Acta Crystallographica Section B

Structural Science

Volume 52, Part 3 (June 1996)

research papers

Acta Cryst. (1996). B52, 458-464 [ doi:10.1107/S0108768195012900 ]

Charge density studies in NH₄[Ti(C₂O₄)₂].2H₂O crystals at two wavelengths

H. S. Sheu, J. C. Wu, Y. Wang and R. B. English

Abstract: The crystal structure of ammonium bis--oxalatotitanate(III) dihydrate, NH₄[Ti(C₂O₄)₂].2H₂O, is reinvestigated by careful single-crystal X-ray diffraction using Mo K [alpha] (room temperature and 130 K) and Ag K [alpha] radiation (room temperature). It crystallizes in noncentrosymmetric hexagonal space group P6₄22, with cell parameters a = 8.947 (2), c = 10.898 (1) Å, Z = 3, F(000) = 423, M_r = 278.1, D_x = 1.833, R = 0.035, wR = 0.030 for 2296 observed reflections with I [greater-than or equal to] 2(I), on Ag K [alpha] data. Accurate data measurement was applied using two wavelengths (0.7107 Å for Mo K [alpha] and 0.5609 Å for Ag K [alpha] in order to study the charge density distribution and also to investigate the wavelength effect in such investigations. A total of 22650 and 20298 reflections were measured using Mo K [alpha] radiation at room temperature and 130 K, respectively, and 18361 reflections using Ag K [alpha] radiation. The Ti atom is coordinated by four oxalate dianions with coordination number 8 in an approximate symmetry of D₄ geometry. Each oxalato ligand is bridged between two Ti atoms and forms an infinite polymeric spiral column along the c axis. The deformation density maps, , obtained from all three data sets are consistent and agree well. Although the formal charge of Ti in this complex is 3+, with only one electron on the 3d orbitals expected, the net atomic charge on Ti from this study is, ~2+. Charge asphericity around the Ti atom caused by the splitting of 3d orbitals is clearly observed in the deformation density. The d-orbital populations are evaluated from multipole refinement. The expected d¹ electron is mainly located in the d_Z² orbital.