Structure of Solvation Sphere of Tris(acetylacetonato)chromium(III) in Acetonitrile

Abstract

Two experimental techniques were used to elucidate how acetonitrile molecules are bound to the title complex, [Cr(acac)3]: (i) measurement of NMR longitudinal relaxation rates of the dipolar nuclei of the solvent (1H, methyl-13C, and cyano-13C of CH3CN) in the presence of [Cr(acac)3], which is a paramagnetic complex, and (ii) X-ray diffraction measurements on acetonitrile solutions of [Cr(acac)3] and [Ru(acac)3] using an isostructural substitution method. The results of both methods are in harmony with each other. Four acetonitrile molecules are found within about 6 × 10-10 m from the chromium atom. They are in the hollows on the peripheral surface of the three acetylacetonato ligands, one or two in the hollows along the C 3 axis of the complex, and two or three in the hollows along the C 2 axes. They are oriented with the methyl ends inward: the angle between the molecular axis of acetonitrile and the vector from the chromium atom to the methyl carbon of acetonitrile was about 100°.

Structure Formation in Metal Complex/Polymer Hybrid Nanomaterials Prepared by Miniemulsion

“…Chromium(III) and cobalt(III) β-diketonato complexes possess five hollows on the peripheral surface of the three ligands. Solvent molecules can be accommodated in the hollows and interact with the metal complex . Even though the ionic radius of the Bi 3+ ion is similar to the lanthanide ions and therefore a flexible coordination sphere is expected, no peak in the SAXS diffractogram of the Bi-containing nanomaterial can be observed.…”

“…Solvent molecules can be accommodated in the hollows and interact with the metal complex. 39 Even though the ionic radius of the Bi 3+ ion is similar to the lanthanide ions and therefore a flexible coordination sphere is expected, no peak in the SAXS diffractogram of the Bi-containing nanomaterial can be observed. Here, it is not possible to give a concluding statement for Bi(tmhd) 3 because the Bi-containing miniemulsion showed a rheopex behavior after ultrasonication.…”

Synthesis and Solvent-Dependent Properties of Ru(acac)2dppz

“…However, the acac ligands do impart to the MLCT transition a sensitivity to environmental polarity that is not observed in the visible absorption spectra of the phen analogue. 8 Crystal structure analysis of transition metal acac complexes (used as hydrogenation catalysts; refs [23][24][25][26] show that the complexes are highly solvated; 27 in one case the solvent penetrates into the hydrophobic "hollows" provided by the acac ligands and is somewhat close to the metal center. 27 For optically interesting Ru(II) complexes, such intimate solvation may be used to advantage in the future design of sensor molecules.…”

Magnetic Interaction of Solution-State Paramagnets with Encapsulated H2O and H2

“…It seems likely, therefore, that the larger relaxivity of free water indicates additional bimolecular contributions. 16,17 The similarities between the R 1 values for the three sets of endohedral protons for a given M(acac) x also indicates that the relaxivity is insensitive to differences in cage shape, cage completeness, or even the presence of an oxygen atom between the protons (water). Additionally, the solubility of 3 in multiple solvents permitted R 1 measurements of endo-H 2 O in 1,2-dichlorobenzene-d 4 and CDCl 3 .…”

“…It seems likely that, in the present case, spin−lattice relaxation should occur by an outer-sphere mechanism, arising from the dipole−dipole interaction between the spins. If it is further assumed that both the proton carriers and the acac complexes behave as classically diffusing spheres of about the same size, R 1 (M −1 s −1 ) at high magnetic fields is expected to follow italicR 1 = 8000 normalπ 2 normalγ normalH 2 normalη normalμ normalB 2 normalμ eff 2 false( normalμ 0 / 4 normalπ false) 2 N normalA / 25 italick normalB italicT where γ H is the proton magnetogyric ratio, η the viscosity of the medium, μ eff is the effective magnetic moment of P in units of the bohr magneton, μ B , N A is the Avogadro constant, and all units are SI. From eq R 1 is predicted to scale as μ eff 2 at a given T .…”