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Herein, why is a quadruple bond not possible?

From a Lewis point of view, there is no reason why carbon can't form a quadruple bond: This model satisfies the Octet Rule and leaves no electrons for further bonding. Transition metals are able to form quadruple bonds because they can involve d atomic orbitals in bonding.

Secondly, can carbon atoms form quadruple bond? Carbon is well known to form single, double, and triple C−C bonds in compounds. There is a recent report (2012) that carbon forms a quadruple bond in diatomic carbon, C2. C2 and its isoelectronic molecules CN+, BN and CB− (each having eight valence electrons) are bound by a quadruple bond.

Also Know, can there be a quadruple covalent bond?

Quadruple bonds between atoms of main group elements are unknown. The molecular orbital diagram of diatomic carbon would show that there are two pi bonds and no sigma bonds. However, a recent paper by S. Shaik et al. has suggested that a quadruple bond exists in diatomic carbon.

Are there quintuple bonds?

A quintuple bond in chemistry is an unusual type of chemical bond, first reported in 2005 for a dichromium compound. Single bonds, double bonds, and triple bonds are commonplace in chemistry. In a quintuple bond, ten electrons participate in bonding between the two metal centers, allocated as σ²π⁴δ⁴.