upon bond formation produces a charge on each atom of the sign which is circletl. Only one C'O group is shown. 1 is fornietl by puttinq the four C O groups tetrahedrally about the cobalt atom in its sp3 orbitals. The negative charge on the cobalt atom is reduced by the transfer of the d elcctrori to the hydrogen atom on the C3axis.
I
111
I1
Structure I1 may be obtained from I by removing an electron pair from one CO s bond and placing it in the p orbital of the oxygen followed by bond formation between the p orbital of the carbon and the s orbital of the hydrogen using the electron pair previously on the hydrogen. Of course there are three resonating structures like 11. Structure I11 enters into the resonance composite to counter-act the negative charge on the cobalt atom in structures I and 11. Comparison with Experiment.-The bonding found for the bridge model is in qualitative agreement with the substantiated experimental facts now known for CO(CO)~H. It predicts a diamagnetic molecule. The weak covalent bonding of the hydrogen atom agrees with the ease of decomposition t o form Hz and c o ~ ( C 0 ) ~T. h e large negative charge on the hydrogen atom calls for the large negative chemical shift found by Gutowsky and coworkers" in the proton magnetic resonance spectrum. And an interesting prediction may be made about the CO stretching vibration in C O ( C O ) ~ - , which may be described as having two electrons in $" and two in followcd by the delocali7ation of (11) H 3 ' Giltowsky, private report
the charge. This latter process will riot chniige the general c-hnractvr of tht: orbitals. Since, $1 1 is ; i i i tibonding will: rpg:tr(:s to the CO bond, cine exl'ccts the frequency oi the CO stretching vibration in Co(CO)1- to be less than those in C O ( C O ) ~ H .The exare6 2122, 2043 perimental values ior C O ( C O ) ~ H and 2062 em.-' while the value for C O ( C O ) ~is3 1S83 cm.-l, in striking agreement with theory. The question naturally arises as to how a 111olccule with a negative charged hytlrogen can tlissolvrin water to form a strong acid. This proccs.: in:iy he divided into the following steps Co(COj,H(gj +Co(CO),*--(g) Co(C0j;" -(g) -+ Co(cOl4-(g) H + ( g ) --+ I l + ( a q ) Co(COJ)-(gi --+Co(CO),-(ayj Co(CO)JI(g) --+ Co(C0j4-(,zqj
+ TWg)
f8.2 e . v . 11 )
-H
( 21 13)
-11.1 -1.7
(1)
- 4 . 9 -I
