ARTICLE DOI: 10.1002/zaac.201300415 Accurate Structure and Bonding Description of the Transition Metal- Disulfur Monoxide Complexes [(PMe 3 ) 2 M(S 2 O)] (M = Ni, Pd, Pt): Grimme Dispersion Corrected DFT Study Krishna K. Pandey,* [a] Sunil K. Patidar, [a] Pankaj Patidar, [a] Ravi Vishwakarma, [a] and Pankaj K. Bariya [a] Keywords: DFT; Dispersion; Disulfur monoxide; Nickel; Palladium; Platinum Abstract. Geometry and bonding energy analysis of M–S 2 O bonds in the metal-disulfur monoxide complexes [(PMe 3 ) 2 M(S 2 O)] of nickel, palladium, and platinum were investigated at DFT, DFT-D3, and DFT- D3(BJ) methods using three different functionals (BP86, PBE, and TPSS). The TPSS/DFT-D3(BJ) yields better geometry, while the BP86 geometry is least accurate for studied complexes. The geometry of platinum complex optimized at TPSS/DFT-D3(BJ) level is in excellent agreement with the available experimental values. The M–S bonds are shorter than the M–S(O) bonds. The Mayer bond orders suggest the presence of M–S and M–S(O) single bonds. Both the M–S and M–S(O) bond lengths vary with the density functionals as Introduction The chemistry of compounds containing sulfur dioxide li- gand has been known for decades, especially among the plati- num complexes. [1–3] In contrast, the complexes of lower sulfur oxide ligands, such as sulfur monoxide (SO) and disulfur mon- oxide (S 2 O) are relatively less explored. [3–6] Free S 2 O is more stable than sulfur monoxide, but it polymerizes readily even at lower temperature. [6] The disulfur monoxide can be stabilized by coordination with transition metals. [5–6] The known syn- thetic routes for the transition metal-disulfur monoxide (M– S 2 O) complexes are: (i) oxidation of disulfur (M–S 2 ) com- plexes with oxygen atom transferring reagents, (ii) oxidation of disulfur (M–S 2 ) complexes with dioxygen, (iii) reaction of imino-oxo-λ 4 -sulfane complexes with H 2 S, and (iv) reactions of solvated S 2 O(thf) x with metal complexes. The first example of the disulfur monoxide complex [(dppe)Ir(S 2 O)]Cl was re- ported by Schmid and co-workers. [7] The field has been ex- panded with well characterized examples of disulfur monoxide complexes of Nb, [8] Mo, [9–12] Re, [13] Rh, [7] Mn, [13–16] Os, [17] * Dr. K. K. Pandey Fax: +91-731-2460208 E-Mail: kkpandey.schem@dauniv.ac.in k_k_pandey3@rediffmail.com [a] School of Chemical Sciences Devi Ahilya University Indore Khandwa Road Campus Indore 452 001, India Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/zaac.201300415 or from the au- thor. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2014, 640, (2), 370–378 370 TPSS-D3(BJ)  TPSS  PBE  BP86. The Hirshfeld charge distribu- tion indicates that the overall charge flows from metal fragment to [S 2 O]. The Ni–S 2 O bond has greater degree of covalent character than the ionic. The contribution of dispersion interactions is large in com- puting accurate bond dissociation energies between the interacting fragments. The BDEs are largest for the functional TPSS and smallest for the functional BP86. The DFT-D3 dispersion corrections to the BDEs between the metal fragments [(PMe 3 ) 2 M] and ligand fragment [(S 2 O)] for the TPSS functional are in the range 7.1–7.3 kcal·mol –1 , which are smaller than the corresponding DFT-D3(BJ) dispersion corrections (9.4–10.6 kcal·mol –1 ). Ir, [6,7,18] and Pt. [19–21] Ishii and co-workers have reported the structure and properties of platinum-S 2 O complex [(Ph 3 P) 2 Pt(S 2 O)]. [21] The X-ray crystal structure of this com- plex is not very clear, having disordered Pt(S 2 O) moieties (Fig- ure S1 in Supporting Information). Shaver and co-workers re- ported an iridium complex [Cp*(PMe 3 )Ir(S 2 O)], in which they represent the existence of two isomeric forms of metal-S 2 O bonding, i.e., exo and endo modes. [18] Structurally charac- terized transition metal-disulfur monoxide complexes and their important structural parameters are presented in Table 1. Electronic structure and molecular orbital calculations of the complex [Mn–S 2 O] + have been theoretically investigated. [22] To the best of our knowledge, the detailed quantum chemical analysis of the M–S 2 O bonding in disulfur monoxide com- plexes and the effect of dispersion interactions on M–S 2 O bonding have not been discussed so for. The investigation of accurate optimized structure and the nature of M–S 2 O bonding analysis are utmost important. Standard Kohn-Sham density functional theory (DFT) fails to correctly describe non-covalent interactions, which are es- sential to understand many important phenomena in chemistry. Dispersion interactions possess a significant attractive compo- nent due to instantaneous dipoles and higher-order multipoles. They typically dominates in regions, where there is little or no overlap of electron densities, i.e., at medium to long range, as compared to the short range covalent and ionic bonds. [23,24] There is a growing interest in treating dispersive interactions correctly within approximate density functional theory (DFT)