Oxalate-Bridged Bimetallic Complexes {NH(prol)₃}[MCr(ox)₃] (M = Mn^II, Fe^II, Co^II; NH(prol)₃⁺ = Tri(3-hydroxypropyl)ammonium) Exhibiting Coexistent Ferromagnetism and Proton Conduction

Abstract

The oxalate-bridged bimetallic complexes {NH(prol)(3)}[M(II)Cr(III)(ox)(3)] (M(II) = Mn(II), Fe(II), Co(II)) with hydrophilic tri(3-hydroxypropyl)ammonium (NH(prol)(3)(+)) were prepared by a new synthetic procedure, and the effects of the NH(prol)(3)(+) ion upon the structure, magnetism, and electrical conduction were studied. An X-ray crystallographic study of the MnCr dihydrate, {NH(prol)(3)}[MnCr(ox)(3)].2H(2)O, was performed. Crystal data: hexagonal, P6(3), a = b = 9.3808(14) A, c = 15.8006(14) A, Z = 2. The structure comprises oxalate-bridged bimetallic layers interleaved by NH(prol)(3)(+) ions. The ions assume a tripodal configuration and are hydrogen bonded to the bimetallic layers together with water molecules, giving rise to a short interlayer separation (7.90 A) and unsymmetrical faces to the bimetallic layer. Cryomagnetic studies demonstrate ferromagnetic ordering with transition temperature of 5.5 K for the MnCr complex, 9.0 K for the FeCr complex, and 10.0 K for the CoCr complex. The interlayer magnetic interaction is negligibly weak in all of the complexes despite the short interlayer separation. A slow magnetization is observed in all the complexes. This is explained by spin canting associated with the unsymmetrical feature of the bimetallic layer. The complexes show proton conduction of 1.2 x 10(-10) to 4.4 x 10(-10) S cm(-1) under 40% relative humidity (RH) and approximately 1 x 10(-4) S cm(-1) under 75% RH. On the basis of water adsorption/desorption profiles, the conduction under 40% RH is mediated through the hydrogen-bonded network formed by the bimetallic layer, NH(prol)(3)(+) ions, and water molecules (two per MCr). Under 75% RH, additional water molecules (three per MCr) are concerned with the high proton conduction. This is the first example of a metal complex system exhibiting coexistent ferromagnetism and proton conduction.

Recent Advances on Anilato-Based Molecular Materials with Magnetic and/or Conducting Properties

“…In the last 20 years many efforts have been addressed to add in these materials a further physical property by playing with the functionality of the A + cations located between the bimetallic layers. This strategy produced a large series of multifunctional molecular materials where the magnetic ordering of the bimetallic layers coexists or even interacts with other properties arising from the cationic layers, such as paramagnetism [2,[76][77][78][79][80], non-linear optical properties [2,81,82], metal-like conductivity [83,84], photochromism [2,81,85,86], photoisomerism [87], spin crossover [88][89][90][91][92][93], chirality [94][95][96][97], or proton conductivity [2,98,99]. Moreover, it is well-established that the ordering temperatures of these layered magnets are not sensitive to the separation determined by the cations incorporated between the layers, which slightly affects the magnetic properties of the resulting hybrid material, by emphasizing its 2D magnetic character [2,[75][76][77][78][79][80]95,100,101].…”

Minerals With Metal-Organic Framework Structures

“…The PXRD patterns of natural and synthetic zhemchuzhnikovite showed excellent fit to that which was calculated on the basis of the herein determined structure ( S5). The structural similarity of stepanovite and zhemchuzhnikovite to the proton-conducting oxalate MOFs is marked (11,21). Proton conductivity in these MOFs results largely from a Grotthuss-type proton-hopping mechanism, enabled by a 2D network of hydrogen bonds involving water molecules in the interlayer space and protic species located either between the MOF layers or lodged in the pores (11,24).…”

“…More recently, analogous metal-oxalate structures based on zinc (19,20) or other transition metals (21) have garnered additional interest as ferromagnetic and/or proton-conducting materials (Fig. 1C) (11,21).…”

Experimental and theoretical studies of hydroxyl-induced magnetism in TiO nanoclusters

“…[36][37][38][39][40][41] Adsorption/desorption of hydroxyls produces the moment variation for our Ti oxide clusters. Adsorption/ desorption of water molecules give rise to the moment variation for molecular magnets.…”