Stoilova Donka
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, bl.11, Sofia 1113, Bulgaria.
Spectrochim Acta A Mol Biomol Spectrosc. 2004 Aug;60(10):2243-51. doi: 10.1016/j.saa.2003.11.023.
Infrared spectra of metal(II) selenate hydrates (MeSeO4.nH2O and Na2Me(SeO4)2.2H2O; n=6, 5, 4, 1; Me=Mg, Mn, Co, Ni, Cu, Zn, Cd) containing matrix-isolated SO42- guest ions are reported and discussed with respect to the S-O stretching modes 3 and 1. An adequate measure for the SO42- guest ion distortion is the site group splitting deltanuas (deltanuab and deltanuac in the case of a doublet and a triplet for 3, respectively; a, being the highest wavenumbered component of nu3) and deltanumax (the difference between the highest and the lowest wave numbered S-O stretching modes). It has been shown that the SO42- guest ion distortion depends on both the number of the sulfate oxygen atoms involved in coordinative bonds with the metal(II) ions and the electronic configuration of the metal(II) ions, i.e. their crystal field stabilization energy (CFSE) additionally to the site symmetry and the local potential at the lattice site of the host lattice. The SO42- guest ions matrix-isolated in MeSeO4.H2O (Me=Mn, Co, Zn) and in Na2Me(SeO4)2.2H2O (Me=Mn, Cu, Cd) exhibit three bands corresponding to the nu3 modes as deduced from the site group analysis and deltanuab approximately equal to deltanubc. When SO42- guest ions are incorporated in the triclinic Na2Me(SeO4)2.2H2O host lattices (Me=Co, Ni, Zn) the nu3 stretching region resembles a higher local symmetry of the SO42- guest ions (an approximate (A1 + E) splitting) than the crystallographic one (i.e. deltanuab>deltanubc instead of deltanuab approximately equal to deltanubc) and, hence, the ratio deltanuab/deltanubc has to be taken into account (the higher value of the ratio deltanuab/deltanubc, the weaker is the distortion of the SO42- guest ions). The SO42- guest ions incorporated in MeSeO4.nH2O (n=6, 5, 4) exhibit a higher local symmetry of the guest ions than that deduced from the site group analysis (D2d for the SO42- guest ions in MeSeO4.5H2O, MeSeO4.4H2O and in the monoclinic MeSeO4.6H2O host lattices and close to Td in the tetragonal MeSeO4.6H2O host lattices). The analysis of the infrared spectra of selenate host lattices containing SO42- guest ions reveals that the guest ions are stronger distorted when the adjacent metal(II) ions have CFSE not equal to 0. These ions are more resistant to angular deformations of the MeO6-octahedra (i.e. changes in the O-Me-O bond angles), thus facilitating the SO42- guest ion distortion as compared to those having CFSE=0 which allow stronger angular deformations of the respective metal octahedra. Infrared spectra of kieserite-type compounds MeSeO4.H2O (Me=Mn, Co, Zn) containing matrix-isolated SO42- guest ions and Me'2+ guest ions different from those of the host ions (i.e. Me'SO4.H2O in MeSeO4.H2O) are also presented and discussed (double matrix-spectroscopy).
报道了含有基质隔离的SO₄²⁻客体离子的金属（II）硒酸盐水合物（MeSeO₄·nH₂O和Na₂Me(SeO₄)₂·2H₂O；n = 6、5、4、1；Me = Mg、Mn、Co、Ni、Cu、Zn、Cd）的红外光谱，并针对S - O伸缩振动模式3和1进行了讨论。对于SO₄²⁻客体离子畸变的一个适当度量是位群分裂Δν₃（对于模式3的双重态和三重态情况分别为Δν₃ab和Δν₃ac；a是ν₃的最高波数分量）和Δνₘₐₓ（最高和最低波数的S - O伸缩振动模式之间的差值）。已经表明，SO₄²⁻客体离子的畸变既取决于与金属（II）离子形成配位键的硫酸根氧原子的数量，也取决于金属（II）离子的电子构型，即除了主体晶格位点的点对称性和局部势之外，还取决于它们的晶体场稳定能（CFSE）。在MeSeO₄·H₂O（Me = Mn、Co、Zn）和Na₂Me(SeO₄)₂·2H₂O（Me = Mn、Cu、Cd）中基质隔离的SO₄²⁻客体离子表现出对应于ν₃模式的三个谱带，这是根据位群分析推导出来的，并且Δν₃ab近似等于Δν₃bc。当SO₄²⁻客体离子掺入三斜晶系的Na₂Me(SeO₄)₂·2H₂O主体晶格中（Me = Co、Ni、Zn）时，ν₃伸缩振动区域类似于SO₄²⁻客体离子具有比晶体学对称性更高的局部对称性（近似（A₁ + E）分裂），即（即Δν₃ab＞Δν₃bc而不是Δν₃ab近似等于Δν₃bc），因此，必须考虑Δν₃ab/Δν₃bc的比值（该比值越高，SO₄²⁻客体离子的畸变越弱）。掺入MeSeO₄·nH₂O（n = 6、5、4）中的SO₄²⁻客体离子表现出比从位群分析推导出来的更高的局部对称性（对于MeSeO₄·5H₂O、MeSeO₄·4H₂O和单斜晶系的MeSeO₄·6H₂O主体晶格中的SO₄²⁻客体离子为D₂d，而在四方晶系的MeSeO₄·6H₂O主体晶格中接近Td）。对含有SO₄²⁻客体离子的硒酸盐主体晶格的红外光谱分析表明，当相邻的金属（II）离子的CFSE不等于0时，客体离子的畸变更强。与CFSE = 0的那些离子相比，这些离子对MeO₆八面体的角变形（即O - Me - O键角的变化）更具抗性，因此促进了SO₄²⁻客体离子的畸变，而CFSE = 0的那些离子允许相应金属八面体有更强的角变形。还给出并讨论了含有基质隔离的SO₄²⁻客体离子和不同于主体离子（即MeSeO₄·H₂O中的Me'SO₄·H₂O）的Me'²⁺客体离子的镁碱沸石型化合物MeSeO₄·H₂O（Me = Mn、Co、Zn）的红外光谱（双基质光谱）。
