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Table 1 Coordination numbers, interatomic distances (in Å) and aqueous free energies (G in Hartrees/molecule) of inorganic aqueous U species.

From: Quantum mechanical calculation of aqueuous uranium complexes: carbonate, phosphate, organic and biomolecular species

Model CN U=O U-O(H2) U-OH G   
Aqueous Uranium        
UO2H2O6•14(H2O) 7 1.79 2.44 ----- -1730.2813   
"(6-311+G(d,p)) 7 1.77 2.47 ----- -----   
UO2OHH2O5•14(H2O) 7 1.80 2.44 2.19 -1729.8137   
UO2OH2H2O4•14(H2O) 7 1.83 2.43 2.23 -1729.3376   
U(V)O2H2O6•14(H2O) 7 1.87 2.52 ----- -1730.5124   
Expt [41] 1.76 ± 0.02 2.41 ± 0.02 ----- -----    
U(IV)H2O8•22(H2O) singlet 8 ----- 2.42 ----- -2343.7790*   
U(IV)H2O9•21(H2O) triplet 9 ----- 2.47 ----- -2343.8518   
Expt [41] ----- 2.41 ± 0.02 ----- -----    
Carbonates        
  CN U=O U-O(H 2 ) U-O(C) U---C U-Ca G
UO2H2O2(CO3)2•28(H2O)        
-trans 8 1.80 2.63 2.47 2.93 ----- -3022.6274
-cis 8 1.80 2.62 2.46 2.94 ----- -3022.6241
UO2H2O2(CO3)2•28(H2O)        
6-31+G(d,p) -trans 8 1.80 2.66 2.47 2.94 ----- -3023.6182
6-31+G(d,p) -cis 8 1.79 2.67 2.47 2.93 ----- -3023.6268
Expt [42] 11 1.80 ----- 2.43 2.88 ----- -----
     4.17 (distal)    
UO2(CO3)3•28(H2O) 8 1.82 ----- 2.50 2.95 ----- -3133.8283
     4.20 (distal)    
UO2(CO3)3•28(H2O) 8 1.82 ----- 2.52 2.97 ----- -3134.8247
6-31+G(d,p)     4.23 (distal)    
Expt [43] 8 1.80 ----- 2.43 2.89 ----- -----
     4.13 (distal)    
Expt [49] 8 1.81 ----- 2.44 2.90 ----- -----
Expt [50] 8 1.81 ----- 2.44 2.92 ----- -----
     4.23 (distal)    
UVO2(CO3)3•28(H2O) 8 1.89 ----- 2.61 3.05 ----- -3134.0109
     4.30 (distal)    
Expt [43] 8 1.90 ----- 2.50 2.94 ----- -----
Expt [44] 8 1.94 ----- 2.47 2.90 ----- -----
Expt [50] 8 1.91 ----- 2.50 2.93 ---- -----
Ca2UO2(CO3)3•28(H2O)A 8 1.84 ----- 2.46 2.93 3.68 -4488.8621
Ca2UO2(CO3)3•28(H2O)B 8 1.81 ----- 2.49 2.95 4.05 -4488.9081
Expt [45] 8 1.78 ----- 2.43 2.86 4.07 -----
Phosphate        
  CN U=O U-O(H 2 ) U-O(P) U---P G  
UO2PO4•30(H2O) 7 1.80 2.49* 2.40 3.10 -3443.3837  
UO2HPO4•30(H2O) mono -- ----- ----- ----- ----- -3520.2502§  
UO2HPO4•30(H2O) bi 7 1.79 2.48 2.445 3.09 -3520.6344  
UO2(HPO4)2•33(H2O) bi 7 1.80 2.45 2.50 3.11 -4163.0025  
" mono** " " " 2.22 3.78 "  
UO2(HPO4)2•33(H2O) bi 8 1.79 2.49 2.55 3.18 -4163.0409  
" bi# 8 1.80 2.58 2.52 3.16 -4163.0190  
UO2H2PO4•30(H2O) mono 7 1.78 2.51 2.28 3.64 -3520.2679  
" bi 7 1.79 2.46 2.46 3.11 -3520.2712  
Expt [46] 6 1.78 2.49 2.30 3.16 -----  
  1. * – One U-OH2 deprotonated to form a U-OH at 2.28 Å and a H3O+ in the solvation sphere
  2. § – No frequency analysis was performed for this unstable configuration.
  3. ** – The UO2(HPO4)2 complex has one HPO42- group attached in a bidentate configuration and the second in a monodentate configuration. This entry accounts for the U-O(P) and U---P distances in the monodentate HPO42- ligand.
  4. # – Second configuration with O atoms of HPO42- bonded to UO22+ in parallel rather than perpendicular as in the lower energy configuration