Effect Of Coordination Geometry Research Articles

Anisotropic Metal-Metal Pauli Repulsion in Polynuclear d10 Metal Clusters.

Metallophilicity has been widely considered to be the driving force for self-assembly of closed-shell d10 metal complexes, but this view has been challenged by recent studies showing that metallophilicity in linear d10-d10 dimers is repulsive. This is due to strong metal-metal (M-M') Pauli repulsion (Wan, Q., Proc. Natl. Acad. Sci. U. S. A. 2021, 118, e2019265118). Here, we study M-M' Pauli repulsion in d10 metal clusters. Our results show that M-M' Pauli repulsion in d10 polynuclear clusters is 6-52% weaker than in similar linear d10 complexes due to the anisotropic shape of (n+1)s-nd hybridized orbitals. The overall M-M' interactions in closed-shell d10 polynuclear metal clusters remain repulsive. The effects of coordination geometry, relativistic effects, and the ligand's electronegativity on M-M' Pauli repulsion in polynuclear d10 clusters have been explored. These findings provide valuable guidance for the design and development of ligands and coordination geometries that alleviate M-M' Pauli repulsion in d10 metal cluster systems.

Effect of Coordination Geometry on Magnetic Properties in a Series of Cobalt(II) Complexes and Structural Transformation in Mother Liquor.

The three Co(II) complexes [Co(bbp)2][Co(NCS)4]·4DMF (1), [Co(bbp)(NCS)2(DMF)]·2DMF (2), and [Co(bbp)(NCS)2] (3) have been synthesized and characterized by single-crystal X-ray diffraction, magnetic, and various spectroscopic techniques. Complexes 1 and 3 are obtained by the reaction of Co(NCS)2 with 2,6-bis(1H-benzo[d]imidazol-2-yl)pyridine (bbp), and complex 1 undergoes a structural transformation to form complex 2. A single-crystal X-ray study revealed that complex 1 is comprised of two Co(II) centers, a cationic octahedral Co(II) unit and an anionic tetrahedral Co(II) unit, while the Co(II) ion is in a distorted-octahedral environment in 2. Moreover, in complex 3, the Co(II) ion is in a distorted-square-pyramidal geometry. The effect of coordination geometry on the magnetic properties was studied by both static and dynamic magnetic measurements. Direct current (dc) magnetic susceptibility measurements showed that all of the Co(II) ions are in high-spin state in these complexes. Alternating current (ac) magnetic susceptibility measurements indicated that complexes 2 and 3 display slow relaxation of magnetization in an external dc magnetic field, while complex 1 displayed no such property. EPR experiments and theoretical calculations were consistent with the above findings.

Effect of coordination geometry on the magnetic properties of a series of Ln2 and Ln4 hydroxo clusters

A series of three isostructural tetranuclear complexes with the general molecular formula [Ln4(μ3-OH)4(L)4(μ2-piv)4(MeOH)4] (Ln = Gd 1, Dy 2 and Ho 3; LH = [1,3-bis(o-methoxyphenyl)-propane-1,3-dione]) were isolated and unambiguously characterized by single crystal XRD. Under similar reaction conditions, simply changing the co-ligand from pivalate to 2,6-bis(hydroxymethyl)-p-cresol (LH'3) led to the isolation of dinuclear Ln(iii) complexes with the general molecular formula [Ln2(L)4(μ2-LH'2)2]·4DMF (Ln = Gd 4, Dy 5 and Ho 6). Direct current magnetic susceptibility data studies on the polycrystalline sample of 1-6 and the results reveal the existence of weak antiferromagnetic exchange interactions between the lanthanide ions in 1 which is evident from the spin Hamiltonian (SH) parameters (J1 = -0.055 cm-1 and g = 2.01) extracted by fitting χMT(T). On the other hand, though complex 4 exhibits weak antiferromagnetic coupling (J1 = -0.048 cm-1 and g = 1.99) between the Gd(iii) ions, the χMT(T) data of complexes 5 and 6 unambiguously disclose the presence of ferromagnetic interactions between Dy(iii) and Tb(iii) ions at lower temperature. Magnetization relaxation dynamics studies performed on 2 show frequency dependent out-of-phase susceptibility signals in the presence of an optimum external magnetic field of 0.5 kOe. In contrast, complex 5 shows slow magnetization relaxation with an effective energy barrier (Ueff) of 38.17 cm-1 with a pre-exponential factor (τ0) of 1.85 × 10-6 s. The magnetocaloric effect (MCE) of complexes 1 and 4 was extracted from the detailed magnetization measurement and the change in the magnetic entropy (-ΔSm) of 1 and 4 was found to be 25.57 J kg-1 K-1 and 12.93 J kg-1 K-1, respectively, at 3.0 K for ΔH = 70 kOe.

Speciation of sulfur in individual aerosol particles from work places by wavelength-dispersive electron-probe microanalysis.

The oxidation state of sulfur has been determined by measuring the energy shift of the S K(alpha) line by wavelength-dispersive electron-probe microanalysis. On flat polished samples the energy shift between sulfate (S(+6)) and sulfide (S(-2)) was 1.3 eV, in good agreement with previous literature data. The observed energy shift of the S K(alpha) line is dominated by the change of the valence state of sulfur--the effects of co-ordination geometry and nearest neighbours are small. The relationship between the energy shift of the S K(alpha) line and the oxidation number of sulfur is linear, to a first approximation. The effect of particle geometry on the position of the S K(alpha) line is usually small and introduces an error of approximately half an oxidation number. The apparent sulfur valence states observed for individual aerosol particles from work places in a nickel refinery are highly variable and most probably result from different mixtures of the two end-members sulfide and sulfate.

The effect of coordination geometry on electrochemical oxidation and reduction of N-methylporphyrin complexes of cobalt(II) and manganese(II)

The effect of coordination geometry on electrochemical oxidation and reduction of N-methylporphyrin complexes of cobalt(II) and manganese(II)