Improved Procedures for the Synthesis of 9,9-Disubstituted 9,10-Dihydroacridines.

We found that a previously reported synthesis of 9,9-disubstituted 9,10-dihydroacridines (DHAs) that relied on an acid-catalyzed cyclization was plagued by a competing elimination reaction, resulting in some elimination products being incorrectly identified as their structural isomer DHAs. In this report, we provide improved synthetic procedures for 9,9-disubstituted DHAs, demonstrated by the synthesis of two 9,9-diethyl DHAs.

An Organic Chemist's Guide to N-Nitrosamines: Their Structure, Reactivity, and Role as Contaminants.

N-Nitrosamines are a class of compounds notorious both for the potent carcinogenicity of many of its members and for their widespread occurrence throughout the human environment, from air and water to our diets and drugs. Considerable effort has been dedicated to understanding N-nitrosamines as contaminants, and methods for their prevention, remediation, and detection are ongoing challenges. Understanding the chemistry of N-nitrosamines will be key to addressing these challenges. To facilitate such understanding, we focus in this Perspective on the structure, reactivity, and synthetic applications of N-nitrosamines with an emphasis on alkyl N-nitrosamines. The role of N-nitrosamines as water contaminants and the methods for their detection are also discussed.

Ag5U(PS4)3: A Transition-Metal Actinide Phosphochalcogenide.

The structure of Ag5U(PS4)3 is unique, as in the literature there are no other structures of the type MAnPQ (M = transition metal, An = actinide, Q = S, Se, or Te). The compound has been synthesized at 1123 K by standard solid-state methods, and its single-crystal X-ray structure has been determined at 100(2) K. Ag5U(PS4)3 crystallizes in a remarkable new structure type in space group P3221 of the trigonal system with three formula units in a hexagonal cell of dimensions a = b = 9.6635(2) Å, c = 17.1834(4) Å, and γ = 120°. In the structure, each U atom is coordinated to eight S atoms in a bicapped trigonal prismatic manner. Each P atom is tetrahedrally coordinated to four S atoms. Two of the three unique Ag atoms are connected to four S atoms in a distorted tetrahedral manner, whereas the third unique Ag atom forms an Ag2S6 species. The overall structure consists of U polyhedra connected to each other via PS4 tetrahedra through edge-sharing in a zigzag fashion along the c axis to form infinite layers. PS4 groups and the Ag atoms pack these layers. From density functional theory calculations, the total density of states of Ag5U(PS4)3 is asymmetric with respect to spin and has finite spin polarization in the crystal cell: the magnetic moments of two of the U atoms are parallel, whereas the magnetic moment of the third U atom is antiparallel.

K(Th0.75Sr0.25)2Se6: Structural Change Resulting from the Disorder of Differently Charged Cations.

Single crystals of K(Th0.75Sr0.25)2Se6 were obtained by a standard solid-state chemistry route at 1173 K. This compound does not belong to the AAn2Q6 family (A = K, Rb, Cs, or Tl; An = Th, U, or Np; Q = S, Se, or Te) that possesses infinite Q-Q-Q chains and where a charge distribution of A+, 2 × An4+, 2 × Q2-, 2 × (Q22.5-) has been proposed and hence a charge of -1.25 on Q of the "dichalcogenide". Rather in K(Th0.75Sr0.25)2Se6, where the Th and Sr cations randomly occupy the same site, incorporation of these differently charged cations breaks the infinite Se-Se-Se chains into a structure that has typical Se22- pairs.

Four new actinide chalcogenides Ba2Cu4USe6, Ba2Cu2ThSe5, Ba2Cu2USe5, and Sr2Cu2US5: crystal structures and physical properties.

Four new actinide chalcogenides­namely, Ba2Cu4USe6, Ba2Cu2ThSe5, Ba2Cu2USe5, and Sr2Cu2US5­were synthesized via solid-state methods at 1173 K. Single-crystal X-ray diffraction studies show that Ba2Cu4USe6 crystallizes in a new structure type in space group C2h5­P21/c of the monoclinic system, whereas the three other compounds are isostructural and adopt the Ba2Cu2US5 structure type in space group C2h3­C2/m, also of the monoclinic system. These Ak/Cu/An/Q structures (Ak = alkaline-earth metal; An = actinide; Q = chalcogen) have no short Q­Q interactions and, hence, are charge-balanced with Ak2+, Cu1+, An4+, and Q2­. Crystal structures of all these compounds are two-dimensional and feature layers that are separated by Ba2+ cations. The compositions of these layers differ. In the structure of Ba2Cu4USe6, the ∞2[Cu4USe64­] layers comprising USe6 octahedra and CuSe4 tetrahedra stack perpendicular to the a-axis. These ∞2[Cu4USe64­] layers show short Cu­Cu interactions. In the three isostructural Ak2Cu2AnQ5 compounds, AnQ6 octahedra and CuQ4 tetrahedra are connected along the c-axis in the sequence "...oct tet tet oct tet tet..." to form the ∞2[Cu2AnQ54­] layers. Resistivity, optical, and DFT calculations show semiconducting behavior for these compounds.

Syntheses, crystal structures, optical and theoretical studies of the actinide thiophosphates SrU(PS4)2, BaU(PS4)2, and SrTh(PS4)2.

Three new actinide thiophosphates, SrU(PS4)2, BaU(PS4)2, and SrTh(PS4)2, have been synthesized by high-temperature solid-state methods, and their crystal structures were determined from single-crystal X-ray diffraction studies. These three isostructural compounds crystallize in a new structure type in space group D4h13-P42/mbc of the tetragonal system. Their structure features infinite one-dimensional chains of ∞1[An(PS4)2(2­)] anions (An = U or Th). Each An atom is coordinated by eight S atoms in a bicapped trigonal prism, and each P atom is tetrahedrally bonded to four S atoms. The compounds are readily charge balanced as Ak2+An4+(P5+(S2­)4)2. Optical studies on single crystals of SrU(PS4)2 and BaU(PS4)2 as well as ground single crystals of SrTh(PS4)2 revealed a direct band gap of 2.13(2) eV and an indirect band gap value of 1.99(2) eV for SrU(PS4)2 and a direct and indirect gap of about 2.28(2) eV for BaU(PS4)2. SrTh(PS4)2 has a relatively large band gap of 3.02(2) eV. DFT calculations for SrU(PS4)2 and BaU(PS4)2 using the HSE functional predict both compounds to be antiferromagnetic and have very similar electronic structures with band gaps of 2.7 eV. The band gap calculated for SrTh(PS4)2 is 3.2 eV.

Positional flexibility: syntheses and characterization of six uranium chalcogenides related to the 2H hexagonal perovskite family.

Six new uranium chalcogenides, Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, Ba3MnUS6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, related to the 2H hexagonal perovskite family have been synthesized by solid-state methods at 1173 K. These isostructural compounds crystallize in the K4CdCl6 structure type in space group D3d6­R3̅c of the trigonal system with six formula units per cell. This structure type is remarkably flexible. The structures of Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 consist of infinite ∞1[MUQ66­] chains (M = Fe or Mn; Q = S or Se) oriented along the c axis that are separated by Ba atoms. These chains are composed of alternating M-centered octahedra and U-centered trigonal prisms sharing triangular faces; in contrast, in the structures of Ba4USe6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, there are U-centered octahedra alternating with Ba-, Rb-, or K-centered trigonal prisms. Moreover, the Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 compounds contain U4+, whereas Ba3.3Rb0.7US6 and Ba3.2K0.8US6 are mixed U4+/5+ compounds. Resistivity and µ-Raman spectroscopic measurements and DFT calculations provide additional insight into these interesting subtle structural variations.