A μ1,1- or μ1,3-carboxylate bridge makes the difference in the magnetic properties of dinuclear MnII compounds

Abstract

Six new dinuclear Mn(II) compounds with carboxylate bridges have been synthesized and characterized by X-ray diffraction: [{Mn(phen)(2)}(2)(μ-RC(6)H(4)COO)(2)](ClO(4))(2) with R = 2-Cl (1), 2-CH(3) (2), 3-Cl (3), 3-CH(3) (4), 4-Cl (5) and 4-CH(3) (6). Compounds 1 and 2 show two μ(1,3)-carboxylate bridges in a syn-anti mode while compounds 3-6 present a very uncommon coordination mode of the carboxylate ligand: the μ(1,1)-bridge. The magnetic properties of these compounds are very sensitive to the bridging mode of the carboxylate ligands. While compounds 1 and 2 (μ(1,3)-bridge) display antiferromagnetic interactions, with J values of -1.41 and -1.66 cm(-1), respectively, compounds 3-6 (μ(1,1)-bridge) show ferromagnetic interactions, with J values of 1.01, 0.98, 1.04 and 1.06 cm(-1), respectively. It is worth noting that compounds 3-6 are the first of their class to be magnetically characterized. The EPR spectra at 4 K for compounds with antiferromagnetic coupling (1 and 2) are more complex than those for compounds with a ferromagnetic interaction (3-6). Quite good simulations can be obtained with the ZFS parameters of the Mn(II) ion D(Mn) ~ 0.095 cm(-1) and E(Mn) ~ 0.025 cm(-1) for compounds 1 and 2 and D(Mn) ~ 0.060 cm(-1) and E(Mn) ~ 0.004 cm(-1) for compounds 3-6.

Versatile coordinating capabilities of thiodibenzoic acid copper complexes bearing N-donor ligands

“…These various coordinating modes can be distinguished by the difference in asymmetric (m a COO -) and symmetric (m s COO -) carboxylate stretching bands [25]. A difference of &200 cm -1 is indicative of a monodentate type of coordination, while (Dm) )200 cm -1 can be ascribed to l-bridging mode [26]. When the difference between the carboxylate frequencies is [100 cm -1 , the carboxylate groups bind to the metal in a bidentate chelating mode, though such values have also been ascribed to l-bridging mode [27].…”

“…2, 3, 4, 5, 6, 7; Tables 3, 4), and a structure description of each complex is as follows. The single-crystal X-ray structures have been determined for C 26 and 3a are given in Table 3. Selected bond lengths and bond angles of the complexes are given in Table 4.…”

Crystal Structures and Thermal Properties of Two Binuclear Cd(II) Supramolecular Complexes Based on Quinolinecarboxylate Ligand

“…And the metal ions are separated by a Cd···Cd distance of 3.835 Å, which is markedly longer than those observed complexes with this mode (3.4-3.7 Å). [29][30][31][32] The bridging carboxylate group adopts the rather rare μ 2 -η 2 :η 0 coordination mode, which is uncommon in metal carboxylate chemistry, leading to a significant difference in the C-O bond lengths (1.282 Å and 1.228 Å) within the carboxylate group. 32 The second carboxylate group of each L ligand is monodentately coordinated to Cd(II) giving rise to a seven-membered chelating ring.…”

A 2D (4,4) network based on tetranuclear manganese(II)-terephthalato building units: Synthesis, crystal structure and magnetic studies

“…In [Mn II 2 (L) 2 (O 2 CMe) 3 ](PF 6 ) (L = the chiral ligand -(À)pinene [5,6]bipyridine) where the Mn II ions are bridged by two benzoate groups in the unsymmetric g 1 : g 2 mode and one benzoate group in symmetric g 1 :g 1 mode, with MnÁ Á ÁMn distance 3.433 Å, a weaker exchange coupling (À0.85 cm À1 ) was observed [18]. Dinuclear [Mn II 2 ] complexes bridged through two carboxylato groups in a syn-anti mode, similar to the Mn(2)/Mn(2 0 ) entity in 1, of the general formula [Mn II 2 (O 2 CR) 2 (N-N) 4 ](ClO 4 ) 2 (R = CH 2 Cl, N-N = phen [19]; R = 2-COOH-C 6 H 4 , N-N = phen [20]; R = 2-Cl-C 6 H 4 , N-N = bpy [21]; R = 2-COOH-C 6 H 4 , N-N = phen [22]; R = 2-Cl or CH 3 , N-N = phen [23]) as well as [Mn II 2 (O 2 CMe) 3 (tpa) 2 ]Á(TCNQ) 2 (tpa = tris(2-pyridylmethyl)amine, TCNQ = tetracyanoquinodimethane [24]) present low J values in the range À0.34 to À1.79 cm À1 comparable to J 2 value found for 1.…”