Solid-State NMR Correlation Experiments and Distance Measurements in Paramagnetic Metalorganics Exemplified by Cu-Cyclam

We show how to record and analyze solid-state NMR spectra of organic paramagnetic complexes with moderate hyperfine interactions using the Cu-cyclam complex as an example. Assignment of the 13C signals was performed with the help of density functional theory (DFT) calculations. An initial assignment of the 1H signals was done by means of 1H-13C correlation spectra. The possibility of recording a dipolar HSQC spectrum with the advantage of direct 1H acquisition is discussed. Owing to the paramagnetic shifting the resolution of such paramagnetic 1H spectra is generally better than for diamagnetic solid samples, and we exploit this advantage by recording 1H-1H correlation spectra with a simple and short pulse sequence. This experiment, along with a Karplus relation, allowed for the completion of the 1H signal assignment. On the basis of these data, we measured the distances of the carbon atoms to the copper center in Cu-cyclam by means of 13C R2 relaxation experiments combined with the electronic relaxation determined by EPR.