Heat Capacities of the Networked System
of Single-Molecule Magnets
with Three-Dimensional Structure

Magnetic-fields dependence of heat capacity of [Mn5(hmp)4(OH)2{N(CN)2}6] 2MeCN · 2THF (hmp = hydroxymethylpyridinate) is investigated by the thermal relaxation calorimetry technique. This compound is a three dimensional system consisting of Mn4 single-molecule magnet (SMM) units and Mn2+ ions, which are linked by the dicyanamide ligands to form a coordination network structure. A sharp peak of Cp being associated with the formation of three-dimensional long-range order is observed around 1.96 K. The thermodynamic discussion based on the magnetic entropy suggests that both SMM's and Mn2+ ions are involved in the formation of the anitiferromagnetic spin ordering. However, this long-range ordering is very sensitive to the external magnetic fields which work to change the magnitude of the Zeeman splitting of the SMM levels. The behavior under magnetic fields is similar to that of the two-dimensional Mn4-network system studied previously.

(by Y. Nakazawa & S. Yamashita)

	Fig. 1. Temperature dependence of heat capacity of [Mn5(hmp)4(OH)2{N(CN)2}6] 2MeCN · 2THF (Mn5-(hmp)4), together with the typical 2D system of [Mn4(hmp)4Br2(OMe)2{N(CN)2}2] 2THF · 0.5H2O (Mn4-(hmp)4) and [Mn4(hmp)6{N(CN)2}2] (ClO4)2 (Mn4-(hmp)6). The peak shapes of three compounds are different each other.
	Fig. 2. The heat capacity of [Mn5(hmp)4(OH)2{N(CN)2}6] 2MeCN · 2THF under magnetic fields.