Carbon dioxide fixation in its intact form is achieved from "bifunctional" complexes containing in their structure a nucleophilic cobalt(I) and an alkali cation: Co(R-salen)M [R-salen = substituted salen ligand; salen = ¿ , ''-ethylenebis(salicylideneaminato); M = Li, Na, K, Cs], The fixation of C02 by such systems displays different degrees of reversibility depending on the reaction solvent and the nature of the alkali cation. The X-ray analysis carried out on [Co(n-Pr-salen)K-(CO)2(THF)] shows carbon dioxide anchored to the cobalt through a Co-C bond, while the oxygens interact with the alkali cation, in a polymeric structure. IR spectra are diagnostic for the presence of C02 bonded as a bent molecule in a reduced form displaying three strong bands in the following ranges: 1700-1650, 1300-1250, and 1250-1200 cm"1. The binding of C02 is partially prevented in the presence of a crown ether, which can complex the alkali cation. The reaction of [Co(salen)Na(CG2)] and [Co(salen)Na(THF)J with dicyclohexano-18-crown-6 (DCHC) gave a complex, [Co(salen)Na]2(DCHC), whose structure shows the presence of the intact bifunctional unit where, however, all the coordination sites around the alkali cation are filled by the oxygens from salen and DCHC and are not further available for binding the oxygen atoms of the C02 molecule. Crystallographic details for [Co(zt-Pr-salen)K(C02)(THF)]", form A, are as follows: space group C2/c (monoclinic); a = 17.805 (4) A, b = 21.251 (5) A, c = 16.192 (3) A; ß = 112.50 (3)°; Z = 8; Z)calcd = 1.325 g cm"3 4. The final R factor was 0.085 for 1096 observed reflections. Crystallographic details for [Co(n-Pr-salen)K(C02)(THF)]", form B, are as follows: space group C2/c (monoclinic); a = 22.921 (4) A, b = 16.388 (3) A, c = 18.800 (3) A; ß = 121.74 (3)°; Z = 8; £>calcd = 1.248 g cm'3. The final R factor was 0.090 for 2287 observed reflections. Crystallographic details for [Co(salen)Na]2(DCHC) are as follows: space group P2¡/a (monoclinic); a = 14.547 (3) A, b = 16.597 (4) A, c = 14.063 (3) A; ß = 116.80 (3)°; Z = 2; Z)calcd = 1.249 g cm"3. The final R factor was 0.076 for 682 observed reflections.
Ternary compounds formed between M (Mg", Ca", Sr", Mn", Co", Cu", or Zn"), adenosine 5'-trip hosp ha te [adenosine 5'trip hosp hate (4 -) = atp] , and bis (2pyridyl ) amine (bi pyam) have been prepared. The solid compounds are crystalline and have a stoicheiometry described by the formula M (Hatp) ( Hbipyam).nH20 (n = 2-9). X-Ray powder diffraction patterns are similar. Potentiometric titrations in aqueous solution show the presence of t w o ionizable protons. Visible spectra suggest an octahedral co-ordination geometry. 1.r. spectra indicated essentially the same type of metal-ligand interactions in all the complexes and show that Hatp3-co-ordinates to the metal through the oxygen atoms of the a, PI and y phosphate groups. The ternary compounds where M = Mg" (I) or Ca" (2) have been studied by single-crystal X-ray diffraction techniques and their molecular structures determined. The two species are isostructural and can be formulated as1) and [Ca(H,O),] [Hbipyam]2[Ca(Hatp)2]-9H,0 (2). Both (1) and (2) crystallise in space group C222, (Z = 4), with a = 22.734(3), b = 10.233(3), c = 30.997(4) A for (1) and a = 22.965(3), b = 10.1 54(3), c = 32.390(4) A for (2). X-Ray diffraction data were collected on a Philips automatic diffractometer and the structures solved by direct methods using the SIR (Semi-invariant Representation) package and refined b y full-matrix least squares to final R values of 0.1 11 and 0.1 24(1 088 and 1 008 independent observed reflections) for (1) and (2) respectively. In the [ M ( H a t ~) ~l ~units the metal ions lie on a two-fold axis with an octahedral co-ordination geometry completed by the oxygen atoms of the a, PI and y phosphate groups of t w o symmetry-related Hatp3-molecules. The co-ordination polyhedron of (1) is nearly regular but in (2) it is significantly distorted. The phosphate chains have a folded configuration in both ( 1) and (2). In both complexes there are no bonding interactions between the metal ions and the adenine base. The metal atoms of the [M(H20),l2+ cations are also located on two-fold axes while the six co-ordinated water molecules form hydrogen bonds with the phosphate chains. The Hbipyam+ molecules d o not co-ordinate to the metal ions and are disordered around two-fold axes. Strong stacking interactions exist between H bipyam+ and purine rings.
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