In the complex, $\left[\mathrm{Ni}_{2}\left(\eta^{5}-\mathrm{Cp}\right)_{2}(\mathrm{CO})_{2}\right]$, the IR stretching frequency appears at $1857 \mathrm{cm}^{-1}$ (strong) and 1897 $\mathrm{cm}^{-1}$ (weak). The valence electron count and the nature of the M-CO bond respectively are