A novel symmetric pyrazine (pyz)-bridged uranyl dimer [UO₂Cl₃(H₂O)(Pyz)_0.5]₂²⁻: synthesis, structure and computational analysis

Abstract

Herein we report on the synthesis of (C4H6N)2[UO2Cl3(H2O)(Pyz)0.5]2.2H2O which features a novel pyrazine-bridged uranyl dimer, [UO2Cl3(H2O)(Pyz)0.5]22-. A rigorous computational and experimental analysis of this compound was performed to fully explore...

Synthesis, Characterization, and Density Functional Theory Investigation of the Solid-State [UO2Cl4(H2O)]2– Complex

“…In order to rationalize the changes in UO and U–Cl bond lengths, Bond Order (BO) analysis (SI eq 1) was performed on (C 4 H 12 N 2 ) 2 [UO 2 Cl 4 (H 2 O)]­Cl 2(s) and the reference compound using the DDEC6 method. − Comparing BOs of [UO 2 Cl 4 (H 2 O)] 2– with [UO 2 Cl 4 ] 2– indicates an ∼12% increase in the UO BO (UO becomes stronger) and ∼23% decrement in the U–Cl BO (U–Cl become weaker). This result agrees with the crystallographic observations of UO bond contraction and U–Cl bond elongation, and similar strengthening of the UO bond is reported by Cahill et al when the pyrazine ligand directly bound to the uranyl center in [UO 2 Cl 3 (H 2 O)­(pyz) 0.5 ] 2– dimer complexes …”

“…In contrast, the analogous (C 4 H 12 N 2 )­[UO 2 Cl 4 ] showed extensive hydrogen bonding through axial oxygen (BO = 0.161) . Within the literature, this phenomenon is typically attributed to the reduced Lewis basicity of axial oxygen due to UO bond strengthening ,, and agrees with observations described in Section . The equatorial water molecule engages in strong H-bonding (Cl equiv ···H–O water 2.167 Å, BO = 0.128) with neighboring uranyl units, forming supramolecular chains of the [UO 2 Cl 4 (H 2 O)] 2– unit extending in the [100] direction (Figure d).…”

“…Comparing [UO 2 Cl 4 (H 2 O)] 2− (Figure 1a) to that of [UO 2 Cl 4 ] 2− (Figure 1b) allows us to consider differences in 22 To further probe changes in the primary coordination sphere, we have plotted the Projected Density of States (PDOS) for the materials containing the [UO 2 Cl 4 (H 2 O)] 2− or [UO 2 Cl 4 ] 2− species (Figure 2). The electronic structure of the gas-phase uranyl cation is well-described experimentally and computationally.…”

“…described the synthesis and characterization of a solid-state [UO 2 Cl 3 (H 2 O)(pyrazine) 0.5 ] 2– complex that contains a bridging pyrazine molecule between the two metal centers. 22 Larger tetranuclear (VI) complexes containing bridging hydroxide and chloride anions have been reported by Aberg, 23 but no additional solid phases have been reported for aquachlorouranium(VI) coordination compounds. More specifically, the [UO 2 Cl 4 (H 2 O)] 2– complex has not yet been isolated in the solid state and represents a unique opportunity to analyze the effect of water coordination on the axial bond, electronic structure, and vibrational properties of uranyl aqua chloro complexes in contrast to the well-studied [UO 2 Cl 4 ] 2– anion.…”

“…Dimeric species that result from hydrolysis of the U­(VI) cation have also been reported, and Cahill et al. described the synthesis and characterization of a solid-state [UO 2 Cl 3 (H 2 O)­(pyrazine) 0.5 ] 2– complex that contains a bridging pyrazine molecule between the two metal centers . Larger tetranuclear (VI) complexes containing bridging hydroxide and chloride anions have been reported by Aberg, but no additional solid phases have been reported for aquachlorouranium­(VI) coordination compounds.…”