# Two atoms are held together in four covalent bonds because of forces between the what?

The classic example is $\text{chromous acetate}$, i.e. [Cr_2{μ_2-"O(O=)CCH"_3}_4*2OH_2], is one well characterized metal complex, whose exceptionally short $\text{metal-metal}$ distance of $2.36 \times {10}^{-} 10 \cdot m$ may be rationalized on the basis of a $C r - C r$ $\sigma \text{-bond}$, $2 \times C r - C r$ $\pi - \text{bonds}$, and $1 \times C r - C r$ $\delta \text{-bond}$.
In each case the bond represents a region of electron density between the metal-metal vector, or above the plane of the metal-metal vector, so that internuclear repulsion between the $C {r}^{2 +}$ centres is minimized, and a NET attractive force results between the metal nuclei and the orbital clouds of the electron.