An algebraic scheme for describing the bending dynamics of tetratomic molecules including linear, bent planar, and bent a-planar species is introduced. The correlation diagram linear-cis-bent and linear-trans-bent is constructed. Effective potential energy functions are evaluated by exploiting the method of coherent states. A sample calculation of the bending vibrations of C2H2 in its (X) over tilde (1)Sigma(+) electronic ground state is performed.