Effect of reduction on the molecular structure, optical and magnetic properties of the fluorinated copper (II) phthalocyanines

Reduction of copper(II) octafluoro- {CuII(F8Pc)} and hexadecafluorophthalocyanines {CuII(F16Pc)} by NaCpCo(CO)2 in the presence of cryptand[2.2.2] yields new crystalline {cryptand(Na+)}[CuII(F8Pc)•3-]- 2C6H4Cl2(1) and {cryptand(Na+)}2[CuII(F16Pc)4-]2- C6H14 (2) salts. Together with two previously characterized salts of CuII(FxPc) (x = 8 and 16), that allows the study of the molecular structure, optical and magnetic properties of fluorinated copper phthalocyanines in different reduction states (-1 and -2). Blue shift of the Q-band increases together with negative charge on the macrocycle as well as new weak bands of the anions appear at 820-1013 nm. Alternation of the Nmeso-C bonds manifests itself in reduced macrocycles due to partial disruption of macrocycle aromaticity. In case of CuII(F8Pc) this effect for the dianions is nearly two times stronger than for monoanions. Alternation of bonds is less pronounced for perfluorinated CuII(F16Pc)n- (n = 1, 2) anions most probably due to partial delocalization of negative charge on fluoro-substituents. Reduction also noticeably elongates average C-F bonds in CuII(F8Pc. First reduction centered on the macrocycle provides the formation of [[CuII(F8Pc)•3-]- in 1 with two S = 1/2 spins positioned on CuII and radical trianion (F8Pc)•3- macrocycle. As a result, a broad EPR signal is observed with g = 2.1652 at RT attributable to both paramagnetic species having exchange interactions. The formation of dimerized stacks from[CuII(F8Pc)•3-]- in 1 results in strong enough magnetic coupling of the (F8Pc)•3- spins within the dimers (J/kB = - 21.8 cm-1), and weaker intramolecular coupling is observed between CuII and (F8Pc)•3- (J/kB = -10.8 cm-1). Coupling between (F8Pc)•3- spins from the neighboring dimers is nearly 1.5 times weaker (-14.6 cm-1). Second electron at the reduction also comes to the macrocycle forming diamagnetic (F16Pc)4- tetraanions. In this case S =1/2 spin is preserved on CuII. Magnetic coupling between these centers is weak due to long distances between them in the [CuII(F16Pc)4-]2- chains of 2. Salt 2 manifests an EPR signal with HF splitting characteristic of CuII with g|| = 2.1806 (A|| = 20.11 mT), and g⊥ = 1.9597 at RT.