Influence of the Organic Species and Oxoanion in the Synthesis of two Uranyl Sulfate Hydrates, (H 3 O) 2 [(UO 2 ) 2 (SO 4 ) 3 (H 2 O)]·7H 2 O and (H 3 O) 2 [(UO 2 ) 2 (SO 4 ) 3 (H 2 O)]·4H 2 O, and a Uranyl Selenate‐Selenite [C 5 H 6 N][(UO 2 )(SeO 4 )(HSeO 3 )]

Two uranyl sulfate hydrates, (H 3 O) 2 [(UO 2 ) 2 (SO 4 ) 3 (H 2 O)] · 7H 2 O (NDUS) and (H 3 O) 2 [(UO 2 ) 2 (SO 4 ) 3 (H 2 O)] · 4H 2 O (NDUS1), and one uranyl selenate‐selenite [C 5 H 6 N][(UO 2 )(SeO 4 )(HSeO 3 )] (NDUSe), were obtained and their crystal structures solved. NDUS and NDUSe result from reactions in highly acidic media in the presence of L ‐cystine at 373 K. NDUS crystallized in a closed vial at 278 K after 5 days and NDUSe in an open beaker at 278 K after 2 weeks. NDUS1 was synthesized from aqueous solution at room temperature over the course of a month. NDUS, NDUS1, and NDUSe crystallize in the monoclinic space group P 2 1 / n , a = 15.0249(4) Å, b = 9.9320(2) Å, c = 15.6518(4) Å, β = 112.778(1)°, V = 2153.52(9) Å 3 , Z = 4, the tetragonal space group P 4 3 2 1 2, a = 10.6111(2) Å, c = 31.644(1) Å, V = 3563.0(2) Å 3 , Z = 8, and in the monoclinic space group P 2 1 / n , a = 8.993(3) Å, b = 13.399(5) Å, c = 10.640(4) Å, β = 108.230(4)°, V = 1217.7(8) Å 3 , Z = 4, respectively.The structural units of NDUS and NDUS1 are two‐dimensional uranyl sulfate sheets with a U/S ratio of 2/3. The structural unit of NDUSe is a two‐dimensional uranyl selenate‐selenite sheets with a U/Se ratio of 1/2. In‐situ reaction of the L ‐cystine ligands gives two distinct products for the different acids used here. Where sulfuric acid is used, only H 3 O + cations are located in the interlayer space, where they balance the charge of the sheets, whereas where selenic acid is used, interlayer C 5 H 6 N + cations result from the cyclization of the carboxyl groups of L ‐cystine, balancing the charge of the sheets.