Strong antiferromagnetic coupling of spins in the (MDABCO+)(C60·-) salt with 3D close packing of the C60·- radical anions (MDABCO+: N-methyldiazabicyclooctanium cation)

A new salt, (MDABCO(+))(C60(·-)) (1; MDABCO(+) = N-methyldiazabicyclooctanium cation), was obtained as single crystals. The crystal structure of 1 determined at 250 and 100 K showed 3D close packing of fullerenes with eight fullerene neighbors for each C60(·-). These neighbors are located at 10.01-10.11 Å center-to-center distances (250 K) and van der Waals interfullerene C⋅⋅⋅C contacts are formed with four fullerene neighbors arranged in the bc plane. Fullerene ordering observed below 160 K is accompanied by the appearance of one and a half independent C60(·-) and trebling of the unit cell along the b axis. Fullerenes are packed closer to each other at 100 K. As a result, fullerenes are located in the three-dimensional packing at 9.91-10.12 Å center-to-center distances and 18 short interfullerene C⋅⋅⋅C contacts are formed for each C60(·-). Although they are closed packed, fullerenes are not dimerized down to 1.9 K. Magnetic data indicate strong antiferromagnetic coupling of spins in the 70-300 K range with a Weiss temperature of Θ = -118 K. Magnetic susceptibility shows a round maximum at 46 K. Such behavior can be described well by the Heisenberg model for square two-dimensional antiferromagnetic coupling of spins with an exchange interaction of J/kB = -25.3 K. This magnetic coupling is one of the strongest observed for C60(·-) salts.

Effect of the Co-C(C60(-)) bond formation on magnetic properties of the ionic complex {cryptand[2,2,2] x (Na+)} x {Co(II)TPP x (C60(-))} x (C6H4Cl2)2

A new ionic complex {cryptand[2,2,2] x (Na(+))} x {Co(II)TPP x (C(60)(-))} x (C(6)H(4)Cl(2))(2) has been obtained as single crystals by a diffusion technique. It involves coordination {Co(II)TPP x u(C(60)(-))} units and bulky {cryptand[2,2,2] x (Na(+))} cations. The Co-C(C(60)(-)) coordination bond is short (2.262(2) A at 100 K) which provides ordering in the C(60)(-) anions. This is the first ordered structure of {Co(II)TPP x (C(60)(-))}. The coordination bonds weaken upon heating to be 2.316(4) A at 250 K. As a result, the C(60)(-) anions begin to rotate at 250 K about the Co-C bond between two orientations. The complex is diamagnetic from 4 up to 320 K. The Co-C bonds dissociate above 320 K only to form unbound paramagnetic Co(II)TPP and C(60)(*-) species. The process is accompanied by the reversible increase in magnetic susceptibility of the complex and the appearance of a new broad EPR signal with g = 2.1187 and a linewidth of approximately 120 mT (350 K). The signal was attributed to both paramagnetic Co(II)TPP and C(60)(*-), which showed strong exchange interaction.

Peculiarities of C60.− Coordination to Cobalt(II) Octaethylporphyrin in Ionic Multicomponent Complexes: Observation of the Reversible Formation of CoC(C60−) Coordination Bonds

Ionic multicomponent complexes containing the C60- anion, cobalt(II) octaethylporphyrin (OEP), and the noncoordinating tetramethylphosphonium cation (TMP+), [(TMP+){Co(II)OEP(C60-)}(C6H5CN)x(C6H4Cl2)(1-x)] (x congruent with 0.75) (1), or the coordinating cation of N-methyldiazabicyclooctane (MDABCO+), [{(MDABCO+)Co(II)OEP(C60-)}(C6H5CN)x(C6H4Cl2)(1-x)] (x congruent with 0.67) (2), were obtained. Diamagnetic sigma-bonded {Co(II)OEP(C60-)} units in 1 have the Co...C(C60-) distance of 2.268(1) A at 100 K and are stable up to 290 K. Both MDABCO+ and C60- coordinate to Co(II)OEP in 2. In this case, a noticeably longer Co...CC60-) distance of 2.508(4) A was observed at 100 K. As a result, the unprecedented reversible formation of the Co-C(C60-) coordination sigma bond is realized in 2 and is accompanied by a transition from a paramagnetic to a diamagnetic state in the 50-250 K range. It was shown, for the first time, that the Co...C distance of about 2.51 A is a boundary distance below which the Co-C(C60-) coordination bond is formed.

Neutral and Ionic Complexes of C60 with Metal Dibenzyldithiocarbamates. Reversible Dimerization of C60•- in Ionic Multicomponent Complex [CrI(C6H6)2•+]·(C60•-)·0.5[Pd(dbdtc)2]

New molecular complexes of C60 with metal(II) dibenzyldithiocarbamates, M(dbdtc)2.C60.0.5(C6H5Cl), where M=Cu(II), Ni(II), Pd(II), and Pt(II) and an ionic multicomponent complex [Cr(I)(C6H6)2*+].(C60*-).0.5[Pd(dbdtc)2] (Cr(C6H6)2: bis(benzene)chromium) were obtained. According to IR, UV-visible-NIR, and EPR spectra, involve neutral components, whereas 5 comprises neutral Pd(dbdtc)2 and C60*- and Cr(I)(C6H6)2*+ radical ions. The crystal structure of at 90 K reveals strongly puckered fullerene layers alternating with those composed of Pd(dbdtc)2. The Cr(I)(C6H6)2*+ radical cations are arranged between the layers. Fullerene radical anions form pairs within the layer with an interfullerene C...C contact of 3.092(2) A, indicating their monomeric state at 90 K. This contact is essentially shorter than the sum of van der Waals radii of two carbon atoms, and consequently, C60*- can dimerize. According to SQUID and EPR, single-bonded diamagnetic (C60-)2 dimers form in below 150-130 K on slow cooling and dissociate above 150-170 K on heating. The hysteresis was estimated to be 20 K. For the (C60-)2 dimers in, the dissociation temperature is the lowest among those for ionic complexes of C60 (160-250 K). Fast cooling of the crystals within 10 min from room temperature down to 100 K shifts dimerization temperatures to lower than 60 K. This shift is responsible for the retention of a monomeric phase of at 90 K in the X-ray diffraction experiment.