Theoretical Study Of The Electron Density Characteristic And The Nature Of Non-classical Hydrogen Bonding Pt(Ⅱ)…H

That metals can serve as hydrogen bond acceptors was first proposed some 40years ago based upon solution-phase IR spectroscopic. Recently, the research havemade breakthrough progress in this aspect. For example, Silvia Rizzato et al. reporteda hydrogen-bonding-like interaction between a water molecule and a d⁸metal ion Pt^â…¡based on neutron diffraction, and pointed out that the distance of Pt^Ⅱ…H was2.885 .Jeffrey R. Long et al.reported the metal-organic framework Fe2（dobdc）（dobdc4-:2,5-dioxido-1,4-benzenedicarboxylate） in the science, which was demonstrated toexhibit excellent performance characteristics for separation of ethylene/ethane andpropylene/propane mixtures at 318 kelvin.They displayed that the distance of Fe…Hwas 2.59（2） in the diamagnetic complex [Fe（C₂H₆）₄], while when binding propane,The distance of Fe…H were 2.86（2） and 2.18（1） . However, these research on thehydrogen bonding limited to the geometric structure characterization. This researchmainly used topology method to study this kind of the non-classical hydrogen bondfrom electronic density angle characterization.In this thesis, We have theoretically characterized two kinds of hydrogenbonding Pt（Ⅱ）…H interactions , which d⁸metal ion Pt^â…¡participated.These two kindsof interactions were intermolecular and intramolecular Pt（Ⅱ）…H hydrogen bridginginteractions .We used atoms in molecule （AIM） and natural bond orbital analysis（NBO） based on the crystallographic geometries, and tried to answer the followingquestions:â‘ Why can a filled d orbitals of square-planar d⁸metal ions such as platinum（Ⅱ）could also act as hydrogen-bond acceptors? Can a study based on the electroncharge density answer this question?â‘¡The formation mechanisms and the nature of this kind of hydrogen bond; â‘¢The differences of electron density characteristics and the nature between theclassical and the non-classical hydrogen bond.The first complex we chose the crystal of trans-[PtCl₂（NH₃）（N-glycine）]·H₂O（1·H₂O）, which was reported by Silvia Rizzato et al. based on neutron diffraction.Andthey provided the first crystallographic evidence for a hydrogen-bonding-likeinteraction between a water molecule and a d⁸metal ion PtIIin this system. Thesecond system was the crystal of [NBu₄][Pt（C₆F₅）₃（8-hydroxy quinaldine）] from JoséMaría Casas et al., which contains intramolecular Pt(Pt^â…¡)…H hydrogen bridginginteractions.The main work and the conclusions are as follows:The method used density functional theory （DFT） with the hybrid B3LYPfunction. In order to theoretically characterize these kind of hydrogen bondingPt(Pt^â…¡)…H interactions ,we used atoms in molecule （AIM） and natural bond orbital（NBO） analysis based on the crystallographic geometries. For platinum atoms, wecomputed with Los Alamos National Laboratory 2-Double-Zeta （LANL2DZ） basisset, and the other atoms were used 6-311++G （d,p） basis sets . Criteria based on atopological analysis of the electron density were used in order to characterize thenature of interactions in the complexes.（1）Silvia Rizzato et al. reported a hydrogen-bonding-like interaction between awater molecule and a d⁸metal ion PtII, based on neutron diffraction，and providedthe first crystallographic evidence for this interaction.They computed at theHartree-Fock （HF） and at the MP2 levels and evaluated that the interaction wasalmost entirely dispersion-driven.We took one cell of the whole crystal oftrans-[PtCl₂（NH₃）（N-glycine）]·H₂O （1.H₂O） to study the intermolecular interaction ofthis complex.The calculation was performed in gas-phase at the b3lyp/6-311++g（d,p）level. The charge densities and their Lapalcians at the BCPs were 0.00896－0.05964and 0.0250－0.1559 a.u., respectively. Depending on Popelier’s criteria thatρbliesbetween 0.002 and 0.035 a.u. for hydrogen bonded system, whereas for an agosticsystem,ρblies outside this range. Further more,â–½2ρblies between 0.024 and0.139 a.u.for a hydrogen bonded system and 0.15–0.25a.u.for an agostic case. These values of the electron density and its Laplacian are well within the range specified for theexistence of the hydrogen bond. Their Laplacianâ–½2ρbwere less than zero, so theinteractions in this complex were electrostatic in the nature.The NBO analysis indicated theΔEi－j^*2values of O－H…Pt, N－H…Pt , O－H…O=C and O－H…OH₂was 0.97, 1.42,9.29 and 38.13a.u, respectively, and thecharge transfer were between 0.0021e and 0.0164 e from donor to acceptor orbitals.Both of the types of charge transfer are n→σ^* in the complexes. And the values ofnPt→σN－H^* interactions, was larger than the values of nPt→σO－H^*. The values ofcharge transfer of O－H…OH₂was largest in these interactions.Compared to thenon-classic hydrogen bondings, the classic hydrogen bond contained more covalentcomposition. This intermolecular interaction was mainly closed-shell and someelectron transfer of this system.（2） In order to study the rule of this interaction ulteriorly, and want to understandwhether the crystal field effects contributed to these interaction ,we took the thecrystal of [NBu₄][Pt（C₆F₅）₃（8-hydroxy quinaldine）] from JoséMaría Casas et al.,which contains intramolecular Pt（Ⅱ）…H hydrogen bridging interactions. Used atomsin molecule （AIM） and natural bond orbital （NBO） analysis .The charge densities andtheir Lapalcians at the BCPs were 0.00259－0.02121 a.u.and 0.01108－0.08867 a.u.,respectively. According to Popelier’s criteria the values of the electron density and theLaplacian of O－H…Pt interaction is well within the range specified for the existenceof the hydrogen bond. Their Laplacianâ–½2ρbwere less than zero, so the interactionsin this complex were closed-shell in the nature primarily.The NBO analysis indicated theΔEi－j^*（2 ）values of O－H…Pt , C－H₆₈…F₁₉－C,C－H₆₁…F₂₀－C and C－H₇₇…F₂₀－C are 2.06, 0.05,0.54 and 0.26a.u., respectively. Andthe charge transfer from donor to acceptor orbitalswas in the range of 0.010－0.0233e,All of the types of charge transfer are n→σ^* in the complexes. The interaction of thecomplex of [NBu₄][Pt（C₆F₅）₃（8-hydroxy quinaldine）] is electrostatic interaction witha little charge transfer. In other words, there is no much difference of the naturebetween intermolecular interaction and intramolecular interaction in these systems. In summary, We are studied the electron density characterization and the natureof intermolecules Pt （Ⅱ）…H and intramolecular Pt （Ⅱ）…H hydrogen bondinginteractions.We found that both of them were closed-shell interaction basically with alittle charge transfer in the nature. The first system Pt （Ⅱ）…H was dispersion driver,and there was no contribution of the crystal field effect to the interaction. The role ofcharge transfer in the Pt （Ⅱ）…H was minimal from the NBO analysis.In addition, we also compared two Pt （Ⅱ）…H with classic hydrogen bondingand organic fluorine hydrogen bonds in the nature and electronic densitycharacteristics existing in these systems.