Weak exchange interactions in the heteronuclear crystal CuPr2(CCl3COO)(8)center dot 6H(2)O

The new heteronuclear crystal CuPr2(CCl3COO)(8). 6H(2)O, constructed of cha ins containing copper and praseodymium atoms, has been synthesized and inve stigated by EPR at 9.3 GHz at temperatures ranging from room temperature do wn to 10 K. At temperatures T similar to 300-130 K, EPR spectra are observe d which are characteristic of isolated polyhedra of copper ions with g(z)=2 .330 +/- 0.005, g(x,y)=2.053 +/- 0.005, A(z)=139x10(-4) cm(-1), and A(x,y)< 26x10(-4) cm(-1). At temperatures T < 130 K a complex spectrum is observed , associated with the appearance of weak exchange interactions between the copper ions in the chain (J(Cu-Cu)Sigma S-i. Si+1), comparable in magnitude with the hyperfine interactions J(Cu-Cu)=0.015 cm(-1) at T=10 K. The magni tude of the exchange interaction decreases smoothly as the temperature is r aised. It is conjectured that orbitals of the praseodymium ions participate in the process of indirect exchange between the copper ions. (C) 1999 Amer ican Institute of Physics. [S1063-7834(99)01012-6].