A New Tetragonal Crystalline Polymorph of Lithium Octa-<i>n</i>-Butoxy-Naphthalocyanine (LiNc-BuO) Radical: Structural, Magnetic and Oxygen-Sensing Properties
作者:Ramasamy P. Pandian、Nandyala P. Raju、Judith C. Gallucci、Patrick M. Woodward、Arthur J. Epstein、Periannan Kuppusamy
DOI:10.1021/cm101733h
日期:2010.12.14
The single-crystal structure, paramagnetic, and oxygen-sensing characteristics of a new tetragonal polymorph of lithium octa-n-butoxynaphthalocyanine, LiNc-BuO (T-g), is reported. The compound was synthesized as fine, diamond-shaped, neutral radical crystals by reacting octa-n-butoxynaphthalocyanine (Nc-BuO) with lithium metal in n-butanol. Single-crystal X-ray diffraction analysis revealed a saddle-shaped conformation of the molecule with a crystallographic 2-fold rotation axis in a tetragonal unit cell. This represents the first single-crystal, structurally characterized, lithium naphthalocyanine complex. Unlike the triclinic polymorph of LiNc-BuO (Pandian, et al. J. Mater. Chem. 2006, 16, 3609), the tetragonal (T-g) form of LiNc-BuO did not show the presence of large open channels in the crystalline packing. The magnetic susceptibility and EPR spectroscopic properties were in agreement with the X-ray crystal structure showing the existence of a high degree of spin exchange in the crystalline system. The effective magnetic moment calculated for the LiNc-BuO (T-g) was 1.56 mu B per formula unit, which was smaller than the expected value of 1.73 mu B for a spin system with S = 1/2. The crystals showed a single, sharp EPR spectrum with an unusually low line width of 20 +/- 5 mG under anoxic conditions. The EPR line width was linearly dependent on partial pressure of oxygen (pO(2)) in the range 0-760 mmHg, with a sensitivity of 4.54 +/- 0.50 mG/mmHg. The LiNc-BuO (T-g) crystals possess several desirable properties for use as a probe for EPR oximetry.