Experimental evidence for magnetic exchange in di- and trinuclear uranium(IV) ethynylbenzene complexes.
Experimental evidence for magnetic exchange in di- and trinuclear uranium(IV) ethynylbenzene complexes.
复制标题
二核和三核铀（IV）乙炔基苯络合物中磁交换的实验证据。
作者：
B. Newell;A. Rappé;M. P. Shores
我们报告了结构相关的单核、双核和三核U（IV）芳基乙炔化合物家族的制备和磁性研究。[（NN '（3））UCl]与锂化芳基乙炔反应生成六配位配合物[（NN'（3））U（CCPh）（2）（Li·THF）]（1）和[（NN '（3））（2）U（2）（p-DEB）（THF）]（2），分别为红棕色和黄绿色晶体固体。相比之下，结合铀循环[（位-NN '（3））U]（bit-NN ′（3）= [N（CH（2）CH（2）NSi（t）BuMe（2））（2）（CH（2）CH（2）Si（t）BuMeCH（2）]）与化学计量的单、双和三（乙炔基）苯反应得到黄绿色五配位芳基乙炔化物配合物[（NN ′（3））U（CCPh）]（3），[（NN ′（3））（2）U（2）（m-DEB）]（4）、[（NN ′（3））（2）U（2）（p-DEB）]（5）和[（NN ′（3））（3）U（3）（TEB）]（6），其中NN ′（3）= [N（CH（2）CH（2）NSi（t）BuMe（2））（3）]。1-6的实测磁化率在低温下趋向于非磁性基态。然而，双核和三核五配位化合物4-6似乎显示出铀中心之间的弱磁通信。该通信通过使用自旋哈密顿量H = -2J（S（i）x S（j））拟合直流（DC）磁化率数据来建模。这些结果与络合物4-6的弱铁磁耦合（分别为J = 4.76、2.75和1.11 cm（-1））一致，而2的拟合与几乎可忽略的交换相互作用（J = -0.05 cm（-1））一致。几何优化的Stuttgart/6-31 g* B3 LYP混合DFT计算在3-5的模型络合物上进行（省略自旋-轨道耦合）。单核配合物显示出三重基态，单占据简并f轨道。计算的Meta桥和对位桥的物种显示非常弱的铁磁和反铁磁耦合，分别。所有这三种配合物只显示小的净自旋密度上的乙炔基含配体。单体苯乙炔配合物3在-1.02 V（相对于[Cp（2）Fe]（+/0））处发生可逆氧化还原对，可归因于U（IV）氧化为U（V）。
We report the preparation and magnetic property investigations of a structurally related family of mono-, di-, and trinuclear U(IV) aryl acetylide complexes. The reaction between [(NN'(3))UCl] and lithiated aryl acetylides leads to the formation of the hexacoordinate complexes [(NN'(3))U(CCPh)(2)(Li.THF)] (1) and [(NN'(3))(2)U(2)(p-DEB)(THF)] (2) as red-brown and yellow-green crystalline solids, respectively. In contrast, combining the uranacycle [(bit-NN'(3))U] (bit-NN'(3) = [N(CH(2)CH(2)NSi(t)BuMe(2))(2)(CH(2)CH(2)Si(t)BuMeCH(2)]) with stoichiometric amounts of mono-, bis-, and tris(ethynyl) benzenes affords the yellow-green pentacoordinate arylacetylide complexes [(NN'(3))U(CCPh)] (3), [(NN'(3))(2)U(2)(m-DEB)] (4), [(NN'(3))(2)U(2)(p-DEB)] (5), and [(NN'(3))(3)U(3)(TEB)] (6), where NN'(3) = [N(CH(2)CH(2)NSi(t)BuMe(2))(3)]. The measured magnetic susceptibilities for 1-6 trend toward non-magnetic ground states at low temperatures. Nevertheless, the di- and trinuclear pentacoordinate compounds 4-6 appear to display weak magnetic communication between the uranium centers. This communication is modeled by fitting of the direct current (DC) magnetic susceptibility data, using the spin Hamiltonian H = -2J(S(i) x S(j)). These results are consistent with weak ferromagnetic coupling for complexes 4-6 (J = 4.76, 2.75, and 1.11 cm(-1), respectively), while the fit for 2 is consistent with a near-negligible exchange interaction (J = -0.05 cm(-1)). Geometry-optimized Stuttgart/6-31 g* B3LYP hybrid DFT calculations were carried out (spin-orbit coupling omitted) on model complexes of 3-5. The mononuclear complex shows a triplet ground state with singly occupied degenerate f orbitals. The meta- and para-bridged species are computed to show very weak ferro- and antiferromagnetic coupling, respectively. All three complexes show only small net spin density on the acetylide-containing ligands. The monomeric phenylacetylide complex 3 undergoes a reversible redox couple at -1.02 V versus [Cp(2)Fe](+/0), assignable to an oxidation of U(IV) to U(V).