posted on 2003-05-15, 00:00authored byDaniel L. Reger, Radu F. Semeniuc, Ioan Silaghi-Dumitrescu, Mark D. Smith
The reactions between silver tetrafluoroborate and the ligands 1,2,4,5-C6H2[CH2OCH2C(pz)3]4 (L1, pz = pyrazolyl
ring), o-C6H4[CH2OCH2C(pz)3]2 (L2), and m-C6H4[CH2OCH2C(pz)3]2 (L3) yield coordination polymers of the formula
{C6H6-n[CH2OCH2C(pz)3]n(AgBF4)m}∞ (n = 4, m = 2, 1; n = 2, ortho substitution, m = 1, 2; meta substitution,
m = 2, 3). In the solid state, L2 molecules dimerize by a pair of C−H···π interactions, forming an arrangement
that resembles the tetratopic ligand L1. In the solid-state structure of 1, each silver atom is κ2-bonded to two
tris(pyrazolyl)methane units from different ligands with the overall structure a polymer made up from 32-atom
macrocyclic rings formed by bonding tris(pyrazolyl)methane groups from nonadjacent positions on the central arene
rings to the same two silver atoms. In 2, each silver is bonded to two tris(pyrazolyl)methane units in the same
κ2−κ2 fashion as with 1, forming a polymer chain. The chains are organized into dimeric units by strong face-to-face π−π stacking between the central arene rings making bitopic L2 act as half of tetratopic L1. The chains in
both structures are organized by weak C−H···F hydrogen bonds and π−π stacking interactions into very similar
3D supramolecular architectures. The structure of 3 contains three types of silvers with the overall 3D supramolecular
sinusoidal structure comprised of 32-atom macrocycles. Infrared studies confirm the importance of the noncovalent
interactions. Calculations at the DFT (B3LYP/6-31G*) level of theory have been carried out on L2 and also support
C−H···π interactions. Electrospray mass spectral data collected from acetone or acetonitrile show the presence of
aggregated species such as [(L)Ag2(BF4)]+ and [(L)Ag2]2+, despite the fact that 1H NMR spectra of all compounds
show that acetonitrile completely displaces the ligand whereas acetone does not.