Magnetic behavior and ground spin states for coordination {L·[MII(Hal)2]3}3- assemblies (Hal = Cl or I) of radical trianion hexacyanohexaazatriphenylenes (L) with three coordinated high-spin FeII (S = 2) or CoII (S = 3/2) centers

Maxim V Mikhailenko; Vladislav V Ivanov; Alexander F Shestakov; Aleksey V Kuzmin; Salavat S Khasanov; Akihiro Otsuka; Hideki Yamochi; Hiroshi Kitagawa; Dmitri V Konarev

doi:10.1039/d3dt01571h

Magnetic behavior and ground spin states for coordination {L·[M^II(Hal)₂]₃}^3- assemblies (Hal = Cl or I) of radical trianion hexacyanohexaazatriphenylenes (L) with three coordinated high-spin Fe^II (S = 2) or Co^II (S = 3/2) centers

Dalton Trans. 2023 Aug 15;52(32):11222-11233. doi: 10.1039/d3dt01571h.

Authors

Affiliations

¹ Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry RAS, Chernogolovka, Moscow region, 142432, Russia. konarev3@yandex.ru.
² Moscow State University, Leninskie Gory, Moscow, 119991 Russia.
³ Institute of Solid State Physics RAS, Chernogolovka, Moscow region, 142432 Russia.
⁴ Division of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.

PMID: 37525575
DOI: 10.1039/d3dt01571h

Abstract

A series of trianion assemblies of hexaazatriphenylenehexacarbonitrile {HAT(CN)₆} and hexaazatrinaphthylenehexacarbonitrile {HATNA(CN)₆} with three Fe(II) or Co(II) ions: {cryptand(K⁺)}₃·{HATNA(CN)₆·(Fe^III₂)₃}^3-·2C₆H₄Cl₂ (1), {cryptand(K⁺)}₃·{HATNA(CN)₆·(Co^III₂)₃}^3-·2C₆H₄Cl₂ (2), and (CV⁺)₃·{HAT(CN)₆·(Co^IICl₂)₃}^3-·0.5(CVCl)·2.5C₆H₄Cl₂ (3) are synthesized (CVCl = crystal violet). Salt 1 has a χ_MT value of 9.80 emu K mol^-1 at 300 K, indicating a contribution of three high-spin Fe^II (S = 2) and one S = 1/2 of HATNA(CN)₆˙^3-. The χ_MT value increases with cooling up to 12.92 emu K mol^-1 at 28 K, providing a positive Weiss temperature of +20 K. Such behavior is described using a strong antiferromagnetic coupling between S = 2 and S = 1/2 with J₁ = -82.1 cm^-1 and a weaker Fe^II-Fe^II antiferromagnetic coupling with J₂ = -7.0 cm^-1. As a result, the spins of three Fe(II) ions (S = 2) align parallel to each other forming a high-spin S = 11/2 system. Density functional theory (DFT) calculations support a high-spin state of Co^II (S = 3/2) for 2 and 3. However, the χ_MT value of 2 and 3 is 2.25 emu K mol^-1 at 300 K, which is smaller than 6 emu K mol^-1 calculated for the system with three independent S = 3/2 and one S = 1/2 spins. In contrast to 1, the χ_MT values decrease with cooling to 0.13-0.36 emu K mol^-1 at 1.9 K, indicating that spins of cobalt atoms align antiparallel to each other. Data fitting using PHI software for the model consisting of three high-spin Co(II) ions and an S = 1/2 radical ligand shows very large Co^II-L˙^3- coupling for 2 and 3 with J₁ values of -442 and -349 cm^-1. The Co^II-Co^II coupling via the ligand (J₂) is also large, being -100 and -84 cm^-1, respectively, which is more than 10 times larger than that of 1. One of the reasons for the J₂ increase may be the shortening of the Co-N(L) bonds in 3 and 2 to 2.02(2) and 1.993(12) Å. DFT calculations support the population of the quartet state for the Co₃ system, whereas the high-spin decet (S = 9/2) state is positioned higher by 680 cm^-1 and is not populated at 300 K. This is explained by the large Co^II-Co^II coupling. Thus, a balance between J₁ and J₂ couplings provides parallel or antiparallel alignment of the Fe^II and Co^II spins, leading to high- or low-spin ground states of {L·[M^II(Hal)₂]₃}^3-.