Nuclear magnetic resonance (NMR) spectroscopy of paramagnetic molecules provides detailed information about their molecular and electron-spin structure. The paramagnetic NMR spectrum is a very rich source of information about the hyperfine interaction between the atomic nuclei and the unpaired electron density. The Fermi-contact contribution to ligand hyperfine NMR shifts is particularly informative about the nature of the metal–ligand bonding and the structural arrangements of the ligands coordinated to the metal center. In this account, we provide a detailed experimental and theoretical NMR study of compounds of Cr­(III) and Cu­(II) coordinated with substituted acetylacetonate (acac) ligands in the solid state. For the first time, we report the experimental observation of extremely paramagnetically deshielded 13C NMR resonances for these compounds in the range of 900–1200 ppm. We demonstrate an excellent agreement between the experimental NMR shifts and those calculated using relativistic density-functional theory. Crystal packing is shown to significantly influence the NMR shifts in the solid state, as demonstrated by theoretical calculations of various supramolecular clusters. The resonances are assigned to individual atoms in octahedral Cr­(acac)3 and square-planar Cu­(acac)2 compounds and interpreted by different electron configurations and magnetizations at the central metal atoms resulting in different spin delocalizations and polarizations of the ligand atoms. Further, effects of substituents on the 13C NMR resonance of the ipso carbon atom reaching almost 700 ppm for Cr­(acac)3 compounds are interpreted based on the analysis of Fermi-contact hyperfine contributions.

Several coordination polymers of silver(i)-pentacyanocyclopentadienide (PCC) were studied by X-ray diffraction to examine the effects of different solvents on supramolecular isomerism of the PCC-ligand. While alcohols yield supramolecular isomers of [Ag(PCC)] without coordination of solvent molecules, less polar solvents show coordinate binding. The influence of solvent polarity can be observed by a gradual change in the lattice structure featuring distinct motifs.

Metathesis reactions of NaCl with the silver salts of substituted tetracyanocyclopentadienides [C 5 (CN) 4 X] À (X = H, CN, NO 2 , NH 2 ) gives the corresponding sodium salts 1-4. While 1-3 give polymeric networks, held together by Pi-stacking as well as multiply bridging polydentate cyanocyclopentadienides and in part hydrogen bonda, the aminotetracyanocyclo-pentadienide 4 forms only a water-bridged dinuclear complexes, which are connected only by an intensive hydrogen bond network. Quite surprisingly, only the NO 2 -substituent in 3 coordinates to Na + besides the cyano groups, while the NH 2 group in 4 is only involved in hydrogen bonds.