Single crystals of two modifications (I and II) of Cr(SeO 2 OH) (Se 2 O 5 ) have been synthesized under low-hydrothermal conditions. Their structures have been investigated using single-crystal X-ray diffraction data up to sin / โซุโฌ 0.76 A s ุ1 [I: monoclinic, space group P2 1 /n, a โซุโฌ 7.517(2) A s , b โซุโฌ 12.516(3) A s , c โซุโฌ 7.381(2) A s , โซุโฌ 91.46(1)ยฐ, Z โซุโฌ 4, R1 โซุโฌ 0.030 for 1562 F o > 4 (F o ) and 114 variables; II: orthorhombic, space group Pnma, a โซุโฌ 8.782(2) A s , b โซุโฌ 11.172(3) A s , c โซุโฌ 7.545(2) A s , Z โซุโฌ 4, R1 โซุโฌ 0.031 for 752 F o > 4 (F o ) and 65 variables]. In Cr(SeO 2 OH) (Se 2 O 5
)-I, sheets-built up from isolated CrO 6 octahedra and Se 2 O 5 groups-are linked via the SeO 2 OH groups and rather strong hydrogen bonds. This structure is isotypic with the corresponding compounds of Mn(III) and Fe(III). Cr(SeO 2 OH) (Se 2 O 5 )-II represents a new framework structure type, also composed of isolated CrO 6 octahedra and Se 2 O 5 and SeO 2 OH groups, but with very weak hydrogen bonds. The hydrogen-bonding schemes of both compounds were further investigated by FTIR microscope spectrometry in the range 7000-1000 cm ุ1 , yielding a typical AB-band spectrum for phase I. Furthermore, polarized electronic absorption spectra were measured in the range 33,000-12,500 cm ุ1 using UV-VIS microscope spectrometric techniques. According to the weak distortions of the CrO 6 octahedra in both compounds, the observed band splittings and polarization effects are rather weak. Hence, crystal field calculations were performed assuming O h symmetry, resulting in the following crystal field parameter sets; I,