The anomalous behavior of trihomonuclear Kramers clusters containing chromium(III), iron(III), copper(II), vanadium(IV) and cobalt(II) atoms in coordination compounds [Cr3O(CH3COO)6(H2O)3]Cl∙6H2O, [Fe3O(CH3COO)6(H2O)3]Cl∙6H2O, [Fe3(RCO2)6(OH)2]∙X∙ nH2O, [Fe6(O)2(OH)2(OOCCMe3)12(HOOCCMe3)(THF)]∙ 1.5C6H6 (where THF is tetrahydrofuran), {[Cu3L(μ-OH)∙(μ3-HPO4)( H2O)][PF6]3∙ 3H2O}n, {[Cu3(μ3-OH)(aaat)3 (H2O)3]∙[NO3]2}∙ H2O (where Haaat = 3-acetylamino-5-amino-1,2,4-triazole), [Cu3(μ3-OH) (aat)3 (μ3-SO4)]∙ 6H2O (where Haat = 3-acetylamino-5amino-1,2,4-triazole), Na9[Cu3(H2O)9(αAsW9 O32)2] ∙ 26H2O, Cu3(O2C16H23)6 ∙1.2C6H12, (CN3H6)4Na 2{H4V6 IVO8(PO4)4∙ [(OCH2)3CCH2OH]2}∙ 14H2O, Na6{H4V6 IVO8(PO4)4[(OCH2)3 CCH2OH]2} 18H2O , K6[V15As6O42(H2O)] ∙8 H2O, [Cu3(cpse)3(H2O)3] ∙8.5 H2O and Na5[Co6(H2O)30│Co9 Cl2(OH)3∙(H2O)9(β-SiW8O31)3~]∙ 37H2O is analyzed. This analysis is based on the fact that a possible spin configuration in magnetic clusters means a spin arrangement that does not violate any of the symmetry principles that are accepted as valid in physics. Many of the spin arrangements, which in this sense are possible, may turn out to be impossible from some specific dynamical considerations. The problem of classification of all possible spin configurations is analogous to the problem of the classification of all possible atom arrangement in clusters [1]. Both problems are not independent because the spins are located at the positions of magnetic atoms. According to result of our analysis only a very limited number of trimer homonuclear clusters with arrangement of magnetic atoms in the vortexes of an equilateral triangle at high temperatures (above 50K) are known at present. Except three above- mentioned copper (II) full-symmetric trimers with ground state total spin ST=1/2 Cu3 (O2C16H23)6∙1.2C6H12 [2], [Cu3(cpse)3(H2O)3]∙8.5 H2O [3] and Na9[Cu3(H2O)9∙(α- AsW9O32)2]∙26 H2O [4], there is also one equilateral triangle related to triangular cation [Cu3(pao)3OH]2+ with Hpao = pyridine-2-aldehyde-oxide [5]. It should be remembered that the last coordination compound was considered [4] as containing equilateral Cu3 triangles while the crystalline structure data demonstrated that there are isosceles one [5-7]. Thus, only three triangles are considered as equilateral and all they are formed by copper atoms. It is curious to note that the first discovered trinuclear clusters Cr3 and Fe3 for a long time were considered as clusters with the symmetric arrangement of the chromium and iron atoms, respectively, in the vortexes of an equilateral triangle. However, later it was established that this conclusion was due to the rather low accuracy of the single crystal X-ray diffraction analysis. A more precise determination of the crystalline structure on the basis of X-ray diffraction at low temperature (190K) showed that there are isosceles triangles. The temperature dependence of XmT product (X being the magnetic susceptibility per [Cu3] entity) shows that at room temperature the XmT values are lower than those expected for three uncoupled S = 1/2 spins and they decrease steadily with decreasing temperature. Magnetic behavior of Cu3 Kramers clusters in the 90-300K temperature range can be interpreted in the framework of an isotropic Heisenberg-Dirac-van Vleck spin Hamiltonian with a single exchange constant. To rationalize the magnetic behavior below 90K, the distortion of the equilateral triangle (C3v point group of symmetry) with its transformation into an isosceles one (C2v point group of symmetry) must be taken in consideration. The experimental results (magnetic susceptibility, EPR in X-, Qand W- bands, NMR, specific heat, IR and UV-VIS spectra, Mossbauer spectroscopy, inelastic neutron scattering) clearly confirm that the existence of a disagreement between the high symmetry of triads at room temperatures (equilateral triangle) and lowered symmetry (isosceles triangle) at low temperatures as a rule is not accompanied by the structural phase transition. It is a general characteristic for all trimer magnetic clusters with Kramers degeneracy of energy levels. In a triangular arrangement of antiferromagnetically coupled metal ions, the description of the magnetic properties of corresponding complexes is complicated in addition by the presence of spin-frustration effects. All Kramers clusters, without exception, must be characterized by the generalized point groups of symmetry (four-color magnetic symmetry groups) with the low symmetry atom arrangement [8]. This follows from specific proprieties of the four-color groups of magnetic symmetry taking into account the existence of correlation between all possible spin configurations and all corresponding arrangements of the magnetic atoms. The structure of four-color point groups of magnetic symmetry depends on the type of simultaneous transformations of space and spin parts of the full time dependent wave function under action of the time-reversal operator. We certify that structural distortions of magnetic clusters leading to lowering of their space symmetry are due to the peculiarity of corresponding four-color point groups of magnetic symmetry. The three Cu3 triangles considered above on basis of X-ray diffraction data as equilateral triangles are, in reality, non equilateral because there are no four-color groups of magnetic symmetry with threefold rotation axes. The X-ray diffraction data lead to conclusion about symmetric copper trimers as consequence of small geometrical distortions of equilateral triangles. In cases when the experimental data about sides of the triangle or exchange interaction constants between magnetic ions lead to conclusion that the triangle is equilateral, it is in reality isosceles one. This can be revealed by more precise experiments. Unlike the non Kramers systems where the 58 two-color (black-and-white) point groups of magnetic symmetry exist, for Kramers spin clusters only four point groups of magnetic symmetry exist and they are four-color. Among the symmetry elements of these groups, there are not threefold rotation axes, and therefore not all atoms of the magnetic trimer clusters are equivalent. The anomalous temperature behavior of trihomonuclear clusters is discussed in terms of four-color point group of magnetic symmetry. It is shown that in the case of high spins Si (i =1,2,3) of the trihomonuclear cluster, as it was established earlier for the case Si=1/2, there is no instability of the spin populations of an equilateral trimer with generated ground state and non-zero spin moment with respect to a weak structural distortion by analogy with Jahn-Teller instability. The distortion-induced spin polarization from two Kramers components is compensated by distortion-induced spin polarization of the same value but opposite sign due to two other Kramers components of the spin trimer ground state.