Exchange variation of hyperfine characteristics of tetrameric [Mn3(III)Mn(IV)] and [Mn3(IV)Mn(III)] clusters Original Research Article

The dependences of the cluster g-factor, the effective hyperfine constants Ai and the hyperfine structure of the EPR signal on the exchange interaction were studied for the [Mn3(III)Mn(IV)] and [Mn3(IV)Mn(III)] clusters - possible prototypes of the Mn center of Photosystem II in the S2 state. The mixing of the states with different S12 intermediate spins in the Heisenberg model HB = −2[J12s1s2 + Jα(s1s3 + s1s4) + Jβ(s2s3 + s2s4) + J34s3s4] leads to essential exchange modification of the expectation values for each manganese ion. The exchange dependence of the Ki = / coefficients results in the exchange modification and reduction of the cluster g-factor. The / variations control also the values and signs of the effective hyperfine constants Ai. The Ai(Jtm) exchange dependences for the S = 12 ground state of the [Mn3(III)Mn(IV)] and [Mn3(IV)Mn(III)] clusters with complex structures were obtained in the framework of the general Heisenberg model of tetramer. The calculated hyperfine structures show a strong dependence on the total spin, intermediate spins and on the variation of the Heisenberg exchange parameters.