Electron-diffraction study of the molecular structure of tetramethyldiphosphine

Abstract

The molecular structure of tetramethyldiphosphine in the gas phase has been determined by electron diffraction. The study required a gas-nozzle temperature of 170°C, obtained by using hot compressed air. The molecule can be described by seven structural parameters from which all the 52 different interatomic distances can be calculated. All 52 distances were included in the fullmatrix least-squares refinements which were performed. The final values of the seven independent parameters are C-H = 1.109f0.009 A, C-P = 1.853f0.003 A, P-P = 2.192f0.009 A, LCPC = 99.6f1.0", LPCH = 108.8&2.5", LCPP = 101.1f0.7°, and$, thedihedralangleexpressing the relative orientation of the dimethylphosphino groups, is 164&23", measured from the cis configuration. The parameters of the dimethylphosphino groups are very similar to the corresponding values for the methyl phosphines. The P-P bond length is at the low end of a range of literature values for this bond. The apparent deviation of 16" from the trans configuration is possibly due to a shrinkage effect involving a low frequency torsional oscillation about the P-P bond.The lengths of bonds between phosphorus atoms have been of interest since the first X-ray crystallographic studies of black ph0sphorus.l However, in most of the compounds so far studied, the phosphorus atoms are linked together in a ring system, or in some type of bridged system, in which there must be considerable angular strain. In the few acyclic systems studied, the phosphorus atoms have more frequently possessed covalencies greater than three, achieved by the sharing of the TABLE 1.-A COMPARISON OF SOME P-P BONDS bond compound P-P (A) environment P (black) 2.224 f0.002 2.244 f0.002 P4 vapour 2.21 f0.02 P4 tetrahedron P (Hittorf's) 2.219 f0.004 p4s7 2.350 fO.O1O cage p4s3 2.230 fO.O1O cage P2Et4S2 2.220 fO.O1O acyclic P2Me4*2BH3 2.204 f0.005 acyclic P2Me4 2.192 f0.009 acyclic (OC)3Ni(PPh2)2Ni(C0)3 2.277 f0.004 acyclic (OC)4Fe(PMe2)2Fe(CO)4 2.23 1 f0.007 acyclic (PCF314 2.213 f0.005 cyclic (PPh)S 2.217 f0.006 cyclic (PPh), 2.237 f0.005 cyclic ref.

Molecular structures of tetrafluorodiphosphine and tetrakis(trifluoromethyl)diphosphine by gas-phase electron diffraction

“…Infrared-Raman vibrational studies on P2(CH3)4 indicate that the structure for the solid phase is trans but that the liquid Hodges, Su, and Bartell is a trans-gauche mixture.43 A gas-phase electron diffraction study of the molecule was interpreted in terms of a "skewed" trans conformation.44 On the basis of vibrational studies, it was concluded that conformational differences also exist between the liquid,45,46 solid,47 and gas48 phases of IPzM4. For example, the P-P bond lengths in P2 (CH3) 44 Tables of other P--P bond lengths and conformations in various diphosphines and hydrazines are included in the supplementa1 y material and in a doctoral dissertation.14 Of the various diphosphines studied to date, F2PPH213 is perhaps the best candidate for K delocalization across the P-P bond. Some rules of thumb for predicting conformation stabilities are discussed by Durig,et ~1 .…”

The nature of the S–S bonds in different compounds. V. The crystal structure of ZnS2O4.pyridine

“…It is further interesting to note that the isoelectronic radicals PF2, SO 2 and C102, in which the central atoms (P, S and C1) are consecutive atoms in the periodic table, have in common that they do not unite to molecules with strong central bonds. Two PF 2 radicals form a (staggered) molecule P2F4 with P-P [2.281 (6) ,~; Hodges, Su & Bartell, 1975] ca 0.1 /~ longer than those in P2(CF3) 4 [2.182 (16) /~; Hodges et al, 1975] and P2(CH3)4 [2.192 (9) ,/k;McAdam, Beagley & Hewitt, 1970]. As we have seen above, in the (eclipsed) $20~-ion the bond between the two SO2 units is extraordinarily long (2.39 /i,).…”

P–P bond cleavage; energetics and structural changes in tetramethyldiphosphine and tetrasilyldiphosphine from ab initio MO calculations

“…2 This may be a consequence of description of the gas-phase mixture of two conformers with considerably different P-P-C angles by a single-conformer model in the original electron diffraction study. 6 The theoretical calculations predict one of the angles to be up to 7Њ larger in the gauche conformer than the corresponding angle in the anti conformer. Unexpectedly, the performance of the B3LYP method worsened with the increase of the basis set, with the closest agreement with the experimental data achieved in the calculations applying the smallest 3-21G* basis set.…”

“…5 A later gas-phase electron diffraction study at 170 ЊC found the experimental data to be consistent with a single distorted anti conformation of the molecule. 6 The observed 16Њ deviation from the anti form was attributed to the large-amplitude torsional motion about the central P-P bond. A study of the gas-phase IR spectrum resulted in the conclusion that the gauche conformer predominates over anti in the ratio 3 : 2.…”