Magnetic Resonance Behavior and Metal-Metal Interactions in Bimetallic Complexes of Pyridylmethylketazine

Owens, Charlotte Joy

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Description

Title

Magnetic Resonance Behavior and Metal-Metal Interactions in Bimetallic Complexes of Pyridylmethylketazine

Author(s)

Owens, Charlotte Joy

Issue Date

1987

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Chemistry, Inorganic

Abstract

• This study is on the NMR proton relaxation rates and metal-metal interactions of MM$\sp\prime$(PMK)$\sb{3}$(NO)$\sb3)\sb{4}\cdot{\rm xH\sb{2}O,}$ where M and M$\sp\prime$ are Co(II), Ni(II), Cu(II), and Zn(II), and PMK (pyridylmethylketazine) is the condensation of two molecules of 2-acetylpyridine with hydrazine. Gatteschi and co-workers obtained interesting proton NMR results on such complexes; they found the normally broad peaks of the Cu(II) and Ni(II) complexes to become much sharper when Co(II) was also in the complex. Because of their results, work was done here to determine the proton relaxation rates, their implications for the electron relaxation rates, and the amount of interaction needed between the ions for this behavior to occur. Among the studies were proton T$\sb{1}$ measurements, EPR spectra, and variable temperature magnetic susceptibility determinations.
• The proton relaxation rates in the CuZn, NiZn, and CoZn complexes could be fit by dipolar interaction of the protons with the paramagnetic ion; use of the $\sp{1}$H T$\sb{1}$ values in the Solomon equation suggested that $\tau\sb{\rm s}$, the electronic spin lifetimes of the CuZn and NiZn complexes, were longer than $\tau\sb{\rm r}$, the correlation lifetime for rotation in solution. In contrast, the $\tau\sb{\rm s}$ value calculated for the CoZn complex was much shorter than $\tau\sb{\rm r}$. Protons in complexes containing Ni(II) and/or Cu(II), but not Co(II), were very effectively relaxed; T$\sb{1}$'s under 1 millisecond were measured. In contrast, the presence of Co(II) in the same complex increased the proton T$\sb{1}$'s at least tenfold, so the effectiveness of the Cu(II) and Ni(II) at relaxing protons had been greatly undercut.
• The data for the complexes containing two paramagnetic ions were compared with values expected for the coupled ($\vert$2J$\vert\ >$ (h$\tau\sb{\rm c}\sp{-1}$/2$\pi$)) and uncoupled cases. Both Cu$\sb{2}$ and Co$\sb{2}$ were better fit by the uncoupled case, while the coupled case was appropriate for Ni$\sb{2}$. Both CuCo and NiCo had interactions greater than h$\tau\sb{\rm c}\sp{-1}\sb{\rm (CuZn,NiZn)}/2\pi$ (about.03 cm$\sp{-1}$) but much less than h$\tau\sb{\rm c}\sp{-1}\sb{\rm (CoZn)}/2\pi$; calculations on these intermediate coupling cases led to estimates of $\vert$2J$\vert$ under 0.2 cm$\sp{-1}$. Thus, a quickly relaxing paramagnetic ion can, through a very small interaction, speed the relaxation rate of another ion while the complex has essentially full magnetism. The unavailability of an EPR spectrum of the CuCo complex at 130K or above was consistent with the Cu(II)'s relaxation rate being increased by Co(II).

Graduation Semester

1987

Type of Resource

text

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