Solid State NMR Studies of H/CO Dynamics on Multi-nuclear Transition-metal Clusters

对H_4Ru_4(CO)_<12>和H_4Ru_4(CO)_<12>{P(OMe)_3}进行了变温、MAS和宽线固体核磁共振测量。两种样品氢化物共振半强度时的自旋-晶格弛豫时间（Ti）和线宽（DELTAupsilonl/2）随温度的变化非常相似，表明在e α =17 * 2 LI mo1^<-1>时发生了共同的氢化物运动。我们将这种运动归因于围绕h占据的Ru-Ru边的2位h翻转，这保持了晶体的位置对称性。（NMe_4）4-x[H_xNi_<12>(CO) _<21>]的分子结构。S （x=1， S=Me2CO; x=2， S=1/2 THF）。两种阴离子相似，均由中心Ni_6(CO)_3(mu-CO)_6 -层和两侧Ni_3(CO)_3(mu-CO)_3-层组成，使得Ni_<12>-芳香剂呈六边形紧密堆积。中心ni_6面(B)与两个外部ni_3面（A， C）的分离与两个八面体中任一面（x=1）或两面（x=2）的h占位一致。两个簇的变温固态^1H MAS和^<13>C CP/MAS NMR谱均有报道。对于二氢化物，固态的^1H和^<13>C核磁共振谱从低温到室温保持不变，与x射线结构一致；在室温下，在Ni_6-八面体腔的中心处存在两个氢化物共振，这与它们在Ni_6-八面体腔的中心处存在高场位移一致。对于[H_2Ni_<12>(CO)_<12>]^<2->，除了内部桥接羰基在溶液中出现为一个共振外，固相^<13>CO的化学位移与固相^<13>CO的化学位移非常一致，而在固相中由于桥接CO在ni6平面以上或以下而出现两个共振。在更高的温度下，有证据表明h运动（可能在对称平面上振荡），但^<13>C光谱表明CO基本上保持静态。对于一氢化物，三个桥接CO几乎与ni_6平面共面，一个C6向氢化物明显弯曲，两个CO处于中间位置；低温固态^<13>CO核磁共振谱与该结构完全一致。在室温下，CO的^<13>共振有一些聚并，表明有一些羰基运动，但没有证据表明h从占位的间隙八面体位置迁移到未占位的八面体位置。少

Variable temperature, MAS and wide-line solid state NMR measurements have been carried out on H_4Ru_4(CO)_<12> and H_4Ru_4(CO)_<12>{P(OMe)_3}. The variation of spin-lattice relaxation time (Ti) and linewidth at half intensity (DELTAupsilonl/2) of the hydride resonance with temperature for both samples are very similar and suggests that a common hydride movement occurs with Ealpha=17 * 2 LI mo1^<-1>. We attribute this movement to a 2-site H-flip about H-occupied Ru-Ru edges which preserves the site symmetry of the crystals.The molecular structures of(NMe_4)4-x[H_xNi_<12>(CO) _<21>].S (x=1, S=Me2CO ; x=2, S=1/2 THF) are reported. Both anions are similar and consist of a central Ni_6(CO)_3(mu-CO)_6 - layer flanked on both sides by two Ni_3(CO)_3(mu-CO)_3-layers such that the Ni_<12>-fragrpent is hexagonal close-packed. The separation between the central Ni_6-plane (B) and the two outer Ni_3-planes (A, C) is consistent with H-occupancy of either one (x=1) or both (x=2) of the two octahedra … More l metal cavities. Variable temperature solid state ^1H MAS and ^<13>C CP/MAS NMR spectra are reported for both clusters. For the dihydride, the solid state ^1H and ^<13>C NMR spectra remain unchanged from low to room temperature and are consistent with the X-ray structure ; at room temperature, there are two hydride resonances consistent with them being on the plane of symmetry on opposite sides of the Ni_6-layer and the highfield shift is consistent with them not being in the center of the Ni_6- octahedral cavity. For [H_2Ni_<12>(CO)_<12>]^<2->, there is close agreement between the solution and solid state ^<13>CO chemical shifts except for the inner bridging carbonyls which appear in solution as one resonance whereas in the solid state occur as two resonances due to the bridging CO's being either above or below the Ni6-plane. At higher temperatures, there is evidence for H-movement (probably oscillation about the plane of symmetry) but ^<13>C spectra indicate that the CO's remain essentially static. For the monohydride, three of the bridging CO's are almost co-planar with the Ni_6-plane, one, C6, is significantly bent towards the hydride and two CO's are in intermediate positions ; the low temperature solid state ^<13>CO NMR spectra appear to be entirely consistent with this structure. At room temperature, there is some coalescence of the ^<13>CO resonances, suggesting some carbonyl-movement, but there is no evidence for H-migration from the occupied interstitial octahedral site to the unoccupied octahedral site. Less