Metal Ion Scrambling in Hexanuclear M₆(Et₂NCO₂)₁₂ Complexes (M = Co, Mg). Synthesis, Solid State Structure, and Solution Dynamics of Heteronuclear Co_nMg_6-n(Et₂NCO₂)₁₂ Complexes

Abstract

Heteronuclear diethylcarbamato complexes of the form Co(n)()Mg(6)(-)(n)()(Et(2)NCO(2))(12) were prepared from the isostructural homonuclear precursors Mg(6)(Et(2)NCO(2))(12), 1, and Co(6)(Et(2)NCO(2))(12), 2, via a solvothermal methodology. Two materials were selected for single-crystal X-ray diffraction analysis: Co(1.6)Mg(4.4)(Et(2)NCO(2))(12) and Co(2.7)Mg(3.3)(Et(2)NCO(2))(12). Both compounds crystallize in the orthorhombic space group Ccca, as do 1 and 2. The molecular structure is best described as two trinuclear M(3) units cross-linked by diethylcarbamate ligands and twisted about one another, so that the complex has overall D(2) symmetry and is chiral. Each trinuclear unit consists of two terminal pentacoordinate metal ions and one central hexacoordinate metal ion. The X-ray diffraction data were unambiguous that the Co(2+) ions migrate exclusively to the pentacoordinate sites in the heteronuclear complexes, thus demonstrating that metal ion scrambling at the molecular level must occur. The composition of individual crystals can be continuously varied for Co(2+) mole fractions chi(Co) < 0.5, and the a and c unit cell distances are linearly related to chi(Co). This indicates that the compounds behave as solid solutions. There appears to be either a chemical or crystallographic phenomenon inherent in the synthetic methodology that prevents isolation of heteronuclear materials having chi(Co) > 0.5. Solution electronic spectroscopy and molecular weight measurements show that 2 can dissociate in chloroform and cyclohexane solution to give a dimeric complex 2'. This behavior contrasts with the stability of 1 in solution, as shown by NMR. The kinetic rate profile for formation of Co(n)Mg(6-n)(Et(2)NCO(2))(12) reveals saturation kinetics and is consistent with direct attack by 2' on 1 to give the heteronuclear complex via a higher nuclearity intermediate. This study illustrates a general method for the preparation of solids based on heteronuclear Werner-type complexes of the M(6)(Et(2)NCO(2))(12) structure type, and the mechanism by which such compounds can be formed from isostructural homonuclear precursors.

18 Macrocyclic and supramolecular coordination chemistry

“…The structures are best described as two trinuclear M 3 units cross-linked by diethylcarbamate ligands and twisted about one another, so that the complex has overall D 2 symmetry. 27 The X-ray data prove that the Co() ions migrate to one particular site in the heteronuclear complexes, Fig. 9.…”

Synthesis and properties of Zn–Mg heterobimetallic carbamates. Crystal structures of the first reported single source precursors for ZnxMg1−xO thin films

“…Characterisation of reactions between 7 and 8 revealed a similar inertness, even with the presence of equivalent coordination sites. In contrast, Caudle et al 15 suggested that a mixed Co-Mg complex was formed by trifurcation in solution of a hexameric Co complex into the dimer Co(O 2 CNEt 2 ) 2 , which then reacted with the stable magnesium hexamer 8 to yield a mixed-metal product. They also reported that the mixing of isostructural magnesium and manganese complexes delivered a mixed-metal product that was isostructural to the two starting materials.…”

“…Caudle and coworkers reported metal-ion scrambling between isostructural diethylcarbamato hexamers of magnesium and manganese, 14 and cobalt and magnesium. 15 These compounds were prepared simply by mixing the two separate complexes in solution, at elevated temperatures, under pressure in a thick-walled flask to avoid displacement of CO 2 from the complexes. It was shown that this reaction proceeded through the dissociation of one of the hexameric complexes present (manganese or cobalt) into a dimeric state that then reacted with the intact magnesium hexamer to form the heterometallic species.…”

Synthesis and Isomerisation Reactions of Tetranuclear and Octanuclear (Carbamato)zinc Complexes

“…The combination of these steps is a reversible cycle, the facile interconversion of 1 and 2 [Equation (1) 4 ] were studied intensively using UV/Vis techniques, with the result that the lowernuclearity dinuclear species dominates in solution. [27] Despite this dominance, the existence of a facile isomerisation pathway allowed the deposition of the hexanuclear isomer as the sole solid product. This isomerisation pathway was reported to be necessary to the formation of mixed-metal [Co x Mg 6-x (O 2 CNEt 2 ) 12 ] complexes.…”

“…This isomerisation pathway was reported to be necessary to the formation of mixed-metal [Co x Mg 6-x (O 2 CNEt 2 ) 12 ] complexes. [27] Heterodimetallic carbamato complexes are attractive from a metal oxide film growth perspective. The homonuclear complex [Mg 6 (O 2 CNEt 2 ) 12 ] is already a proven precursor for MgO thin-film growth, [28] and when mixed with the (µ-oxido)zinc analogue [Zn 4 (µ 4 -O)(O 2 CNEt 2 ) 6 ] has been used to deposit dimetallic Zn x Mg 2-x O films of high quality and reproducibility.…”