Orotate complexes of rhodium(I) and iridium(I): effect of coligand, counter ion, and solvent of crystallisation on association via complementary hydrogen bonding

Abstract

The new complexes [NEt3H][M(HL)(cod)] (M = Rh 1 or Ir 2; H3L = 2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid, orotic acid; cod = cycloocta-1,5-diene) have been prepared by the reaction between [M2Cl2(cod)2] and orotic acid in dichloromethane in the presence of Ag2O and NEt3. They crystallise as dichloromethane adducts 1·CH2Cl2 and 2·CH2Cl2 from dichloromethane–hexane solutions. These isomorphous structures contain doubly hydrogen-bonded dimers, with additional hydrogen bonding to NEt3H+ cations and bridging CH2Cl2 molecules to form tapes. The use of NBun4OH instead of NEt3 gave the related complex [NBun4][Rh(HL)(cod)] 1′ which has an innocent cation not capable of forming strong hydrogen bonds and in contrast to 1 exists as discrete doubly hydrogen-bonded dimers. Complex 1′ cocrystallises with 2,6-diaminopyridine (dap) via complementary triple hydrogen bonds to give [NBun4][Rh(HL)(cod)]·dap·CH2Cl2 3. Complex 3 exhibits an extended sheet structure of associated [2 + 2] units, with layers of NBun4 cations separating the sheets. These structural data together with those reported previously for platinum orotate complexes suggest that the steric requirements of the other ligands co-ordinated to the metal are important in influencing their hydrogen-bonding abilities. The solvent of crystallisation, the hydrogen-bonding propensity of the coligand and the nature of the counter ion also determine the type of association in the solid state.