Regular octahedral coordination has been reported for some copper() complexes in the solid state on the basis of crystallographic studies, e.g. hexaaquacopper() bromate, [Cu(OH 2 ) 6 ](BrO 3 ) 2 , hexaaquacopper() hexafluorosilicate, [Cu(OH 2 ) 6 ]SiF 6 , and hexakis(pyridine-1-oxide)copper() perchlorate, [Cu(ONC 5 H 5 ) 6 ](ClO 4 ) 2 . These results are not consistent with the elongated octahedral configuration expected from the Jahn-Teller theorem for the d 9 copper() ion nor, in some cases, with results from electron spin resonance studies. The present lattice-independent EXAFS study confirms that the local structure in the copper() complexes mentioned above is, in all cases, consistent with a Jahn-Teller induced elongation. Mean equatorial and axial Cu-O bond distances of 1.96(1) and 2.32(2) Å, and 1.95(1) and 2.27(3) Å, were obtained for the hexaaquacopper() ions in the bromate and hexafluorosilicate salts, respectively. For the hexakis(pyridine-1-oxide)copper() perchlorate only the equatorial mean Cu-O bond distance of 1.96(1) Å could be observed. Evidently, there is orientational disorder of the tetragonally elongated octahedral complexes resulting in too high crystallographic space group symmetry and copper sites in apparently regular coordination geometry. For the hydrated copper() ion in aqueous solution, fiveand six-coordinated models with different geometries have been evaluated by means of EXAFS and large angle X-ray diffraction (LAXS) data. The combined results are consistent with a Jahn-Teller elongated octahedral configuration with Cu-O eq 1.95(1) Å, Cu-O ax 2.29(3) Å, and a distinct second hydration sphere with about eight water molecules and a mean Cu ؒ ؒ ؒ O II distance of 4.17(3) Å. In dimethylsulfoxide solution EXAFS and LAXS methods show the solvated copper() ions to have mean equatorial and axial Cu-O bond distances of 1.96(1) and 2.24(2) Å, respectively. As a model compound for the EXAFS studies, the crystal structure of hexakis(dimethylsulfoxide)copper() perchlorate dimethylsulfoxide (1/2), [Cu(OS(CH 3 ) 2 ) 6 ](ClO 4 ) 2 ؒ2(CH 3 ) 2 SO, was determined.
The structure and bonding in bisaquamercury() trifluoromethanesulfonate, [Hg(OH 2 ) 2 (CF 3 SO 3 ) 2 ] ∞ , and trisaquathallium() trifluoromethanesulfonate, [Tl(OH 2 ) 3 (CF 3 SO 3 ) 3 ], have been studied by means of single-crystal X-ray diffraction, EXAFS and vibrational spectroscopy. The crystal structure of bisaquamercury() trifluoromethanesulfonate shows an unusual connectivity pattern. The mercury() ion strongly binds two water molecules axially with the Hg-O bond distance 2.11 Å, and four oxygen atoms from four trifluoromethanesulfonate ions complete a tetragonally compressed octahedral coordination geometry, at the mean Hg-O distance 2.53 Å. Two trifluoromethanesulfonate ions form double bridges between the bisaquamercury() entities giving rise to infinite >Hg(OH 2 ) 2 <(CF 3 SO 3 ) 2 >Hg(OH 2 ) 2 < chains. The parallel chains are held together in layers by relatively strong hydrogen bonds with O(-H) ؒ ؒ ؒ O distances in the range 2.688(9)-2.735(9) Å. The O-D stretching vibrational frequencies of the hydrogen bonds in the partly deuterated compound occur in a broad band at about 2400 cm Ϫ1 , bandwidth ca. 170 cm Ϫ1 . The layers are connected only via van der Waals interactions between the protruding CF 3 groups, consistent with the fragile sheet-like structure of the crystalline compound. Trisaquathallium() trifluoromethanesulfonate crystallises as molecular complexes where each thallium() ion binds three water molecules and three oxygen atoms from trifluoromethanesulfonate ions, with Tl-O bond distances in the range 2.18-2.24 Å. A hydrogen bond network between the water molecules and trifluoromethanesulfonate ions with O(-H) ؒ ؒ ؒ O distances in the range 2.65(1)-2.80(1) Å holds the structure together. Raman and infrared spectra have been recorded and analysed. The changes in force constants and vibrational frequencies have been correlated with bond lengths for the S-O bond in the coordinated trifluoromethanesulfonate ion and for the Hg-O and Tl-O bonds, also including the hexaaquaions in the comparisons.
The ammonia solvated mercury(II) ion has been structurally characterized in solution by means of EXAFS, (199)Hg NMR, and Raman spectroscopy and in solid solvates by combining results from X-ray single crystal and powder diffraction, thermogravimetry, differential scanning calorimetry, EXAFS, and Raman spectroscopy. Crystalline tetraamminemercury(II) perchlorate, [Hg(NH3)4](ClO4)2, precipitates from both liquid ammonia and aqueous ammonia solution, containing tetraamminemercury(II) complexes. The orthorhombic space group ( Pnma) imposes C s symmetry on the tetraamminemercury(II) complexes, which is lost at a phase transition at about 220 K. The Hg-N bond distances are 2.175(14), 2.255(16), and 2 x 2.277(9) A, with a wide N-Hg-N angle between the two shortest Hg-N bonds, 122.1(7) degrees , at ambient temperature. A similar distorted tetrahedral coordination geometry is maintained in liquid ammonia and aqueous ammonia solutions with the mean Hg-N bond distances 2.225(12) and 2.226(6) A, respectively. When heated to 400 K the solid tetraamminemercury(II) perchlorate decomposes to diamminemercury(II) perchlorate, [Hg(NH3)2](ClO4)2, with the mean Hg-N bond distance 2.055(6) A in a linear N-Hg-N unit. The mercury atoms in the latter compound form a tetrahedral network, connected by perchlorate oxygen atoms, with the closest Hg...Hg distance being 3.420(3) A. The preferential solvation and coordination changes of the mercury(II) ion in aqueous ammonia, by varying the total NH 3:Hg(II) mole ratio from 0 to 130, were followed by (199)Hg NMR. Solid [Hg(NH 3)4](ClO4)2 precipitates while [Hg(H2O)6](2+) ions remain in solution at mole ratios below 3-4, while at high mole ratios, [Hg(NH3)4](2+) complexes dominate in solution. The principal bands in the vibrational spectrum of the [Hg(NH3)4](2+) complex have been assigned.
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