W. Roy Mason

Platinum-195 magnetic resonance spectra of some platinum(II) and platinum(IV) complexes

Abstract The 195Pt magnetic resonance spectra of fourteen symmetrical, substitutionally inert octahedral Pt(IV) and square-planar Pt(II) complexes have been measured at 9.75 MHz using Fourier transform techniques. Chemical shifts observed in aqueous solutions of the PtL6m complexes cover a range of 6033 ppm and the shielding of the 195Pt nucleus is in the order Cl > 1 2 en > Br > SCN > CN > I. For aqueous solutions of the PtL4m complexes, the chemical shifts cover a range of 3876 ppm and the order of shielding is CI > NO2 > NH3 > Br > 1 2 en > SCN > CN > I. These results are interpreted in terms of covalency effects in the σp contribution to shielding. Relaxation times T1 and T2 have been measured in several cases where the signal to noise was favorable. In addition the temperature dependence of T1 has been investigated for H2PtCl6 and H2PtCl4 in aqueous HCl. The relaxation process for these two complexes appears consistent with a spin-rotation mechanism. The solvent dependence of the 195Pt resonance in PtCl62− and PtCl42− has also been measured for solutions tetra-n-butylammonium salts in a variety of nonaqueous solvents. Some proton and 13C NMR spectra have also been obtained for Pt(en)34+ and Pt(en)22+ in aqueous solution and some 13C spectra for Pt(CN)62− and Pt(CN)42− in D2O/H2O. Platinum-195 spin-coupling constants have been determined and some of the factors affecting coupling are discussed.

Electronic spectra of some tetragonal complexes of rhodium(III), iridium(III) and platinum(IV) [1]

Abstract Solution electronic spectral data are reported for 30 tetragonal complexes of the types trans-M(en)2Xn+2, M(NH3)5Xn+ (M = Rh(III), Ir(III), or Pt(IV); X = Cl, Br, or I); trans-M(NH3)4Xn+2 (M = Rh(III) or Pt(IV); X = Cl, Br, or I); trans-PtL4X2−2 (L = CN− or NO−2, X = Cl or Br); and Pt(CN)5X2− (X = Cl, Br, or I). These data are interpreted in terms of ligand field (LF) excited states in C4v or D4h symmetry and ligand to metal charge transfer (LMCT) excited states involving the halide ligands. Intensity patterns among the LMCT transitions of intermediate intensity are rationalized by including halide spin-orbit coupling in excited configurations. Trends in LF and LMCT excited state energies are discussed.

Magnetic circular dichroism spectra of the tetraammineplatinum(II) cation

Though considerable spectroscopic and theoretical work has accumulated in the last several years, the nature of metal ligand bonding in squareplanar p lat inum(l l ) complexes remains obscure. For example, the anionic PtCI42and Pt(CN)42complexes have been studied in some detai l ( I 3). Yet the ordering of the occupied d orb i ta ls and the energies of s inglet and t r i p l e t excited states are not free of disagreement. As part of our continued e f fo r t to explore the electronic structures of square-planar complexes, the present l e t t e r reports measurements of the magnetic c i rcu lar dichroism (MCD) spectra of the Pt(NH3)42+ cation in aqueous and ace ton i t r i l e solutions. The tetraammineplatinum(ll) complex is of in terest 2because the ammonia ligand is a simple sigma donor, and unlike PtCI 4 or Pt(CN)42-, pi bonding is expected to be unimportant. Further, MCD measurements can provide information as to the degeneracy of excited states, which can corroborate electronic t rans i t ion assignments, and thus provide support for electronic structural n~dels (4, 5). For example, the Pt(NH3)42+ cation has a d 8 electronic configuration and has a diamagnetic, nondeaenerate ground state ( iA lg) . Contributions to the MCD may arise from two sources: a Zeeman s p l i t t i n g of a degenerate excited state (A term) or a mixing of energy states

Structure of tetra(n-butyl)ammonium tetraiodo-μ,-μ′-diiododiplatinate(II), [(n-C4H9)4N]2[Pt2I6]

The crystal structure of [(n-C4H9)4N]2[Pt2I6] has been determined from X-ray data measured by counter methods. It crystallizes in the monoclinic space groupP21/c (C2h-5, No. 14) with unit cell constantsa=14.457(4),b=14.036(4),c=23.696(5) Å,β=101.02(3)°, andDc=2.30 g cm−3 forZ=4. Full-matrix least-squares refinement led to a finalR value of 0.049 for 1786 independent observed reflections. The [Pt2I6]2− anion is planar to within 0.07 Å and exhibits an average Pt-I bridging bond length of 2.559(4) Å and average Pt-I terminal distance of 2.571(7) Å. Of the two independent [(n-C4H9)4N]+ cations, one approaches a ¯42m-D2d conformation, the other an approximate ¯4-S4 conformation.

Electronic absoprtion and MCD spectra for the Pt(PPh3) (AuPPh3)62+ and Pt(H) (PPh3) (AuPPh3)7staggered2+ cluster complexes

Abstract Electronic absorption and 7.0 tesla magnetic dichroism (MCD) spectra are reported for acetonitrile solutions of [Pt(PPh3)(AuPPh3)6] (NO3)2 and [Pt(H)(PPh3) (AuPPh3)7] (NO3)2 at room temperature in the range of 1.8 to 3.7 μ 1 ( 1 μ m 1 = 10 4 cm 1 ). The spectra are assigned to intraframework (IF) transitions from an Au based HOMO to empty Au framework orbitals. In addition evidence is presented for Pt(5d)→Au transitions for Pt(PPh3)(AuPPh3)62+ from intense low energy MCD features.