Spirocyclic derivatives of nitronyl nitroxides in the design of heterospin CuII complexes manifesting spin transitions

Spin Transition in the Cu(hfac)2 Complex with (4-Ethylpyridin-3-yl)-Substituted Nitronyl Nitroxide Caused by the “Asymmetric” Structural Rearrangement of Exchange Clusters in the Heterospin Molecule

“…This transition is unusual, since it causes spin coupling in half of all terminal {>N-•O-Cu 2+ } exchange clusters, which leads to spin compensation of only two paramagnetic centers of the six centers present in the molecule. This "asymmetric" coupling of the electrons of the paramagnetic centers inside one molecule, that has not been observed earlier for multinuclear Cu(II) complexes with nitroxides [4,5,18]. This effect can evidently be responsible for the appearance of stepwise spin transitions in multinuclear compounds with several exchange clusters in the molecule.…”

“…A spin-crossover-like Earlier, it was shown that Cu(hfac)2 forms binuclear and tetranuclear complexes with both L R * and L R ( Figure 1); it also forms chain polymers {[[Cu(hfac)2]2L2][Cu(hfac)2]}∞, in which the binuclear fragments are linked into chains via additional Cu(hfac)2 fragments. The spin transitions were recorded for [Cu(hfac)2L H ]2 [18], [Cu(hfac)2L Me ]2•Solv (Solv = n-C6H14, n-C10H22, n-C16H34) [9], [[Cu(hfac)2]4(L H )2] [18], and [[Cu(hfac)2]4(L H *)2] complexes [4,16]. We synthesized the binuclear [Cu(hfac)2L Et ]2 and tetranuclear [[Cu(hfac)2]4(L Et )2] and studied their structure and magnetic properties.…”

“…Cu(hfac)2 [22], 1,1'-dihydroxylamino-bis-cyclopentyl sulfate monohydrate [18], and 4-ethyl nicotinaldehyde [23] used in the present study were synthesized by the known procedures.Commercial reagents and solvents were used without any additional purification. For Earlier, it was shown that Cu(hfac) 2 forms binuclear and tetranuclear complexes with both L R * and L R ( Figure 1); it also forms chain polymers {[[Cu(hfac) 2 ] 2 L 2 ][Cu(hfac) 2 ]} ∞ , in which the binuclear fragments are linked into chains via additional Cu(hfac) 2 fragments.…”

“…Cu(hfac) 2 [22], 1,1'-dihydroxylamino-bis-cyclopentyl sulfate monohydrate [18], and 4-ethyl nicotinaldehyde [23] used in the present study were synthesized by the known procedures.Commercial reagents and solvents were used without any additional purification. For chromatographic procedures, TLC plates Silica Gel 60 F 254 , aluminum sheets (Macherey-Nagel, Düren, Germany), and silica gel "0.063-0.200 mm for column chromatography" (Merck KGaA, Darmstadt, Germany) were used.…”

Spirocyclic Nitroxides as Versatile Tools in Modern Natural Sciences: From Synthesis to Applications. Part I. Old and New Synthetic Approaches to Spirocyclic Nitroxyl Radicals

“…Recently, the vast class of stable nitronyl nitroxyl radicals (NNRs) of the 4,5-dihydroimidazole series, introduced into practice by Ullmann et al [ 170 , 171 ] and represented mostly as 4,4,5,5-tetramethyl (tetra-alkyl) derivatives, was supplemented with spirocyclic analogs (SNNRs). First, α,β-di-SNNRs were prepared by Ovcharenko et al via five-step synthesis starting with cyclopentylbromide 290 ( Scheme 52 ) [ 172 ]. Nucleophilic substitution of the bromine atom affords a nitro compound with a moderate yield.…”