STRUCTURES OF MO2(CH3)4(PR3)4 MOLECULES - CONSTANCY OF COVALENT RADIUS OF MOLYBDENUM IN THESE AND OTHER MO2X4(PR3)4 MOLECULES

The crystal and molecular structures of authentic, pure samples of Mo2Cl3(CH2C6H5)(PMe3)4 (1), Mo2(CH3)4(PMe3)4 (2), and Mo2(CH3)4(PMe2Ph)4 (3) are reported. Special care was exercised in the preparation of 2 and 3 to exclude chloride and thus obviate the presence of chloride-containing contaminants. A previously reported structure for what was thought to be 2 is thus shown to be invalid owing to serious contamination by Cl−-containing impurities. The Mo-C distances in 1 and 2 are then compared to those in other Mo2X4(PR3)4 compounds, and it is shown that the molybdenum atom in such compounds displays an essentially constant covalent radius of 1.40 ± 0.02 Å. Crystal data for 1–3 are as follows. 1: space group P21/c with a = 14.319 (5) Å, b= 10.612 (1) Å, c = 21.004 (5) Å, β = 106.62 (6)°, V = 3058 (4) Å3, and Z = 4. 2: space group C2/c with a = 18.464 (4) Å, b = 9.453 (2) Å, c = 17.477 (4) Å, β = 116.33 (1)°, V = 2734 (2) Å3, and Z = 4. 3: space group P2/c with a = 18.478 (4) Å, b = 11.820 (2) Å, c = 18.567 (8) Å,β= 109.89 (2)°, V= 3813 (4) Å3, and Z = 4. For 1, the Mo-Mo, Mo-C, average Mo-Cl, and Mo-P distances are 2.1382 (3), 2.248 (3), 2.431 [2], and 2.56 [I] Å. The average Mo-Mo, Mo-C, and Mo-P distances in 2 and 3, respectively, are 2.1489 (4) and 2.164 [1] Å, 2.244 [4] and 2.242 [8] Å, and 2.504 [1] and 2.534 [2] Å. © 1990, American Chemical Society. All rights reserved.