Contrast in magnetic resonance imaging (MRI) is largely determined by differences in the relaxation times of protons in tissues. Therefore, contrast agents (CAs) for this diagnostic methodology have mainly been sought among the coordination compounds of metal ions with several unpaired electrons,
[SbO 3 FE]) and secondary building units (Sb 2 P, [14] Sb 2 P 2 , [9, 11±14] Sb 4 P 2 , [10, 14] Sb 3 P 3 , [14] and Sb 5 P 3 [14] rings), as well as the new Sb 6 P 2 and Sb 8 P 4 rings of the title compound. We have recently discovered additional molecular, chain, layered, and three-dimensional materials belonging to this large family. In addition to their novel architectures, Sb III -based materials, unlike closed-shell zeolites and AlPO 4 s, may have redox behavior or other interesting properties associated with their lone pairs of electrons.
Experimental Section
Hydrofluoric acid (49 wt %, Fisher) was added to antimony(iii) oxide (Aldrich), and the mixture was stirred to give a clear solution. Phosphoric acid (85 wt %, Fisher), en (Aldrich), eg (Fisher), and water, were added with stirring to give a mixture with composition 1 Sb:0.6 P:3.1 F:1.0 en: 11 H 2 O:37 eg. This was sealed in a PTFE-lined stainless steel autoclave and heated at 135 8C under autogeneous pressure for 5 d. The crystalline product was filtered, washed with ethanol, and dried at 90 8C in air. A single crystal (0.08 Â 0.04 Â 0.03 mm) was mounted on a glass fiber, and room temperature X-ray diffraction data were collected with a Siemens SMART CCD diffractometer equipped with a normal focus 2.4-kW sealed X-ray tube (Mo Ka radiation, l 0.71073 ) operating at 45 kV and 35 mA. About 1.3 hemispheres of intensity data were collected in 1321 frames with w scans (width 0.308, exposure time 10 s per frame). A total of 8328 reflections were collected in the range 2.8 2 q 46.68 and merged to give 2648 unique reflections. Unit cell parameters were determined by a leastsquares fit of 1724 reflections: monoclinic, space group P2 1 /c (no. 14), a 14.8222( ), b 13.7657(13), c 9.3022( ) , b 105.341(2)8, V 1830.4(3) 3 , Z 2, M 935.09, 1 calcd 3.393. Absorption correction was performed with the program SADABS. Positions of Sb and P atoms were determined by direct methods with SHELXS-97. Other non-hydrogen atoms were located in subsequent difference Fourier maps. Bond-valence parameters unambiguously distinguished bridging atoms. The final structure model was established by full-matrix least-squares refinement against j F j 2 with SHELXTL-PLUS. The hydrogen atoms were placed in calculated positions and held in the riding model. The final reliability factors obtained in the fitting of 265 parameters with 1809 independent reflections with I b 2.0 s(I) were R 1 (F) 0.0387, wR(F 2 ) 0.0843, S 0.985. The final difference Fourier map had maximum and minimum peaks of 0.936 and À 1.325 e À3 .