Conformational analysis of coordination compounds. XIII. Complexes of 2-methylpentane-2,4-diamine

Abstract

The crystal structures of tetraammine{(�)-2-methylpentane-2,4-diamine} cobalt(III) tetrachlorozincate chloride and 2,2'-bipyridine{(�)-2-methylpentane-2,4-diamine)platinum(II) nitrate semihydrate have been determined by X-ray structure analysis. The former crystals are orthorhombic with the space group P212121, with a 12.49, b 20.16 and c 7.68 �. The latter crystals are also orthorhombic but with the space group Pbca with a 14.96, b 28.69 and c 19.45 �. Both structures have been refined by least-squares methods to weighted R values of 0.034 (1407 reflections) and 0.055 (2301 reflections), respectively. The six-membered diamine chelate ring has a flattened chair conformation in the cobalt complex, and an unsymmetric boat conformation in the platinum complex. Strain-energy-minimization calculations show these structures correspond to energy minima and the calculated geometrical parameters are in good agreement with those observed for the chelate ring. Proton n.m.r. spectra are consistent with the chair conformation being almost exclusively populated in the ammine complex and in the tetracyanocobaltate(III) complex in aqueous solution, but the and 13C n.m.r. spectra of the platinum(II) complex show that, although the chair conformer predominates, the boat conformation is significantly populated in solution.

A molecular mechanics study of dioxygen binding by lacunar cobalt dioxygen carriers

“…The conformations of the bridging group have been examined in detail, both by analyzing the results of the X-ray crystal structure determinations6 and through the present MM calculations. When the torsional angles of the C-C bonds in the bridging group are discussed, the following conformations have been labeled as indicated: [16]cyclidene complexes: top, edge views of Z-shaped (left) and Ushaped complexes (right) at extreme M-N distances; bottom, graph of energy versus M-N.…”

“…The following discussion begins with consideration of the geometries of the unbridged cyclidenes (structure I), establishing the causes of the saddle shape of the cyclidenes and ring-size/ metal-donor distance relationships. It then proceeds to treat polymethylene-bridged [16]cyclidenes (structures II and III) in two groups, respectively, those with short polymethylene chains (from three to five carbons) and those having chains of intermediate length (six to eight carbons). contain clefts,5 and this greatly facilitates the synthesis of species containing cavities.4 The 14-, 15-, and 16-membered-ring cyclidenes (structure I) differ in the number of methylene groups in their saturated chelate rings.…”

“…Figure4. M-N bond distance dependence of conformational energy for[16]cyclidene complexes: top, edge views of Z-shaped (left) and Ushaped complexes (right) at extreme M-N distances; bottom, graph of energy versus M-N.…”

Probabilistic model-based methodology for the conformational study of cyclic systems: application to copper complexes double-bridged by phosphate and related ligands

“…The points-on-a-sphere approach (Hambley et al, 1981) was used, which implies that the O-Cu-O terms are replaced by OÁ Á ÁO van der Waals terms. The torsion term O-Cu-O-P was omitted following a general practice in molecular mechanics calculations (Comba, 2001).…”

Aplicação de mecânica molecular em química inorgânica

“…Este campo de força apresenta as seguintes contribuições: deformação do ângulo da ligação (Eθ), deformação do comprimento da ligação (E l ), interações não-ligadas (E nl ), deformação do ângulo de torção (E ω ) e deformação fora do plano (E dfp ), não sendo incluídas as interações eletrostáticas e ligações hidrogênio. A maioria dos parâmetros foi retirada dos trabalhos de Allinger 6,7 e Hambley et alli 49 ou desenvolvidos por Comba e Bernhardt 48 e incorporados ao programa MOMEC 87 50 . A Tabela 3 compara os comprimentos de ligação metal-Nitrogênio calculado pelo MOMEC 87 com os valores observados experimentalmente.…”