Photooxidation of Platinum(II) Diimine Dithiolates

The violet color of Pt(bpy)(bdt) (bpy = 2,2‘-bipyridine; bdt = 1,2-benzenedithiolate) is due to a Pt/S → diimine charge-transfer transition; the emission originates from the corresponding triplet state (τ = 460 ns). Photochemical oxidation of Pt(bpy)(bdt) occurs in the presence of oxygen in N,N-dimethylformamide, acetonitrile, or dimethyl sulfoxide solution; the reaction has been investigated by ^1H NMR and UV−visible absorption spectroscopy. Singlet oxygen produced by energy transfer from the excited complex is implicated as the active oxygen species, in sequential formation of sulfinate, Pt(bpy)(bdtO_2), and disulfinate, Pt(bpy)(bdtO_4), products. Both products have been characterized by X-ray crystallography. The rate of photooxygenation is strongly dependent on water concentration, and transient absorption spectra are consistent with the formation of at least one intermediate. As a whole, our data suggest that the photooxidation chemistry of platinum(II) diimine dithiolates is similar to that of organic sulfides

A revision of the structure of (bipyridyl-N,N')-dicyanoplatinum(II)

In a previous X-ray crystallographic study of crystals of Pt(bpy)(CN)_2 (bpy = 2,2'-bipyridine) the planar molecules were reported to be exactly eclipsed, stacked directly on top of one another with a spacing of 3.33 Å so as to form a linear Pt· · ·Pt· · ·Pt chain. A reinvestigation shows this structure to be incorrect. The presence of weak intermediate layer lines indicates that the repeat distance along the stacking direction is 6.66 Å rather than 3.33 Å. Successive molecules within the stack are rotated by 180° and the resulting Pt-atom chain is slightly zigzag with a Pt· · ·Pt· · ·Pt angle of 168.6 (1)°. The implications are discussed of the determination and refinement of an apparently satisfactory, although grossly wrong, structure that was based on an incorrect unit cell and an incorrect space group

Emission Spectroscopic Properties of the Red Form of Dichloro(2,2‘-bipyridine)platinum(II). Role of Intermolecular Stacking Interactions

The structure of the red form of Pt(bpy)Cl_2 (bpy = 2,2‘-bipyridine) has been studied by variable-temperature X-ray crystallography. The stack of square-planar Pt(bpy)Cl_2 units in the linear-chain material contracts with decreasing temperature; in the interval between 294 and 20 K, the platinum−platinum distance shortens from 3.449(1) to 3.370(2) Å. Both absorption and emission spectra of the red compound depend strikingly on temperature; as previously found for tetracyanoplatinate salts, the emission maximum red-shifts as the temperature drops (613 nm at 300 K; 651 nm at 10 K), with the peak energy decreasing linearly with the inverse cube of the metal−metal separation

(Bipyridyl-N,N')diiodoplatinum(II)

Square-planar (bipyridyl-N,N')diiodoplatinum(II), [PtI_2(C_(10)H_8N_2)], has normal Pt--N(bipyridyl) [2.029 (7) Å] and Pt--I bonds [2.589 (2) Å]. The bipyridyl ligand exhibits normal distances and angles. Because of steric effects, the intramolecular I...I separation [3.587 (1) Å] and the corresponding I--Pt--I angle [87.7 (1)°] are significantly smaller than those observed for other cis-bis(iodo)bis(N-donor) complexes. The parallel square-planar units stack to form a chain structure. Relative lateral displacement of consecutive molecules along a chain results in a Pt..-Pt distance [5.291 (1) Å] considerably longer than the interplanar spacing [3.510 (11) Å]

Photooxidation of Platinum(II) Diimine Dithiolates

The violet color of Pt(bpy)(bdt) (bpy = 2,2‘-bipyridine; bdt = 1,2-benzenedithiolate) is due to a Pt/S → diimine charge-transfer transition; the emission originates from the corresponding triplet state (τ = 460 ns). Photochemical oxidation of Pt(bpy)(bdt) occurs in the presence of oxygen in N,N-dimethylformamide, acetonitrile, or dimethyl sulfoxide solution; the reaction has been investigated by ^1H NMR and UV−visible absorption spectroscopy. Singlet oxygen produced by energy transfer from the excited complex is implicated as the active oxygen species, in sequential formation of sulfinate, Pt(bpy)(bdtO_2), and disulfinate, Pt(bpy)(bdtO_4), products. Both products have been characterized by X-ray crystallography. The rate of photooxygenation is strongly dependent on water concentration, and transient absorption spectra are consistent with the formation of at least one intermediate. As a whole, our data suggest that the photooxidation chemistry of platinum(II) diimine dithiolates is similar to that of organic sulfides

(Bipyridyl-N,N')diiodoplatinum(II)

Square-planar (bipyridyl-N,N')diiodoplatinum(II), [PtI_2(C_(10)H_8N_2)], has normal Pt--N(bipyridyl) [2.029 (7) Å] and Pt--I bonds [2.589 (2) Å]. The bipyridyl ligand exhibits normal distances and angles. Because of steric effects, the intramolecular I...I separation [3.587 (1) Å] and the corresponding I--Pt--I angle [87.7 (1)°] are significantly smaller than those observed for other cis-bis(iodo)bis(N-donor) complexes. The parallel square-planar units stack to form a chain structure. Relative lateral displacement of consecutive molecules along a chain results in a Pt..-Pt distance [5.291 (1) Å] considerably longer than the interplanar spacing [3.510 (11) Å]

Electronic Structures of Nitridomanganese(V) Complexes

The single-crystal polarized absorption and circular dichroism spectra of the nitridomanganese(V) complexes (salen)Mn⋮N (1), (1S,2S-(−)-saldpen)Mn⋮N (2), and (1R,2R-(+)-saldpen)Mn⋮N (3) have been measured [salen = N,N‘-ethylenebis(salicylideneaminato) dianion, 1S,2S-(−)-saldpen = N,N‘-(1S,2S-(−)-diphenyl)ethylenebis(salicylideneaminato) dianion, and 1R,2R-(+)-saldpen = N,N‘-(1R,2R-(+)-diphenyl)ethylenebis(salicylideneaminato) dianion]. As revealed by X-ray crystal structure analyses, these molecules have a distorted square-pyramidal geometry with a short Mn⋮N bond distance (1.52(3) Å for 2). The Cs compounds have a low-spin^ 1A‘[a‘(x^2 − y^2)]^2 ground state. The lowest absorption system (∼600 nm) consists of two components that are separated by approximately 4000 cm^(-1); these are assigned to ^1A‘ → ^1A‘[a‘(x^2 − y^2)a‘(yz)] (14 900 cm^(-1)) and ^1A‘ → ^1A‘‘[a‘(x^2 − y^2)a‘‘(xz)] (18 900 cm^(-1)) transitions

Linear-Chain Structures of Platinum(II) Diimine Complexes

The structures of three linear-chain platinum(II) diimine complexes have been determined [Pt···Pt, Å]:  Pt(bpm)Cl_2·0.5(nmp) (3) [3.411(1), 3.371(1)], Pt(phen)(CN)_2 (6) [3.338(1), 3.332(1)], and Pt(bpy)(NCS)_2 (7) [3.299(2)] (bpm = 2,2‘-bipyrimidine, phen = 1,10-phenanthroline, bpy = 2,2‘-bipyridine, nmp = 1-methyl-2-pyrrolidinone). The Pt···Pt distances in these and in seven related compounds range from 3.24 to 3.49 Å. While we find evidence of interligand interactions influencing these structures, the Pt···Pt bonds are the most important of the stacking forces. The metal−metal distances are generally consistent with an electronic structural model in which σ-donor/π-acceptor ligands strengthen Pt···Pt bonding interactions (for example, the Pt···Pt distances in 3 are 0.04 and 0.08 Å shorter than in the bpy analogue). We have also found that the yellow form of Pt(dmbpy)(NCO)_2 (1b) (4,4‘-dimethyl-2,2‘-bipyridine) has a columnar structure; however, in contrast to the linear-chain form (1), which is orange, the Pt atoms are well separated (>4.9 Å). Interestingly, the yellow form is 7% denser than the orange form; this result is consistent with the concept that directed intermolecular interactions give rise to lower density polymorphs. Crystal data:  (3) monoclinic, C2/m (No. 12), a = 12.668(4) Å, b = 15.618(6) Å, c = 6.704(3) Å, β = 93.43(3)°, Z = 4; (6) orthorhombic, Pbca (No. 61), a = 38.731(13) Å, b = 18.569(3) Å, c = 6.628(1) Å, Z = 16; (7) orthorhombic, Pbcm (No. 57), a = 10.349(3) Å, b = 19.927(5) Å, c = 6.572(3) Å, Z = 4; (1b) monoclinic, C2/c (No. 15), a = 17.313(4) Å, b = 12.263(3) Å, c = 14.291(4) Å, β = 114.00(2)°, Z = 8

A Bis(pyrazolyl)(bipyridyl)platinum Complex

(4,4' -Dimethyl-2,2'-bipyridyl)bis(3,5-dimethylpyrazolium) platinum(II) 0.5-tetrahydrofuran solvate monohydrate, [Pt(C_5H_7N_2MC_(12)H_(12)-N2)].0.5C_4H_80.H_2O, M_r = 623.65, monoclinic, P2_1/n, ɑ = 8.625 (2), b = 20.593 (8), c = 14.451(4) Å, β = 90.32 (2)°, v = 2566.7 (14) Å^3, Z = 4, D_x = 1.61 g cm^(-3), λ(Mo Kɑ)= 0.71073 Å, μ = 55.50 cm^(-1), F(000) = 1232, room temperature, R = 0.0387 for 2874 reflections with F_o^2 > 3σ(F_o^2). The square-planar Pt complex has normal Pt-N(bipyridyl) bonds [2.009 (8) Å] and slightly short Pt-N(pyrazolyl) bonds [1.983 (7) Å]. The ligand molecules have normal distances and angles; the planes of the pyrazolyl ligands are twisted by about 60° to the bipyridyl-Pt plane, with the closest contacts between the pyrazolyls being -3.3 Å (Cl4···N5 and C19···N3)

Grandpa Bulbrook

A series of platinum­(II) complexes with the formulas Pt­(diimine)­(pip₂NCNH₂)­(L)²⁺ [pip₂NCNH₂⁺ = 2,6-bis­(piperidiniummethyl)­phenyl cation; L = Cl, Br, I, NCS, OCN, and NO₂; diimine = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO₂phen), and 5,5′-ditrifluoromethyl-2,2′-bipyridine (dtfmbpy)] were prepared by the treatment of Pt­(pip₂NCN)­Cl with a silver­(I) salt followed by the addition of the diimine and halide/pseudohalide under acidic conditions. Crystallographic data as well as ¹H NMR spectra establish that the metal center is bonded to a bidentate phenanthroline and a monodentate halide/pseudohalide. The pip₂NCNH₂⁺ ligand with protonated piperidyl groups is monodentate and bonded to the platinum through the phenyl ring. Structural and spectroscopic data indicate that the halide/pseudohalide group (L^–) and the metal center in Pt­(phen)­(pip₂NCNH₂)­(L)²⁺ behave as Brønsted bases, forming intramolecular NH···L/NH···Pt interactions involving the piperidinium groups. A close examination of the 10 structures reported here reveals linear correlations between N–H···Pt/L angles and H···Pt/L distances. In most cases, the N–H bond is directed toward the Pt–L bond, thereby giving the appearance that the proton bridges the Pt and L groups. In contrast to observations for Pt­(tpy)­(pip₂NCN)⁺ (tpy = 2,2′;6′,2″-terpyridine), the electrochemical oxidation of deprotonated adducts, Pt­(diimine)­(L)­(pip₂NCN), is chemically and electrochemically irreversible