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.

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·(FeIII2)3}3-·2C6H4Cl2 (1), {cryptand(K+)}3·{HATNA(CN)6·(CoIII2)3}3-·2C6H4Cl2 (2), and (CV+)3·{HAT(CN)6·(CoIICl2)3}3-·0.5(CVCl)·2.5C6H4Cl2 (3) are synthesized (CVCl = crystal violet). Salt 1 has a χMT value of 9.80 emu K mol-1 at 300 K, indicating a contribution of three high-spin FeII (S = 2) and one S = 1/2 of HATNA(CN)6˙3-. The χMT 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 FeII-FeII 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 CoII (S = 3/2) for 2 and 3. However, the χMT 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 χMT 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 CoII-L˙3- coupling for 2 and 3 with J1 values of -442 and -349 cm-1. The CoII-CoII 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 CoII-CoII coupling. Thus, a balance between J1 and J2 couplings provides parallel or antiparallel alignment of the FeII and CoII spins, leading to high- or low-spin ground states of {L·[MII(Hal)2]3}3-.

Trinuclear coordination assemblies of low-spin dicyano manganese(II) (S = 1/2) and iron(II) (S = 0) phthalocyanines with manganese(II) acetylacetonate, tris(cyclopentadienyl)gadolinium(III) and neodymium(III).

The reaction of MnIIPc, FeIIPc or FeIIPcCl16 with KCN in the presence of cryptand[2.2.2] yielded dicyano-complexes {cryptand(K+)}2{MII(CN)2(macrocycle2-)}2-·XC6H4Cl2 (M = Mn and Fe, X = 1 and 2) that were used for the preparation of trinuclear assemblies of the general formula {cryptand(K+)}2{MII(CN)2Pc·(ML)2}2-·nC6H4Cl2 (MII = MnII and FeII; n = 1, 4 and 5). These assemblies were formed via coordination of two manganese(II) acetylacetonate (ML = MnII(acac)2, S = 5/2), tris(cyclopentadienyl)gadolinium (ML = Cp3GdIII, S = 7/2) or tris(cyclopentadienyl)neodymium (ML = Cp3NdIII, S = 3/2) units to the nitrogen atoms of bidentate cyano ligands. The N(CN)-Mn{MnII(acac)2} bond is 2.129(3) Å long but the bonds are elongated to 2.43-2.49 Å for tris(cyclopentadienyl)lanthanides. {Cryptand(K+)}2{MnII(CN)2Pc·(MnII(acac)2)2}2-·5C6H4Cl2 (2) contains three Mn(II) ions in different spin states (S = 5/2 and 1/2). Strong antiferromagnetic coupling of spins observed between them with the exchange interaction (J) of -17.6 cm-1 enables the formation of a high S = 9/2 spin state for {MnII(CN)2Pc·(MnII(acac)2)2}2- dianions at 2 K. The estimated exchange interaction between MnII (S = 1/2) and GdIII (S = 7/2) spins in {MnII(CN)2Pc·(Cp3GdIII)2}2- is only -1.1 cm-1, and in contrast to 2, nearly independent GdIII and MnII centers are formed. As a result, no transition to the high-spin state is observed in {MnII(CN)2Pc·(Cp3GdIII)2}2-. The {MnII(CN)2Pc·(Cp3NdIII)2}2- and{FeII(CN)2Pc·(Cp3NdIII)2}2- dianions with Cp3NdIII show a decrease of χMT values in the whole studied temperature range (300-1.9 K). A similar behaviour was found previously for pristine Cp3NdIII and Cp3NdIII·L complexes (L = alkylisocyanide ligand).

Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of FeII (S=2) Spins in Differently Charged {HAT ⋠(FeII Cl2 )3 }n (n=2- and 3-) Assemblies of Hexaazatriphenylenes (HAT).

Hexaazatrianthracene (HATA) and hexaazatriphenylenehexacarbonitrile {HAT(CN)6 } are reduced by metallic iron in the presence of crystal violet (CV+ )(Cl- ). Anionic ligands are produced, which simultaneously coordinate three FeII Cl2 to form (CV+ )2 {HATA ⋅ (FeII Cl2 )3 }2- ⋅ 3 C6 H4 Cl2 (1) and (CV+ )3 {HAT(CN)6. (FeII Cl2 )3 }3- ⋅ 0.5CVCl ⋅ 2.5 C6 H4 Cl2 (2). High-spin (S=2) FeII atoms in both structures are arranged in equilateral triangles at a distance of 7 Å. An antiferromagnetic exchange is observed between FeII in {HATA ⋅ (FeII Cl2 )3 }2- (1) with a Weiss temperature (Θ) of -80 K, the PHI estimated exchange interaction (J) is -4.7 cm-1 . The {HAT(CN)6 ⋅ (FeII Cl2 )3 }3- assembly is obtained in 2. The formation of HAT(CN)6 .3- is supported by the appearance of an intense EPR signal with g=2.0037. The magnetic behavior of 2 is described by a strong antiferromagnetic coupling between the FeII and HAT(CN)6 .3- spins with J1 =-164 cm-1 (-2 J formalism) and by a weaker antiferromagnetic coupling between the FeII spins with J2 =-15.4 cm-1 . The stronger coupling results in the spins of the three FeII Cl2 units to be aligned parallel to each other in the assembly. As a result, an increase of the χM T values is observed with the decrease of temperature from 9.82 at 300 K up to 15.06 emu ⋅ K/mol at 6 K, and the Weiss temperature is also positive being at +23 K. Thus, a change in the charge and spin state of the HAT-type ligand to ⋅3- results in ferromagnetic alignment of the FeII spins, yielding a high-spin (S=11/2) system. DFT calculations showed that, due to the high symmetry and nearly degenerated LUMO of both HATA and HAT(CN)6 , their complexes with FeII Cl2 have a variety of closely lying excited high-spin states with multiplicity up to S=15/2.

Solid-State Properties of Hexaazatriphenylenehexacarbonitrile HAT(CN)6 .- Radical Anions in Crystalline Salts Containing Cryptand(M+ ) and Crystal Violet Cations.

Crystalline {Cryptand[2.2.2](Na+ )}{HAT(CN)6 .- }⋅0.5C6 H4 Cl2 (1), {Cryptand[2.2.2](K+ )}{HAT(CN)6 .- } (2), (CV+ ){HAT(CN)6 .- } (3), and (CV+ ){HAT(CN)6 .- }⋅2C6 H4 Cl2 (4) salts (where CV+ is the crystal violet cation) containing hexaazatriphenylenehexacarbonitrile radical anions have been obtained. The solid-state molecular structure as well as the optical and magnetic properties of HAT(CN)6 .- are studied. The formation of HAT(CN)6 .- in 1-4 leads to the appearance of new bands in the visible range, at 694 and 740 nm. The HAT(CN)6 .- radical anions have spin state S=1/2 and are packed in one-dimensional stacks containing the {HAT(CN)6 .- }2 dimers alternated with weaker interacting pairs of HAT(CN)6 .- in 1 and nearly isolated {HAT(CN)6 .- }2 dimers in 2. The {HAT(CN)6 .- }2 dimers are diamagnetic in 1 but they effectively mediate one-dimensional antiferromagnetic coupling of spins within the stacks with moderate exchange interaction of J/kB = -80 K. The behaviour of salt 2 is described by a singlet-triplet model for the {HAT(CN)6 .- }2 dimers with an energy gap of 434(±7) K. Magnetic behaviour of both salts agree well with the data of extended Hückel calculations. Salts 3 and 4 contain isolated stacks of alternated HAT(CN)6 .- and CV+ ions, and in this case, nearly paramagnetic behaviour is observed with Weiss temperatures of -1 and -7 K, respectively. Narrow Lorentzian EPR signals with g = 2.0033-2.0039 were found for the HAT(CN)6 .- radical anions in 1 and 4 but in solution g-factor shifts to 1.9964. The electronic structure of HAT(CN)6 .- is analysed based on X-ray diffraction data for 2, showing a Jahn-Teller distortion of the radical anion that reduces the symmetry from D3h to Cs and splits the initially degenerated LUMOs.