Luminescent Pt(II) Complexes Containing (1-Aza-15-crown-5)dithiocarbamate and (1-Aza-18-crown-6)dithiocarbamate: Mechanochromic and Solvent-Induced Luminescence

The strong tendency to stack in the solid state and rich luminescence for the Pt(II) complexes makes them potential candidates as new mechanochromic materials and sensing applications. Six mononuclear complexes [Pt(ppy)(O₄NCS₂)] (1), [Pt(bpy)(O₄NCS₂)]ClO₄ (2), [Pt(ppy)(O₅NCS₂)] (3), [Pt(phen)(O₄NCS₂)]ClO₄·CH₃OH (5a), [Pt(phen)(O₄NCS₂)]ClO₄ (5b), and [Pt(phen)(O₅NCS₂)]ClO₄ (6a), one dinuclear complex [Pt₂(phen)₂(NaO₅NCS₂)₂(ClO₄)₃]ClO₄ (6b), and one one-dimensional (1-D) coordination polymer {[Pt₂(bpy)₂(NaO₅NCS₂)₂(ClO₄)₂](ClO₄)₂}_n (4) were synthesized by reacting [Pt(ppy)Cl]₂, Pt(bpy)Cl₂, and Pt(phen)Cl₂ (ppy = 2-phenylpyridine, bpy = 2,2'-bipyridine, and phen = 1,10-phenanthroline) with (1-aza-15-crown-5)dithiocarbamate (O₄NCS₂) or (1-aza-18-crown-6)dithiocarbamate (O₅NCS₂), respectively, which have been isolated and structurally characterized by X-ray diffraction. Neutral complexes 1 and 3 contain no intermolecular Pt(II)···Pt(II) contact, whereas cationic complexes 2, 5a, 5b, and 6a with ClO₄^- as counteranions show alternative intermolecular Pt(II)···Pt(II) contacts of 3.535/4.091, 3.480/5.001, 3.527/4.571, and 3.446/4.987 Å in the solid state, respectively. Interestingly, complex 4 forms a 1-D coordination polymer through coordination between the encapsulated Na⁺ ions inside the azacrown ether rings of O₅NCS₂ and ClO₄^- anions with respective intra- and intermolecular Pt(II)···Pt(II) contacts of 3.402 and 3.847 Å in crystal lattices, whereas a dinuclear complex 6b was surprisingly formed and also connected by the encapsulated Na⁺ ions and ClO₄^- anions with alternative intra- and intermolecular Pt(II)···Pt(II) contacts of 3.650 and 3.677/4.4.372 Å, respectively. Upon excitation, complexes 1 and 3 showed similar vibronic luminescence at 507, 534, and 502, 532 nm, respectively, and the other complexes 2 and 4-6 showed broad luminescence with maxima at 537-567 nm. The B3LYP/LanL2DZ calculation was carried out and used to clarify their excited-state properties. In addition, the powder samples for complexes 1-4 almost showed no energy shift for the luminescence and significantly those of complexes 5-6 exhibited the mechanochromic luminescence upon grinding. It is noted that complexes 5a and 6a only showed minor red shifts (i.e., from 544 to 556 nm for complex 5a and from 551 to 565 nm for complex 6a), whereas complex 6b exhibited a remarkable red shift from 558 to 603 nm upon grinding. Besides, their luminescence reversibility was also examined toward various solvents.

Dithiocarbamate Complexes of Platinum Group Metals: Structural Aspects and Applications

The incorporation of dithiocarbamate ligands in the preparation of metal complexes is largely prompted by the versatility of this molecule. Fascinating coordination chemistry can be obtained from the study of such metal complexes ranging from their preparation, the solid-state properties, solution behavior as well as their applications as bioactive materials and luminescent compounds, to name a few. In this overview, the dithiocarbamate complexes of platinum-group elements form the focus of the discussion. The structural aspects of these complexes will be discussed based upon the intriguing findings obtained from their solid- (crystallographic) and solution-state (NMR) studies. At the end of this review, the applications of platinum-group metal complexes will be discussed.

Solvent-Induced Formation of Novel Ni(II) Complexes Derived from Bis-Thiosemicarbazone Ligand: An Insight from Experimental and Theoretical Investigations

In this work, we report solvent-induced complexation properties of a new N₂S₂ tetradentate bis-thiosemicarbazone ligand (H₂L^I), prepared by the condensation of 4-phenylthiosemicarbazide with bis-aldehyde, namely 2,2'-(ethane-1,2-diylbis(oxy)dibenzaldehyde, towards nickel(II). Using ethanol as a reaction medium allowed the isolation of a discrete mononuclear homoleptic complex [NiL^I] (1), for which its crystal structure contains three independent molecules, namely 1-I, 1-II, and 1-III, in the asymmetric unit. The doubly deprotonated ligand L^I in the structure of 1 is coordinated in a cis-manner through the azomethine nitrogen atoms and the thiocarbonyl sulfur atoms. The coordination geometry around metal centers in all the three crystallographically independent molecules of 1 is best described as the seesaw structure. Interestingly, using methanol as a reaction medium in the same synthesis allowed for the isolation of a discrete mononuclear homoleptic complex [Ni(L^II)₂] (2), where L^II is a monodeprotonated ligand 2-(2-(2-(2-(dimethoxymethyl)phenoxy)ethoxy)benzylidene)-N-phenylhydrazine-1-carbothioamide (HL^II). The ligand L^II was formed in situ from the reaction of L^I with methanol upon coordination to the metal center under synthetic conditions. In the structure of 2, two ligands L^II are coordinated in a trans-manner through the azomethine nitrogen atom and the thiocarbonyl sulfur atom, also yielding a seesaw coordination geometry around the metal center. The charge and energy decomposition scheme ETS-NOCV allows for the conclusion that both structures are stabilized by a bunch of London dispersion-driven intermolecular interactions, including predominantly N-H∙∙∙S and N-H∙∙∙O hydrogen bonds in 1 and 2, respectively; they are further augmented by less typical C-H∙∙∙X (where X = S, N, O, π), CH∙∙∙HC, π∙∙∙π stacking and the most striking, attractive long-range intermolecular C-H∙∙∙Ni preagostic interactions. The latter are found to be determined by both stabilizing Coulomb forces and an exchange-correlation contribution as revealed by the IQA energy decomposition scheme. Interestingly, the analogous long-range C-H∙∙∙S interactions are characterized by a repulsive Coulomb contribution and the prevailing attractive exchange-correlation constituent. The electron density of the delocalized bonds (EDDB) method shows that the nickel(II) atom shares only ~0.8|e| due to the σ-conjugation with the adjacent in-plane atoms, demonstrating a very weak σ-metalloaromatic character.

On the Coordination Role of Pyridyl-Nitrogen in the Structural Chemistry of Pyridyl-Substituted Dithiocarbamate Ligands

A search of the Cambridge Structural Database was conducted for pyridyl-substituted dithiocarbamate ligands. This entailed molecules containing both an NCS2− residue and pyridyl group(s), in order to study their complexation behavior in their transition metal and main group element crystals, i.e., d- and p-block elements. In all, 73 different structures were identified with 30 distinct dithiocarbamate ligands. As a general observation, the structures of the transition metal dithiocarbamates resembled those of their non-pyridyl derivatives, there being no role for the pyridyl-nitrogen atom in coordination. While the same is true for many main group element dithiocarbamates, a far greater role for coordination of the pyridyl-nitrogen atoms was evident, in particular, for the heavier elements. The participation of pyridyl-nitrogen in coordination often leads to the formation of dimeric aggregates but also one-dimensional chains and two-dimensional arrays. Capricious behaviour in closely related species that adopted very different architectures is noted. Sometimes different molecules comprising the asymmetric-unit of a crystal behave differently. The foregoing suggests this to be an area in early development and is a fertile avenue for systematic research for probing further crystallization outcomes and for the rational generation of supramolecular architectures.

Electron belt-to-σ-hole switch of noncovalently bound iodine(i) atoms in dithiocarbamate metal complexes

The nature of metals in the isostructural series of dithiocarbamate complexes affects the electron belt-to-σ-hole switch of noncovalently bound iodine(i) leading to either semicoordination, or halogen bonding.

The remarkable propensity for the formation of C–H⋯π(chelate ring) interactions in the crystals of the first-row transition metal dithiocarbamates and the supramolecular architectures they sustain

C–H⋯π(chelate ring) interactions play an important role in assembling first-row transition metal dithiocarbamates in their crystals.

New main-group ferrocenyldithiocarbamates and conversion to ferrocene oxazolidine-2-thione and -2-one

Three new main-group ferrocenyl dithiocarbamates and a pure cyclised product, 3-ferrocenylmethyl-oxazolidine-2-thione, were isolated using copper powder.

Spin crossover in 2D iron(ii) phthalazine cyanometallic complexes

Two new spin-crossover analogues of Hofmann clathrates based on a bicyclic ligand phthalazine have been synthesized.

Impact of Group 10 Metals on the Solvent-Induced Disproportionation of o-Semiquinonato Complexes

The oxidation of [M^II (3,5-DTBCat)(DTBbpy)] (M=Ni ([Ni]), Pd ([Pd]), and Pt ([Pt]); 3,5-DTBCat=3,5-di-tert-butylcatecholato; DTBbpy=4,4'-di-tert-butyl-2,2'-bipyridine) afforded the dimeric {[Ni^II (3,5-DTBSQ)(DTBbpy)](PF₆ )}₂ ({[Ni](PF₆ )}₂ ; 3,5-DTBSQ=3,5-di-tert-butylsemiquinonato) and monomeric semiquinonato (SQ) complexes [M^II (3,5-DTBSQ)(DTBbpy)](PF₆ ) (M=Pd ([Pd](PF₆ )) and Pt ([Pt](PF₆ ))). The negative solvatochromic properties of the SQ complexes allowed us to estimate the relative order of their dipole moments: [Pd](PF₆ )>[Pt](PF₆ )>{[Ni](PF₆ )}₂ . The complexes [Pd](PF₆ ) and [Pt](PF₆ ) adopt monomeric structures and are stable in CH₂ Cl₂ and toluene, whereas they gradually disproportionate at room temperature to [M] and 3,5-di-tert-butylbenzoquinone (3,5-DTBBQ) in polar solvents such as THF, MeOH, EtOH, DMF, or DMSO. The results of spectroscopic studies suggested that the oxidized nickel complex adopts a monomeric structure ([Ni](PF₆ )) in CH₂ Cl₂ , but a dimeric structure ({[Ni](PF₆ )}₂ ) in the other investigated solvents. In polar solvents, {[Ni](PF₆ )}₂ may disproportionate to [Ni] and 3,5-DTBBQ at 323 K, thereby demonstrating a significant solvent- and metal-dependence in temperature. The relative activities of {[Ni](PF₆ )}₂ and [M](PF₆ ) toward disproportionation are related to the electrochemically estimated K_dis values in CH₂ Cl₂ and DMF. The present work demonstrates that solvent polarity and the dipole moments of the SQ complexes promote disproportionation, which can be controlled by a judicious choice of the metal ion, solvent, and temperature.

Cooperative metal–ligand influence on the formation of coordination polymers, and conducting and photophysical properties of Tl(i) β-oxodithioester complexes

Eight novel luminescent and semiconducting Tl(i) β-oxodithioester complexes forming 1D/2D coordination polymeric structures were investigated using single crystal X-ray diffraction.

Quantifying conventional C–H⋯π(aryl) and unconventional C–H⋯π(chelate) interactions in dinuclear Cu(ii) complexes: experimental observations, Hirshfeld surface and theoretical DFT study

Conventional C–H⋯π(aryl) and unconventional C–H⋯π(chelate) interactions are explored in detail.

A luminescent bis(pyridyl)-substituted benzimidazole platinum(II) complex exhibiting an intermolecular anagostic interaction

The photophysical properties of transition metal complexes of the 5,6-dimethyl-2-(pyridin-2-yl)-1-(pyridin-2-ylmethyl)-1H-benzimidazole ligand are of interest. Dichlorido[5,6-dimethyl-2-(pyridin-2-yl)-1-(pyridin-2-ylmethyl)-1H-benzimidazole-κ2 N 2,N 3]platinum(II), [PtCl2(C20H18N4)], is luminescent in the solid state at room temperature. The compound displays a distorted square-planar coordination geometry. The Pt—N(imidazole) bond length is shorter than the Pt—N(pyridine) bond length. The extended structure reveals that symmetry-related molecules display weak C—H...N, C—H...Cl, and C—H...Pt hydrogen-bonding interactions that are clearly discernable in the Hirshfeld surface and fingerprint plots. The intermolecular C—H...Pt and C—H...N interactions have been explored using density functional theory. The result of an analysis of the distance dependence of C—H...Pt yields a value consistent with that observed in the solid-state structure. The energy of interaction for the C—H...Pt interaction is found to be about −11 kJ mol−1.

Large d–d luminescence energy variations in square-planar bis(dithiocarbamate) platinum(ii) and palladium(ii) complexes with near-identical MS4 motifs: a variable-pressure study

A surprising variation of luminescence maxima occurs for crystalline dithiocarbamate platinum(ii) complexes with very similar square-planar coordination geometries but different peripheral substituents R, R′.

Mono urotropine adducts of some binary zinc xanthates and dithiocarbamates: solid-state molecular structures and supramolecular self-assembly

The molecular structures of [Zn(S2COR)2(hmta)], R=Et (I) and iPr (II), and [Zn(S2CNRR′)2(hmta)], R=R′=Et (III) and R=iPr, R′=CH2CH2OH (IV), feature chelating 1,1-dithiolate ligands and monodentate hmta molecules; hmta=hexamethylenetetramine. The resulting NS4 donor sets are highly distorted, with tendencies towards square pyramidal. Systematic differences in the structures are related to the greater chelating ability of the dithiocarbamate ligands leading to, e.g., elongated Zn–N bond lengths in III and IV. In the molecular packing, an unusual C–H···π(chelate ring) interaction is noted in III, which is correlated with the close to symmetric Zn–S bond lengths formed by the relevant dithiocarbamate ligand and resultant greater metalloaromatic character of the resulting ZnS2C chelate ring, and to the greater distortion of the coordination geometry compared with literature precedents. A three-dimensional architecture found for IV is sustained by hydroxyl-O-H···O, S and N hydrogen bonding.

Characterization of PdH-C interactions in bis-dimethyldithiocarbamate palladium(ii) and its deuterated analog by luminescence spectroscopy at variable pressure

We present the variable-pressure d-d luminescence spectra of crystalline bis-dimethyldithiocarbamate palladium(ii) and its deuterated analog. The energies and shifts of the band maxima provide evidence for intermolecular PdH-C interactions, with quantitative differences observed for the deuterated complex. Shifts show distinct interactions in three pressure ranges between 1 bar and 85 kbar.

Bis[bis(N-2-hydroxyethyl,N-isopropyl-dithiocarbamato)mercury(II)]2: crystal structure and Hirshfeld surface analysis

The presence of both κ2-chelating and μ2,κ2-tridentate bridging dithiocarbamate ligands in centrosymmetric {Hg[S2CN(iPr)CH2CH2OH]2}2 (1) leads to globular aggregates that are linked into a three-dimensional architecture via hydroxyl-O–H···O(hydroxy) hydrogen bonding. The structure contrasts that of Hg[S2CN(CH2CH2OH)2]2 (2; this is a literature structure) in which square planar units are connected into supramolecular chains via Hg···S secondary bonding; chains are connected in the crystal structure by hydroxyl-O–H···O(hydroxy) hydrogen bonding. A Hirshfeld surface analysis on 1 and 2 reveal the influence of O–H···O and Hg···S interactions on the molecular packing as well as the distinctive interactions, such as C–H···S interactions in 1 and C–H···π (HgS2C) contacts in 2. A bibliographic survey shows the different structural motifs observed for 1 and 2 are complimented by an additional five motifs for binary mercury(II) dithiocarbamates revealing a fascinating structural diversity for this class of compound.

Temperature and pressure variations of d-d luminescence band maxima of bis(pyridylalkenolato)palladium(II) complexes with different ligand substituents: opposite-signed trends

Luminescence spectra of two d(8)-configured bis(pyridylalkenolato)palladium(ii) complexes, [Pd{PyCHC(C3F7)O}2] and [Pd{PyCHC(CH3)O}2], are presented at variable temperature and pressure. Bands are assigned as d-d transitions. The heptafluoropropyl and methyl substituents on the ligands have different steric demands, influencing luminescence spectra. Broad bands with maxima at approximately 12 700 cm(-1) (790 nm) for ligands with heptafluoropropyl substituents and 12,100 cm(-1) (830 nm) for ligands with methyl substituents and widths of approximately 2100 cm(-1) for both complexes are observed at 80 K. Quenching of the luminescence is observed as temperature increases. The maxima of [Pd{PyCHC(C3F7)O}2] show a shift of -0.9 ± 0.1 cm(-1) K(-1) due to broadening of the spectra to lower energy. The luminescence maxima of [Pd{PyCHC(CH3)O}2] shift in the opposite direction by +7.2 ± 0.7 cm(-1) K(-1). Shifts with different signs are also obtained from variable-pressure luminescence spectra, with values of +13 ± 2 cm(-1) kbar(-1) and -15 ± 7 cm(-1) kbar(-1) for [Pd{PyCHC(C3F7)O}2] and [Pd{PyCHC(CH3)O}2], respectively. The pressure-induced decrease is unusual and likely caused by intermolecular interactions involving the palladium(ii) center and a vinylic proton of a neighboring complex.

Persistence of C–H⋯π(chelate ring) interactions in the crystal structures of Pd(S2COR)2. The utility of Pd(S2COR)2as precursors for palladium sulphide materials

The influence of C–H⋯π(PdS₂C) interactions in the molecular packing of Pd(S₂COR)₂increases as the steric bulk ofRincreases.

Intermolecular Tl⋯H–C anagostic interactions in luminescent pyridyl functionalized thallium(i) dithiocarbamates

Rare intermolecular C–H⋯Tl anagostic and C–S⋯Tl interactions forming a six-membered chelate ring.