Use of 73Ge NMR spectroscopy for the study of electronic interactions

Claude H. Yoder, Franklin and Marshall College, Lancaster
Tamara M. Agee, Franklin and Marshall College, Lancaster
Charles D. Schaeffer, Elizabethtown College
Mary J. Carroll, Elizabethtown College
Adam J. Fleisher, Elizabethtown College
Alaina S. DeToma, Elizabethtown College


The lack of understanding of the structural and electronic factors that affect the often difficult to observe germanium resonance has been a major deterrent to studies of bonding interactions at germanium. We utilized the symmetrical system GeR to determine what structural factors inherent in the R group affect the shape and position of the Ge resonance. The Ge resonances of symmetrical tetrakis germanium compounds of the type GeR (R = alkyl, aryl), GeX (X = F, Cl, Br, I), Ge(OR) (R = alkyl, methoxyalkyl, dimethylaminoalkyl), Ge(NR ) (R = alkyl), and Ge(SR) (R = alkyl, dimethylaminoalkyl) were examined for evidence of intramolecular coordination. Although many of these compounds have sharp resonances due to idealized tetrahedral symmetry with relatively long relaxation times, others have broad or no observable resonances due to fast quadrupolar relaxation. We hypothesize that the perturbation of symmetry by even weak Lewis interactions or conformational changes causes broadening of the resonance before the interaction can become sufficiently strong to cause the significant low-frequency shift generally associated with hypercoordination in most nuclei. Intermolecular coordination to GeCl is believed to be responsible for the low-frequency shifts in Ge resonances and the associated changes in peak widths in mixtures with bases such as tributylphosphine oxide (TBPO) and triethylphosphine oxide (TEPO). Adduct formation with these bases is confirmed by broad P resonances that are resolved into five peaks at -40°C. The exchange-broadened resonances due to the 1:1 and 1:2 TEPO adducts are also observed at -40°C in the Ge spectrum. Thus, relatively strong bonding to the germanium in GeCl results in both low-frequency shifts and broadening of the resonance. The broad Ge resonances that occur in some compounds may be in part due to exchange as well as quadrupolar relaxation. © 2008 American Chemical Society. 4 4 4 4 2 4 4 4 4 73 73 73 31 73 73