Magnetic Properties of the Two-Dimensional Bimetallic Compounds (NBu₄)[M^IIRu^III(ox)₃] (NBu₄ = Tetra-n-butylammonium; M = Mn, Fe, Cu; ox = Oxalate)

Abstract

Three compounds of general formula (NBu4)[MIIRuIII(ox)3] have been synthesized; NBu4 + stands for tetra-n-butylammonium, M for Mn, Fe, and Cu, and ox2- for the oxalate dianion. The X-ray powder patterns for the three derivatives have revealed that these compounds are isostructural with (NBu4)[MnIICrIII(ox)3], whose crystal structure was known, and the cell parameters have been refined in the R3c space group. The (NBu4)[MIIRuIII(ox)3] compounds are new examples of two-dimensional bimetallic assemblies with oxalate bridges. The temperature (T) dependences of the magnetic susceptibility (χM) in both the dc and ac modes and the field dependences of the magnetization have been investigated. The local spins are S Ru = S Cu = 1/2, S Mn = 5/2, and S Fe = 2. The RuIII−MII interaction has been found to be antiferromagnetic for M = Fe and Cu and ferromagnetic for M = Mn. The two compounds (NBu4)[FeIIRuIII(ox)3] and (NBu4)[CuIIRuIII(ox)3] exhibit a ferrimagnetic behavior, characterized by a minimum in the χM T versus T plots. (NBu4)[FeIIRuIII(ox)3] exhibits a long-range magnetic ordering at T c = 13 ± 1 K. A slight frequency dependence of the out-of-phase ac magnetic response has been observed. The field dependence of the magnetization in the magnetically ordered state has revealed a rather strong coercivity, with a coercive field of 1.55 kOe at 2 K. A theoretical model has been used to determine the magnitude of the RuIII−MII interactions, with M = Mn and Fe. This model is based on a quantum−classical spin approach together with Monte Carlo simulations. The interaction parameters have been found as J = 1.04 cm-1 for (NBu4)[MnIIRuIII(ox)3] and −9.7 cm-1 for (NBu4)[FeIIRuIII(ox)3], with a spin Hamiltonian of the type −J∑ i,j S Ru, i · S M, j . The magnetic properties of these compounds have been discussed. In particular, it has been emphasized that the symmetry rules governing the nature and the magnitude of the interaction between two 3d magnetic metal ions seem not to be valid anymore for 4d ions such as RuIII.

Exchange Coupling in Metal Complexes of the Second Transition Series: A Theoretical Exploration

“…[41] The interaction of the π-system of the pyrazine with one of the t 2g orbitals produces the largest stabilization due to the π-acid character of the pyrazine ligands while the one that combines slightly with the σ-system remains at an intermediate energy. Each Ru III cation is low-spin d 5 , and the unpaired electron is placed in the only t 2g orbital that interacts neither with the π-system of the bridging ligand, nor with the σ-system (see Figure 2). Therefore, the two combinations of the orbitals bearing the unpaired electron cannot have large contributions towards the bridging ligand and we expect a small energy splitting between the in-phase and out-of-phase combinations of such d orbitals and, consequently, a small exchange coupling constant for this complex.…”

Funktionale poröse Koordinationspolymere

“…[192] {Cu[Cu(tpyp)]} n (H 2 tpyp = 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphyrin) enthält gemäß Strukturanalyse ein mit PtS verwandtes Gerüst. [192] [196] Fe, [198] Ru [199] ) aufgebaut. Ein ähnlicher Metalloligand, [Cr(dto) 3 ] 3À (dto = Dithioacetat), wird für Dimetallaggregate wie {NPr 4 [MCr(dto) 3 ]} n (M = Fe, Co, Ni, Zn) verwendet.…”

“…Das 1D-Strukturmotiv von {Cu(ca)(ROH) 2 } enthält Wasserstoffbrückenstellen, ca-O (H-Acceptor) und ROH (H-Donor), [111] sodass [195,235] Die Verbindungen zeigen ferromagnetisches, [196] ferrimagnetisches [199,236,237] oder gekippt-antiferromagnetisches Verhalten [238,239] mit kritischen Temperaturen zwischen 5 und 44 K. Die Strukturen [197,240] bestehen aus einem kontinuierlichen anionischen Netzwerk von Oxalat-verbrückten hexagonalen Schichten der beiden Metallatome. Zwischen den Schichten befindet sich ein organisches Gegenion des Typs [XR 4 ] + (X = N, P; R = Ph, nPr, nBu), das wahrscheinlich als Templat fungiert und den Aufbau der Netzstruktur beeinflusst.…”

[Cr(dmbipy)(ox)2]−: a new bis-oxalato building block for metal assembling. Crystal structures and magnetic properties of XPh4[Cr(dmbipy)(ox)2]·5H2O (X = P and As), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n·17/2nH2O and {Ag(H2O)[Cr(dmbipy)(ox)2]}n·3nH2O

“…These advantages account for the impressive success of this preparative route of oxalate-bridged heterobimetallic compounds with controlled nuclearity and dimensionality. [2][3][4][5][6][7][8][9][10][11][12] In the light of these results, it is clear now that their dimensionality is controlled by the templating counterion. So, layered honeycomb 8b,11,12 All these two-and three-dimensional systems are examples of polyfunctional molecular-based materials in which the magnetic properties are often complemented by additional properties such as electrical conductivity, 10c prefixed chirality 8 and non-linear optical activity.…”