Crystalline Trinuclear Exo- and Endocyclic Complexes of a Tetrapyrazinoporphyrazine Ligand with 3 d - and 4 f -Metals

A redox-active tetrapyrazinoporphyrazine ligand was used as a platform for the design of multimetallic coordination complexes. The first paramagnetic homo- and heterotrimetallic complexes have been obtained as crystals through the reaction of iron(II) octaethyltetrapyrazinoporphyrazine, Fe II (Et 8 TPyzPz), with 3 d - (Fe II, Co II ) and 4 f -metal (Dy III ) iodides. In these conditions, tetrapyrazinoporphyrazine can coordinate to metals to form exo- and endocyclic complexes when coordination is observed both in the center and on the periphery of a macrocycle. Crystal structures of the complexes have been determined from single-crystal X-ray diffraction analysis, and their compositions are {TBA + } 2 [Fe II I 2 (Et 8 TPyzPz)·(Fe II I 2 ) 2 ] 2– ( 1 ), {TBA + } 2 [Fe II I 2 (Et 8 TPyzPz)·(Co II I 2 ) 2 ] 2– ( 2 ), and {TBA + } 2 [Fe II I 2 (Et 8 TPyzPz)·(Dy III I 3 ) 2 ] 2– ·4C 6 H 4 Cl 2 ( 3 ). The central iron(II) atom forms four shorter N–Fe bonds (1.917(3)–1.927(3) Å) and two longer I–Fe bonds (2.68 Å).Two exocyclic metal iodides are coordinated to the periphery of the Et 8 TPyzPz macrocycle. The iron(II) and cobalt(II) atoms are tetracoordinated when inserted into the N2-pockets to form both M–N meso and M–N pyrazine bonds of 2.14 and 2.24 Å for Fe(II) and 2.10 and 2.16 Å for Co(II), respectively. The exocyclic Dy ions, when introduced into the N3-pockets to form the Dy–N bonds of 2.43 and 2.66–2.75 Å, respectively, have distorted octahedral geometry. Optical and magnetic properties of the solids were investigated. The [Fe II I 2 (Et 8 TPyzPz) 2– ·(MI x ) 2 ] 2– units contain a low-spin diamagnetic central Fe(II) ion and high-spin exocyclic Fe II, Co II, and Dy III nuclei. Exocoordinated metal ions are antiferromagnetically coupled through the diamagnetic {Fe II I 2 (Et 8 TPyzPz)} 2– unit. The Soret and the Q-bands are observed in the spectra of starting {Fe II (Et 8 TPyzPz)} and complexes 1 – 3 at 336–348and 645–655nm, supporting preservation of the Et 8 TPyzPz 2– macrocycle at complex formation. At the same time, broad and intense bands appear at 495–526 nm in the visible range, and lower-energy bands are observed near the Q -band at 700 nm. The latter bands can be attributed to metal-to-macrocycle charge transfer (CT) in 1 – 3 . CT is supported by DFT calculations.