文摘
The Pd(II) complexes [Pd([9]aneS3)2](PF6)2路2MeCN (1) ([9]aneS3 = 1,4,7-trithiacyclononane) and [Pd([18]aneS6)](PF6)2 (2) ([18]aneS6 = 1,4,7,10,13,16-hexathiacyclooctadecane) can be oxidized electrochemically or chemically oxidized with 70% HClO4 to [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+, respectively. These centers have been characterized by single crystal X-ray diffraction, and by UV/vis and multifrequency electron paramagnetic resonance (EPR) spectroscopies. The single crystal X-ray structures of [PdIII([9]aneS3)2](ClO4)6路(H3O)3路(H2O)4 (3) at 150 K and [Pd([18]aneS6)](ClO4)6路(H5O2)3 (4) at 90 K reveal distorted octahedral geometries with Pd鈥揝 distances of 2.3695(8), 2.3692(8), 2.5356(9) and 2.3490(6), 2.3454(5), 2.5474(6) 脜, respectively, consistent with Jahn鈥揟eller distortion at a low-spin d7 Pd(III) center. The Pd(II) compound [Pd([9]aneS3)2](PF6)2 shows a one-electron oxidation process in MeCN (0.2 M NBu4PF6, 293 K) at E1/2 = +0.57 V vs. Fc+/Fc assigned to a formal Pd(III)/Pd(II) couple. Multifrequency (Q-, X-, S-, and L-band) EPR spectroscopic analysis of [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+ gives giso = 2.024, |Aiso(Pd)| = 18.9 脳 10鈥? cm鈥?; gxx = 2.046, gyy = 2.041, gzz = 2.004;聽|Axx(Pd)| = 24 脳 10鈥? cm鈥?, |Ayy(Pd)| = 22 脳 10鈥? cm鈥?, |Azz(Pd)| = 14 脳 10鈥? cm鈥?, |axx(H)| = 4 脳 10鈥? cm鈥?, |ayy(H)| = 5 脳 10鈥? cm鈥?, |azz(H)| = 5.5 脳 10鈥? cm鈥? for [Pd([9]aneS3)2]3+, and giso = 2.015, |Aiso(Pd)| = 18.8脳 10鈥? cm鈥?; gxx = 2.048 gyy = 2.036, gzz = 1.998; |axx(H)| = 5, |ayy(H)| = 5, |azz(H)| = 6 脳 10鈥? cm鈥?; |Axx(Pd)| = 23脳 10鈥? cm鈥?, |Ayy(Pd)| = 22 脳 10鈥? cm鈥?, |Azz(Pd)| = 4 脳 10鈥? cm鈥? for [Pd([18]aneS6)]3+. Both [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+ exhibit five-line superhyperfine splitting in the gzz region in their frozen solution EPR spectra. Double resonance spectroscopic measurements, supported by density functional theory (DFT) calculations, permit assignment of this superhyperfine to through-bond coupling involving four 1H centers of the macrocyclic ring. Analysis of the spin Hamiltonian parameters for the singly occupied molecular orbital (SOMO) in these complexes gives about 20.4% and 25% Pd character in [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+, respectively, consistent with the compositions calculated from scalar relativistic DFT calculations.