NMR properties of platinumthallium bonded complexes: analysis of relativistic density functional theory results

Abstract

The metal NMR parameters of the complexes [(NC)(5)Pt-Tl(CN)(n)](n -) (n = 0-3, I-IV) and [(NC)(5)Pt-Tl-Pt(CN)(5)](3-) (V), as well as [{Pt(NO(3))(NH(3))(2)L(2)}Tl(NO(3))(2)(MeOH)] (VI) and [{Pt(NO(3))(NH(3))(2)L(2)}(2)Tl](+) (VII) with L = NHCO(t)Bu, were computationally investigated by relativistic density functional theory. Complexes I-V were previously studied by us. We briefly review the main findings here. Their spin-spin coupling constants are analyzed in terms of molecular orbital and fragment orbital contributions which demonstrate the various influences of the solvent and of the ligands on the extraordinarily large metal-metal coupling constants. Complexes VI and VII and various model systems were investigated in more detail. It is shown that the same computational model which performs best for I-V yields too large metal-metal coupling constants for VI and VII. The analysis shows that this is likely to be attributable to a strong sensitivity of the coupling constants to the rather small Pt 6s contributions in the occupied metal-metal sigma-bonding orbitals. Bulk solvent effects on the metal-metal couplings are sizeable and should be considered in the computational model. Both calculated and experimental Pt--Tl coupling constants for VI and VII are substantially larger than those for I-V, thereby representing the largest heteronuclear coupling constants known so far experimentally. Metal chemical shifts for VI and VII were also investigated. The computational results indicate that the choice of the Pt reference is rather problematic. Tl chemical shifts agree much better with experimental data.

Analyzing Pt chemical shifts calculated from relativistic density functional theory using localized orbitals: The role of Pt 5d lone pairs

“…Similar findings for Pt shifts were also reported by Fowe et al, [21] Koch et al, [22] Gilbert and Ziegler, [23] and in earlier work by our group, [24,25] and for Pb and W shifts by Ziegler et al [61] . In the numerical integration method used for the computations, [62] the general accuracy parameter (roughly corresponding to the number of significant digits to which the integration of the electron density is correct) was set to 6.5, while for the atomic core regions the accuracy parameter was set to 7.5.…”

“…For example, we have previously found a strong axial bond delocalization in a related Pt-Tl bonded complex, [30] and in related systems. [25] However, the Pt-ligand NBOs in [PtCl 6 ] 2− , [PtCl 4 ] 2− , and the other Pt complexes also indicate strong multicenter bonding [31] with NBO occupancies in the order of 1.8 or even less. In this sense the Pt-Pt bond does not appear to play a particularly special role for the Pt shielding in M3.…”

“…[33 -35] Regarding localized orbital chemical shift analyses, we also note a study of oxovanadium compounds [36] employing the 'individual gauge for localized orbitals' (IGLO) method [38] (which by construction yields a localized orbital decomposition of the result), and Bohmann et al's nonrelativistic version of NLMO shift analyses. [39] These and other localized orbital-based methods for NMR parameters that we reported in earlier work [25,40,41] provide an intuitive breakdown of the total computed tensor in terms of the molecule's bonds, lone pairs, core shells, etc. for each of its principal components.…”

“…Pioneering first-principles computations of Pt shifts have met with some difficulties in the sense that excellent agreement with experiment was obtained only when a complex similar to the probe was used as a reference [21][22][23][24][25]. We have recently found [26] that two of the many potential reasons are (i) solvent effects, which influence differently coordinated complexes in different ways (e.g.…”

Modeling of Heavy‐Atom–Ligand NMR Spin–Spin Coupling in Solution: Molecular Dynamics Study and Natural Bond Orbital Analysis of HgC Coupling Constants

“…Similar effects can be found and rationalized accordingly for other complexes as well. For instance, in binuclear Pt systems [6] and Pt À Tl bonded complexes [28] ligand interactions with the metalmetal fragment reduce the magnitude of the metal-metal J coupling. 2) On the other hand, in linear [X-Hg-Y] complexes in which X = halide, methyl, CN and Y = methyl or CN, solvation of the complex around Hg in the equatorial plane results in an increase in the one-bond Hg-ligand J couplings.…”