Structural, magnetic and electrical properties of one-dimensional tetraamidatodiruthenium compounds

Abstract

The first bromo and iodo tetraamidatodiruthenium compounds of the type [Ru2X(μ-NHOCC6H4-R)4]n [X = Br, R = o-Me (1), m-Me (2), p-Me (3); X = I, R = o-Me (4), m-Me (5), p-Me (6)] have been prepared using solvothermal or microwave activation procedures. In these reactions ethanol or methanol as solvents have been used to make the synthesis procedures more environment-friendly. Solvothermal synthesis has allowed us to isolate single crystals of these extremely insoluble compounds and the crystal structures of all of them have been determined using single crystal X-ray diffraction. The change of the bridging halide ligand permits us to discuss the properties of these complexes on the basis of their structure. Complex 1 shows a Ru-Br-Ru angle of 180.0° whereas in complexes 2-6 the Ru-X-Ru angle varies from 110.16(2) to 115.39(4)°. In all compounds the ruthenium atom has a cis-RuN2O2 environment except in compound 1 that shows a positional disorder of N and O atoms. The bromide complex 1 shows a linear arrangement of the paddlewheel units in the resulting 1D coordination polymer. The fit of the magnetic data indicates that these compounds have non-negligible values of zero-field splitting with D values ranging from 41.10 to 60.10 cm(-1) and antiferromagnetic coupling constants from 0.00 to -4.13 cm(-1). Compound 1 is the first linear paddlewheel diruthenium compound that does not show a maximum in the representation of the magnetic susceptibility towards temperature. The electrical conductivity measurements in the temperature range 300-400 K of compounds 1, 4 and [Ru2Cl(μ-NHOCC6H4-o-Me)4]n (7) show that these compounds present semiconducting behaviours with conductivity values at 400 K in the range 0.3-3.0 × 10(-8) S cm(-1) for the Cl derivative (7), 7-18 × 10(-8) S cm(-1) for the Br derivative (1) and 27-68 × 10(-8) S cm(-1) for the I derivative (4) with average values of 1.4 × 10(-8), 13 × 10(-8) and 47 × 10(-8) S cm(-1), respectively.

Synthesis, Crystal Structure, and Magnetic Properties of Amidate and Carboxylate Dimers of Ruthenium

“…In the 1-3 amidate complexes, due to the asymmetry of the amidate ligands, four linkage isomers are possible, depending on the relative coordination of the ligands [17]. However, the three complexes show a cis-RuN 2 O 2 environment similar to that observed in the other tetraamidatodiruthenium complexes described in the literature [8,9,[11][12][13]17,18]. Thus, in these complexes, each diruthenium unit resides on a center of inversion, and the asymmetric unit consists of two half dimers linked by the halide ligand, resulting in zigzag chains.…”

“…This variation has been attributed to the increase of the atomic volume of the halide ligand which determines a longer distance between the dimer units allowing the decrease of the Ru-X-Ru angle [18]. Similarly, in the carboxylate compounds 4 and 5, this angle is slightly acute in the bromo derivative.…”

“…Therefore, each diruthenium unit adopts a cis-RuN 2 O 2 arrangement required by the inversion symmetry. Moreover, only two amidate complexes described in the literature [17,18] Table 1). The higher donor character of the amidate ligands with respect to the carboxylate groups produces a higher electronic density on the ruthenium atoms giving a larger Ru-Ru distance.…”

“…This is an important advantage in the preparation of the very insoluble tetraamidatodiruthenium complexes. Due to this low solubility the number of bromo-and iodotetraamidatodiruthenium(II,III) compounds are very scarce and only recently some examples have been prepared using solvothermal methods [18].…”

“…Johnson and Powell [14] demonstrated some years ago that the microwave activation is useful to prepare dimolybdenum compounds in short periods of time and with good yields. More recently, the microwave activation and the solvothermal methods have proven to be as a very effective synthetic methods for the substitution process of acetate groups in [Ru 2 Cl(µ-O 2 CMe) 4 ] by N,N-or N,O-donor ligands (N,N = triazenide, formamidinate or guanidinate; N,O = arylamidate) [15][16][17][18]. On the other hand, the solvothermal reactions are carried out in a closed system at relatively high temperature and pressure and in these conditions the compounds increase their solubility.…”