Silva Rosalice M, Gwengo Chengeto, Lindeman Sergey V, Smith Mark D, Long Gary J, Grandjean Fernande, Gardinier James R
Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881, USA.
Inorg Chem. 2008 Aug 18;47(16):7233-42. doi: 10.1021/ic8005794. Epub 2008 Jul 23.
The second-generation Janus scorpionate ligand [HB(mtda (Me)) 3] (-) (mtda (Me) = 2-mercapto-5-methyl-1,3,4-thiadiazolyl) with conjoined ( N, N, N-) and ( S, S, S-) donor faces has been prepared. This second-generation Janus scorpionate ligand [HB(mtda (Me)) 3] (-) differs from the first-generation [HB(mtda) 3] (-) ligand by the replacement of hydrogens on the heterocyclic rings proximal to the nitrogenous face with methyl groups. This study probed whether steric interactions introduced by such methyl group substitution could modulate the reactivity and coordination preferences of these ambidentate ligands. The crystal structures of a sodium complex Na[HB(mtda (Me)) 3].3(MeOH), the potassium complexes K[HB(mtda) 3].MeOH, and K 2[HB(mtda (Me)) 3] 2.3MeOH, and several iron complexes were obtained. The difference between first- and second-generation Janus scorpionate ligands is most obvious from the discrepancy between the properties and structures of the two iron(II) compounds with the formula Fe[HB(mtda (R)) 3] 2.4DMF (R = H or Me). The complex with the first-generation ligand (R = H) is pink and diamagnetic. An X-ray structural study revealed two facially coordinated kappa (3)N-scorpionates with no bound solvent molecules. The average Fe-N bond distance of 1.97 A is indicative of the low-spin t 2g (6)e g* (0) electron configuration. In contrast, the iron(II) complex of the second-generation ligand (R = Me) is yellow and paramagnetic. This structure shows two trans-kappa (1)S-scorpionates and four equatorial-bound DMF where the average Fe-O and Fe-S distances of 2.12 and 2.51 A, respectively, are indicative of the high-spin t 2g (4)e g* (2) electron configuration. The discrepancy in binding modes and spin-states of iron(II) is carried over to the solvent-free Fe[HB(mtda (R)) 3] 2 (R = H, Me) complexes, as determined from Mossbauer spectral studies. The Mossbauer spectral parameters for Fe[HB(mtda) 3] 2 are fully consistent with low-spin iron(II) in a FeN 6 environment, whereas those for Fe[HB(mtda (Me)) 3] 2 are most consistent with high-spin iron(II) in a FeS 6 environment. Interestingly, when either complex is dissolved in highly polar solvents (DMF, DMSO, or H 2O), the ligand completely dissociates forming [Fe(solvent) 6][HB(mtda (R)) 3] 2 (R = H, Me).
第二代具有相连的（N，N，N-）和（S，S，S-）供体面的双齿蝎型配体[HB(mtda (Me)) 3] (-)（mtda (Me) = 2-巯基-5-甲基-1,3,4-噻二唑基）已被制备出来。这种第二代双齿蝎型配体[HB(mtda (Me)) 3] (-)与第一代[HB(mtda) 3] (-)配体的不同之处在于，靠近含氮面的杂环上的氢被甲基取代。本研究探讨了这种甲基取代引入的空间相互作用是否能够调节这些两可配体的反应活性和配位偏好。得到了钠配合物Na[HB(mtda (Me)) 3].3(MeOH)、钾配合物K[HB(mtda) 3].MeOH和K 2[HB(mtda (Me)) 3] 2.3MeOH以及几种铁配合物的晶体结构。第一代和第二代双齿蝎型配体之间的差异从两种化学式为Fe[HB(mtda (R)) 3] 2.4DMF（R = H或Me）的铁（II）化合物的性质和结构差异中最为明显地体现出来。与第一代配体（R = H）形成的配合物呈粉红色且抗磁性。一项X射线结构研究表明，有两个面配位的κ(3)N-蝎型配体且没有结合的溶剂分子。平均Fe-N键长为1.97 Å，表明其为低自旋t 2g (6)e g* (0)电子构型。相比之下，第二代配体（R = Me）的铁（II）配合物呈黄色且顺磁性。该结构显示有两个反式κ(1)S-蝎型配体和四个赤道面配位的DMF，其中平均Fe-O和Fe-S键长分别为2.12 Å和2.51 Å，表明其为高自旋t 2g (4)e g* (2)电子构型。铁（II）的配位模式和自旋态的差异延续到了无溶剂的Fe[HB(mtda (R)) 3] 2（R = H，Me）配合物中，这是通过穆斯堡尔光谱研究确定的。Fe[HB(mtda) 3] 2的穆斯堡尔光谱参数与FeN 6环境中的低自旋铁（II）完全一致，而Fe[HB(mtda (Me)) 3] 2的参数与FeS 6环境中的高自旋铁（II）最为一致。有趣的是，当将任何一种配合物溶解在高极性溶剂（DMF、DMSO或H 2O）中时，配体完全解离，形成[Fe(溶剂) 6][HB(mtda (R)) 3] 2（R = H，Me）。
