Crystalline Trinuclear Exo- and Endocyclic Complexes of a Tetrapyrazinoporphyrazine Ligand with 3 <i>d</i> - and 4 <i>f</i> -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, FeII(Et8TPyzPz), with 3d- (FeII, CoII) and 4f-metal (DyIII) 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[FeIII2(Et8TPyzPz)·(FeIII2)2]2– (1), {TBA+}2[FeIII2(Et8TPyzPz)·(CoIII2)2]2– (2), and {TBA+}2[FeIII2(Et8TPyzPz)·(DyIIII3)2]2– ·4C6H4Cl2 (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 Et8TPyzPz macrocycle. The iron(II) and cobalt(II) atoms are tetracoordinated when inserted into the N2-pockets to form both M–Nmeso and M–Npyrazine 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 [FeIII2(Et8TPyzPz)2–·(MIx)2]2– units contain a low-spin diamagnetic central Fe(II) ion and high-spin exocyclic FeII, CoII, and DyIII nuclei. Exocoordinated metal ions are antiferromagnetically coupled through the diamagnetic {FeIII2(Et8TPyzPz)}2– unit. The Soret and the Q-bands are observed in the spectra of starting {FeII(Et8TPyzPz)} and complexes 1–3 at 336–348and 645–655nm, supporting preservation of the Et8TPyzPz2– 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.