Choose the isoelectronic pair among the following:
A. $\mathrm{[V(CO)_6]}$
B. $\mathrm{[Cu(\eta^{5}\text{-}\,C_5H_5)\,(CO)]}$
C. $\mathrm{[Co(CO)_4]^{-}}$
D. $\mathrm{[IrCl\,(CO)(PPh_3)]}$
(a)A and B
(b)B and C
(c)C and D
(d)A and D
Answer
Answer (as printed): B
Explanation
The species having same number of electrons are called isoelectronic.$A=[\mathrm{V(CO)_6}]=5+12=17e^{-}$$B=[\mathrm{Cu}(\eta^5\text{-}\mathrm{C_5H_5})(\mathrm{CO})]=11+5+2=18e^{-}$$C=[\mathrm{Co(CO)_4}]^{-}=9+8+1=18e^{-}$$D=[\mathrm{IrCl(CO)(PPh_3)_2}]=9+1+2+4=16e^{-}$Therefore B and D are isoelectronic species.