Ferrimagnetic-like ordering in a unique three-dimensional coordination polymer featuring mixed azide/carboxylate-bridged trinuclear manganese (II) clusters as subunits

An Uneven Chain-like Ferromagnetic Copper(II) Coordination Polymer Displaying Metamagnetic Behavior and Long-Range Magnetic Ordering

Ferromagnetic coupling exists in an uneven chain-like copper(II) complex with both end-on azido and syn-syn carboxylato bridges, (Cu3(L)2(N3)4(H2O)3)n (1, HL = 6-hydroxynicotinic acid). It is the first example of one-dimensional (1D) chain-like copper(II) coordination polymer showing both metamagnetic behavior and long-range magnetic ordering (Tc = 6.7 K), thanks to the interchain hydrogen bonds, which make a three-dimensional (3D) supramolecular array of the entire molecular structure and mediate the interchain antiferromagnetic interaction.

Metal-Organic Framework Magnets

Metal-organic frameworks represent the ultimate chemical platform on which to develop a new generation of designer magnets. In contrast to the inorganic solids that have dominated permanent magnet technology for decades, metal-organic frameworks offer numerous advantages, most notably the nearly infinite chemical space through which to synthesize predesigned and tunable structures with controllable properties. Moreover, the presence of a rigid, crystalline structure based on organic linkers enables the potential for permanent porosity and postsynthetic chemical modification of the inorganic and organic components. Despite these attributes, the realization of metal-organic magnets with high ordering temperatures represents a formidable challenge, owing largely to the typically weak magnetic exchange coupling mediated through organic linkers. Nevertheless, recent years have seen a number of exciting advances involving frameworks based on a wide range of metal ions and organic linkers. This review provides a survey of structurally characterized metal-organic frameworks that have been shown to exhibit magnetic order. Section 1 outlines the need for new magnets and the potential role of metal-organic frameworks toward that end, and it briefly introduces the classes of magnets and the experimental methods used to characterize them. Section 2 describes early milestones and key advances in metal-organic magnet research that laid the foundation for structurally characterized metal-organic framework magnets. Sections 3 and 4 then outline the literature of metal-organic framework magnets based on diamagnetic and radical organic linkers, respectively. Finally, Section 5 concludes with some potential strategies for increasing the ordering temperatures of metal-organic framework magnets while maintaining structural integrity and additional function.

Ultrasonic assisted synthesis of a new one-dimensional nanostructured Mn(II) coordination polymer derived from azide and new multi-topic nitrogen donor ligand

A new Mn(II) coordination polymer, [Mn(L₁)₂(N₃)₂]_n (1), L₁  = 3,4-bis(4-pyridyl)-5-(2-pyridyl)-1,2,4-triazole, was synthesized by the reaction of ligand L₁ and mixtures of manganese(II) acetate and sodium azide via branched tube method. Compound 1 was structurally characterized by single-crystal X-ray diffraction. The results show that 1 is a 1D helix coordination polymer. Also nanostructures of 1 have been prepareded by sonochemical process at ambient temperature. The effects of two different concentrations of initial reagents on the size and morphology of the nanoparticles were studied and the products were characterized by X-ray powder diffraction and scanning electron microscopy (SEM). Also the comparison of the thermal stability of bulk form and nanoparticles of 1 was investigated by thermal gravimetric and differential thermal analyses.

Distinct Chromic and Magnetic Properties of Metal-Organic Frameworks with a Redox Ligand

An electron-deficient and potentially chromic ligand has been utilized to impart redox activity, photo- and hydrochromism, and solvotomagnetism to metal-organic frameworks (MOFs). A pair of MOFs were constructed from the flexible zwitterionic viologen-tethered tetracarboxylate linker N,N'-bis(3,5-dicarboxylatobenzyl)-4,4'-bipyridinium (L^2-): [Co₃(L)(N₃)₄] (1) and [Mn₂(L)(N₃)₂(H₂O)₂]·3H₂O (2). Both compounds show three-dimensional frameworks in which mixed azido- and carboxylato-bridged chains are connected through the electron-deficient viologen moieties. The chain in 1 is built from alternating bis(azide) and (azide)bis(carboxylate) bridges, while that in 2 contains uniform (azide) (carboxylate) bridges. The MOFs shows the characteristic redox properties of the viologen moieties. The redox activity affords the MOFs with different chromic properties, owing to subtle differences in chemical environments. 1 shows reversible photochromism, which is related to the radical formation through photoinduced electron transfer from azide-carboxylate to viologen according to UV-vis, X-ray photoelectron, and electron spin resonance spectroscopy and DFT calculations. 2 is nonphotochromic for lack of appropriate pathways for electron transfer. Unexpectedly, 2 shows a novel type of solid-state hydrochromism. Upon the removal and reabsorption of water, the compound shows remarkable color change because of reversible electron transfer accompanying a reversible structural transformation. The radical mechanism is distinct from those for traditional hydrochromic inorganic and organic materials. Magnetic studies indicate ferro- and antiferromagnetic coupling in 1 and 2, respectively. What's more, 2 shows marked magnetic response to the removal of water molecules owing to the formation of radicals. The compound illustrates a unique material exhibiting dual responses (color and magnetism) to water.

Novel manganese(ii) and cobalt(ii) 2D polymers containing alternating chains with mixed azide and carboxylate bridges: crystal structure and magnetic properties

Two new Mn(ii) and Co(ii) complexes based on AABAA alternating chains with mixed azide and carboxylate bridges were synthesized, structurally and magnetically studied.

A unusual two-dimensional azido-Cu(ii) network with benzoate derivative as a co-ligand exhibiting ferromagnetic order and slow magnetic relaxation

A 2D layer-like Cu(ii) compound with multiple-bridges of azido, carboxylate and hydroxyl ligands, featuring strong ferromagnetic coupling and slow magnetic relaxation.

A 3D mixed-valence Cu(I)/Cu(II) coordination polymer constructed by 2-(2-fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline and 1,3-benzenedicarboxylate

A mixed-valence Cu(I)/Cu(II) coordination polymer, namely, [Cu2(L)(1,3-BDC)] n (1), has been synthesized under hydrothermal conditions (HL = 2-(2-fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline and 1,3-H2BDC = 1,3-benzenedicarboxylic acid). Its structure has been determined by single crystal X-ray diffraction analysis and powder X-ray diffraction. The crystals are the monoclinic space group P21/c with a = 10.686(4), b = 17.376(8), c = 11.759(4) Å, β = 92.072(14)°, C27H14Cu2FN4O4, M r = 604.50, V = 2182.1(15) Å3, Z = 4, D calcd. = 1.84 g cm–3, R = 0.0588 and wR = 0.1202 (all data). In complex 1, the mixed-valence Cu(I)/Cu(II) atoms are linked by L and 1,3-BDC to give a rare 3D (3,3,4)-connected (4.7.9)(7.8.9)(4.7.8.93) framework. The temperature-dependent magnetic susceptibility of 1 was investigated in the temperature range of 2–300 K.

Mn(ii) coordination polymers assembled from 8 or 9-connected trinuclear secondary building units: topology analysis and research of magnetic properties

Two highly-connected trinuclear Mn(ii)-cluster polymers were successfully fabricated. The FC and ZFC data of 1 show a divergence over a temperature range of 40–3.5 K. 2 features a ferrimagnetic chain with a (5/2, 10/2) spin topology.