Journal ArticleSummary The molecular conformations of two square   pyramidal species, one violet the other orange, both   composition (Ph3P)2[(CF3)2C2S2]Ru(CO) are described

Bernal, I.

Miller, Joel Steven

English

The University of Utah: J. Willard Marriott Digital Library

Isomeric Conformations in a Pentaco-ordinated Ruthenium Compound; Crystal and Molecular Structures of the. Orange and Violet Isomers of (Ph3P)1[(CF3)lC1S1]Ru(CO) By 1. BERNAL,. A. CLEARFIELD, E. F. EpSTEIN, and J. S. RICCI, JUN. (Department of Chemistry, Brookhaven National Laboratory, Upton, Long I sland, New York 11973) and A. BALCH and J. S. MILLER (Department of Chemistry, University of California, Davis , California 95616) Summary The molecular conformations of two square pyramidal species, one violet the other orange, both of composition (PhaPM(CFa)2C2S2JRu(CO) are described. THEORETICAL studies of preferential isomeric conformation in the case of pentaco-ordination favour the trigonal bipyramid,I,2 although the predicted energy difference is small (about 3 to 5 kcal mol-I). A recent review3 states that ... . . pentaco-ordinate substances are, in general, remarkably free of isomeric conformations, ... ". We report the crystal and molecular structures of two Ru complexes of the same composition which co-exist in solution and which can be isolated in pure crystalline form. In both cases the co-ordination around the central atom is square pyramidal and the data available thus far4 show no evidence of a trigonal bipyramidal species. TABLE. Bond angles (0) in the co-ordination sphere P(1)-Ru-P(2) P(l)-Ru-S(l) P(1)-Ru-S(2) P(l)-Ru-C .. P(2)-Ru-S(1) P(2)-Ru-S(2) P(2)-Ru-C " S(1)-Ru-S(2) S(l)-Ru_C S(2)-Ru-C Ru-C-O Violet Orange 105·2(1) 100·8(1) 162·3(1) 85·8(1) 88·3(1) 168·7(1) 89·6(3) 89·3(2) 92'5(1) 150·6(1) 111·8(1) 84·0(1) 94·3(3) 92·2(2) 86·5(3) 85· 1(1) 87·5(3) 116'7(2) 153'2(3) 100·8(2) 171·8(9) 173·8(6) Crystal data: Violet form, a = 22'394(8), b = 19'107(6), c = 17'480(5) A; Dm = 1'56(2), Dc = 1·56 gcm-a, for Z= 8, space group Pbca. Data were collected with a diffracto-meter using Mo-Ko: radiation.· The discrepancy inde~, R(F), is 0·060. Orange form; a = 10'147(3), b = 10'081(4), c = 38·627(9) A, f1 = 102·27(W; Dm = 1'50(2), Dc = 1-49 gcm-a for Z = 4, space group P2dc. Diffractometer data were recorded with Cu-Ko: radiation, final R(F) is 0·047. Both sets of data were corrected for absorption and both structures were solved by the heavy-atom method and refined by standard least-squares techniques. Most of the important bond distances appear in the Figure and a selec-tion of bond angles is given in the Table. FIGURE. Distances characterizing the pentaco-ordinate arrange-ment of the ligands around the Ru species found in the orange (left) and the violet isomers (right). The standard deviations in the bond lengths are: Ru-P and Ru-S bonds 0·003 A; other bonds 0·010 A. The following comments summarize the results: solution studies' indicate that the orange form is the favoured isomer; the violet form can be obtained only under very specific conditions' and even then the orange isomer is present in the solution and as orange crystalline material. Only a single molecular species is found in each type of crystal. If there are any other species (i.e., trigonal bipyramidal) in solution their lifetimes must be very short and attempts to obtain other crystalline forms have, so far, failed. There are very small differences in the bonding parameters obtained for the orange and violet species; the small differences in the Ru-S, Ru-P and Ru-C distances could be due to changes in steric hindrance between the two phosphines. However, due to the conformational changes electronic effects could also contribute. This is being -1 J. Zemann, Z. anorg. Chem., 1963,324, 24l. • R. J. Gillespie, J. Chem. Soc., 1963,4672. 3 R. R. Holmes, Accounts Chem. Res., 1972, 5, 296. , J. Miller and A. Balch, Inorg. Chem., 1971, 10, 1410. 5 M. L. Good, personal communication. j.C.S. CHEM. COMM., 1973 studied by Mossbauer spectroscopy.5 If steric hindrance effects are of significant magnitude to be responsible for the changes, it is interesting to note that the most hindered (potentially) form is the orange, which apparently is also the preferred one. The height of the metal above the plane: of the basal ligands is essentially the same (0·34 vs. 0·35 A' for the orange and violet forms, respectively). The Ru-C-O angle is not significantly affected by exchanging from the axial (orange) to the equatorial (violet) position and the differences in bond lengths in this fragment are minor. This investigation was supported financially by the U. Atomic Energy Commission. (Received, 30th October 1972; Com. 1843.) 

Isomeric conformations in a pentaco-ordinated ruthenium compound: crystal and molecular structures of the orange and violet isomers of (Ph3P)2[(CF3)2C2S2]Ru(CO)

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Isomeric conformations in a pentaco-ordinated ruthenium compound: crystal and molecular structures of the orange and violet isomers of (Ph3P)2[(CF3)2C2S2]Ru(CO)

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