X-ray structures of trans-dichloro(4-methylpyrimidine) (eta(1)-phenyl)bis(pyridine) rhodium(III) hydrate and trans-dichloro(phenyl)tris(triphenylstibine)rhodium(III) ethylacetate solvate. Molecular orbital analysis of trans-dichloro (4-methylpyrimidine)(eta(1)-phenyl)bis(pyridine)rhodium(III)

The crystal and molecular structure of trans-dichloro(4-methylpyrimidine)(e ta(1)-phenyl)cis-bis(pyridine)rhodium(III) water solvate, 1 x 0.17H(2)O, an d trans-dichloro(eta(1)-phenyl)tris(triphenylstibine)rhodium(III) ethylacet ate solvate, 2 x CH3CO2CH2CH3 have been studied via X-ray diffraction from a single crystal at room temperature. The final refinement converged to R1 conventional index of 0.0350 and 0.0361 for the structural analysis of Ix 0 .17H(2)O [space group R(-3)] and 2 x CH3CO2CH2CH3 [P(-1)], respectively. Th e 4-methylpyrimidine ligand (Pym) is only weakly bound to Rh in i, as shown by the long Rh-N distance (2.251(4)Angstrom), compared to the Rh-N(pyridin e) lengths [average, 2.066(4)]. N-C bond distances involving the N donor av erage 1.329(6) and 1.345(6) for Pym and pyridine (Py) ligands, respectively . The C-N-C bond angle on the donor is 114.1(5)degrees for Pym and average 117.4(4)degrees for Py. The structure of the complex molecule of 2 x CH3CO2CH2CH3 has some differen ces when compared to that of the corresponding acetone solvate previously s tudied in this laboratory (Cini, R., Giorgi, G. and Pasquini, L., Inorg. Ch im. Acta, 1992, 196, 7). The two structures differ mainly by the orientatio n of the phenyl donor with respect to the Cl-Rh-Cl axis (which is more ecli psed for the ethylacetate solvate) and by the conformation of the SbPh3 lig ands. Density functional calculations at the B3LYP/LANL2DZ level with full geomet ry optimization were carried out on the free Pym molecule and on some Sc(N- 1-Pym)(3+) and Sc(N-2-Pym)(3+) model molecules. The effect of metal coordin ation consists: mainly in enlarging the (Sc)N-C bond distances up to 0.150 Angstrom, whereas the C-N(Sc)-C bond angle decreases of 1.9 degrees. Signif icant changes on other bond lengths and angles relevant to ring atoms of Py m occur upon metal coordination to the nitrogen atom. The metal coordinatio n to N(2) is less favorable than to N(1) of 7.5 kcal for 1:1 species of Sc3 +. Extended Huckel calculations showed that HOMO consists mostly of metal-d or bitals with some character of chloride and phenyl and pyrimidine ligands, w hereas LUMO is composed of phenyl, pyridine and pyrimidine orbitals. The me thod well reproduces the Rh-N and Rh-C bonding distances and gives Rh-C dis sociation energy 2.38 and 5.48 times that for the Rh-N(Py) and Rh-N(Pym) bo nds, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.