Spin transitions in non-classical systems

Peculiarities of synthesis of chain polymeric, copper(II) hexafluoroacetylacetonate based complexes with stable nitroxyl radicals and the results of studies on correlations between the magnetic properties and structure of these compounds are summarized. Temperature variation causes structural rearrangements in the solid phases of the compounds, accompanied by the magnetic effects similar to spin crossover phenomena. Magnetic anomalies induced by phase transitions originate from specific motions in the Jahn—Teller coordination units containing two types of exchange clusters, Cu²⁺—O^·—N< or >N—^·O—Cu²⁺—O^·—N<, and are accompanied by significant changes in the crystal volume after multiple cooling/heating cycles. Chemical methods of controlling the character and temperature of spin transitions by both the formation of solid solutions of mixed metal hexafluoroacetylacetonates with the same nitroxyl radical, {Cu_1–xM_x(hfac)₂L} (M = Mn, Ni, Co), and by the formation of solid solutions based on copper(II) hexafluoroacetylacetonate with different nitroxyl radicals, {Cu(hfac)₂L_xL_1–x}, are discussed. Specific influence of isotope substitution CH₃ CD₃ in the paramagnetic ligand on both the structure of the heterospin polymer chain and the temperature of the magnetic anomaly is discussed.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2304–2325, November, 2004.