Mechanism of Pyridine−Ligand Exchanges at the Different Labile Sites of 3d Heterometallic and Mixed Valence μ₃-oxo Trinuclear Clusters

Abstract

The syntheses and single crystal X-ray structural analysis of five novel hetero-and homometallic µ 3 -oxo trinuclear cluster with the formula [Fe 2) and Co (4.7; 55.37; +11.2; +10.9). A limiting D mechanism is assigned to these exchange reactions. This assignment is based on a first-order rate law, the detection of intermediates, the positive and large entropies and volumes of activation. The order of reactivity k Co > k Ni is expected for a D mechanism at these metal centers: their low exchange rates are due to their strong binding with the 4-Rpy donor. Surrounded by oxygen donors the d 5 iron(III) usually reacts associatively; however, here due to low affinity of this ion for nitrogen the mechanism is D and the rate of exchange is very fast, even faster than on the divalent ions. There is no significant effect of the divalent ion in cluster 2, 3, and 5 on the exchange rates of 4-Phpy at the iron center, which seems to indicate that the specific electronic interactions between the three ions making the clusters do not influence the Fe III -N bond strength.

Synthesis and engineering porosity of a mixed metal Fe2Ni MIL-88B metal–organic framework

“…And since bonding to each metal atom in the MIL-88B structure is a terminal ligand (H 2 O or DMF), which is ready to be replaced, it is possible to introduce larger terminal ligands into the MIL-88B structure which helps retain the breathing effect. Common terminal ligands for trimeric clusters are pyridine and its derivatives such as pyrazine and 4,4′-bipyridine, 14,43 which have different steric hindrances and thus can be used as the breathing agent of the MIL-88B structure, as illustrated in Scheme 2.…”

Synthetic Design of Heterometallic Cluster Compounds with Site‐Selective and Stepwise Substitution of Bridging Carboxylates

“…Compounds 1-4, which contain a Ru 2 III,III Mg II O core, are all diamagnetic and the structural confirmation has been further substantiated by 1 H NMR spectra measured in CDCl 3 , which show resonances due to aromatic protons on the ancillary pyridyl rings, methyl groups of acetato ligands, and ethyl groups of the propionato ligands being consistent with the expected numbers and intensity ratio for the respective compounds. [9] As already shown in Scheme 1, complex 2 turned out to be a mixture of three "coordination position isomers" with respect to the location of two acetato and two proponato ligands on the Mg···Ru bridging sites.…”

“…This distinctive character is, in principle, extended to synthesize new compounds incorporating differentiated ligands at distinct metal sites through coordination. Such siteselectivity is well documented by solution kinetic studies in many heterometallic systems, [3, 4] but its the usefulness and applications to synthetic aspects remain little explored to date.Oxo-centered, acetato-bridged trinuclear complexes [Ru, where M = the first-row transition-metal divalent ions and Mg II and py = pyridine, constitute a rare but crucial class of heterometallic compounds, in which two distinct metal centers with remarkably different degrees of substitution-lability are incorporated. [5][6][7][8] This feature has been solely demonstrated by kinetic studies for the substitution of monodentate ancillary ligands.…”

“…Oxo-centered, acetato-bridged trinuclear complexes [Ru 6 (py) 3 ], where M = the first-row transition-metal divalent ions and Mg II and py = pyridine, constitute a rare but crucial class of heterometallic compounds, in which two distinct metal centers with remarkably different degrees of substitution-lability are incorporated. [5][6][7][8] This feature has been solely demonstrated by kinetic studies for the substitution of monodentate ancillary ligands.…”

“…This solvent system afforded crystals with the formula 3 ]·py (4'·py), in which pyridine occupies the Mg center as a result of ligand replacement during crystallization. [10] The molecular structure, shown in Figure 1, clearly reveals site-selective substitution on the Ru 2 MgO core, where four propionato ligands bridge the Mg···Ru edges, while two acetato ligands still remain on the Ru···Ru edge.…”