Antiferromagnetic spin chain behavior and a transition to 3D magnetic order in Cu(D,L-alanine)(2): Roles of H-bonds

作者：Calvo Rafael^*; Sartoris Rosana P; Calvo Hernan L; Chagas Edson F; Rapp Raul E

来源：Solid State Sciences, 2016, 55: 144-151.

DOI：10.1016/j.solidstatesciences.2016.03.005

• Spin chains
• Phase transition
• Exchange interactions
• H-bonds

We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)(2)center dot H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B-0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J(0)=(-2.12 +/- 0.08) cm(-1) (defined as H-ex(i,i+1) = -2J(0)S(i)center dot Si+1), between neighbor coppers at 4.49 angstrom along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B-0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B-0 were globally fitted by an intrachain AFM exchange coupling constant 2J(0)=(=2.27 +/- 0.02) cm(-1) and g = 2.091 +/- 0.005. Interchain interactions J(1) between coppers in neighbor chains connected through long chemical paths with total length of 9.51 angstrom cannot be estimated from magnetization curves. However, observation of the phase transition in the specific heat data allows estimating the range 0.1 <=vertical bar 2J(1)vertical bar <= 0.4 cm(-1), covering the predictions of various approximations. We analyze the magnitudes of 2J(0) and 2J(1) in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain interactions.

• 出版日期2016-5