks into mixed metal–organic frameworks (MM′MOFs) is proposed. Ni­(II) complexes of dipyrrin (dpm) ligands bearing peripheral pyridyl or imidazolyl units have been shown to self-assemble into coordination polymers with the metal cation in an octahedral environment coordinated to two bis-pyrrolic chelates and two neutral monodentate coordinating units such as pyridyl or imidazolyl moieties. Taking advantage of the chelate effect, the two monodentate units may be replaced by a diimine ligand leading to the disassembly of the networks by the formation of discrete soluble complexes. The latter can be employed as metallatectons for the construction of heterometallic architectures upon reaction with a secondary metal salt. This approach was applied using either 1,10-phenanthroline (phen) or 2,2′-bipyrimidine (bpm) as chelates leading to a series of mono- and binuclear metallatectons of the (phen)­Ni­(dpm)₂ and (bpm)­[Ni­(dpm)₂]₂ type. Subsequent assembly with CdCl₂ afforded either interpenetrated 2D grid-type architectures or 3D MM′MOFs

Ferromagnetic Coupling in Copper(II) [2 × 2] Grid-like Complexes

Two copper­(II) [2 × 2] grid-like complexes were synthesized and structurally characterized. Investigation of the magnetic properties showed for both the occurrence of intramolecular ferromagnetic interactions

Nitrate-Bridged “Pseudo-Double-Propeller”-Type Lanthanide(III)–Copper(II) Heterometallic Clusters: Syntheses, Structures, and Magnetic Properties

Two discrete nitrate-bridged novel “pseudo-double-propeller”-shaped hexanuclear Cu/Ln clusters of the formula [Cu₄Ln₂L₄L′₄(NO₃)₂(OH₂)₂]·3NO₃·4H₂O [Ln = Dy, Gd; LH = <i>o</i>-vanilin; L′H = 2-(hydroxyethyl)­pyridine] were synthesized and characterized. Single-crystal X-ray diffraction studies revealed the trimeric half-propeller-type Cu₂/Ln core connected to other opposite-handed similar trimers by a bridging nitrate ligand. The Dy analogue, [Cu₄Dy₂L₄L′₄(NO₃)₂(OH₂)₂]·3NO₃·4H₂O, shows frequency-dependent out-of-phase alternating-current magnetic susceptibility, which indicates that this novel discrete [Cu₄Dy₂] heterometallic cluster may exhibit single-molecule-magnet behavior

Synthesis, Structure, and Magnetic Properties of a New Eight-Connected Metal–Organic Framework (MOF) based on Co₄ Clusters

A hydrothermal reaction of cobalt nitrate, 4,4′-oxybis­(benzoic acid) (OBA), 1,2,4-triazole, and NaOH gave rise to a deep purple colored compound [Co₄(triazolate)₂(OBA)₃], <b>I</b>, possessing Co₄ clusters. The Co₄ clusters are connected together through the tirazolate moieties forming a two-dimensional layer that closely resembles the TiS₂ layer. The layers are pillared by the OBA units forming the three-dimensional structure. To the best of our knowledge, this is the first observation of a pillared TiS₂ layer in a metal–organic framework compound. Magnetic studies in the temperature range 1.8–300 K indicate strong antiferromagetic interactions for Co₄ clusters. The structure as well as the magnetic behavior of the present compound has been compared with the previously reported related compound [Co₂(μ₃-OH)­(μ₂-H₂O)­(pyrazine)­(OBA)­(OBAH)] prepared using pyrazine as the linker between the Co₄ clusters

Synthesis, Structure, and Magnetic Properties of a New Eight-Connected Metal–Organic Framework (MOF) based on Co₄ Clusters

A hydrothermal reaction of cobalt nitrate, 4,4′-oxybis­(benzoic acid) (OBA), 1,2,4-triazole, and NaOH gave rise to a deep purple colored compound [Co₄(triazolate)₂(OBA)₃], <b>I</b>, possessing Co₄ clusters. The Co₄ clusters are connected together through the tirazolate moieties forming a two-dimensional layer that closely resembles the TiS₂ layer. The layers are pillared by the OBA units forming the three-dimensional structure. To the best of our knowledge, this is the first observation of a pillared TiS₂ layer in a metal–organic framework compound. Magnetic studies in the temperature range 1.8–300 K indicate strong antiferromagetic interactions for Co₄ clusters. The structure as well as the magnetic behavior of the present compound has been compared with the previously reported related compound [Co₂(μ₃-OH)­(μ₂-H₂O)­(pyrazine)­(OBA)­(OBAH)] prepared using pyrazine as the linker between the Co₄ clusters

Nitrate-Bridged “Pseudo-Double-Propeller”-Type Lanthanide(III)–Copper(II) Heterometallic Clusters: Syntheses, Structures, and Magnetic Properties

Two discrete nitrate-bridged novel “pseudo-double-propeller”-shaped hexanuclear Cu/Ln clusters of the formula [Cu₄Ln₂L₄L′₄(NO₃)₂(OH₂)₂]·3NO₃·4H₂O [Ln = Dy, Gd; LH = <i>o</i>-vanilin; L′H = 2-(hydroxyethyl)­pyridine] were synthesized and characterized. Single-crystal X-ray diffraction studies revealed the trimeric half-propeller-type Cu₂/Ln core connected to other opposite-handed similar trimers by a bridging nitrate ligand. The Dy analogue, [Cu₄Dy₂L₄L′₄(NO₃)₂(OH₂)₂]·3NO₃·4H₂O, shows frequency-dependent out-of-phase alternating-current magnetic susceptibility, which indicates that this novel discrete [Cu₄Dy₂] heterometallic cluster may exhibit single-molecule-magnet behavior

Post-Synthesis Modification of the Aurivillius Phase Bi₂SrTa₂O₉ via <i>In Situ</i> Microwave-Assisted “Click Reaction”

A new strategy for the functionalization of layered perovskites is presented, based on the <i>in situ</i> post-synthesis modification of a prefunctionalized phase by copper­(I)-catalyzed alkyne–azide cycloaddition (CuAAC). The microwave-assisted protonation and grafting of an alkyne alcohol provides the alkyne-functionalized precursor within a few hours, starting from Bi₂SrTa₂O₉. The subsequent microwave-assisted <i>in situ</i> “click reaction” allows the post-synthesis modification of the precursor within ∼2 h, providing a layered perovskite functionalized by an alcohol-grafted 1,4-disubstituted-1<i>H</i>-1,2,3-triazole. Two compounds are described here, bearing an aliphatic and an aromatic substituent, which illustrates the general application of the method. This work opens new perspectives for the functionalization of layered perovskites, going beyond mere insertion/grafting reactions, and thus broadens the design possibilities and the range of applications of these hybrid systems

New Metal Phthalocyanines/Metal Simple Hydroxide Multilayers: Experimental Evidence of Dipolar Field-Driven Magnetic Behavior

A series of new hybrid multilayers has been synthesized by insertion-grafting of transition metal (Cu^II, Co^II, Ni^II, and Zn^II) tetrasulfonato phthalocyanines between layers of Cu^II and Co^II simple hydroxides. The structural and spectroscopic investigations confirm the formation of new layered hybrid materials in which the phthalocyanines act as pillars between the inorganic layers. The magnetic investigations show that all copper hydroxide-based compounds behave similarly, presenting an overall antiferromagnetic behavior with no ordering down to 1.8 K. On the contrary, the cobalt hydroxide-based compounds present a ferrimagnetic ordering around 6 K, regardless of the nature of the metal phthalocyanine between the inorganic layers. The latter observation points to strictly dipolar interactions between the inorganic layers. The amplitude of the dipolar field has been evaluated from X-band and Q-band EPR spectroscopy investigation (<i>B</i>_dipolar ≈ 30 mT)