ABSTRACT
Complexes of Sm(III), Eu(III), and Yb(III) with a new polydentate ether ligand with amide arms were synthesized. Solid state X-ray structures of the complexes reveal all three complexes crystallize in monoclinic unit cells. The mononuclear complexes have nine coordinate tricapped trigonal prismatic geometries with coordination of all four amide carbonyl oxygen and all three of the backbone ether oxygen atoms. The molecules possess a pseudo C(2) symmetry axis. The complexes were characterized by solution and solid state emission spectroscopy and IR spectroscopy. Solution state behavior of the complexes was further explored using NMR. The (1)H NMR spectra show 16 peaks suggesting the complexes are slow in exchanging on the NMR time scale and that the C(2) symmetry axis is maintained. The NMR spectra were assigned using (1)H, (13)C, COSY, and HMQC experiments. The Eu(III) complex was tested for the recently explored Magnetic Resonance Imaging phenomenon called paramagnetic chemical exchange saturation transfer (PARACEST). At physiological pH and temperature two CEST peaks were observed that caused a decrease in the bulk water molecule signal intensity of 10 and 16%.
ABSTRACT
The title compound, [Fe(C(5)H(5))(C(9)H(5))], crystallizes in a form of a π-π-stacked assembly formed as a result of strong inter-molecular π-π inter-actions between (a) the triple bonds of two neighboring butadiyne substituents overlapping in a 'head-to-tail' fashion [characterized by Câ¯C short contacts of 3.622â (5), 3.567â (6) and 3.556â (6)â Å] and (b) the triple bonds of the butadiyne substituent and substituted cyclo-pendadiene ring of neighboring mol-ecules [Câ¯C = 3.474â (5) and 3.492â (6)â Å]. The linear butadiyne substituent has alternating C-C triple and single bonds, while the unsubstituted cyclo-penta-diene ring is slightly positionally disordered (although the structure reported here was solved as non-disordered) and retains a close to eclipsed conformation.
