Triggering the Sign of Magnetic Exchange Coupling in a Dinuclear Copper(II) Complex by Solvent Molecule Coordination

Abstract

The magnetic properties of a dinuclear copper(II) complex of the Schiff base ligand bis(N,N′‐3‐formylsalicylidene)‐1,3‐diaminopropan‐2‐ol (H3L) with an exogenous acetate bridging group, [Cu2L(CH3COO)] (2), and the product of its crystallization from dimethyl sulfoxide (DMSO) solution, [Cu2L(CH3COO)(DMSO)] (3), are studied experimentally and theoretically. The coordination of a DMSO molecule triggers exchange coupling from antiferromagnetic in 2 (2J = –94.8 cm–1) to ferromagnetic in 3 (2J = +121 cm–1). A combination of experimental data [XRD, X‐ray absorption spectroscopy (XAS)] and the results of DFT calculations with a broken‐symmetry approach show that the different magnetic behaviour of 2 and 3 is explained by a different conformation of the dinuclear unit, which is “symmetric” in 2 and roof‐shaped in 3. The role of the DMSO molecule in exchange‐coupling sign inversion is limited to the stabilisation of the roof‐shaped conformation of the complex.

A computational study of structural and magnetic properties of bi- and trinuclear Cu(II) complexes with extremely long Cu---Cu distances

“…Nowadays, the most prevalent and well studied organometallic magnetic systems are dinuclear copper(II) complexes with different types of linkers between the ligand-coordinated magnetic centers (-Hal-, [6,7], -OH-, [4,6,8,9] -OR-, [10][11][12][13] CN-, [14] -N^N-, [8,9,15] -N^O- [16,17] etc.). These complexes can demonstrate a variety of coupling types from strongly antiferomagnetic (exchange coupling constant J CuCu is strongly negative up to -1000 cm -1 ) [4][5][6] to moderately ferromagnetic (J CuCu is positive, typically of order 100 cm -1 ) [10,18]. Herein the J CuCu constant originates from the standard Heisenberg-Dirac-Van Vleck spin-Hamiltonian Ĥ = −J 12 Ŝ 1 Ŝ 2 ,…”

Influence of the bridging coordination of DMSO on the exchange interaction character in the binuclear copper(II) complex with the nonsymmetrical exchange fragment

“…The single (up to now) case of obtaining two ace tate bridged copper(II) complexes with the same ligand, N,N bis(5 tert butyl 3 formylsalicylidene) 1,3 diaminopropan 2 ol, having both the "symmetri cal" (2J = -94.8 cm -1 ) and "roof shaped" (with the bridging coordination of the DMSO molecule, 2J = 121 cm -1 ) conformations has previously been described by us [36]. Complexes I and II represent the second example showing that the character of mag netic exchange in similar systems is determined by the geometric factors rather than the nature of the exo genic bridge.…”

“…According to these parameters, the first coordination sphere of the copper ion in com plex I is formed by the nitrogen/oxygen atoms arranged at a distance of 1.9-2.0 Å. The copper-cop per distance in complex I (3.51 Å) considerably exceeds that for complex II and corresponds to the copper-copper distance in all structurally character ized acetate bridged copper(II) complexes with bis(azomethines) based on 1,3 diaminopropan 2 ol in which the "symmetrical" conformation of the metal chelates is observed [5,36].…”

“…The distorted structure similar to that of complex II is typical of a series of acetate bridged copper(II) complexes with bis(azomethines) based on the deriva tives of salicylaldehyde and 1,3 diaminopropan 2 ol [11,[34][35][36]. In all cases, the bridging coordination of the solvent molecule (DMF or DMSO) is observed.…”

“…The pre dominant majority of the described complexes based on N,N bis(salicylidene) 1,3 diaminopropan 2 ol and its analogs with the exogenic carboxylate bridge demonstrates a fairly strong antiferromagnetic exchange (the values of 2J range from -100 to ⎯200 cm -1 ), and all of them have a "symmetrical" conformation of the binuclear fragment [5,11,30,[31][32][33]. The exchange is ferromagnetic in a few com plexes of this type with the "roof shaped" conforma ( ) ' M χ tion [11,35,[36][37][38][39]. The exclusion is the described [34] acetate bridged complex based on N,N bis(3 methoxy)salicylidene 1,3 diaminopropan 2 ol for which the authors give the value of exchange parame ter equal to -185 cm -1 , while the complex, according to the X ray diffraction data, has a "roof shaped" con formation of the binuclear fragment (copper-copper distance 3.154(2) Å, bond angle at the alkoxyl bridging oxygen atom 107.0(2)°).…”