Tulsky Eric G, Crawford Nathan R M, Baudron Stéphane A, Batail Patrick, Long Jeffrey R
Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA.
J Am Chem Soc. 2003 Dec 17;125(50):15543-53. doi: 10.1021/ja037444q.
The first face-capped octahedral clusters with 25 metal-based valence electrons are shown to provide versatile building units capable of engaging in magnetic exchange coupling. Reactions of Re(5)OsSe(8)Cl(6) and Re(4)Os(2)Se(8)Cl(6) with NaCN in a melt of NaNO(3) or KCF(3)SO(3) afford the 24-electron clusters Re(5)OsSe(8)(CN)(6) and Re(4)Os(2)Se(8)(CN)(6). The 13C NMR spectrum of a 13C-labeled version of the latter species indicates a 1:2 mixture of cis and trans isomers. Cyclic voltammograms of the clusters in acetonitrile display reversible Re(5)OsSe(8)(CN)(6), cis-Re(4)Os(2)Se(8)(CN)(6), and trans-Re(4)Os(2)Se(8)(CN)(6) couples at E(1/2) = -1.843, -0.760, and -1.031 V vs FeCp(2)(0/+), respectively, in addition to other redox processes. Accordingly, reduction of Re(5)OsSe(8)(CN)(6) with sodium amalgam and Re(4)Os(2)Se(8)(CN)(6) with cobaltocene produces the 25-electron clusters Re(5)OsSe(8)(CN)(6) and Re(4)Os(2)Se(8)(CN)(6). EPR spectra of these S = 1/2 species in frozen DMF solutions exhibit isotropic signals with g = 1.46 for the monoosmium cluster and g = 1.74 and 1.09 for the respective cis and trans isomers of the diosmium cluster. In each case, results from DFT calculations show the unpaired spin to delocalize to some extent into the pi* orbitals of the cyanide ligands, suggesting the possibility of magnetic superexchange. Reaction of Re(5)OsSe(8)(CN)(6) with Ni(H(2)O)(6) in aqueous solution generates the porous Prussian blue analogue Ni(3)Re(5)OsSe(8)(CN)(6).32H(2)O; however, the tendency of the 25-electron clusters to oxidize in water prohibits their use in reactions of this type. Instead, a series of cyano-bridged assemblies, Re(6-n)Os(n)Se(8)CNCu(Me(6)tren) (n = 0, 1, 2; Me(6)tren = tris(2-(dimethylamino)ethyl)amine), were synthesized to permit comparison of the exchange coupling abilities of clusters with 23-25 electrons. As expected, the results of magnetic susceptibility measurements show no evidence for exchange coupling in the assemblies containing the 23- and 24-electron clusters, but reveal the presence of weak ferromagnetic coupling in Re(4)Os(2)Se(8)CNCu(Me(6)tren). Assuming all cluster-Cu(II) exchange interactions to be equivalent, the data were fit to give an estimated coupling strength of J = 0.4 cm(-1). To our knowledge, the ability of such clusters to participate in magnetic exchange coupling has never previously been demonstrated.
首个具有25个金属基价电子的面封端八面体簇合物被证明能提供可参与磁交换耦合的通用结构单元。Re(5)OsSe(8)Cl(6)和Re(4)Os(2)Se(8)Cl(6)在NaNO(3)或KCF(3)SO(3)熔体中与NaCN反应，得到24电子簇合物Re(5)OsSe(8)(CN)(6)和Re(4)Os(2)Se(8)(CN)(6)。后一种物质的13C标记版本的13C NMR谱表明存在顺式和反式异构体的1:2混合物。这些簇合物在乙腈中的循环伏安图显示了可逆的Re(5)OsSe(8)(CN)(6)、顺式-Re(4)Os(2)Se(8)(CN)(6)和反式-Re(4)Os(2)Se(8)(CN)(6)电对，其E(1/2)分别为相对于FeCp(2)(0/+)为-1.843、-0.760和-1.031 V，此外还有其他氧化还原过程。因此，用钠汞齐还原Re(5)OsSe(8)(CN)(6)以及用二茂钴还原Re(4)Os(2)Se(8)(CN)(6)，得到25电子簇合物Re(5)OsSe(8)(CN)(6)和Re(4)Os(2)Se(8)(CN)(6)。这些S = 1/2物种在冷冻DMF溶液中的EPR谱显示，单锇簇合物的各向同性信号g = 1.46，二锇簇合物的顺式和反式异构体的g值分别为1.74和1.09。在每种情况下，DFT计算结果表明未成对电子在一定程度上离域到氰化物配体的π*轨道中，这表明存在磁超交换的可能性。Re(5)OsSe(8)(CN)(6)与水溶液中的Ni(H(2)O)(6)反应生成多孔普鲁士蓝类似物Ni(3)Re(5)OsSe(8)(CN)(6).32H(2)O；然而，25电子簇合物在水中氧化的倾向使其无法用于此类反应。相反，合成了一系列氰基桥连组装体Re(6-n)Os(n)Se(8)CNCu(Me(6)tren)（n = 0, 1, 2；Me(6)tren = 三(2-(二甲基氨基)乙基)胺），以比较含23 - 25个电子的簇合物的交换耦合能力。正如预期的那样，磁化率测量结果表明，在含有23电子和24电子簇合物的组装体中没有交换耦合的证据，但揭示了Re(4)Os(2)Se(8)CNCu(Me(6)tren)中存在弱铁磁耦合。假设所有簇 - Cu(II)交换相互作用都是等效的，对数据进行拟合得到估计的耦合强度J = 0.4 cm(-1)。据我们所知，此前从未证明过此类簇合物参与磁交换耦合的能力。
