Steric Effects on Uranyl Complexation: Synthetic, Structural, and Theoretical Studies of Carbamoyl Pyrazole Compounds of the Uranyl(VI) Ion

Abstract

New bifunctional pyrazole based ligands of the type [C(3)HR(2)N(2)CONR'] (where R = H or CH(3); R' = CH(3), C(2)H(5), or (i)C(3)H(7)) were prepared and characterized. The coordination chemistry of these ligands with uranyl nitrate and uranyl bis(dibenzoyl methanate) was studied with infrared (IR), (1)H NMR, electrospray-mass spectrometry (ES-MS), elemental analysis, and single crystal X-ray diffraction methods. The structure of compound [UO(2)(NO(3))(2)(C(3)H(3)N(2)CON{C(2)H(5)}(2))] (2) shows that the uranium(VI) ion is surrounded by one nitrogen atom and seven oxygen atoms in a hexagonal bipyramidal geometry with the ligand acting as a bidentate chelating ligand and bonds through both the carbamoyl oxygen and pyrazolyl nitrogen atoms. In the structure of [UO(2)(NO(3))(2)(H(2)O)(2)(C(5)H(7)N(2)CON {C(2)H(5)}(2))(2)], (5) the pyrazole ligand acts as a second sphere ligand and hydrogen bonds to the water molecules through carbamoyl oxygen and pyrazolyl nitrogen atoms. The structure of [UO(2)(DBM)(2)C(3)H(3)N(2)CON{C(2)H(5)}(2)] (8) (where DBM = C(6)H(5)COCHCOC(6)H(5)) shows that the pyrazole ligand acts as a monodentate ligand and bonds through the carbamoyl oxygen to the uranyl group. The ES-MS spectra of 2 and 8 show that the ligand is similarly bonded to the metal ion in solution. Ab initio quantum chemical studies show that the steric effect plays the key role in complexation behavior.

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes

“…Electrospray ionization (ESI) provides easy access to a wide range of gasphase complexes containing uranium in high oxidation states (+5 and +6) for studies of intrinsic structure and reactivity (i.e., outside of the influence of solvent or other condensed phase effects) in a species specific fashion. For example, the transfer of uranium as mono-positive, pentavalent U V O 2 + from solution to the gas phase using ESI was first reported in 1992 [5] and since then, advances in the fundamental understanding of uranyl coordination chemistry have been made using the ionization method [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Most importantly, ESI has been used to generate gas-phase, doubly charged complexes containing UO 2…”

Collision‐induced dissociation of uranyl‐methoxide and uranyl‐ethoxide cations: Formation of UO 2 H + and uranyl‐alkyl product ions

“…The transfer of uranium as monopositive pentavalent U V O 2 + , from solution to the gas phase using electrospray ionization (ESI), was first reported in 1992 . Thereafter, advances in the fundamental understanding of uranyl coordination chemistry have been achieved by using ESI, including the generation of a wide range of singly and doubly charged complexes that contain actinyl cations …”

“…[15] Thereafter, advances in the fundamental understanding of uranyl coordination chemistry have been achieved by using ESI, including the generation of a wide range of singly and doubly charged complexes that contain actinyl cations. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] In an earlier study, ESI and multiple-stage tandem mass spectrometry (MS n ) were used to characterize the dissociation pathways for uranyl nitrate or hydroxide cations coordinated by water or alcohol ligands. [36] In general, collision-induced dissociation (CID) of the uranyl complexes resulted in the elimination of coordinating water and alcohol ligands.…”

Collision‐induced dissociation of [UVIO2(ClO4)]+ revisited: Production of [UVIO2(Cl)]+ and subsequent hydrolysis to create [UVIO2(OH)]+

“…outside the influence of solvent or other condensed phase effects) in a species‐specific fashion . Since then, ESI has been used to create gas‐phase uranyl species for a range of tandem mass spectrometry (MS/MS), anion photoelectron spectroscopy, and ion mobility studies . ESI and MS/MS have also been used to study and compare the intrinsic dissociation and ion‐molecule reactions of transuranic species …”