ring of 1 (mean values 207.3(7) and 192.5(7) pm), which, however, can only be referred to for comparison with care because of the different orientation (apical and equatorial in 1, apical in 3a). The formation of unsymmetrical Sb-0 -S b bridges in 3a can be attributed to the positive partial charge of the outer antimony atoms. This elicits a stronger interaction between metal atom and the lone pair of the bridge oxygen atom and a strengthening of the p-0-Sb bond.Experimental 3: A subpension of 1 (1.107 g, 1.5 mmol) 12, 41 and 2a (0.496 g, 2 mmol) or 2b (0.586 g. 2 mmol) in acetone (15 mL) was prepared at room temperature. After a short time a clear yellow solution formed, which, after addition of 10 m L of 2.2-dimethoxypropane. was stirred overnight and finally evaporated down under vacuum to about 10 mL. The precipitated microcrystalline, y e l l o~ powder was filtered off and washed with a small amount of ether. M p.: 3a 204-206°C (decomp.): 3b 202-206°C (decomp.): yield 3a 30%; 3b 3 Z"' 0.