PtII Coordination to N1 of 9‐Methylguanine: Why it Facilitates Binding of Additional Metal Ions to the Purine Ring

The preparation and X‐ray crystal structure analysis of {trans‐[Pt(MeNH₂)₂(9‐MeG‐N1)₂]} ? {3 K₂[Pt(CN)₄]} ? 6 H₂O ( 3 a ) (with 9‐MeG being the anion of 9‐methylguanine, 9‐MeGH) are reported. The title compound was obtained by treating [Pt(dien)(9‐MeGH‐N7)]²⁺ ( 1 ; dien=diethylenetriamine) with trans‐[Pt(MeNH₂)₂(H₂O)₂]²⁺ at pH 9.6, 60 °C, and subsequent removal of the [(dien)Pt^II] entities by treatment with an excess amount of KCN, which converts the latter to [Pt(CN)₄]^2?. Cocrystallization of K₂[Pt(CN)₄] with trans‐[Pt(MeNH₂)₂(9‐MeG‐N1)₂] is a consequence of the increase in basicity of the guanine ligand following its deprotonation and Pt coordination at N1. This increase in basicity is reflected in the pK_a values of trans‐[Pt(MeNH₂)₂(9‐MeGH‐N1)₂]²⁺ (4.4±0.1 and 3.3±0.4). The crystal structure of 3 a reveals rare (N7,O6 chelate) and unconventional (N2,C2,N3) binding patterns of K⁺ to the guaninato ligands. DFT calculations confirm that K⁺ binding to the sugar edge of guanine for a N1‐platinated guanine anion is a realistic option, thus ruling against a simple packing effect in the solid‐state structure of 3 a . The linkage isomer of 3 a , trans‐[Pt(MeNH₂)₂(9‐MeG‐N7)₂] ( 6 a ) has likewise been isolated, and its acid–base properties determined. Compound 6 a is more basic than 3 a by more than 4 log units. Binding of metal entities to the N7 positions of 9‐MeG in 3 a has been studied in detail for [(NH₃)₃Pt^II], trans‐[(NH₃)₂Pt^II], and [(en)Pd^II] (en=ethylenediamine) by using ¹H NMR spectroscopy. Without exception, binding of the second metal takes place at N7, but formation of a molecular guanine square with trans‐[(Me₂NH₂)Pt^II] cross‐linking N1 positions and trans‐[(NH₃)₂Pt^II] cross‐linking N7 positions could not be confirmed unambiguously, despite the fact that calculations are fully consistent with its existence.     

Mixed Adenine/Guanine Quartets with Three trans‐a2PtII (a=NH3 or MeNH2) Cross‐Links: Linkage and Rotational Isomerism,Base Pairing,and Loss of NH3

Of the numerous ways in which two adenine and two guanines (N9 positions blocked in each) can be cross‐linked by three linear metal moieties such as trans‐a₂Pt^II (with a=NH₃ or MeNH₂) to produce open metalated purine quartets with exclusive metal coordination through N1 and N7 sites, one linkage isomer was studied in detail. The isomer trans,trans,trans‐[{Pt(NH₃)₂(N7‐9‐EtA‐N1)₂}{Pt(MeNH₂)₂(N7‐9‐MeGH)}₂][(ClO₄)₆] ? 3H₂O ( 1 ) (with 9‐EtA=9‐ethyladenine and 9‐MeGH=9‐methylguanine) was crystallized from water and found to adopt a flat Z‐shape in the solid state as far as the trinuclear cation is concerned. In the presence of excess 9‐MeGH, a meander‐like construct, trans,trans,trans‐[{Pt(NH₃)₂(N7‐9‐EtA‐N1)₂}{Pt(MeNH₂)₂(N7‐9‐MeGH)₂}][(ClO₄)₆] ? [(9‐MeGH)₂] ? 7 H₂O ( 2 ) is formed, in which the two extra 9‐MeGH nucleobases are hydrogen bonded to the two terminal platinated guanine ligands of 1 . Compound 1 , and likewise the analogous complex 1 a (with NH₃ ligands only), undergo loss of an ammonia ligand and formation of NH₄⁺ when dissolved in [D₆]DMSO. From the analogy between the behavior of 1 and 1 a it is concluded that a NH₃ ligand from the central Pt atom is lost. Addition of 1‐methylcytosine (1‐MeC) to such a DMSO solution reveals coordination of 1‐MeC to the central Pt. In an analogous manner, 9‐MeGH can coordinate to the central Pt in [D₆]DMSO. It is proposed that the proton responsible for formation of NH₄⁺ is from one of the exocyclic amino groups of the two adenine bases, and furthermore, that this process is accompanied by a conformational change of the cation from Z‐form to U‐form. DFT calculations confirm the proposed mechanism and shed light on possible pathways of this process. Calculations show that rotational isomerism is not kinetically hindered and that it would preferably occur previous to the displacement of NH₃ by DMSO. This displacement is the most energetically costly step, but it is compensated by the proton transfer to NH₃ and formation of U(?H⁺) species, which exhibits an intramolecular hydrogen bond between the deprotonated N6H^? of one adenine and the N6H₂ group of the other adenine. Finally the question is examined, how metal cross‐linking patterns in closed metallacyclic quartets containing two adenine and two guanine nucleobases influence the overall shape (square, rectangle, trapezoid) and the planarity of a metalated purine quartet.     

Bis­[S‐methyl 3‐(2‐bromo­benzyl­idene)­di­thio­cab­aza­to‐N3,S]­platinum(II)

The Schiff base ligand in the title complex, [Pt(C₉H₈BrN₂S₂)₂], is deprotonated from its tautomeric thiol form and coordinated to Pt^IIvia the mercapto S and β–N atoms. The configuration about Pt^II is a perfect square‐planar, with two equivalent Pt—N [2.023 (3) Å] and Pt—S [2.293 (1) Å] bonds. The phenyl ring is twisted against the coordination moiety Pt1/N1/N1′/S2′/S2 by 31.8 (2)°, due to the steric hindrance induced by ortho‐substituted bulky Br atom.     

A one‐dimensional iodine‐bridged PtII/PtIV mixed‐valence complex,catena‐poly[[[bis­(ethyl­ene­diamine)­platinum(II)]‐μ‐iodo‐[bis­(ethyl­ene­di­amine)platinum(IV)]‐μ‐iodo] hydrogenphosphate dihydrogenphosphate iodide trihydrate]

The title compound, {[Pt^IIPt^IVI₂(C₂H₈N₂)₄](HPO₄)(H₂PO₄)I·3H₂O}_n, has a chain structure composed of square‐planar [Pt(en)₂]²⁺ and elongated octa­hedral trans‐[PtI₂(en)₂]²⁺ cations (en is ethyl­ene­diamine) stacked alternately along the c axis and bridged by the I atoms; a three‐dimensionally valence‐ordered system exists with respect to the Pt sites. The title compound also has a unique cyclic tetra­mer structure composed of two hydrogenphosphate and two dihydrogenphosphate ions connected by strong hydrogen bonds [O⋯O = 2.522 (10), 2.567 (10) and 2.569 (11) Å]. The Pt and I atoms form a zigzag ⋯I—Pt^IV—I⋯Pt^II⋯ chain, with Pt^IV—I bond distances of 2.6997 (7) and 2.6921 (7) Å, inter­atomic Pt^II⋯I distances of 3.3239 (8) and 3.2902 (7) Å, and Pt^IV—I⋯Pt^II angles of 154.52 (3) and 163.64 (3)°. The structural parameters indicating the mixed‐valence state of platinum, expressed by δ = (Pt^IV—I)/(Pt^II—I), are 0.812 and 0.818 for the two independent I atoms.     

A one‐dimensional chloride‐bridged PtII/PtIV mixed‐valence complex with a 4‐[(4‐hydroxyphenyl)diazenyl]benzenesulfonate counter‐ion

The title compound, catena‐poly[[[bis(ethylenediamine‐κ²N,N′)platinum(II)]‐ μ‐chlorido‐[bis(ethylenediamine)platinum(IV)]‐μ‐chlorido] tetrakis{4‐[(4‐hydroxyphenyl)diazenyl]benzenesulfonate} dihydrate], {[Pt^IIPt^IVCl₂(C₂H₈N₂)₄](HOC₆H₄N=NC₆H₄SO₃)₄·2H₂O}_n, has a linear chain structure composed of square‐planar [Pt(en)₂]²⁺ (en is ethylenediamine) and elongated octahedral trans‐[PtCl₂(en)₂]²⁺ cations stacked alternately, bridged by Cl atoms, along the b axis. The Pt atoms are located on an inversion centre, while the Cl atoms are disordered over two sites and form a zigzag ...Cl—Pt^IV—Cl...Pt^II... chain, with a Pt^IV—Cl bond length of 2.3140 (14) Å, an interatomic Pt^II...Cl distance of 3.5969 (15) Å and a Pt^IV—Cl...Pt^II angle of 170.66 (6)°. The structural parameter indicating the mixed‐valence state of the Pt atom, expressed by δ = (Pt^IV—Cl)/(Pt^II...Cl), is 0.643.     

π–π Dimerization of a mono(pyridyl–imine) platinum(II) chelate

The cation of the title complex salt, chlorido{2,2‐dimethyl‐N‐[(E)‐1‐(pyridin‐2‐yl)ethylidene]propane‐1,3‐diamine}platinum(II) tetrafluoridoborate, [PtCl(C₁₂H₁₉N₃)]BF₄, exhibits a nominally square‐planar Pt^II ion coordinated to a chloride ion [Pt—Cl = 2.3046 (9) Å] and three unique N‐atom types, viz. pyridine, imine and amine, of the tridentate Schiff base ligand formed by the 1:1 condensation of 1‐(pyridin‐2‐yl)ethanone and 2,2‐dimethylpropane‐1,3‐diamine. The cations are π‐stacked in inversion‐related pairs (dimers), with a mean plane separation of 3.426 Å, an intradimer Pt...Pt separation of 5.0785 (6) Å and a lateral shift of 3.676 Å. The centroid (Cg) of the pyridine ring is positioned approximately over the Pt^II ion of the neighbouring cation (Pt...Cg = 3.503 Å).     

Platinum‐Containing Polyoxometalates: syn‐ and anti‐[PtII2(α‐PW11O39)2]10− and Formation of the Metal–Metal‐Bonded di‐PtIII Derivatives

The first examples of dimeric, di‐Pt^II‐containing heteropolytungstates are reported. The two isomeric di‐platinum(II)‐containing 22‐tungsto‐2‐phosphates [anti‐Pt^II₂(α‐PW₁₁O₃₉)₂]^10? ( 1 a ) and [syn‐Pt^II₂(α‐PW₁₁O₃₉)₂]^10? ( 2 a ) were synthesized in aqueous pH 3.5 medium using one‐pot procedures. Polyanions 1 a and 2 a contain a core comprising two face‐on PtO₄ units, with a Pt???Pt distance of 2.9–3 Å. Both polyanions were investigated by single‐crystal XRD, IR, TGA, UV/Vis, ³¹P NMR, ESI‐MS, CID‐MS/MS, electrochemistry, and DFT. On the basis of DFT and electrochemistry, we demonstrated that the {Pt₂^II} moiety in 1 a and 2 a can undergo fully reversible two‐electron oxidation to {Pt₂^III}, accompanied by formation of a single Pt?Pt bond. Hence we have discovered the novel subclass of Pt^III‐containing heteropolytungstates.     

"Directed" assembly of metallacalix[n]arenes with pyrimidine nucleobase ligands of low symmetry: interchanging metals in mixed-metal metallacalix[4]arenes and incorporating additional metals at the exocyclic groups

The pyrimidine (pym) nucleobase cytosine (H₂C) forms cyclic ring structures (“metallacalix[n]arenes”) when treated with square‐planar cis‐a₂M^II entities (M=Pt, Pd; a=NH₃ or a₂=diamine). The number of possible linkage isomers for a given n and the number of possible rotamers can be substantially reduced if a “directed” approach is pursued. Hence, two cytosine ligands are bonded in a defined way to a kinetically robust platinum corner stone. In the accompanying paper (Part I: A. Khutia, P. J. Sanz Miguel, B. Lippert, Chem. Eur. J. 2010 , 17, DOI: 10.1002/chem.2010002722) we have demonstrated this principle by allowing cis‐[Pta₂(H₂C‐N3)₂]²⁺ to react with (en)Pd^II to give cycles of (N1,N3 ? N3,N1?)_x (with x=2 or 3; ? represents Pt^II and ? represents Pd^II). In an extension of this work we have now prepared cis‐[Pta₂(HC‐N1)₂] ( 1 ; HC=monoanion of cytosine) and treated it with (bpy)Pd^II (bpy=2,2′‐bipyridine) to give the Pt₂Pd₂ cycle cis‐[{Pt(NH₃)₂(N1‐HC‐N3)₂Pd(bpy)}₂](NO₃)₄ ? 13H₂O ( 5 ) with the coordination sites of the metals inverted; hence, platinum is bonded to N1 and palladium is bonded to N3 sites. Again, not only the expected single linkage isomer is formed, but at the same time the solid‐state structure and ¹H NMR spectroscopy reveal the preferential occurrence of a single rotamer (1,3‐alternate). The addition of (bpy)Pd^II to 5 led to the formation of Pd₆Pt₂ complex 6 in which the exocyclic N4H₂ groups of the cytosine ligands have undergone deprotonation and chelate four more (bpy)Pd^II entities through the O2 and N4H sites. With a large excess of (bpy)Pd^II over 5 (4:1), cis‐(NH₃)₂Pt^II is eventually substituted by (bpy)Pd^II to give the Pd₈ complex 7 . In both 6 and 7 stacks of three (bpy)Pd^II entities occur. The linkage isomer of 5 , cis‐[{Pt(NH₃)₂(N3‐HC‐N1)₂Pd(bpy)}₂](NO₃)₄ ? 9H₂O ( 8 ), has been structurally characterized and the two complexes compared. The acid/base properties of cis‐[Pt(NH₃)₂(H₂C‐N1)₂] ( 1 ) have been determined and compared with those of the corresponding N3 isomer. The complexation of AgCl by 1 is reported.     

Unusual Metal–Metal Bonding in a Dinuclear Pt–Au Complex: Snapshot of a Transmetalation Process

The dinuclear Pt–Au complex [(CNC)(PPh₃)Pt Au(PPh₃)](ClO₄) ( 2 ) (CNC=2,6‐diphenylpyridinate) was prepared. Its crystal structure shows a rare metal–metal bonding situation, with very short Pt–Au and Au–C_ipso(CNC) distances and dissimilar Pt–C_ipso(CNC) bonds. Multinuclear NMR spectra of 2 show the persistence of the Pt–Au bond in solution and the occurrence of unusual fluxional behavior involving the [Pt^II] and [Au^I] metal fragments. The [Pt^II]??? [Au^I] interaction has been thoroughly studied by means of DFT calculations. The observed bonding situation in 2 can be regarded as a model for an intermediate in a transmetalation process.     

A one‐dimensional platinum mixed‐valence complex with bridging thiocyanate S atoms: [[PtII(en)2](μ‐SCN)[PtIV(en)2](μ‐SCN)](ClO4)4 (en is ethane‐1,2‐diamine)

A new one‐dimensional platinum mixed‐valence complex with nonhalogen bridging ligands, namely catena‐poly[[[bis(ethane‐1,2‐diamine‐κ²N,N′)platinum(II)]‐μ‐thiocyanato‐κ²S:S‐[bis(ethane‐1,2‐diamine‐κ²N,N′)platinum(IV)]‐μ‐thiocyanato‐κ²S:S] tetrakis(perchlorate)], {[Pt₂(SCN)₂(C₂H₈N₂)₄](ClO₄)₄}_n, has been isolated. The Pt^II and Pt^IV atoms are located on centres of inversion and are stacked alternately, linked by the S atoms of the thiocyanate ligands, forming an infinite one‐dimensional chain. The Pt^IV—S and Pt^II...S distances are 2.3933 (10) and 3.4705 (10) Å, respectively, and the Pt^IV—S...Pt^II angle is 171.97 (4)°. The introduction of nonhalogen atoms as bridging ligands in this complex extends the chemical modifications possible for controlling the amplitude of the charge‐density wave (CDW) state in one‐dimensional mixed‐valence complexes. The structure of a discrete Pt^IV thiocyanate compound, bis(ethane‐1,2‐diamine‐κ²N,N′)bis(thiocyanato‐κS)platinum(IV) bis(perchlorate) 1.5‐hydrate, [Pt(SCN)₂(C₄H₈N₂)₂](ClO₄)₂·1.5H₂O, has monoclinic (C2) symmetry. Two S‐bound thiocyanate ligands are located in trans positions, with an S—Pt—S angle of 177.56 (3)°.     

On Mixed-Valence Dinuclear PtII,PtIII Nucleobase Complexes Derived from cis-Diamineplatinum(II): Effect of steric bulk of amine ligands on the Pt-oxidation state

A series of closely related dinuclear (head-head) Pt^II complexes of general composition cis-[a₂PtL₂Pta′₂]²⁺ with a,a′ = NH₃ or CH₃NH₂ and L = 1-methyluracilate-N3,O4 (1-MeU) or 1-methylthyminate-N3,O4 (1-MeT) has been prepared and the solution behavior toward Ce^IV oxidation studied. The X-ray crystal structure of a representative example cis-[(CH₃NH₂)₂Pt(1-MeU)₂Pt(CH₃NH₂)₂](ClO₄)₂ · 0.5 H₂O ( 1b ), has been determined: Monoclinic, space group P2₁/c, a = 11.907(7) Å, b = 19.087(14) Å, c = 12.525(7) Å, β = 90.49(4)°, Z = 4. Oxidation of these diplatinum(II) complexes ([Pt^2.0]₂) with Ce^IV in aqueous solution to the corresponding diplatinum(III) species ([Pt^3.0]₂) proceeds via tetranuclear [Pt^2.25]₄ or dinuclear [Pt^2.5]₂ mixed-valence state compounds, depending on the nature of the a′ ligands: with a′ = NH₃, blue green [Pt^2.25]₄ forms, whereas with a′ = CH₃NH₂, purple [Pt^2.5]₂ represents the intermediate. This difference is interpreted in terms of differences in bulk between NH₃ and CH₃NH₂ ligands trans to the O(4) positions of the bridging nucleobases which influence the ability of dinuclear species to associate via the O(4)₂ Pt a₂′ faces.     

Factors Affecting DNA–DNA Interstrand Cross‐Links in the Antiparallel 3′–3′ Sense: A Comparison with the 5′–5′ Directional Isomer

Reported herein is a study of the unusual 3′–3′ 1,4‐GG interstrand cross‐link (IXL) formation in duplex DNA by a series of polynuclear platinum anticancer complexes. To examine the effect of possible preassociation through charge and hydrogen‐bonding effects the closely related compounds [{trans‐PtCl(NH₃)₂}₂(μ‐trans‐Pt(NH₃)₂{NH₂(CH₂)₆NH₂}₂)]⁴⁺ (BBR3464, 1 ), [{trans‐PtCl(NH₃)₂}₂(μ‐NH₂(CH₂)₆NH₂)]²⁺ (BBR3005, 2 ), [{trans‐PtCl(NH₃)₂}₂(μ‐H₂N(CH₂)₃NH₂(CH₂)₄)]³⁺ (BBR3571, 3 ) and [{trans‐PtCl(NH₃)₂}₂{μ‐H₂N(CH₂)₃‐N(COCF₃)(CH₂)₄}]²⁺ (BBR3571‐COCF₃, 4 ) were studied. Two different molecular biology approaches were used to investigate the effect of DNA template upon IXL formation in synthetic 20‐base‐pair duplexes. In the “hybridisation directed” method the monofunctionally adducted top strands were hybridised with their complementary 5′‐end labelled strands; after 24 h the efficiency of interstrand cross‐linking in the 5′–5′ direction was slightly higher than in the 3′–3′ direction. The second method involved “postsynthetic modification” of the intact duplex; significantly less cross‐linking was observed, but again a slight preference for the 5′–5′ duplex was present. 2D [¹H, ¹⁵N] HSQC NMR spectroscopy studies of the reaction of [¹⁵N]‐ 1 with the sequence 5′‐d{TATACATGTATA}₂ allowed direct comparison of the stepwise formation of the 3′–3′ IXL with the previously studied 5′–5′ IXL on the analogous sequence 5′‐d(ATATGTACATAT)₂. Whereas the preassociation and aquation steps were similar, differences were evident at the monofunctional binding step. The reaction did not yield a single distinct 3′–3′ 1,4‐GG IXL, but numerous cross‐linked adducts formed. Similar results were found for the reaction with the dinuclear [¹⁵N]‐ 2 . Molecular dynamics simulations for the 3′–3′ IXLs formed by both 1 and 2 showed a highly distorted structure with evident fraying of the end base pairs and considerable widening of the minor groove.     

Synthese und Struktur der Nitrido‐Komplexe [(n‐Bu)4N]2[{(L)Cl4Re≡N}2PtCl2] (L = THF und H2O) und [(n‐Bu)4N]2[(H2O)Cl4Re≡N‐PtCl(μ‐Cl)]2

Synthesis and Crystal Structure of the Nitrido Complexes [(n‐Bu)₄N]₂[{(L)Cl₄Re≡N}₂PtCl₂] (L = THF und H₂O) and [(n‐Bu)₄N]₂[(H₂O)Cl₄Re≡N‐PtCl(μ‐Cl)]₂ The threenuclear complex [(n‐Bu)₄N]₂[{(THF)Cl₄Re≡N}_2—PtCl₂] ( 1a ) is obtained by the reaction of [(n‐Bu)₄N][ReNCl₄] with [PtCl₂(C₆H₅CN)₂] in THF/CH₂Cl₂. It forms red crystals with the composition 1a · 2 CH₂Cl₂ crystallizing in the tetragonal space group I4₁/a with a = 3186.7(2); c = 1311.2(1) pm and Z = 8. If the reaction of the educts is carried out without THF, however under exposure to air the compound [(n‐Bu)₄N]₂[{(H₂O)Cl₄Re≡N}₂PtCl₂] ( 1b ) is obtained as red trigonal crystals with the space group R3 and a = 3628.3(3), c = 1231.4(1) pm and Z = 9. In the centrosymmetric complex anions [{(L)Cl₄Re≡N}₂PtCl₂]^2— a linear PtCl₂moiety is connected in a trans arrangement with two complex fragments [(L)Cl₄Re≡N]^— via asymmetric nitrido bridges Re≡dqN‐Pt. For Pt^II such results a square‐planar coordination PtCl₂N₂. The linear nitrido bridges are characterized by distances Re‐N = 169.5 pm and Pt‐N = 188.8 pm ( 1a ), respectively, Re‐N = 165.6 pm and Pt‐N = 194.1 pm ( 1b ). By the reaction of [(n‐Bu)₄N][ReNCl₄] with PtCl₄ in CH₂Cl₂ platinum is reduced forming the heterometallic Re^VI/Pt^II complex, [(n‐Bu)₄N]₂[(H₂O)Cl₄Re≡N‐PtCl(μ‐Cl)]₂ ( 2 ). It crystallizes in the monoclinic space group C2/c with a = 2012.9(1); b = 1109.0(2); c = 2687.4(4) pm; β = 111.65(1)° and Z = 4. In the central unit ClPt(μ‐Cl)₂PtCl of the anionic complex [(H₂O)Cl₄Re≡N‐PtCl(μ‐Cl)]₂^2— with the symmetry C₂ the coordination of the Pt atoms is completed by two nitrido bridges Re≡N‐Pt to nitrido complex fragments [(H₂O)Cl₄Re≡N] ^— forming a square‐planar arrangement for the Pt atoms. The distances in the linear nitrido bridges are Re‐N = 165.9 pm and Pt‐N = 190.1 pm.     

Stabilization of an Intramolecularly Coordinated Stannylidenium Cation

The treatment of trans‐{[2, 6‐(Me₂NCH₂)₂C₆H₃]SnI}₂PtI₂ with Na(pyt) (pyt = 2‐mercaptopyridine) yielded the unprecedented complex {{[2, 6‐(Me₂NCH₂)₂C₆H₃]Sn}Pt(μ‐pyt)₂I} ( 1 ), where a Sn←N coordinated stannylidenium (LSn^II)⁺ fragment donates a to a [Pt^II(pyt)₂I]^– anion. Compound 1 was characterized by NMR spectroscopy and molecular structure was determined by X‐ray diffraction analysis. The bonding situation in 1 was analyzed by DFT studies.     

Pt2II and Pt2III dimers containing a Pt2(2,2′‐bipyridine)2(μ‐N,N‐dimethyl­guanidinato)2 unit

The syntheses and crystal structures of the title Pt₂^II and Pt₂^III dimers doubly bridged with N,N‐dimethyl­guanidinate ligands, namely bis­(μ‐N,N‐dimethyl­guanidinato)bis­[(2,2′‐bipyridine)platinum(II)](Pt—Pt) bis­(hexa­fluoro­phosphate) acetonitrile disolvate, [Pt₂^II(C₃H₈N₃)₂(C₁₀H₈N₂)₂](PF₆)₂·2CH₃CN, (I), and guanidinium bis­(μ‐N,N‐dimethyl­guanidinato)bis­[(2,2′‐bipyridine)sulfatoplatinum(III)](Pt—Pt) bis­(hexa­fluoro­phosphate) nitrate hexa­hydrate, (C₃H₁₀N₃)[Pt^III₂(C₃H₈N₃)₂(SO₄)₂(C₁₀H₈N₂)₂]NO₃·6H₂O, (II), are reported. The oxidation of the Pt₂^II dimer into the Pt₂^III dimer results in a marked shortening of the Pt—Pt distance from 2.8512 (6) to 2.5656 (4) Å. The change is mainly compensated for by the change in the dihedral angle between the two Pt coordination planes upon oxidation, from 21.9 (2) to 16.9 (3)°. We attribute the relatively strong one‐dimensional stack of dimers achieved in the Pt₂^II compound in part to the strong Pt^II⋯C(bpy) associations (bpy is 2,2′‐bipyridine) in the crystal structure [Pt⋯C = 3.416 (10) and 3.361 (12) Å].     

trans‐Dichloro(dimethyl sulfide‐κS)(pyridine‐κN)platinum(II)

The structure of the title compound, [PtCl₂(C₅H₅N)(C₂H₆S)], consists of discrete mol­ecules in which the Pt‐atom coordination is slightly distorted square planar. The Cl atoms are trans to each other, with a Cl—Pt—Cl angle of 176.60 (7)°. The pyridine ligand is rotated 64.5 (2)° from the Pt square plane and one of the Pt—Cl bonds essentially bisects the C—S—C angle of the di­methyl sulfide ligand. In the crystal structure, there are extensive weak C—H⋯Cl interactions, the shortest of which connects mol­ecules into centrosymmetric dimers. A comparison of the structural trans influence on Pt—S and Pt—­N distances for PtS(CH₃)₂ and Pt(pyridine) fragments, respectively, in square‐planar Pt^II complexes is presented.     

Highly Efficient Deep‐Blue Emitters Based on cis and trans N‐Heterocyclic Carbene PtII Acetylide Complexes: Synthesis,Photophysical Properties,and Mechanistic Studies

We have synthesized cis and trans N‐heterocyclic carbene (NHC) platinum(II) complexes bearing σ‐alkynyl ancillary ligands, namely [Pt(dbim)₂(C?CR)₂] [DBIM=N,N′‐didodecylbenzimidazoline‐2‐ylidene; R=C₆H₄F ( 4 ), C₆H₅ ( 5 ), C₆H₂(OMe)₃ ( 6 ), C₄H₃S ( 7 ), and C₆H₄C?CC₆H₅ ( 8 )] and [Pt(ibim)₂(C?CC₆H₅)₂] ( 9 ) (ibim=N,N′‐diisopropylbenzimidazoline‐2‐ylidene), starting from [Pt(cod)(C?CR)₂] (COD=cyclooctadiene) and 2 equivalents of [dbimH]Br ([ibimH]Br for complexes 9 ) in the presence of tBuOK and THF. Mechanistic investigations aimed at uncovering the cis to trans isomerization reaction have been performed on the representative cis complex 5 a [Pt(dbim)₂(C?CC₆H₅)₂] and revealed the isomerization to progress smoothly in good yield when 5 a was treated with catalytic amounts of [Pt(cod)(C?CR)₂] at 75 °C in THF or when 5 a was heated at 200 °C in the solid state under an inert atmosphere. Detailed examination of the reactions points to the possible involvement, in a catalytic fashion, of a solvent‐stabilized Pt^II dialkyne complex in the former case and a Pt⁰ NHC complex in the latter case, for the transformation of the cis isomer to the corresponding trans complex. Thermal stability and the isomerization process in the solid state have been further investigated on the basis of TGA and DSC measurements. X‐ray diffraction studies have been carried out to confirm the solid‐state structures of 4 b , 5 a , 5 b , and 9 b . All of the synthesized dialkyne complexes 4 – 9 exhibit phosphorescence in solution, in the solid state at room temperature (RT), and also in frozen solvent glasses at 77 K. The emission wavelengths and quantum yields have been found to be highly tunable as a function of the alkynyl ligand. In particular, the trans isomer of complex 9 in a spin‐coated film (10 wt % in poly(methyl methacrylate), PMMA) exhibits a high phosphorescence quantum yield of 80 %, which is the highest reported for Pt^II‐based deep‐blue emitters. Experimental observations and time‐dependent density functional theory (TD‐DFT) calculations are strongly indicative of the emission being mainly governed by metal‐perturbed interligand (³IL) charge transfer.     

Flat vs. Folded Chelate Rings in cis‐PtIIa2 (a = NH3, a2 = en,a2 = 2, 2′‐bpy) Complexes of Twofold Substituted Diazine Ligands

Acid‐base and ligating properties of three bis(substituted)pyrazine (pz) and pyrimidine (pym) ligands (pyrazine‐2, 5‐dicarboxylic acid, 2, 5‐pzdcH2, 2, 3‐bis(pyridine‐2‐yl)pyrazine, 2, 3‐bppz, pyrimidine‐4, 6‐dicarboxylic acid, 4, 6‐pmdcH₂) toward cis‐Pt^IIa₂ (a = NH₃, a₂ = en, a₂ = 2, 2′‐bpy) have been studied. Combinations of pz‐N/pym‐N with donor atoms of the substituents lead to 5‐membered platinum chelates, but exclusive N, N‐coordination through the pyridyl substituents of 2, 3‐bppz can lead to a 7‐membered platinum chelate with a characteristic L‐shape of the resulting cation. It is observed for Pt^II(2, 2′‐bpy), yet not for Pt^II(en), and is a consequence of differences in sterical interactions between the 2, 3‐bppz ligand and the coligands of Pt^II.     

Novel Platinum(II) Complexes with Dipyridyl Containing Chelating Ligands and their Products with the Model Nucleobases 1‐Methylthymine and 1‐Methyluracil

The reactions of [Pt(dpma)(H₂O)₂]²⁺ (dpma = 2,2′‐dipyridylmethylamine) and [Pt(dpk)(H₂O)₂]²⁺ (dpk = 2,2′‐dipyridylketone) with the model nucleobases 1‐methylthymine (1‐MeT) and 1‐methyluracil (1‐MeU) were studied. Reaction products were characterized by ¹⁹⁵Pt NMR spectroscopy and by X‐ray structure analysis. The symmetric dpma and dpk diaqua complexes form dinuclear complexes with 1‐methylthymine, acting as secondary bridging ligand via its N3 and O4 donor atoms. [Pt₂(dpma)₂(1‐MeT)₂](ClO₄)₂ · H₂O ( 5 ) and [Pt₂(dpk)(dpk · H₂O)(1‐MeT)₂](PF₆)₂ · 4 H₂O ( 6 ) both show a head‐to‐head arrangement. Biological tests show a significant in vitro antitumor activity of [Pt(dpk)Cl₂] against the human glioma cell line U 87.     

Observation of the Properties of a Single Unit of a Limited CDW Structure in a PtII/PtIV Host–Guest Binary System Based on a Square‐Shaped Complex

A macrocyclic tetranuclear platinum(II) complex [Pt(en)(4,4′‐bpy)]₄(NO₃)₈ ( 1 ?(NO₃)₈; en=ethylenediamine, 4,4′‐bpy=4,4′‐bipyridine) and a mononuclear platinum(IV) complex [Pt(en)₂Br₂]Br₂ ( 2 ?Br₂) formed two kinds of Pt^II/Pt^IV mixed valence assemblies when reacted: a discrete host–guest complex 1 ? 2 ?Br₁₀ ( 3 ) and an extended 1‐D zigzag sheet 1 ?( 2 )₃?Br₈(NO₃)₆ ( 4 ). Single crystal X‐ray analysis showed that the dimensions of the assemblies could be stoichiometrically controlled. Resonance Raman spectra suggested the presence of an intervalence interaction, which is typically observed for quasi‐1‐D halogen‐bridged M^II/M^IV complexes. The intervalence interaction indicates the presence of an isolated {Pt^II???X? Pt^IV? X???Pt^II} moiety in the structure of 4 . On the basis of electronic spectra and polarized reflectance measurements, we conclude that 4 exhibits intervalence charge transfer (IVCT) bands. A Kramers–Kronig transformation was carried out to obtain an optical conductivity spectrum, and two sub‐bands corresponding to slightly different Pt^II–Pt^IV distances were observed.