In this chapter is shown that structural distortions of trihomonuclear Kramers clusters occur as a consequence of the time-reversal symmetry. These distortions are caused by the fact that the time-reversal operator T is not a separate element of the magnetic point group G', but forms a combined T element with other g elements of the original point group G. The order of the element g cannot be an odd number, otherwise it would lead to T G', which contradicts the definition of the group G'. Forbidden rotations by (forumala Presented). in the group G' lead to the fact that metal ions of homonuclear magnetic clusters in a magnetic ordered state cannot occupy the vertices of an equilateral triangle or those of a regular pentagon. The distortion of the regular triangle or pentagon occurs only if the time-reversal operator T is taken into account. Hence these structural distortions are due to the time-reversal symmetry. There are presented and discussed experimental data concerning the anomalous behavior of chromium(II), iron(III), copper(II), vanadium(II) and cobalt(II) trihomonuclear clusters determined by their four-color symmetry.