• Neutral Molecules
• HNgY
• Si=CH-ArF
• FArCHCH2
• FArC4H5
   
• HNgY
  
  The most generic type is HNgY where Y is an electronegative atom or group. For Y = F, the calculated structures are the following. All structures are linear.

  	MP2/apdz	MP2/aptz	CCSD(T)/aptz
  HHeF (H-He) (He-F)	0.796 1.420	0.789 1.409	0.811 1.415
  HArF	1.338 2.023	1.321 1.983	1.338 1.993
  HKrF	1.480 2.060	1.462 2.034	1.478 2.041

  
  The energies of HNgF relative to HF + Ng and H + Ng + F are:
   

  	MP2/apdz	MP2/aptz	CCSD(T)/aptz
  HHeF (rel.  HF+He) (rel. H+He+F)	156.3 17.7	156.7 13.0	157.0 17.7
  HArF	137.8 -0.7	134.0 -9.7	133.9 -5.4
  HKrF	116.0 -22.5	112.8 -30.9	112.4 -26.9

• Si=CH-ArF
  
  MP2/6-31+G**

   

• FArCHCH2

       MP2/6-31+G**

F-Ar = 2.053
C-Ar = 1.848

• FArC4H5

MP2/6-31+G**

F-Ar = 2.057
C-Ar = 1.837



 

• Anions
  
  FNgO-
  
  We recently found that some noble-gas containing anions can also be kinetically stable, in particular, the FNgO- anions. The F- induced the formation of the Ng=O bond and the singlet-state anions were found to have large dissociation barriers. The lifetime of the anions may be determined by the S-T intersystem crossing rates. The calculated structures are the following:
  

  Method	FHeO-			FArO-			FKrO-
  	F-He	He-O		F-Ar	Ar-O		F-Kr	Kr-O
  MP2/aug-cc-pVDZ	1.640	1.050		2.271	1.729		2.251	1.817
  MP2/aug-cc-pVTZ	1.606	1.043		2.214	1.685		2.211	1.786
  MP2/aug-cc-pVQZ	1.601	1.038		2.196	1.672		2.198	1.780
  CCSD(T)/aug-cc-pVDZ	1.660	1.130		2.280	1.846		2.297	1.903
  CCSD(T)/aug-cc-pVTZ	1.630	1.110		2.241	1.781		2.259	1.854
  CCSD(T)/aug-cc-pVQZ	1.624	1.101		2.224	1.763

  
  The relative energies are

  	S-T gap	Relative to	Relative to	Relative to	Relative to	Relative to	Bending Barrier
  		F-+Ng+O(S)	F-+NgO	F+Ng+O-	F-+Ng+O(T)	FO-+Ng
  Ng = He
  MP2/aug-cc-pVDZ	108.4	-26.8	NA	-11.3	41.1	56.7	24.3 [20.5]
  MP2/aug-cc-pVTZ	118.2	-39.4	NA	-24.7	26.6	48.7	29.0 [25.0]
  MP2/aug-cc-pVQZ	121.3	-32.9	NA	-19.1	32.2	55.8	29.9 [26.0]
  CCSD(T)/aug-cc-pVTZ	90.9	-23.6	NA	-18.4	27.3	50.9	22.1 [18.7]
  CCSD(T)/aug-cc-pVQZ	90.8	-20.5	NA	-15.9	29.8	54.8	19.0
  CCSD(T)/CBS	91.1	-24.0	NA	-16.4	26.0	54.7	19.3
  Ng = Ar
  MP2/aug-cc-pVDZ	45.6	-41.9	-28.9	-26.4	26.1	41.7	36.5 [34.9]
  MP2/aug-cc-pVTZ	61.0	-51.4	-31.1	-36.6	14.7	36.8	44.6 [43.0]
  MP2/aug-cc-pVQZ	65.6	-53.7	-31.8	-30.5	11.3	35.0	46.6 [45.0]
  CCSD(T)/aug-cc-pVTZ	38.0	-37.1	-29.7	-32.0	13.7	37.4	31.9 [30.6]
  CCSD(T)/aug-cc-pVQZ	42.2	-40.4	-31.9	-34.1	9.9	36.5	33.1
  CCSD(T)/CBS	41.9	-42.5	-34.0	-34.9	7.5	36.2	33.4
  Ng = Kr
  MP2/aug-cc-pVDZ	61.6	-66.0	-38.0	-50.5	2.0	17.6	57.9 [56.4]
  MP2/aug-cc-pVTZ	72.2	-76.0	-35.9	-61.2	-9.9	12.2	65.5 [64.0]
  MP2/aug-cc-pVQZ	74.4	-77.8	-39.9	-64.0	-12.7	10.9	66.9 [65.4]
  CCSD(T)/aug-cc-pVTZ	52.7	-58.1	-37.4	-52.9	-7.3	16.4	49.0
  CCSD(T)/aug-cc-pVQZ	52.8	-59.3	-37.7	-54.7	-9.0	15.9	50.4
  CCSD(T)/CBS	52.4	-60.0	-41.0	-52.3	-10.0	18.7	49.7

  This has been published on J. Am. Chem. Soc. 2005, 127, 9241.
  
  Are there other anions that can also induce the formation of stable Ng=O bonds? If we consider the prototype X-...Ng=O ion. If the anion is stable, it must be lower in energy than X- + Ng + O (S). To induce the formation of Ng=O, the X- need to have high charge density. That is,  the negative charge needs to be localized on a small atom. In this respect, the F- is unique in its high charge density, and it induces ~20 kcal/mol He=O bond energies.  It is hard to imagine any other anions with even higher charge density. In addition, we need to consider the dissociation channel of X + Ng + O-. The singlet O atom has a very high electron affinity ~80 kcal/mol. Thus if X has a much lower EA, the negative charge would stay on O instead of X, and the X-...Ng=O would dissociate to X + Ng + O- easily. The energy difference of the two dissociation channels is the EA difference of X and O. As a result, for X with EA less than 60 kcal/mol, the X-...Ng=O anions are probably not even dynamically stable. From the above, two factors determine the stability of the X-...Ng=O ions towards "linear" dissociation. For  stable X-...Ng=O anions, the negative charge of X needs to be concentrated on an electronegative atom, such as F, O, and N. Also the X group must have high EA to keep the negative charge from moving to the oxygen atom on Ng=O. Some of the calculated EAs for potential X group are listed below. Groups such as H, CH3, OH, NH2 are not good candidates for X because of the low EAs even though the charge density of the negative ions might be reasonably high.
   

  	MP2	MP2	CCSD(T)
  	apdz	aptz	aptz (SP)
  H	-7.9	-10.1	-16.8
  O	-97.2	-98.7	-81.5
  F	-81.7	-83.9	-76.4
  Cl	-82.0	-83.7	-80.8
  BO	-53.0	-55.3	-57.3
  CN	-106.1	-107.8	-92.3
  OH	-44.8	-47.7	-40.1
  CH3	1.4	-1.2	0.2
  C2H	-79.9	-80.4	-70.4
  HBN	-74.3	-76.7	-69.9
  HBeO	-73.5	-76.5	-68.1
  NCN	-85.0	-87.0	-84.9
  OBO	-112.8	-115.8	-104.6
  H2BO	-63.3	-65.6	-55.3
  NCO	-90.3	-93.2	-82.8

      

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