Recent progress in dichalcophosphate coinage metal clusters and superatoms

Atomically precise clusters of group 11 metals (Cu, Ag, and Au) attract considerable attention owing to their remarkable structure and fascinating properties. One of the unique subclasses of these clusters is based on dichalcophosphate ligands of [(RO)₂PE₂]^- type (E = S or Se, and R = alkyl). These ligands successfully stabilise the most diverse Cu, Ag, and Au clusters and superatoms, spanning from simple ones to amazing assemblies featuring unusual structural and bonding patterns. It is noteworthy that such complicated clusters are assembled directly from cheap and simple reagents, metal(I) salts and dichalcophosphate anions. This reaction, when performed in the presence of a hydride or other anion sources, or foreign metal ions, results in hydrido- or anion-templated homo- or heteronuclear structures. In this feature article, we survey the recent advances in this exciting field, highlighting the powerful synthetic capabilities of the system "a metal(I) salt - [(RO)₂PX₂]^- ligands - a templating anion or borohydride" as an inexhaustible platform for the creation of new atomically precise clusters, superatoms, and nanoalloys.

Copper Dithiocarbamates: Coordination Chemistry and Applications in Materials Science, Biosciences and Beyond

Copper dithiocarbamate complexes have been known for ca. 120 years and find relevance in biology and medicine, especially as anticancer agents and applications in materials science as a single-source precursor (SSPs) to nanoscale copper sulfides. Dithiocarbamates support Cu(I), Cu(II) and Cu(III) and show a rich and diverse coordination chemistry. Homoleptic [Cu(S2CNR2)2] are most common, being known for hundreds of substituents. All contain a Cu(II) centre, being either monomeric (distorted square planar) or dimeric (distorted trigonal bipyramidal) in the solid state, the latter being held together by intermolecular C···S interactions. Their d9 electronic configuration renders them paramagnetic and thus readily detected by electron paramagnetic resonance (EPR) spectroscopy. Reaction with a range of oxidants affords d8 Cu(III) complexes, [Cu(S2CNR2)2][X], in which copper remains in a square-planar geometry, but Cu–S bonds shorten by ca. 0.1 Å. These show a wide range of different structural motifs in the solid-state, varying with changes in anion and dithiocarbamate substituents. Cu(I) complexes, [Cu(S2CNR2)2]−, are (briefly) accessible in an electrochemical cell, and the only stable example is recently reported [Cu(S2CNH2)2][NH4]·H2O. Others readily lose a dithiocarbamate and the d10 centres can either be trapped with other coordinating ligands, especially phosphines, or form clusters with tetrahedral [Cu(μ3-S2CNR2)]4 being most common. Over the past decade, a wide range of Cu(I) dithiocarbamate clusters have been prepared and structurally characterised with nuclearities of 3–28, especially exciting being those with interstitial hydride and/or acetylide co-ligands. A range of mixed-valence Cu(I)–Cu(II) and Cu(II)–Cu(III) complexes are known, many of which show novel physical properties, and one Cu(I)–Cu(II)–Cu(III) species has been reported. Copper dithiocarbamates have been widely used as SSPs to nanoscale copper sulfides, allowing control over the phase, particle size and morphology of nanomaterials, and thus giving access to materials with tuneable physical properties. The identification of copper in a range of neurological diseases and the use of disulfiram as a drug for over 50 years makes understanding of the biological formation and action of [Cu(S2CNEt2)2] especially important. Furthermore, the finding that it and related Cu(II) dithiocarbamates are active anticancer agents has pushed them to the fore in studies of metal-based biomedicines.

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.

Crystal structure of tetrakis (N-(2-hydroxyethyl)-N-isopropylcarbamodithioato-κS,S′)-(μ2(2-(pyridin-4-yl)vinyl)pyridine-κN,N′)dicadmium(II), C36H58Cd2N6O4S8

C36H58Cd2N6O4S8, monoclinic, P21/c (no. 14), a = 7.82927(4) Å, b = 11.64209(5) Å, c = 26.2493(1) Å, β = 95.6985(4)°, V = 2380.775(18) Å3, Z = 2, R gt(F) = 0.0158, wR ref(F 2) = 0.0411, T = 100(2) K.

Crystal structure of bis[μ2-(N,N-diethylcarbamodithioato-κS:κS,κS′)]-bis(triethylphosphine-P)-di-silver(I), C22H50Ag2N2P2S4

C22H50Ag2N2P2S4, triclinic, P1̄ (no. 2), a = 9.0672(2) Å, b = 11.2091(3) Å, c = 16.6853(4) Å, α = 91.097(2)°, β = 90.363(2)°, γ = 110.989(2)°, V = 1582.85(7) Å3, Z = 2, R gt(F) = 0.0241, wR ref(F 2) = 0.0653, T = 100(2) K.

In vitro anti-bacterial and time kill evaluation of binuclear tricyclohexylphosphanesilver(I) dithiocarbamates, {Cy3PAg(S2CNRR')}2

Four binuclear phosphanesilver(I) dithiocarbamates, {cyclohexyl₃PAg(S₂CNRR')}₂ for R = R' = Et (1), CH₂CH₂ (2), CH₂CH₂OH (3) and R = Me, R' = CH₂CH₂OH (4) have been synthesised and characterised by spectroscopy and crystallography, and feature tri-connective, μ₂-bridging dithiocarbamate ligands and distorted tetrahedral geometries based on PS₃ donor sets. The compounds were evaluated for anti-bacterial activity against a total of 12 clinically important pathogens. Based on minimum inhibitory concentration (MIC) and cell viability tests (human embryonic kidney cells, HEK 293), 1-4 are specifically active against Gram-positive bacteria while demonstrating low toxicity; 3 and 4 are active against methicillin resistant S. aureus (MRSA). Across the series, 4 was most effective and was more active than the standard anti-biotic chloramphenicol. Time kill assays reveal 1-4 to exhibit both time- and concentration-dependent pharmacokinetics against susceptible bacteria. Compound 4 demonstrates rapid (within 2 h) bactericidal activity at 1 and 2 × MIC to reach a maximum decrease of 5.2 log₁₀ CFU/mL against S. aureus (MRSA).

1-(2-Hydroxyethyl)imidazolidine-2-thione

1-(2-Hydroxyethyl)imidazolidine-2-thione (1) was obtained as a product from an in situ reaction between N-(2-hydroxyethyl)ethylenediamine, carbon disulfide, potassium hydroxide, and di(4-fluorobenzyl)tin dichloride. Compound 1 was characterized by IR, UV, 1H, 13C{1H}, and 2D (COSY, NOESY, HSQC, and HMBC) NMR spectroscopies. The cyclic molecular structure was confirmed by single crystal X-ray crystallography which showed the five-membered ring to be non-planar and the π-electron density to be localized over the CN2S chromophore. In the crystal, thioamide–N–H…O(hydroxy) and hydroxy–O–H…S(thione) hydrogen bonds lead to supramolecular layers in the bc-plane.

A 1:2 co-crystal of 2,2'-thiodi-benzoic acid and tri-phenyl-phosphane oxide: crystal structure, Hirshfeld surface analysis and computational study

The asymmetric unit of the title co-crystal, 2,2'-thiodi-benzoic acid-tri-phenyl-phosphane oxide (1/2), C14H10O4S·2C18H15OP, comprises two mol-ecules of 2,2'-thiodi-benzoic acid [TDBA; systematic name: 2-[(2-carb-oxy-phen-yl)sulfan-yl]benzoic acid] and four mol-ecules of tri-phenyl-phosphane oxide [TPPO; systematic name: (di-phenyl-phosphor-yl)benzene]. The two TDBA mol-ecules are twisted about their di-sulfide bonds and exhibit dihedral angles of 74.40 (5) and 72.58 (5)° between the planes through the two SC6H4 residues. The carb-oxy-lic acid groups are tilted out of the planes of the rings to which they are attached forming a range of CO2/C6 dihedral angles of 19.87 (6)-60.43 (8)°. Minor conformational changes are exhibited in the TPPO mol-ecules with the range of dihedral angles between phenyl rings being -2.1 (1) to -62.8 (1)°. In the mol-ecular packing, each TDBA acid mol-ecule bridges two TPPO mol-ecules via hy-droxy-O-H⋯O(oxide) hydrogen bonds to form two three-mol-ecule aggregates. These are connected into a three-dimensional architecture by TPPO-C-H⋯O(oxide, carbon-yl) and TDBA-C-H⋯(oxide, carbon-yl) inter-actions. The importance of H⋯H, O⋯H/H⋯O and C⋯H/H⋯C contacts to the calculated Hirshfeld surfaces has been demonstrated. In terms of individual mol-ecules, O⋯H/H⋯O contacts are more important for the TDBA (ca 28%) than for the TPPO mol-ecules (ca 13%), as expected from the chemical composition of these species. Computational chemistry indicates the four independent hy-droxy-O-H⋯O(oxide) hydrogen bonds in the crystal impart about the same energy (ca 52 kJ mol-1), with DTBA-phenyl-C-H⋯O(oxide) inter-actions being next most stabilizing (ca 40 kJ mol-1).

Crystal structure of bis(μ 2-diethyldithiocarbamato-κ 3 S,S′:S′)-bis(tricyclohexylphosphane-κP)dicopper(I), C46H86Cu2N2P2S4

C46H86Cu2N2P2S4, triclinic, P1̄ (no. 2), a = 9.9626(3) Å, b = 11.0489(3) Å, c = 12.3604(3) Å, α = 106.205(3)°, β = 99.165(2)°, γ = 100.306(3)°, V = 1253.53(6) Å3, Z = 1, R gt(F) = 0.0232, wR ref(F 2) = 0.0555, T = 100(2) K.

Crystal structure of bis(μ2-pyrrolidine-1-carbodithioato-κ3S,S′:S;κ3S:S:S′)-bis(tricyclohexylphosphane-P)-di-copper(I), C46H82Cu2N2P2S4

C46H82Cu2N2P2S4, triclinic, P1̄ (no. 2), a = 11.6189(2) Å, b = 12.2846(2) Å, c = 18.1744(2) Å, α = 97.3210(10)°, β = 106.3080(10)°, γ = 99.312(2)°, V = 2415.65(7) Å3, Z = 2, Rgt(F) = 0.025, wRref(F2) = 0.066, T = 100(2) K.

A triclinic polymorph of bis(μ-N,N-bis(2-hydroxyethyl)dithiocarbamato-κ3S,S′:S′) bis(N,N-bis(2-hydroxyethyl)dithiocarbamato-κ2S:S′)zinc(II), C20H40N4O8S8Zn2

C20H40N4O8S8Zn2, triclinic, P1̄ (no. 2), a = 7.0675(10) Å, b = 9.9000(10) Å, c = 12.9252(17) Å, α = 106.813(10)°, β = 93.741(9)°, γ = 109.863(8)°, V = 800.65(18) Å3, Z = 2, Rgt(F) = 0.069, wRref(F2) = 0.176, T = 98(2) K.

Crystal structures of {μ2-N,N'-bis-[(pyridin-3-yl)meth-yl]ethanedi-amide}tetra-kis-(di-methyl-carbamodi-thio-ato)dizinc(II) di-methyl-formamide disolvate and {μ2-N,N'-bis-[(pyridin-3-yl)meth-yl]ethanedi-amide}tetra-kis-(di-n-propyl-carbamodi-thio-ato)dizinc(II)

The title structures, [Zn2(C3H6NS2)4(C14H14N4O2)]·2C3H7NO (I) and [Zn2(C7H14NS2)4(C14H14N4O2)] (II), each feature a bidentate, bridging bipyridyl-type ligand encompassing a di-amide group. In (I), the binuclear compound is disposed about a centre of inversion, leading to an open conformation, while in (II), the complete mol-ecule is completed by the application of a twofold axis of symmetry so that the bridging ligand has a U-shape. In each of (I) and (II), the di-thio-carbamate ligands are chelating with varying degrees of symmetry, so the zinc atom is within an NS4 set approximating a square-pyramid for (I) and a trigonal-bipyramid for (II). The solvent di-methyl-formaide (DMF) mol-ecules in (I) connect to the bridging ligand via amide-N-H⋯O(DMF) and various amide-, DMF-C-H⋯O(amide, DMF) inter-actions. The resultant three-mol-ecule aggregates assemble into a three-dimensional architecture via C-H⋯π(pyridyl, chelate ring) inter-actions. In (II), undulating tapes sustained by amide-N-H⋯O(amide) hydrogen bonding lead to linear supra-molecular chains with alternating mol-ecules lying to either side of the tape; no further directional inter-actions are noted in the crystal.

μ3-Chlorido-μ2-chlorido-(μ3-pyrrolidine-1-carbo-dithio-ato-κ4S:S,S':S')tris-[(tri-ethyl-phosphane-κP)copper(I)]: crystal structure and Hirshfeld surface analysis

The title trinuclear compound, [Cu3(C5H8NS2)Cl2(C6H15P)3], has the di-thio-carbamate ligand symmetrically chelating one CuI atom and each of the S atoms bridging to another CuI atom. Both chloride ligands are bridging, one being μ3- and the other μ2-bridging. Each Et3P ligand occupies a terminal position. Two of the CuI atoms exist within Cl2PS donor sets and the third is based on a ClPS2 donor set, with each coordination geometry based on a distorted tetra-hedron. The constituents defining the core of the mol-ecule, i.e. Cu3Cl2S2, occupy seven corners of a distorted cube. In the crystal, linear supra-molecular chains along the c axis are formed via phosphane-methyl-ene-C-H⋯Cl and pyrrolidine-methyl-ene-C-H⋯π(chelate) inter-actions, and these chains pack without directional inter-actions between them. An analysis of the Hirshfeld surface points to the predominance of H atoms at the surface, i.e. contributing 86.6% to the surface, and also highlights the presence of C-H⋯π(chelate) inter-actions.

Crystal structure and photoluminescence properties of a new monomeric copper(II) complex: bis(3-{[(3-hydroxypropyl)imino]methyl}-4-nitrophenolato-κ3O,N,O')copper(II)

Copper(II)-Schiff base complexes have attracted extensive interest due to their structural, electronic, magnetic and luminescence properties. The title novel monomeric Cu^II complex, [Cu(C₁₀H₁₁N₂O₄)₂], has been synthesized by the reaction of 3-{[(3-hydroxypropyl)imino]methyl}-4-nitrophenol (H₂L) and copper(II) acetate monohydrate in methanol, and was characterized by elemental analysis, UV and IR spectroscopies, single-crystal X-ray diffraction analysis and a photoluminescence study. The Cu^II atom is located on a centre of inversion and is coordinated by two imine N atoms, two phenoxy O atoms in a mutual trans disposition and two hydroxy O atoms in axial positions, forming an elongated octahedral geometry. In the crystal, intermolecular O-H...O hydrogen bonds link the molecules to form a one-dimensional chain structure and π-π contacts also connect the molecules to form a three-dimensional structure. The solid-state photoluminescence properties of the complex and free H₂L have been investigated at room temperature in the visible region. When the complex and H₂L are excited under UV light at 349 nm, the complex displays a strong green emission at 520 nm and H₂L displays a blue emission at 480 nm.

A triclinic polymorph of tri-cyclo-hexyl-phosphane sulfide: crystal structure and Hirshfeld surface analysis

The title compound, (C6H11)3PS (systematic name: tri-cyclo-hexyl-λ5-phosphane-thione), is a triclinic (P-1, Z' = 1) polymorph of the previously reported ortho-rhom-bic form (Pnma, Z' = 1/2) [Kerr et al. (1977 ▸). Can. J. Chem. 55, 3081-3085; Reibenspies et al. (1996 ▸). Z. Kristallogr. 211, 400]. While conformational differences exist between the non-symmetric mol-ecule in the triclinic polymorph, cf. the mirror-symmetric mol-ecule in the ortho-rhom-bic form, these differences are not chemically significant. The major feature of the mol-ecular packing in the triclinic polymorph is the formation of linear chains along the a axis sustained by methine-C-H⋯S(thione) inter-actions. The chains pack with no directional inter-actions between them. The analysis of the Hirshfeld surface for both polymorphs indicates a high degree of similarity, being dominated by H⋯H (ca 90%) and S⋯H/H⋯S contacts.

Supramolecular association in (μ2-pyrazine)-tetrakis(N,N-bis(2-hydroxyethyl)dithiocarbamato)dizinc(II) and its di-dioxane solvate

The crystal and molecular structures of {Zn[S2CN(CH2CH2OH)2]2}2(pyrazine), (1), and its di-dioxane solvate, (2), are described. In each of these, the centrosymmetric, binuclear molecule features a five-coordinated, highly distorted square-pyramidal geometry based on a NS4 donor set. The three-dimensional architectures in 1 and 2 are sustained by extensive networks of distinctive hydroxyl-O–H···O(hydroxyl) hydrogen bonding. The topology of the lattices are very different with that of 2 having a more regular appearance. The dioxane molecules reside in channels defined by the host molecules in 2 but, do not make many significant interactions with the host. The fact that 1 exhibits a significantly greater packing efficiency and a higher density suggests 1 is more stable than 2. The retention of dioxane in crystals of 2 probably reflects its intimate involvement in nucleation and high boiling point, meaning it is retained during crystallisation. Hirshfeld surface analyses were conducted and confirm the importance of the hydroxyl-O–H···O(hydroxyl) hydrogen bonding but, also reveal the presence of other interactions, most notably C–H···π(chelate) interactions.

Bis(N,N-di-ethyl-dithio-carbamato-κ2S,S')(3-hy-droxy-pyridine-κN)zinc and bis-[N-(2-hy-droxy-eth-yl)-N-methyldithio-carbamato-κ2S,S'](3-hy-droxy-pyridine-κN)zinc: crystal structures and Hirshfeld surface analysis

The common feature of the mol-ecular structures of the title compounds, [Zn(C5H10NS2)2(C5H5NO)], (I), and [Zn(C4H8NOS2)2(C5H5NO)], (II), are NS4 donor sets derived from N-bound hy-droxy-pyridyl ligands and asymmetrically chelating di-thio-carbamate ligands. The resulting coordination geometries are highly distorted, being inter-mediate between square pyramidal and trigonal bipyramidal for both independent mol-ecules comprising the asymmetric unit of (I), and significantly closer towards square pyramidal in (II). The key feature of the mol-ecular packing in (I) is the formation of centrosymmetric, dimeric aggregates sustained by pairs of hy-droxy-O-H⋯S(di-thio-carbamate) hydrogen bonds. The aggregates are connected into a three-dimensional architecture by methyl-ene-C-H⋯O(hy-droxy) and methyl-C-H⋯π(chelate) inter-actions. With greater hydrogen-bonding potential, supra-molecular chains along the c axis are formed in the crystal of (II), sustained by hy-droxy-O-H⋯O(hy-droxy) hydrogen bonds, with ethyl-hydroxy and pyridyl-hydroxy groups as the donors, along with ethyl-hydroxy-O-H⋯S(di-thio-carbamate) hydrogen bonds. Chains are connected into layers in the ac plane by methyl-ene-C-H⋯π(chelate) inter-actions and these stack along the b axis, with no directional inter-actions between them. An analysis of the Hirshfeld surfaces clearly distinguished the independent mol-ecules of (I) and reveals the importance of the C-H⋯π(chelate) inter-actions in the packing of both (I) and (II).

[N,N-Bis(2-hy-droxy-eth-yl)di-thio-carbamato-κ2S,S']bis-(tri-phenyl-phosphane-κP)copper(I) chloro-form monosolvate: crystal structure, Hirshfeld surface analysis and solution NMR measurements

The title compound, [Cu(C5H5NO2S2)(C18H15P)2]·CHCl3, features a tetra-hedrally coordinated CuI atom within a P2S2 donor set defined by two phosphane P atoms and by two S atoms derived from a symmetrically coordinating di-thio-carbamate ligand. Both intra- and inter-molecular hy-droxy-O-H⋯O(hydroxy) hydrogen bonding is observed: the former closes an eight-membered {⋯HOC2NC2O} ring, whereas the latter connects centrosymmetrically related mol-ecules into dimeric aggregates via eight-membered {⋯H-O⋯H-O}2 synthons. The complex mol-ecules are arranged to form channels along the c axis in which reside the chloro-form mol-ecules, being connected by Cl⋯π(arene) and short S⋯Cl [3.3488 (9) Å] inter-actions. The inter-molecular inter-actions have been investigated further by Hirshfeld surface analysis, which shows the conventional hydrogen bonding to be very localized with the main contributors to the surface, at nearly 60%, being H⋯H contacts. Solution NMR studies indicate that whilst the same basic mol-ecular structure is retained in solution, the tri-phenyl-phosphane ligands are highly labile, exchanging rapidly with free Ph3P at room temperature.

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.

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.