Synthesis and crystal engineering of new halogenated tetrathiafulvalene (TTF) derivatives and their charge transfer complexes and radical ion salts
作者:Andrei S. Batsanov、Martin R. Bryce、Antony Chesney、Judith A. K. Howard、Derek E. John、Adrian J. Moore、Clare L. Wood、Hagit Gershtenman、James Y. Becker、Vladimir Y. Khodorkovsky、Arkady Ellern、Joel Bernstein、Igor F. Perepichka、Vincent Rotello、Mark Gray、Alejandro O. Cuello
DOI:10.1039/b101866n
日期:——
Efficient syntheses are reported for tetraiodotetrathiafulvalene 2, 4-iodo-5-methyl-4′,5′-bis(methylsulfanyl)TTF 3, and 4-iodo-4′,5′-bis(methylsulfanyl)TTF 4 by iodination, using perfluorohexyl iodide, of lithiated derivatives of the corresponding TTF system. Bromination and chlorination of lithiotrimethylTTF using 1,2-dibromotetrafluoroethane and hexachloroethane gave 4-bromo- and 4-chloro-4′,5,5′-trimethylTTF 6 and 7, respectively. Phosphite-induced self-coupling or cross-coupling reactions of 4-iodo-1,3-dithiole-2-thione or 4,5-diiodo-1,3-dithiole-2-thione(one) half-units resulted in TTF derivatives with partial loss of the iodine substituent(s). 4,5-Dibromo-4′,5′-bis(cyanoethylsulfanyl)TTF 15 was prepared by cross-coupling methodology, and converted into 4,5-dibromo-4′,5′-bis(methylsulfanyl)TTF 16 by reaction with caesium hydroxide and then methyl iodide. EPR data are reported for the electrochemically generated cation radicals of trimethylTTFX derivatives (X = I, Br and Cl)
5–7, respectively. For the neutral donors, the X-ray crystal structures are reported for 2, 5, 6, tetramethylTTF 8 and 15. Structure 2 is characterised by a particularly dense packing with continuous chains of intra-stack I⋯I contacts (4.17–4.19 Å).
The crystals of 6 and 8 are isomorphous, while the structure of 5 is different. The iodo-substituent in 5 affects the packing in a way the bromo-substituent in 6 does not, due to differences in specific interactions rather than steric demands of I and Br, which are similar. Structure 15 comprises face-to-face dimers with inter-dimer Br⋯Br (3.57 Å) and Br⋯S (3.55 Å) contacts: a remarkable difference in bond distances between the Br and S-substituted dithiole rings is observed. The 1 ∶ 1 charge-transfer (CT) complexes 3·TCNQ and 4·TCNQ (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane, 17) display mixed stair-like stacks of alternating D and A moieties: the overall degree of CT is estimated from bond length analysis to be 0.2 e and 0.3 e, respectively. In 3·TCNQ either position of the disordered iodine atom has one short (inter-stack, but intra-layer) contact with a cyano group (I⋯N distances of 3.14 and 3.18 Å). In 4·TCNQ a similar I⋯N contact is much longer (3.35 Å). In the structure of 5+·I3−·½I2 the cation radical is disordered; dimeric cation radicals display short intra-dimer contacts (S⋯S 3.38–3.39 Å, C⋯C 3.35 Å) consistent with electron coupling. Each dimer is surrounded
by four I3− anions. The crystal structure of 16+·I3− is comprised of layers with interplanar separations of 3.55 Å. Cations of one layer overlap with anions of the next, and the packing can be described as mixed stacks parallel to the a axis. The remarkably high conductivity of this salt for a system of 1 ∶ 1 stoichiometry (σrt = 8 × 10−2 S cm−1) is ascribed to partial charge transfer (the charge on the TTF moiety is estimated as +⅔ from bond length analysis) and a continuous system of short non-bonding contacts.
报道了四碘四硫富瓦烯的高效合成方法,4-碘-5-甲基-4′,5′-双(甲基硫巴)TTF 3,以及4-碘-4′,5′-双(甲基硫巴)TTF 4,该方法通过用全氟己基碘对相应TTF体系的锂化衍生物进行碘化反应。使用1,2-二溴四氟乙烷和六氯乙烷对锂三甲基TTF进行溴化和氯化,分别得到了4-溴-和4-氯-4′,5,5′-三甲基TTF 6和7。由磷酸酯诱导的4-碘-1,3-二噁烯-2-硫酮或4,5-二碘-1,3-二噁烯-2-硫酮(一个)半单元的自偶联或交叉偶联反应导致TTF衍生物伴有部分碘取代基的损失。通过交叉偶联方法合成了4,5-二溴-4′,5′-双(氰乙基硫巴)TTF 15,并通过与氢氧化铯和随后与碘甲烷的反应转化为4,5-二溴-4′,5′-双(甲基硫巴)TTF 16。报告了为电化学生成的三甲基TTF衍生物(X = I, Br和Cl)的阳离子自由基进行的电子顺磁共振(EPR)数据。对于中性给体,报告了2、5、6、四甲基TTF 8和15的X射线晶体结构。结构2的特征在于具有特别密集的堆积形态,形成连续的堆叠内I⋯I接触(4.17–4.19 Å)。6和8的晶体是同构的,而5的结构则不同。由于特定相互作用的差异,而不是I和Br相似的立体要求,使得5中的碘取代基影响了堆积,而6中的溴取代基则没有。结构15由面对面二聚体组成,具有二聚体间的Br⋯Br(3.57 Å)和Br⋯S(3.55 Å)接触:观察到Br和S取代的二噁烯环之间的键长距离存在显著差异。1:1电荷转移(CT)复合物3·TCNQ和4·TCNQ(TCNQ = 7,7,8,8-四氰基-p-奎诺二甲烷,17)显示出交替的D和A基团的混合阶梯状堆叠:通过键长分析估计的CT整体程度分别为0.2 e和0.3 e。在3·TCNQ中,无序的碘原子在某个位置与一个氰基之间有一个短的(堆叠间,但层内)接触(I⋯N距离为3.14和3.18 Å)。在4·TCNQ中,类似的I⋯N接触则较长(3.35 Å)。在结构5+·I3−·½I2中,阳离子自由基无序;二聚阳离子自由基显示短的二聚内接触(S⋯S 3.38–3.39 Å, C⋯C 3.35 Å),与电子耦合一致。每个二聚体周围都有四个I3−阴离子。16+·I3−的晶体结构由层组成,层间距离为3.55 Å。一个层的阳离子与下一个层的阴离子重叠,堆积可描述为沿a轴的混合堆叠。这种1:1化学计量比体系的盐具有显著高的导电性(σrt = 8 × 10−2 S cm−1),归因于部分电荷转移(通过键长分析估计TTF基团的电荷为+⅔)和一种连续的短非键接触体系。