Near-IR Absorbers Based on Pt(II)-Dithiolene Donor-Acceptor Charge-Transfer (CT) Systems: A Structural Analysis to Highlight DA Interactions.

The packing interactions of a series of electron donor (D) and electron acceptor (A) charge transfer (CT) near-IR absorbers based on platinum-dithiolene complexes are reinvestigated here as a case study also by using the Hirshfeld surface analysis. This analysis on systems, which exhibit the 1:1, 2:1 and 2:2 columnar stacking patterns between D and A, allows us to point out that several interactions of atoms and fragments are involved in the stacking interactions but also that only a limited fraction of these interactions, limited to the 1:1 D/A columnar stacking case, can be relatable to the absorption features of this class of compounds.

Insight into the Properties of Heteroleptic Metal Dithiolenes: Multistimuli Responsive Luminescence, Chromism, and Nonlinear Optics.

A comprehensive investigation of the functional properties of heteroleptic donor-M-acceptor dithiolene complexes BuN[M(L1)(L2)] is presented (M = Pd, Pt). The acceptor L1 consists of the chiral ()-(+)α-methylbenzyldithiooxamidate (()-α-MBAdto), the donor L2 is 2-thioxo-1,3-dithiole-4,5-dithiolato (dmit) in (Pd) and (Pt), 1,2-dicarbomethoxyethylenedithiolate (ddmet) in (Pd) and (Pt), or [4',5':5,6][1,4]dithiino[2,3-]quinoxaline-1',3'-dithiolato (quinoxdt) in (Pd) and (Pt). L1 is capable of undergoing proton exchange and promoting crystal formation in noncentrosymmetric space groups.

Uncommon Optical Properties and Silver-Responsive Turn-Off/On Luminescence in a Pt Heteroleptic Dithiolene Complex.

Complex [Pt(iPr pipdt)(Quinoxdt)] (iPr pipdt=1,4-diisopropyl-piperazine-2,3-dithione; Quinoxdt=[1,4]dithiino[2,3-b]quinoxaline-2,3-dithiolate) exhibits a remarkable green emission at 570 nm (room temperature), which is above the lowest excited state. The complex is characterized by negative solvatochromism as well as a high second-order polarizability. Addition of Ag ions induces 1) hypsochromic shift of the lowest frequencies and 2) reversible quenching of luminescence.

Optically Multiresponsive Heteroleptic Platinum Dithiolene Complex with Proton-Switchable Properties.

Both linear- and nonlinear-optical properties of BuN[Pt(L1)(L2)] (1; L1 = [4',5':5,6][1,4]dithiino[2,3-b]quinoxaline-1',3'dithiolato; L2 = (R)-α-MBAdto dithiooxamidate, where (R)-α-MBA = (R)-(+)-α-methylbenzyl) upon HCl addition at room temperature change dramatically: the color turns from deep blue to green; the luminescence switches from deep red to green; the nonlinear-optical response (first hyperpolarizability) increases by a factor of 12. Thus, 1 behaves as a unique multiresponsive optical switch whose properties can be followed by the naked eye.

A Platinum-Dithiolene Monoanionic Salt Exhibiting Multiproperties, Including Room-Temperature Proton-Dependent Solution Luminescence.

The platinum salt C[PtL2], where C = [(R)-Ph(Me)HC*-NMe3](+) and [PtL2](-) = radical monoanion based on [4', 5': 5, 6][1, 4]dithiino[2,3-b]quinoxaline-1',3'dithiolato, shows a variety of properties both in solution and in the solid state thanks to the electronic and/or structural features of the ligand. The complex crystallizes in the chiral space group P1 due to the presence of the enantiopure cation (R)-Ph(Me)HC*-NMe3(+), and it shows paramagnetic behavior relatable to the [PtL2](-) radical monoanion. This anionic complex is redox active and shows a strong near-infrared absorbance peak at 1085 nm tunable with the oxidation state of the complex.

Ultrafast electronic and vibrational relaxations in mixed-ligand dithione-dithiolato Ni, Pd, and Pt complexes.

Ultrafast excited-state dynamics of planar Pt, Pd, and Ni dithione-dithiolato complexes were investigated by transient absorption spectroscopy on the femtosecond-picosecond timescale. All studied complexes show a common photobehaviour, although individual kinetics parameters and quantum yields vary with the metal, the dithione ligand and, namely the solvent (DMF, MeCN). Laser pulse irradiation at 800 nm populates the lowest singlet excited state of a dithiolato → dithione charge transfer character, (1)LL'CT.

Role of the acceptor in tuning the properties of metal [M(II) = Ni, Pd, Pt] dithiolato/dithione (donor/acceptor) second-order nonlinear chromophores: combined experimental and theoretical studies.

The mixed-ligand complexes [M(II)(Et2dazdt)(mnt)] (M = Ni, 1; Pd, 2; Pt, 3) [Et2dazdt = N,N'-diethyl-perhydrodiazepine-2,3-dithione; mnt = maleonitrile-2,3-dithiolate] have been prepared and fully characterized. X-ray diffractometric studies on 1-3 (the structure of 1 was already known) show that the crystals are isostructural (triclinic, P-1), and two independent molecular entities are present in the unit cell. These entities differ in the orientation of the ethyl substituents with respect to the epta-atomic ring.

Near-infrared pigments based on ion-pair charge transfer salts of dicationic and dianionic metal-dithiolene [M(II) = Pd, Pt] complexes.

Mixing [M(Et2dazdt)2](BF4)2 [M = Ni(II), Pd(II), Pt(II); Et2dazdt = N,N'-diethyl-perhydrodiazepine-2,3-dithione] with (Bu4N)2[M(mnt)2] (mnt = maleonitrile-2,3-dithiolate) in CH3CN produces the known mixed ligand dithiolene complex [Ni(Et2dazdt)(mnt)] in the nickel case and ion-pair salts [M(Et2dazdt)2][M(mnt)2] in the palladium (1) and platinum (2) cases. Structural characterization of 2 shows that the anionic (donor) and cationic (acceptor) complexes form an irregular stack that lies in the bc crystallographic plane. The shortest contacts exchanged by the anion and cation molecules within each stack are those occurring through the hydrogen atoms of the CH2 groups of Et2dazdt and the Pt(2)-S(22) segment (d(H(81a)-S(22) = 2.

Electrochromic second-order NLO chromophores based on M(II) (M = Ni, Pd, Pt) complexes with diselenolato-dithione (donor-acceptor) ligands.

The donor-acceptor type mixed-ligand complexes [M(Bz(2)pipdt)(dsit)]; dsit = 2-thioxo-1,3-dithiole-4,5-diselenolato (donor); Bz(2)pipdt = 1,4-dibenzyl-piperazine-2,3-dithione (acceptor); M(II) = Ni (1), Pd (2), and Pt (3) were prepared and characterized to investigate the variation of the properties by substituting selenium for sulfur in the donor ligand dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato of the corresponding known complexes. Both these classes of complexes exhibit large negative second-order polarizabilities, amongst the highest values determined so far for metal-complexes, and are potential candidates for redox switchability of the molecular first hyperpolarizability due to the bleaching/restoring of the solvatochromic peak for mono-reduction/oxidation. DFT and TD-DFT calculations on 1-3 allow one to correlate geometries and electronic structures and are in agreement with the observed minor changes following the substitution of selenium for sulfur atoms in the dichalcogenolato ligand.

Mixed-ligand Pt(II) dithione-dithiolato complexes: influence of the dicyanobenzodithiolato ligand on the second-order NLO properties.

The mixed-ligand dithiolene complex [Pt(Bz(2)pipdt)(dcbdt)] (1) bearing the two ligands Bz(2)pipdt = 1,4-dibenzyl-piperazine-3,2-dithione and dcbdt = dicyanobenzodithiolato, has been synthesized, characterized and studied to evaluate its second-order optical nonlinearity. The dithione/dithiolato character of the two ligands gives rise to an asymmetric distribution of the charge in the molecule. This is reflected by structural data showing that in the C(2)S(2)PtS(2)C(2) dithiolene core the four sulfur atoms define a square-planar coordination environment of the metal where the Pt-S bond distances involving the two ligands are similar, while the C-S bond distances in the C(2)S(2) units exhibit a significant difference in Bz(2)pipdt (dithione) and dcbdt (dithiolato).

Redox-switchable chromophores based on metal (Ni, Pd, Pt) mixed-ligand dithiolene complexes showing molecular second-order nonlinear-optical activity.

The synthesis and full characterization of the redox-active nickel triad mixed-ligand dithiolene complexes based on Bz(2)pipdt = 1,4-dibenzylpiperazine-3,2-dithione and dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate ligands are reported. These complexes show a reversibly bleacheable solvatochromic peak and a remarkably high negative molecular first hyperpolarizability, whose values depend on the metal being highest for the platinum(II) compound.

New sulfur-oxygen mixed-donor ligand N,N'-dimethyl-piperazine-3-oxo-2-thione (Me2pipto) and its Ni(II) and Fe(II) complexes.

Structural and electronic features of the novel title sulfur-oxygen donor ligand Me(2)pipto (1), are discussed in comparison with those of the corresponding dithione ligand Me(2)pipdt. A tuning of the electronic and coordination properties of the ligand, relatable to the soft/hard power of the donor atoms, is achieved. Coordination properties have been checked towards Ni(II) and Fe(III) cations obtaining [Ni(Me(2)pipto)(3)](BF(4))(2) (2) and [Fe(Me(2)pipto)(3)](BF(4))(2) (4) complexes, which show significant differences when compared with the corresponding reaction products when using Me(2)pipdt.