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.

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 II I 2 ) 3 } 3- ·2C 6 H 4 Cl 2 (1), {cryptand(K + )} 3 ·{HATNA(CN) 6 ·(Co II I 2 ) 3 } 3- ·2C 6 H 4 Cl 2 (2), and (CV + ) 3 ·{HAT(CN) 6 ·(Co II Cl 2 ) 3 } 3- ·0.5(CVCl)·2.5C 6 H 4 Cl 2 (3) are synthesized (CVCl = crystal violet). Salt 1 has a χ M T 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 M T 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 J 1 = -82.1 cm -1 and a weaker Fe II -Fe II antiferromagnetic coupling with J 2 = -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 M T 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 M T 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 J 1 values of -442 and -349 cm -1 . The Co II -Co II coupling via the ligand ( J 2 ) 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 J 2 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 Co 3 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 J 1 and J 2 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- .