Perplexing Coordination Behaviour of Potentially Bridging Bipyridyl-Type Ligands in the Coordination Chemistry of Zinc and Cadmium 1,1-Dithiolate Compounds

The X-ray structural chemistry of zinc and cadmium 1,1-dithiolates (for example, xanthate, dithiophosphate and dithiocarbamate) with potentially bridging bipyridyl-type ligands (for example, 4,40-bipyridine) is reviewed. For zinc, the xanthates and dithiophosphates uniformly form one-dimensional coordination polymers, whereas the zinc dithiocarbamates are always zero-dimensional, reflecting the exceptional chelating ability of dithiocarbamate ligands compared with xanthates and dithiophosphates. For cadmium, one-dimensional coordination polymers are usually found, reflecting the larger size of cadmium compared with zinc, but zero-dimensional aggregates are sometimes found. Steric effects associated with the 1,1-dithiolate-bound R groups are shown to influence supramolecular aggregation and, when formed, polymer topology in order to reduce steric hindrance; the nature of the bipyridyl-type ligand can also be influential. For the dithiocarbamates of both zinc and cadmium, in instances where the dithiocarbamate ligand is functionalised with hydrogen bonding potential, extended supramolecular architectures are often formed via hydrogen bonding interactions. Of particular interest is the observation that the bipyridyl-type ligands do not always bridge zinc or cadmium 1,1-dithiolates, being monodentate instead, often in the presence of hydrogen bonding. Thus, hydroxyl-O–H . . . N(pyridyl) hydrogen bonds are sometimes formed in preference toM N(pyridyl) coordinate-bonds, suggesting a competition between the two modes of association

Adventures in crystal engineering

Crystals are all around us and are aesthetically pleasing as they arise from the ordered, three-dimensional assembly of chemical species which can be minerals (e.g. salt), macromolecules (e.g. proteins) or smaller chemical species (e.g. drugs, natural products, coordination complexes, etc.). Scientists need to know the precise structure of all these materials in order to rationalise the way they work. To put it in another way, “structure determines function”. Single-crystal X-ray crystallography is the crucial technique behind the determination of crystal structure. Despite the prevalence and obvious importance of crystals, what remains an enormous challenge in contemporary science is to answer the fundamental question of “How do crystals form?”. The goal of crystal engineering is to control the way molecules self-assemble in the condensed phase and the present discussion relates to this topic, an on-going research programme undertaken at Sunway University

Exploring the topological landscape exhibited by Binary Zinc-triad 1,1-dithiolates

The crystal chemistry of the zinc-triad binary 1,1-dithiolates, that is, compounds of xanthate [−S2COR], dithiophosphate [−S2P(OR)2], and dithiocarbamate [−S2CNR2] ligands, is reviewed. Owing to a wide range of coordination modes that can be adopted by 1,1-dithiolate anions, such as monodentate, chelating, μ2-bridging, μ3-bridging, etc., there exists a rich diversity in supramolecular assemblies for these compounds, including examples of zero-, one-, and two-dimensional architectures. While there are similarities in structural motifs across the series of 1,1-dithiolate ligands, specific architectures are sometimes found, depending on the metal centre and/or on the 1,1-dithiolate ligand. Further, an influence of steric bulk upon supramolecular aggregation is apparent. Thus, bulky R groups generally preclude the close approach of molecules in order to reduce steric hindrance and therefore, lead to lower dimensional aggregation patterns. The ligating ability of the 1,1-dithiolate ligands also proves crucial in determining the extent of supramolecular aggregation, in particular for dithiocarbamate species where the relatively greater chelating ability of this ligand reduces the Lewis acidity of the zinc-triad element, which thereby reduces its ability to significantly expand its coordination number. Often, the functionalisation of the organic substituents in the 1,1-dithiolate ligands, for example, by incorporating pyridyl groups, can lead to different supramolecular association patterns. Herein, the diverse assemblies of supramolecular architectures are classified and compared. In all, 27 structurally distinct motifs have been identified

Crystal structure of bis[N-(2-hydroxyethyl)-N-methyldithiocarbamato-κ2 S,S′](pyridine)zinc(II) pyridine monosolvate and its N-ethyl analogue

The common structural feature of the title compounds, [Zn(C4H8NOS2)2(C5H5N)]·C5H5N (I) and [Zn(C5H10NOS2)2(C5H5N)]·C5H5N (II), which differ by having dithiocarbamate N-bound methyl (I) and ethyl (II) groups, is the coordination of each ZnII atom by two non-symmetrically chelating dithiocarbamate ligands and by a pyridine ligand; in each case, the non-coordinating pyridine molecule is connected to the Zn-containing molecule via a (hydroxy)O—H...N(pyridine) hydrogen bond. The resulting NS4 coordination geometry is closer to a square-pyramid than a trigonal bipyramid in the case of (I), but almost intermediate between the two extremes in (II). The molecular packing features (hydroxy)O—H...O(hydroxy) hydrogen bonds, leading to supramolecular chains with a zigzag arrangement along [10-1] (I) or a helical arrangement along [010] (II). In (I), π–π [inter-centroid distances = 3.4738 (10) and 3.4848 (10) Å] between coordinating and non-coordinating pyridine molecules lead to stacks comprising alternating rings along the a axis. In (II), weaker π–π contacts occur between centrosymmetrically related pairs of coordinating pyridine molecules [inter-centroid separation = 3.9815 (14) Å]. Further interactions, including C—H...π(chelate) interactions in (I), lead to a three-dimensional architecture in each case.</jats:p

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, P¯1 (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 structure and molecular packing of O-ethyl (2-chlorophenyl)carbamothioate, C9H10ClNOS

The asymmetric unit of the title crystal structure is shown in the figure. Tables 1 and 2 contain details of the measurement method and a list of the atoms including atomic coordinates and displacement parameters

Crystal structure of bis(μ-N-i-propyl-N-n-propyldithiocarbamato-κ2S:S′) bis(N-i-propyl-N-n-propyldithiocarbamato-κ2S,S′)dizinc(II), C28H56N4S8Zn2

C28H56N4S8Zn2, monoclinic, P21/n (no. 14), a=9.4123(2) Å, b=19.2708(4) Å, c=11.5228(3) Å, β=107.202(2)°, V= 1996.54(8) Å3, Z=2, Rgt(F)=0.0254, wRref(F2)=0.0572, T=100(2)

Crystal structure of the bis((E)-O-ethyl-N-phenylthiocarbamate) – 4,4′-bipyridine co-crystal (2/1), C28H30N4O2S2

C12H11N5, monoclinic, P21/n (no. 14), a=7.3455(1) Å, b=12.2470(1) Å, c=12.1689(1) Å, β=103.505(1)°, V =1064.45(2) Å3, Z =4, Rgt(F)=0.0365, wRref(F2)=0.0987, T =100 K

Crystal structures of the 1:1 salts of 2-amino-4-nitrobenzoate with each of (2-hydroxyethyl)dimethylazanium, tert-butyl(2-hydroxyethyl)azanium and 1,3-dihydroxy-2-(hydroxymethyl)propan-2-aminium

The crystal and molecular structures of the title molecular salts,C4H12NO+C7H5N2O4, (I), C6H16NO+C7H5N2O4, (II), and C4H12NO3+-C7H5N2O4, (III), are described. The common feature of these salts is thepresence of the 2-amino-4-nitrobenzoate anion, which exhibit non-chemicallysignificant variations in the conformational relationships between the carboxylate and nitro groups, and between these and the benzene rings they are connected to. The number of ammonium-N—H H atoms in the cations increases from one to three in (I) to (III), respectively, and this variation significantly influences the supramolecular aggregation patterns in the respective crystals. Thus, a linear supramolecular chain along [100] sustained by charge-assisted tertiary-ammonium-N—HO(carboxylate), hydroxy-O—HO(carboxylate) and amino-N—HO(carboxylate) hydrogen-bonds is apparent in the crystal of (I). Chains are connected into a three-dimensional architecture by methyl-C—HO(hydroxy) and – interactions, the latter between benzene rings [intercentroid separation = 3.5796 (10) A˚ ]. In the crystal of (II), a supramolecular tube propagating along [901] arises as a result of charge-assisted secondaryammonium-N—HO(carboxylate) and hydroxy-O—HO(carboxylate) hydrogen-bonding. These are connected by methylene- and methyl-C— HO(nitro) and – stacking between benzene rings [inter-centroid separation = 3.5226 (10) A˚ ]. Finally, double-layers parallel to (100) sustained by charge-assisted ammonium-N—HO(carboxylate), ammonium-N—H O(hydroxy) and hydroxy-O—HO(carboxylate) hydrogen-bonds are apparent in the crystal of (III). These are connected in a three-dimensional architecture by amine-N—HO(nitro) hydrogen-bonds