The phenomenon of conglomerate crystallization. XV. Spontaneous resolution in coordination compounds. XIII. The crystallization behaviour and the crystal and molecular structure of Δ(λδ)- cis-Rh(en) 2(NO 2) 2]Cl

• Published in: Inorganica Chimica Acta Vol. 150; no. 1; pp. 75 - 80
• Main Authors: Bernal, Ivan, Cetrullo, James
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.1988
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(00)87627-6

The title compound, I, crystallizes in the monoclinic space group P2 1 with cell constants: a = 6.599(3), b = 11.121(2), c = 8.375(1) Å and β = 106.35(2)°; V = 589.74 Å 3 and D(calc; Z = 2) = 1.974 g cm −3. The compound is isomorphous and isostructural with its Co analogue. A total of 2982 data were collected over the range of 4°  20  70°; of these, 2537 (independent and with I ⩾ 3σ( I)) were used in the structural analysis. Data were corrected for absorption (μ = 16.6 cm −1) and the relative transmission coefficients ranged from 1.000 to 0.9504. Refinement was carried out for both enantiomeric configurations and the crystal used was found to contain cations with Δ(λδ) absolute configuration. The final R( F) and R w( F) residuals were, respectively 0.0220 and 0.0239 for (−−−; i.e.Δ(λδ)) and 0.0231 AND 0.0317 FOR (+++; i.e.Λ(δλ)). Thus, the former was selected as correct for our specimen. In the case of I, as well as in the Co derivative [ cis-Co(en) 2(NO 2) 2]Cl ( II), the conformation of one of the rings is opposite that expected for the lowest energy conformation, which in the current case should be Δ(λλ)). The RhN(NO) 2 distances are 2.020(2) and 2.010(2) Å, while the RhN(amine) distances, trans to the NO 2 ligands are 2.085(2) and 2.093(1) Å, values distinctly longer than the other two RhN distances (2.064(1) and 2.068(1) Å). The latter are the RhN distances to the terminalNH 2 ligands located trans to each other. Thus, we observe a trans effect, which is more pronounced in I than in II, and which is of comparable magnitude to that observed in the case of the trien derivative, [ cis-α-Rh(trien)(NO 2) 2]Cl( III). Parallel with an increase in metalN distances in going from [ cis-α-Co(trien)NO 2) 2]Cl·H 2) ( IV) to ( III) is an increase in the torsional angles of the outer rings (NCCN) of about 10°. Comparison of these parameters in I and II reveal that this change is not so marked for this pair since in I they are −54.9° and 52.8° while in II they are 50.2° and −48.1°; i.e. a change of only 4°. This important difference between trien and en derivatives is caused by the presence of the central five-membered ring, which for compounds III and IV remains largely unchanged, except for the metalN distances. The NO bond lengths are 1.244(3), 1.220)(2), 1.237(2) and 1.211(2) Å, which are similar to those found for the analogous Co isomer. The CN bond lengths are 1.492(3), 1.474(2), 1.486(2) and 1.475(2) Å, while the CC bonds are 1.509(3) and 1.524(3) Å. These values are also comparable with those obtained for the Co isomer and, in fact, the pattern of the bonds is nearly identical in both, including the common feature of having a longer CC bond for the en ring with the conformation opposite that expected. As was the case with the Co analogue, the Cl − anion is associated with the hydrogens of the secondary nitrogen ( trans to the −NO 2) ligands, the Cl…H7 distance being 2.18(3) Å and the <Cl…H7N2 = 163°.