Discrete trinuclear copper(ii) compounds as building blocks: the influence of the peripheral substituents on the magnetic coupling in oxamato-bridged complexes

Abstract

Two new trinuclear copper(ii) complexes without end-capping ligands, (Bu4N)2[Cu(dmso)2{Cu(dnopba)(dmso)}2] () and (Bu4N)2[Cu(dmso)2{Cu(dcopba)(dmso)}2] () [dnopba = 4,5-dinitro-ortho-phenylenebis(oxamate), dcopba = 4,5-dichloro-ortho-phenylenebis(oxamate), Bu4N(+) = tetra-n-butylammonium and dmso = dimethylsulfoxide], were synthesized and their structures were determined by single crystal X-ray diffraction. The crystal structures of and consist of two outer bis(oxamato)(dmso)cuprate(ii) units which act as bidentate ligands toward a trans-bis(dmso)copper(ii) inner entity leading to centrosymmetric tricopper(ii) complexes with copper-copper separations across the oxamate bridges of 5.1916(3) () and 5.1776(3) Å (). The peripheral copper(ii) ions in and are five-coordinate in somewhat distorted square pyramidal environments with a dmso molecule filling the apical position whereas the inner copper(ii) ion is six-coordinate in an elongated octahedral environment with two dmso molecules in the axial sites. The investigation of their magnetic properties in the temperature range 2.0-300 K shows the occurrence of a strong intramolecular antiferromagnetic coupling between the copper(ii) ions through the oxamate bridges [J1 = -296(1) () and -334(1) cm(-1) (), the Hamiltonian being defined as Ĥ = -J1(ŜCu2·ŜCu1 + ŜCu2·ŜCu1')], which leads to a low-lying spin doublet at low temperatures. Density functional theory calculations (DFT) have been used to substantiate these magnetic couplings and also to analyse the influence exerted on these interactions by the type of substituent at the 4,5-positions from the phenylene ring of the bis(oxamate) ligand.

Solid-State Self-Assembly of a Linear Hexanuclear Copper(II) Oxamate Complex with Alternating Antiferro- and Ferromagnetic Coupling

“…deviation of fitted atoms = 0.0039) formed by N1N2O3O4 atoms by 0.063(1) Å toward the apical position, whereas Cu3 is shifted by 0.106(1) Å from the least-squares plane through N6N7N8C5 (r.m.s = 0.0468). The basal Cu-N and Cu-O distances from the dmopba ligand in the [Cu(dmopba)(H 2 O)] 2− fragment, as well as the basal/equatorial Cu-N distances from the bpca ligand in the [Cubpca)] + ones, are significantly shorter than the apical Cu-Ow or axial Cu-O distances (see Table S2), being within the ranges found in similar compounds [18,43,52,54]. Within the trinuclear unit, the mean basal plane of the Cu2 atom is perpendicularly oriented to the mean equatorial/basal planes of the Cu1 and Cu3 atoms (78.09 and 81.67 • ), which in turn have a parallel planar disposition between each other (20.49 • ).…”

“…The moderate intratrinuclear antiferromagnetic coupling through the oxamato bridge observed for 1 (J = −31.96 cm −1 ) is an order of magnitude smaller than that found for trinuclear compounds with bidentate blocking ligands (~−350 cm −1 ), comparable to that found for tri-and hexanuclear compounds with tridentate blocking ligands (~−84 cm −1 ) [18,36]. It is well known that the strength of magnetic coupling is directly linked to the The moderate intratrinuclear antiferromagnetic coupling through the oxamato bridge observed for 1 (J = −31.96 cm −1 ) is an order of magnitude smaller than that found for trinuclear compounds with bidentate blocking ligands (~−350 cm −1 ), comparable to that found for tri-and hexanuclear compounds with tridentate blocking ligands (~−84 cm −1 ) [18,36]. It is well known that the strength of magnetic coupling is directly linked to the symmetry and relative orientation of the magnetic orbitals involved, which ultimately depend on the geometry of the metal ions and the nature of the blocking ligands [57].…”

“…The great versatility of polychelating oxamate ligands in the coordination of transition metal ions has been described in several reports [12][13][14]. Due to the presence of several sites of coordination and bridging nature [14], they can be used to form discrete mono- [15,16], di- [17], and trinuclear species [18], up to deca-or dodecanuclear nanowheel systems [19,20], as well as extended chains [21], planes [22], and 3D networks [23], so-called metal-organic frameworks [12,13,24]. Supramolecular chemistry plays an important role in this synthetic strategy because it can also drive the dimensionality of the network through coordinative interactions, hydrogen bonds, the interaction between cations and anions, Van der Waals forces, and π-π stacking interactions, to cite some examples [25,26].…”

“…Focusing on molecule-based magnetic materials made of homotrinuclear copper(II) oxamate systems, there are a few examples of discrete units described in the literature [18,[36][37][38][39]. These compounds were built using the self-assembly of discrete mononuclear oxamate complexes and copper(II) complexes acting as blocking ligands such as N,N,N ,Ntetramethylethylenediamine (tmen) [36][37][38][39], N,N,N ,N ,N -pentaethyldiethylenetriamine (pet), N,N,N ,N ,N -pentamethyldiethylenetriamine (pmd), bis(3-aminopropyl)amine (bapa), and 2,2 :2 ,6 -terpyridine (terpy) [36].…”

Structural and Magnetic Properties of a Pyridyl(vinyl)benzoate-Based Metal–Organic Framework with Iron(II) as Spin Carrier

“…The design of coordination polymers (CPs), especially metal–organic frameworks (MOFs), constitutes a great challenge for the development of molecular systems with remarkable chemical and physical properties, such as magnetic, optical, sorption, and electronic properties. − The nature of metal ions, ligands, coligands, the use of different solvents, and experimental conditions play an important role in the preparation of distinct molecular structures, ranging from discrete mono-, di-, tri-, or polynuclear molecular systems − to extended oligomeric or polymeric one-, two-, or three-dimensional structures (i.e., 1D, 2D, or 3D). − …”