Nitrogen-14 Nuclear Quadrupole Resonance Spectra of Metal Anthranilate Complexes

The ¹⁴N nuclear quadrupole resonance (NQR) spectra at 77 K have been obtained for solid divalent metal ion complexes ML₂ of the anthranilate anion, L = CO₂C₆H₄NH₂⁻, where M = Zn, Cd, Hg, Pd(II), Ca, Mg, Ba, Sr, Pb, and Sn(II), and for Hg(CO₂C₆H₄NH₂)Cl. The ¹⁴N NQR data permit the evaluation of the quadrupole coupling constant e²q_zzQ/h and asymmetry parameter η, the two independent components of the electric field gradient tensor at nitrogen, in all the complexes. The NQR data can be interpreted in terms of a coordinated nitrogen model, on the basis of a modified Townes-Dailey analysis, to yield an estimate of the extent of withdrawal of electronic charge from nitrogen in the metal ion complexes, as compared with that of the protonated amino group as reference compound. The results show that electron withdrawal varies in the order Hg > Pd >> Sn > Pb > Cd ≈ Zn > Ca ≈ Mg > Sr > Ba. The results for the Hg(C-O₂C₆H₄NH₂)₂ complex are anomalous, suggesting that the electronic environment about nitrogen is different in this complex than that in the others.