DFT study of the role of intermolecular interactions in the formation of stable halogeno– and ammineaqua– platinum(II) coordination compounds

Abstract

Density functional theory (DFT) and Hartree-Fock (HF) 2ϩ , the conditions for the formation of linear polynuclear complexes with PtOPt bonds (the so-called "platinum blues") are created.

Synthesis and Structural Characterisation of cis‐ and trans‐[(hppH)2PtCl2], [(hppH)3­PtCl]+Cl– and Some New Salts of the [hppH2]+ Cation (hppH = 1,3,4,6,7,8‐Hexahydro‐2H‐pyrimido[1,2‐a]pyrimidine): The Importance of Hydrogen Bonding

“…[1] According to recent quantum chemical calculations, the Pt-NH 3 bond in cisplatin is around 50 kJ mol -1 stronger than the Pt-Cl bond. [5] Nevertheless, it has been shown that the Pt II complex [Pt(NH 3 ) 3 Cl]Cl cannot easily be obtained in high yield as the direct reaction between cis-or trans-[Pt(NH 3 ) 2 Cl 2 ] and 1 mol-equiv. of NH 3 4 ]Cl 2 .…”

“…[(hppH) 2 NiCl 2 ] has already been synthesised by treating (hpp) 3 SiMe with NiCl 2 (py) 4 (py = pyridine) in toluene at room temperature and has been shown to feature a more or less tetrahedrally coordinated Ni atom. [15] Furthermore, the reaction between [PdCl 2 (cod)] (cod = cyclooctadiene) and hppH in CH 2 Cl 2 affords trans-[(hppH) 2 PdCl 2 ]. [16] Fast isomerisation seems to occur from a cis arrangement of the chlorido ligands to a more stable trans configuration during the course of the reaction such that it proved impossible to isolate the cis isomer.…”

“…[14] As a consequence, the C1-N1 and C1-N2 bond lengths (see Scheme 2 for the atom numbering) in crystalline hppH are almost equal (133.1 and 132.8 pm), whereas C1-N3 is significantly longer (136.7 pm). [(hppH) 2 NiCl 2 ] has already been synthesised by treating (hpp) 3 SiMe with NiCl 2 (py) 4 (py = pyridine) in toluene at room temperature and has been shown to feature a more or less tetrahedrally coordinated Ni atom. [15] Furthermore, the reaction between [PdCl 2 (cod)] (cod = cyclooctadiene) and hppH in CH 2 Cl 2 affords trans-[(hppH) 2 PdCl 2 ].…”

“…Intermolecular interactions, including H···Cl and Pt···Pt contacts (distances of 337.2/340.9 pm), are important in this complex in the crystalline phase. [1] According to quantum chemical calculations (B3LYP/6-31G**) and using a model consisting of four molecules, the intermolecular interactions in cis-[Pt(NH 3 ) 2 Cl 2 ] were estimated to be of the order of 360 kJ mol -1 . [2] The trans form of the molecule is more stable than the cis form, and the trans-cis energy difference has been calculated to be -55, -76, -55 and -57 kJ mol -1 by B3LYP, [2] HF, [3] MP2 [4] and G3 methods, respectively.…”

“…The nitrogen base 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH, 4) is a much stronger base than NH 3 [12] and should also form stable complexes with Ni, Pd and Pt (M) of the formula [(hppH) 2 MCl 2 ]. Interestingly, although not unprecedented for guanidines or amidines, [13] the crystal structure of uncoordinated hppH reveals the presence of dimers that interact strongly through NH···N contacts, which results in a disorder of the NH atoms over two positions and a delocalised binding situation.…”