Structural, vibrational and solid-state NMR studies of the halogenocuprate(I) complexes [(PPh3)2CuI2]- and [(PPh3)CuI3Cu(PPh3)

Abstract

Single-crystal X-ray diffraction, vibrational spectroscopy, and solid state NMR spectroscopy have been used to characterize two new types of ionic copper(1) complexes. The anion in [PPh3Me]+[(PPh3)2Cu12]c-o ntains two PPh, ligands coordinated to the copper atom of a Cu12 unit in a pseudotetrahedral arrangement, with Cu-P = 2.292 (2), 2.288 (2) A, Cu-I = 2.692 (I), 2.702 ( I ) A, P-Cu-P = 121.24 (9), and I-Cu-I = 108.62 (4)' (monoclinic, P21/c, a = 12.138 (5) A, b = 14.776 (6) A, c = 28.197 (14) A, 0 = 103.76 (4)O, Z = 4, R = 0.040 for 4490 'observed (I > 3 4 ) ) reflections). The far-IR spectrum shows a strong band at 118 cm-l that is assigned to the antisymmetric Cu-I stretching mode of the CUI, unit. The CPMAS ,*P NMR spectrum shows a strong singlet at 18.1 ppm (relative to 85% H3Po4) due to the cation and a weaker quartet centered at -16.7 ppm due to the coordinated PPh, in the anion, with line spacings due to Cu-P coupling of 1.08, 1.20, and 1.23 kHz. The anion in [PPh,Me]+[ (PPh,)CuI,Cu(PPh,)]- consists of an approximately D,h Cu213 unit with three iodine atoms bridging the two copper atoms and with one PPh, molecule completing a pseudotetrahedral arrangement around each copper atom. The crystallographically imposed symmetry of the ion is C,,, with the 3-fold axis passing through the P-Cu bonds. The core structural parameters are (5)O, and Cu-I-Cu = 54.88 (4)' (cubic, P2,3, a = 17.744 (IO) A, Z = 4, R = 0.036 for 1390 observed reflections). This is the first reported example of a binuclear copper(1) complex with three bridging ligands and is an example of an unusual bonding situation in which two coordination tetrahedra are linked by sharing a common face. This has the effect of producing an unusually short Cu-- -Cu separation of 2.50 A. The far-IR spectrum shows a band at 127 cm-' that is assigned to the doubly degenerate perpendicular Cu-I stretching mode of the CutIl unit. The CPMAS NMR spectrum shows a strong singlet at 20.1 ppm due to the cation and a broad quartet centered at -15.8 ppm due to the coordinated PPh, in the anion. The splitting pattern for this quartet does not conform to expectations for an AX spin system involving coupling between I = I / , and I = ,/, nuclei. The assignments of the ~(CU-I)I R bands in both complexes are supported by approximate normal-wordinate analyses, and the resulting Cu-I force constants are compared with the values obtained in similar analyses of related iodocopper(1) complexes.