J. Am. Chem. Soc., ASAP Article 10.1021/ja0566634 S0002-7863(05)06663-1
Web Release Date: February 22, 2006
Structure and Multinuclear Solid-State NMR of a Highly Birefringent Lead-Gold Cyanide Coordination Polymer
Michael J. Katz, Pedro M. Aguiar, Raymond J. Batchelor, Alexei A. Bokov, Zuo-Guang Ye,* Scott Kroeker,* and Daniel B. Leznoff*
The coordination polymer Pb(H2O)[Au(CN)2]2 (1) was synthesized by the reaction of KAu(CN)2 and Pb(NO3)2. The structure contains 1-D chains of lead(II)-OH2 linked via Au(CN)2- moieties, generating a 2-D slab; weak aurophilic interactions of 3.506(2) and 3.4885(5) Å occur within and between slabs. The geometry about each lead(II) is bicapped trigonal prismatic, having six N-bound cyanides at the prism vertices and waters at two of the faces. Dehydration at 175 C yields microcrystalline Pb[Au(CN)2]2 (2), which, along with 1, was examined by 13C, 15N, 1H, and 207Pb solid-state NMR methods. Two 15N resonances are assigned to the 2-bridging and hydrogen-bonding cyanides in 1. Upon dehydration, the 207Pb NMR spectrum becomes axially symmetric and yields a reduced shielding span, indicating higher site symmetry, while the 13C and 15N spectra reveal a single cyanide. Although no single-crystal X-ray structure of 2 could be obtained, a structure is proposed on the basis of the NMR and X-ray powder data, consisting of a lead(II) center in a distorted square-prismatic environment, with cyanides present at each corner. The birefringence of single crystals of 1 is found to be 7.0 × 10-2 at room temperature. This value is large compared to that of most optical materials and can be attributed to the anisotropy of the 2-D slabs of 1, with all CN bonds aligned in the same direction by the polarizable lead(II) center.