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)center dot{HATNA (CN)(6)center dot((FeI2)-I-II)(3)}(3-) center dot 2C(6)H(4)Cl(2) (1), {cryptand(K+)}(3)center dot{HATNA(CN)(6)center dot((CoI2)-I-II)(3)}(3-) center dot 2C(6)H(4)Cl(2) (2), and (CV+)(3)center dot{HAT (CN)(6)center dot(CoIICl2)(3)}(3-) center dot 0.5(CVCl)center dot 2.5C(6)H(4)Cl(2) (3) are synthesized (CVCl = crystal violet). Salt 1 has a chi T-M 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)center dot(3-). The chi T-M 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 highspin S = 11/2 system. Density functional theory (DFT) calculations support a high-spin state of CoII (S = 3/ 2) for 2 and 3. However, the.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 chi T-M 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 center dot 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 J2 increase may be the shortening of the Co-N(L) bonds in 3 and 2 to 2.02(2) and 1.993(12) angstrom. 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 FeII and Co-II spins, leading to high- or low-spin ground states of {L center dot[M-II(Hal)(2)](3)}(3-).