Competing Exchange Interactions and Ground-State Variability:  Linear Homo- and Heterotrinuclear Manganese(III, IV) Complexes with Tris(dimethylglyoximato)metalate(II) Tetraanions as Bridging Ligands

Abstract

Two series of linear homo- and heterotrinuclear complexes, MnIIIMIIMnIII and MnIVMIIMnIV, where MII represents MnII (1 and 5), NiII (2 and 6), CuII (3 and 7), or ZnII (4 and 8), containing three dimethylglyoximato dianions (dmg2-) as bridging ligands and 1,4,7-trimethyl-1,4,7-triazacyclononane (L) as the capping ligand for the terminal MnIII or MnIV ions, have been synthesized. Compounds 1−8 have been characterized on the basis of elemental analyses, IR, UV−vis, and EPR spectroscopy, and variable-temperature (2−295 K) magnetic susceptibility measurements. The trinuclear complexes are quasi-isostructural with the terminal manganese ions in a distorted octahedral environment, MnIII/IVN3O3, and the divalent metal ions M are six-coordinate with the MIIN6 chromophore. The molecular structures of the compounds [LMnIII{(μ-dmg)3MnII}MnIIIL](ClO4)2 (1) and [LMnIII{(μ-dmg)3CuII}MnIIIL](ClO4)2 (3) have been established by X-ray diffraction. 1 crystallizes in the monoclinic system, space group C2/c, with cell constants a = 32.472(6) Å, b = 9.058(2) Å, c = 16.729(3) Å, β = 107.60(3)°, V = 4690.2(16) Å3, and Z = 4. The crystal data for 3 are as follows: monoclinic, space group C2/c, a = 32.686(5) Å, b = 8.870(1) Å, c = 16.867(2) Å, β = 108.65(1), V = 4633(1) Å3, and Z = 4. Analyses of the susceptibility data indicate the presence of weak to moderate exchange interactions, both ferro- and antiferromagnetic, between the paramagnetic centers. It has been conclusively demonstrated that there are indeed two different coupling constants, J = J 12 = J 23 and J 13, operative in these linear trinuclear complexes. J 13 represents the exchange interaction between two terminal paramagnetic centers separated by a distance of ∼7 Å. The effect of J 13 on the energy-splitting pattern has been demonstrated by the variability of the ground states. A qualitative rationale has been provided for the difference in magnetic behaviors. The cyclic voltammograms of complexes 1−8 reveal two reversible and two quasireversible one-electron redox processes. The central divalent metal ion in these complexes is redox-inactive.

About the calculation of exchange coupling constants in polynuclear transition metal complexes

“…41 For the analysis of the exchange coupling constants in model compounds we selected the oxalato-bridged Cu(II) complexes. Because we have previously studied 42 the magnetostructural correlations and the influence of the ligands on the exchange coupling of oxalato-bridged Cu(II) dinuclear complexes using the same computational approach, we wish to find out if new unenvisaged features appear in the case of polynuclear analogues.…”

“…41 We have chosen this compound to consider a case with different paramagnetic centers having more than one unpaired electron in two of the paramagnetic centers. The calculated coupling constants are Ϫ141.3 cm Ϫ1 for the Mn(III)Cu(II) interaction and Ϫ6.2 cm Ϫ1 for the Mn(III)Mn(III) one, that com- …”

Unique tetranuclear heterometallic compound [Na2Zn2{(4-py)C(H)(NOH)}2(CH3COO)6(H2O)4].2H2O with luminescent properties

“…The search for new materials with potential adsorption and luminescent properties explains recent interest in d 10 transition metal polynuclear compounds and coordination polymers [1,2]. Oxime ligands exhibit a notable ability to bridge metal ions [3].…”

Metallomacrocycles as ligands: synthesis and characterisation of aluminium-bridged bisglyoximato complexes of palladium and iron

“…39,40 Additionally there are several examples of cryptands consisting of tris-glyoximato moieties with the oxygen donors bound to antimony, tin, iron, manganese, or chromium. [41][42][43][44][45][46][47] Given the utilization of macrocycles for many applications including biomimetic chemistry, catalysis, and solar fuels, facile synthetic access to diverse metallomacrocycles is of interest as a complementary strategy for tuning of the electronic and steric environment of coordinated metal centers. We report herein on the synthesis of metallomacrocycles based on aluminium bridged bisglyoximato frameworks and their coordination chemistry with iron and palladium.…”