Table 2.

IR Data for Compounds [1a–1d]BF₄ and [2b]BF₄ in a CH₂Cl₂ Solution and the Ni-SI_a State in Selected Organisms

compound	ν̃CO (cm−1)
	expt	calca
[(C5H5)Ni(pdt)Fe(dppe)(CO)]BF4 ([1a]BF4)	1943	1948/1946
[(C5H5)Ni(pdt)Fe(dppv)(CO)]BF4 ([1b]BF4)	1951	1951/1949
[(C5H5)Ni(Me2pdt)Fe(dppe)(CO)]BF4 ([1c]BF4)	1940	1937/1935
[(CH3C5H4)Ni(pdt)Fe(dppe)(CO)]BF4 ([1d]BF4)	1943	1947/1945
[(C5H5)Ni(SPh)2Fe(dppv)(CO)]BF4 ([2b]BF4)	1956	1959
Ni-SIa (Synechocytis SH)6	1947	n/a
Ni-SIa (D. vulgaris Miyazaki F)32	1943	n/a
Ni-SIa (D. gigas)32	1934	n/a
Ni-SIa (A. aeolicus)6	1927	n/a
Ni-SIa (Allochromatium vinosum)32	1931	n/a

^aThe first value corresponds to the conformer in which the central CH₂ of the Fe(pdt)Ni core is oriented toward iron, and the second value corresponds to the conformer in which the same CH₂ is oriented toward nickel. The calculations were performed in the absence of BF₄⁻.