Contained within this body of work is a study that aims to quantify spin density delocalization in 3,6-R2-phenanthrenesemiquinone (3,6-R2-PSQ, where R = OMe and H) radicals and their metal complexes (where metals=ZnII, GaIII and NiII), of the form [M(tren)(PSQ)](BPh4)n, where M is a metal that is listed above, tren = tris(2-aminoethyl)amine, PSQ = phenanthrenesemiquinone and BPh4 = tetraphenylborate. Spin delocalization will be scrutinized by analyzing carbonyl carbon hyperfine coupling constants by continuous wave electron paramagnetic resonance (CW-EPR) spectroscopy, electron spin echo envelope modulation (ESEEM) spectroscopy, and hyperfine sublevel correlation (HYSCORE) spectroscopy. These examinations will reveal the influence molecular structure has on the hyperfine coupling at the carbonyl carbon nuclei. Spin delocalization has been quantified by isotopically labeling the carbonyl carbon nuclei with carbon-13 nuclei. 13C-labelled quinones were synthesized from a sequence of reactions, beginning with 13C-α-N,N’-dimethylformamide and 2,2’-dibromobiphenyl to form a diformyl-biphenyl. The carbonyl carbons were then coupled with hydrazine via a reductive cyclisation reaction, followed by oxidation with CrO3 to afford the quinone. CW-EPR of the 12C isotopologues revealed 1H fine structure in the organic radicals and the ZnII-PSQ complex. Inspection of the 13C-labeled compounds provided isotropic hyperfine coupling constants for all compounds studied except for NiII complexes; any fine structure from NiII CW-EPR spectra was unable to be resolved. The magnitude of all isotropic coupling constants fell within the range of 0 – 3 MHz. ESEEM and HYSCORE spectroscopies allowed for scrupulous investigation of the dipolar coupling. Carbonyl carbon dipolar couplings varied across the spectrum of compounds examined. This study shows promise for the use of ESEEM and especially HYSCORE spectroscopies for examining the spin properties of molecules in the field of molecular magnetic materials.
Read
