Exchange interaction at the supramolecular level.: EPR investigation of two copper (II) compounds:: [Cu2(acae)2(phen)2(bpe)](ClO4)2•(bpe)•CH3CN•H2O and [Cu2(acae)2(phen)2(bpp)](ClO4)2•6H2O (bpe = trans-1,2-bis(4-pyridyl)ethylene, bpp = bis(4-pyridyl)propane)

Intra- and intermolecular exchange and dipole-dipole interactions in two supramolecular compounds, [Cu-2(acac)(2)(phen)(2)(bpe)](ClO4)(2)center dot(bpe)center dot CH3CN center dot H2O (1) and [Cu-2(acac)(2)(phen)(2)(bpp)] X (ClO4)(2) center dot 6H(2)O (II), which are built up of binuclear fragments through pi-pi stacking interactions, are investigated. The electron paramagnetic resonance (EPR) spectra of the polycrystalline samples of I and II were measured in the X-band in the temperature range of 300-4.2 K, and in the Q-band at T = 300 and 4.2 K. The EPR spectra were interpreted as being due to weakly interacting dimer fragments. Triplet and singlet states of dimer fragments arise from a larger interaction JS(1)S(2\) between two nearest copper complexes of two neighboring binuclear fragments. The theoretical analysis of the EPR spectrum of the polycrystalline sample for weakly interacting triplet states is carried out. The influence of the weak interaction between triplet states with value of X is considered in the model of the frequency exchange. A special attention is focused on the presence of the additional signal due to the exchange merging in some orientations where the J' value exceeds the fine structure parameters of the spectrum. The analysis of the conditions for the detection of the additional signal and of the influence of this signal on the form of the EPR spectrum allows us to estimate the value of the exchange interaction J' = 0.025 +/- 0.005 cm(-1) for compounds I and II and anisotropic part of exchange interaction between two nearest copper complexes as J(zz) = -0.02 cm(-1), J(xx,yy) = 0.01 cm(-1) for compound I.