No abstract

No abstract

Improved syntheses of the mixed oxathia crown ligands 1-oxa-4,7-dithiacyclononane (9S2O) and 1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane (18S4O2) are presented. The single-crystal X-ray structure of 18S4O2 has also been obtained. Crystal data for 18S4O2:  C12H24O2S4; triclinic, space group P1̄; a = 7.188(3) Å, b = 5.240(1) Å, c = 10.743(3) Å; α = 99.30(2)°, β = 98.09(3)°, γ = 92.19(3)°; V = 394.57 Å3; Z = 1, R = 0.067, R w = 0.103 for 2419 reflections. The ligand structure shows the two oxygen atoms point into the macrocycle cavity while the four sulfur atoms are oriented in an exodentate fashion. Therefore, this ligand is poorly preorganized for hexadentate complexation and will have to undergo substantial reorganization to be able to complex in a multidentate fashion using its sulfur atoms. The syntheses of homoleptic complexes for both of these macrocycles with the platinum group metal ions, Pd(II) and Pt(II), are also described. The single-crystal X-ray structures for three of the complexes have been obtained, and all show that only the sulfur atoms are bound to the metal center. Crystal data for [Pt(9S2O)2](PF6)2·2CH3NO2:  C14H30N2O6F12P2S4Pt; triclinic, space group P1̄; a = 9.996(5) Å, b = 11.019(3) Å, c = 8.253(2) Å; α = 92.79(2)°, β = 110.18(2)°, γ = 64.04(2)°; V = 761.5(5) Å3 ; Z = 1; R = 0.0365, R w = 0.0543 for 2680 reflections. Crystal data for [Pt(18S4O2)](PF6)2:  C14H24O2F12P2S4Pt; monoclinic, space group P21/n; a = 11.110(3) Å, b = 9.244(1) Å, c = 12.642(2) Å; β = 111.48(1)°; V = 1208.2(3) Å3; Z = 2; R = 0.0343, R w = 0.0428 for 1696 reflections. Crystal data for [Pd(9S2O)2](PF6)2·2CH3CN:  C14H30N2O6F12P2S4Pd; monoclinic, space group C2/c; a = 12.535(2) Å, b = 19.463(2) Å, c = 12.127(2) Å; β = 95.68(1)°, V = 2944.0(7) Å3; Z = 4; R = 0.0493, R w = 0.0651 for 1959 reflections. The oxygen atoms in all of the structures are oriented exodentate to the metal center and lie at too great of a distance (3.443(5), 3.730(5), or 3.379(5) Å, respectively) to exhibit the long-distance metal interactions exhibited in related crown thioether complexes. The effects of the lack of axial metal−oxygen interactions are seen in the absence of visible d−d electronic transitions, and the lack of any oxidation electrochemistry in the complexes. Additionally for the Pt(II) complexes, 195Pt NMR chemical shifts are observed near −4650 ppm which are consistent with a square planar S4 coordination environment around the platinum. The complexation behavior of these ligands toward Pt(II) and Pd(II) contrasts that of analogous crown thioethers ligands and mixed azathia macrocycles which show significant metal−axial donor atom interactions. The general ligand complexation characteristics of oxathia crowns are dominated by metal−ligand electronic interactions as opposed to ligand conformational factors.