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

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