Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland.
Dalton Trans. 2019 Jan 22;48(4):1404-1417. doi: 10.1039/c8dt03965h.
The preparation, X-ray crystal structure, spectroscopic and variable-temperature dc and ac magnetic properties of two six-coordinate cobalt(ii) complexes of formula [Co(bim)4(tcm)2] (1) and [Co(bmim)4(tcm)2] (2) (bim = 1-benzylimidazole, bmim = 1-benzyl-2-methylbenzimidazole and tcm- = tricyanomethanide ion) are reported. 1 and 2 crystallize in the monoclinic P21/n and C2/c space groups with the asymmetric units composed of one tcm- ion and half the [Co(bim)4]2+ and [Co(bmim)4]2+ complex cations, respectively. Their cobalt atoms are in compressed (1)/rhombic (2) CoN6 octahedral environments, the axial positions being occupied by monodentate tricyanomethanide anions. The neutral molecules in 1 are linked through weak C-HN type interactions into supramolecular chains, which are further interconnected into supramolecular 2D motifs by C-Hπ stacking. No short intermolecular interactions occur in 2. The values of the shortest intermolecular cobalt-cobalt separation are 10.901(1) (1) and 10.577(3) Å (2). Detailed ac and dc magnetic studies indicate that 1 and 2 are field-induced single-ion magnets (SIMs) with D = +46.1 (1)/+80.1 cm-1 (2) thus presenting new examples of SIMs with transversal magnetic anisotropy. Theoretical calculations by CASSCF/NEVPT2 support these results and suggest that the relaxation of the magnetization occurs in the ground state under applied fields through two Orbach processes possibly bound to low-lying vibrational modes. Q-band EPR study for polycrystalline samples 1 and 2 at low temperatures confirms the positive sign of D, allows the rough estimation of the E/D ratio [0.144 (1) and 0.180 (2)] and reveals the occurrence of a strong asymmetry in the g-tensors. The values found for the spin-reversal barrier, Ea ≈ 28 and 11 cm-1 (1) and 20 and 9 cm-1 (2), are within the range of those found in other cobalt(ii) field-induced SIMs with a pseudooctahedral trans-CoN4N'2 chromophore.
报道了分子式为[Co(bim)4(tcm)2] (1)和[Co(bmim)4(tcm)2] (2)（bim = 1-苄基咪唑，bmim = 1-苄基-2-甲基苯并咪唑，tcm- = 三氰基甲烷阴离子）的两种六配位钴(II)配合物的制备、X射线晶体结构、光谱以及变温直流和交流磁性。1和2分别在单斜晶系P21/n和C2/c空间群中结晶，不对称单元分别由一个tcm-离子和一半的[Co(bim)4]2+和[Co(bmim)4]2+配合物阳离子组成。它们的钴原子处于压缩的（1）/菱形的（2）CoN6八面体环境中，轴向位置由单齿三氰基甲烷阴离子占据。1中的中性分子通过弱的C-HN型相互作用连接成超分子链，这些链通过C-Hπ堆积进一步相互连接成超分子二维结构单元。2中未发生短程分子间相互作用。最短分子间钴-钴间距的值分别为10.901(1) Å（1）和10.577(3) Å（2）。详细的交流和直流磁性研究表明，1和2是场诱导单离子磁体（SIMs），D = +46.1（1）/+80.1 cm-1（2），因此呈现出具有横向磁各向异性的SIMs的新例子。CASSCF/NEVPT2的理论计算支持了这些结果，并表明在施加磁场时，基态下的磁化弛豫通过两个可能与低振动模式相关的奥巴赫过程发生。对多晶样品1和2在低温下进行的Q波段EPR研究证实了D的正值，允许对E/D比值进行粗略估计[0.144（1）和0.180（2）]，并揭示了g张量中存在强烈的不对称性。自旋反转势垒Ea的值约为28和11 cm-1（1）以及20和9 cm-1（2），处于其他具有伪八面体反式-CoN4N'2发色团的钴(II)场诱导SIMs中发现的值的范围内。
