Crystal structure and Hirshfeld surface analysis of {2-[bis-(pyridin-2-ylmeth-yl)amino]-ethane-1-thiol-ato}-chlorido-cadmium(II).

The title compound, [Cd(C14H16N3S)Cl] or [CdLCl] (1), where LH = 2-[bis-(pyridin-2-ylmeth-yl)amino]-ethane-1-thiol, was prepared and structurally characterized. The Cd2+ complex crystallizes in P21/c with a distorted trigonal-bipyramidal metal coordination geometry. Supra-molecular inter-actions in 1 include parallel offset face-to-face inter-actions between inversion-related pyridyl rings and potential hydrogen bonds with chlorine or sulfur as the acceptor. Additional cooperative pyrid-yl-pyridyl inter-actions with roughly 45° tilt angles and centroid-centroid distances of less than 5.5 Šlikely also contribute to the overall solid-state stability. Hirshfeld surface analysis indicates that H⋯H (51.2%), Cl⋯H/H⋯Cl (13.9%), C⋯H/H⋯C (12.3%) and S⋯H/H⋯S (11.8%) inter-actions are dominant in the solid state.

Crystal structure and Hirshfeld surface analysis of cyclo-tetra-bromido-1κ2Br,3κ2Br-tetra-kis-(µ2-2-{[(pyridin-2-yl)meth-yl]amino}-ethane-1-thiol-ato-κ3N,S:S)tetra-mercury(II).

The macrometallacyclic title compound, [Hg4Br4(C8H11N2S)4] or [((HgL 2)(HgBr2))2] (1) where HL = 2-{[(pyridin-2-yl)meth-yl]amino}-ethane-1-thiol, was prepared and structurally characterized. The Hg2+ complex crystallizes in the P21/c space group. The centrosymmetric Hg4S4 metallacycle is constructed from metal ions with alternating distorted tetra-hedral Br2S2 and distorted seesaw N2S2 primary coordination environments with pendant pyridyl groups. The backfolded extended chair metallacycle conformation suggests inter-actions between each of the bis-chelated mercury atoms and Br atoms lying above and below the central Hg2S4 plane. Supra-molecular inter-actions in 1 include a fourfold aryl embrace and potential hydrogen bonds with bromine as the acceptor. Hirshfeld surface analysis indicates that H⋯H (51.7%), Br⋯H/H⋯Br (23.0%) and C⋯H/H⋯C (9.5%) inter-actions are dominant.

Homo- and Heteronuclear Group 12 Metallothionein Type B Cluster Analogs: Synthesis, Structure, 1H NMR and ESI-MS.

Metallothioneins (MTs) are a ubiquitous class of small cysteine-rich metal-binding proteins involved in metal homeostasis and detoxification with highly versatile metal binding properties. Despite the long-standing association of MT with M3S3 and M4S5 metal clusters, synthetic complexes with these core architectures are exceptionally rare. Here, we demonstrate an approach to synthesizing and characterizing aggregates of group 12 metal ions with monocyclic M3S3 cores in acetonitrile solution without the protection of a protein. Multidentate monothiol ligand N,N-bis(2-pyridylmethyl)-2-aminoethanethiol (L1H) provided [Cd3(L1)3](ClO4)3 (1), the first structurally characterized nonproteinaceous aggregate with a metallothionein-like monocyclic Cd3S3 core. In addition, [Zn3(L1)3](ClO4)3·4CH3CN (2·4CH3CN) was characterized by X-ray crystallography. The complex cations of 1 and 2 had comparable structures despite being nonisomorphic. Variable temperature and concentration 1H NMR were used to investigate aggregation equilibria of 1, 2, and a precipitate with composition "Hg(L1)(ClO4)" (3). Cryogenic 1H NMR studies of 3 revealed a J(199Hg1H) coupling constant pattern consistent with an aggregate possessing a cyclic core. ESI-MS was used for gas-phase characterization of 1-3, as well as mixed-metal [M2M'(L1)3(ClO4)2]+ ions prepared in situ by pairwise acetonitrile solution combinations of the group 12 complexes of L1. Access to synthetic variants of metallothionein-like group 12 aggregates provides an additional approach to understanding their behavior.

Metal Substitution and Solvomorphism in Alkylthiolate-Bridged Zn3 and HgZn2 Metal Clusters.

The impact of substituting Hg(II) for Zn(II) in a thiolate-bridged trinuclear cluster with parallels to a metallothionein metal cluster was investigated. A new solvomorph of [Zn(ZnL)2](ClO4)2 (1) (L = N-(2-pyridylmethyl)-N-(2-(ethylthiolato)-amine) and five solvomorphs of a new compound [Hg(ZnL)2](ClO4)2 (2) were characterized by single-crystal X-ray crystallography. The interplay of hydrogen bonding and aromatic-packing interactions in producing lamellar, 2D lamellar, and columnar arrangements of complex cations in the crystalline state is discussed. Both variable temperature proton nuclear magnetic resonance and electrospray ion-mass spectrometry (ESI-MS) suggest that the complex ions of 1 and 2 are the predominant solution species at moderate concentrations. ESI-MS was also used to monitor differences in metal ion redistribution as 1 was titrated with Hg(ClO4)2 and [HgL(ClO4)]. These studies document the facile replacement of Zn(II) by Hg(II) with the preservation of the overall structure in thiolate-rich clusters.

Contrasting coordination behavior of Group 12 perchlorate salts with an acyclic N3O2 donor ligand by X-ray crystallography and (1)H NMR.

An unbranched N3O2 ligand 2,6-bis[((2-pyridinylmethyl)oxy)methyl]pyridine (L1) was used to prepare new mononuclear heteroleptic Group 12 perchlorate complexes characterized by IR, (1)H NMR and X-ray crystallography. Racemic complexes with pentadentate L1 and one to four oxygens from either water or perchlorate bound to a metal ion were structurally characterized. Octahedral [Zn(L1)(OH2)](ClO4)2 (1) and pentagonal bipyramidal [Cd(L1)(OH2)(OClO3)]ClO4 (2) structures were found with lighter congeners. The polymorphic forms of [Hg(L1)(ClO4)2] characterized (3 in P1[combining macron] and 4 in P21/c) had a mix of monodentate, anisobidentate and bidentate perchlorates, providing the first examples of a tricapped trigonal prismatic Hg(ii) coordination geometry, as well as additional examples of a rare square antiprismatic Hg(ii) coordination geometry. Solution state (1)H NMR characterization of the Group 12 complexes in CD3CN indicated intramolecular reorganization remained rapid under conditions where intermolecular M-L1 exchange was slow on the chemical shift time scale for Zn(ii) and on the J(M(1)H) time scale for Cd(ii) and Hg(ii). Solution studies with more than one equivalent of ligand also suggested that a complex with a 1 : 2 ratio of M : L1 contributed significantly to solution equilibria with Hg(ii) but not the other metal ions. The behavior of related linear pentadentate ligands with Group 12 perchlorate salts is discussed.

Bis-tetradentate complexes of Cd(II) and Hg(II) with N8 coordination: structural and NMR comparisons.

Tripodal N4 ligands tris[(1-methylimidazol-2-yl)methyl]amine (L1), bis[(1-methylimidazol-2-yl)methyl][(2-pyridyl)methyl]amine (L2) and [(1-methylimidazol-2-yl)methyl]-bis-[(2-pyridyl)methyl]amine (L3) were used to prepare five new [ML2](ClO4)2 (M = Cd(II), Hg(II)) complexes. All complexes had N8 metal coordination and a trans-bicapped octahedral structure as determined by X-ray crystallography. Metal-nitrogen bond distances generally decreased in the order M-Namine > M-Npyridyl > M-Nimidazoyl, and the perchlorates were well separated from the metal ions. Variable temperature solution state (1)H NMR spectroscopy revealed conditions for slow intramolecular reorganization were more readily accessible for the Cd(II) complexes than for the Hg(II) complexes. Both protons of imidazoyl ring ligand components had large, comparable J((199)Hg(1)H) despite sizable differences in nuclear separation.

Structure and isomerization comparison of Zn(II), Cd(II) and Hg(II) perchlorate complexes of 2,6-bis([(2-pyridyl-methyl)amino]methyl)pyridine.

The divalent zinc triad perchlorate coordination chemistry of 2,6-bis([(2-pyridyl-methyl)amino]methyl)pyridine (L) was investigated by X-ray crystallography and solution state (1)H NMR. New complexes [HgL(ClO4)2] (1) and [CdL(ClO4)2] (2) were isolated as bicapped distorted square pyramidal racemates, contrasting with the approximate trigonal bipyramidal structure of [ZnL](ClO4)2 (3). Although rapid inter- and intramolecular exchange is common for simple complexes of zinc triad metal ions, conditions for slow intramolecular isomerization on both the δ and J(HH) time scales were established for 1, 2 and 3. Trends in geminal (1)H coupling suggested that an asymmetric structure was favored for all three metal ions at or below 40 °C. Contributions of a symmetric structure to solution equilibria were both temperature- and metal ion-dependent. Spectral trends were consistent with interconversion of a pair of enantiomeric square pyramidal ligand conformers through a symmetric trigonal bipyramidal ligand conformer by M-N bond cleavage and nitrogen inversion. Racemization was slower than the coupling constant time scale up to 40 °C for all complexes. Differential stabilization of specific small ligand conformations in solution has potential toxicological significance.

Carbonate-templated self-assembly of an alkylthiolate-bridged cadmium macrocycle.

In the presence of Cd(ClO4)2 and a base, a new mixed N,S-donor alkylthiolate ligand supported both carbonate formation from atmospheric CO2 and the self-assembly of a novel bicapped puckered (CdS)6 molecular wheel. The remarkable stability of the complex was demonstrated by slow intermolecular ligand exchange on the (2)J(HH) and J((111/113)Cd(1)H) time scales at elevated temperature. Both CO2 and the base were required to convert amorphous "CdLClO4" precipitated in the absence of air to the carbonate complex. The complex shares structural features with the ζ-carbonic anhydrase class associating cadmium(II) with the biogeochemical cycling of carbon and is the first structurally characterized carbonate complex of any metal involving an alkylthiolate ligand.

A synthetic model of Hg(II) sequestration.

Tridentate ligand N-(2-pyridylmethyl)-N-(2-(ethylthiolato)amine (L) forms the novel complex [Hg(5)(L)(6)](ClO(4))(4).toluene () with a bicyclo[3.3.3] Hg(5)S(6) core and 4-, 5- and 6-coordinate metal centers; characterization of a solution of by ESI-MS revealed elaborate speciation involving [Hg(n)L(n+1)(ClO(4))(n-2)](+), [Hg(n)L(n)(ClO(4))(n-1)](+) and [Hg(n)L(n-1)(ClO(4))(n)](+) ion families.

Bis-tridentate Chelates of an Asymmetric Ligand: X-ray Structures and Solution NMR Characterization of Divalent Zinc Triad Metal Ion Complexes of N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine.

Divalent zinc triad metal ion complexes of type M(L)(2)(ClO(4))(2) (L = N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine) with N(4)S(2) metal coordination spheres were isolated and characterized by X-ray crystallography and variable temperature proton NMR. Although bis-tridentate chelates have nine geometric isomers, the crystallographically characterized complexes of all three metal ions had trans facial octahedral coordination geometry with C(i) symmetry. Despite the low coordination number and geometric preferences of d(10) metal ions, which facilitate inter- and intramolecular exchange processes, dilute solutions of these bis-tridentate chelates exhibited slow geometric isomerization. Symmetry, sterics and shielding arguments supported specific isomeric assignments for the major and minor chemical shift environments observed at low temperature. At elevated temperature, rapid intramolecular exchange occurred for all three complexes but slow intermolecular exchange on the coupling constant time scale was evidenced through detection of J(HgH) interactions for Hg(L)(2) (2+). These unusual observations are discussed in the context of the zinc triad metal ion coordination chemistry of related bis-tridentate chelates.

Investigation of group 12 metal complexes with a tridentate SNS ligand by X-ray crystallography and 1H NMR spectroscopy.

Two series of zinc triad complexes containing the ligand 2,6-bis(methylthiomethyl)pyridine (L1) were synthesized and characterized by X-ray crystallography and solution-state 1H NMR spectroscopy. The distorted meridional octahedral M(L1)2(ClO4)2 series includes the first structurally characterized Zn(II) and Cd(II) complexes with N2(SR2)4 coordination spheres. Coordination of HgCl2 and ZnCl2 with 1 equiv of ligand afforded mononuclear, five-coordinate species Hg(L1)Cl2 and Zn(L1)Cl2, respectively, with distorted square-pyramidal and trigonal-bipyramidal geometries. With CdCl2, the dimeric [Cd(L1)Cl(mu-Cl)]2 complex was obtained. The distorted octahedral coordination geometry of each Cd(II) center in this complex is formed by one tridentate ligand, two bridging chloride ions, and one terminal chloride ion. NMR spectra indicate that the intermolecular ligand-exchange rate of [M(L1)2](2+) decreased in the order Cd(II) > Zn(II) > Hg(II). Slow intermolecular ligand-exchange conditions on the chemical-shift time scale were found for 1:2 metal-to-ligand complexes of L(1) with Hg(II) and Zn(II) but not Cd(II). Slow intermolecular ligand-exchange conditions in acetonitrile-d(3) solutions permitting detection of (3-5)J(199Hg1H) were found for 1:1 and 1:2 Hg(ClO4)2/L1 complexes, but not for the related Cd(ClO4)2) complexes. The magnitudes of J(199Hg1H) for equivalent protons were smaller in [Hg(L1)2](2+) than in [Hg(L1)(NCCH3)x](2+). The relative intermolecular ligand-exchange rates of the zinc triad complexes investigated here suggest that the toxicity of Hg(II) is accentuated by the relative difficulty of displacing it from the coordination sites encountered.

Solid-state and solution-state coordination chemistry of the zinc triad with the mixed N,S donor ligand bis(2-methylpyridyl) sulfide.

The binding of group 12 metal ions to bis(2-methylpyridyl) sulfide (1) was investigated by X-ray crystallography and NMR. Seven structures of the chloride and perchlorate salts of Hg(II), Cd(II), and Zn(II) with 1 are reported. Hg(1)(2)(ClO(4))(2), Cd(1)(2)(ClO(4))(2), and Zn(1)(2)(ClO(4))(2).CH(3)CN form mononuclear, six-coordinate species in the solid state with 1 binding in a tridentate coordination mode. Hg(1)(2)(ClO(4))(2) has a distorted trigonal prismatic coordination geometry while Cd(1)(2)(ClO(4))(2) and Zn(1)(2)(ClO(4))(2).CH(3)CN have distorted octahedral geometries. With chloride anions, the 1:1 metal to ligand complexes Hg(1)Cl(2), [Cd(1)Cl(2)](2), and Zn(1)Cl(2) are formed. A bidentate binding mode that lacks thioether coordination is observed for 1 in the four-coordinate, distorted tetrahedral complexes Zn(1)Cl(2) and Hg(1)Cl(2). [Cd(1)Cl(2)](2) is dimeric with a distorted octahedral coordination geometry and a tridentate 1. Hg(1)Cl(2) is comprised of pairs of loosely associated monomers and Zn(1)Cl(2) is monomeric. In addition, Hg(2)(1)Cl(4) is formed with alternating chloride and thioether bridges. The distorted square pyramidal Hg(II) centers result in a supramolecular zigzagging chain in the solid state. The solution (1)H NMR spectra of [Hg(1)(2)](2+) and [Hg(1)(NCCH(3))(x)()](2+) reveal (3)(-)(5)J((199)Hg(1)H) due to slow ligand exchange found in these thioether complexes. Implications for use of Hg(II) as a metallobioprobe are discussed.

Sterically demanding multidentate ligand tris[(2-(6-methylpyridyl))methyl]amine slows exchange and enhances solution state ligand proton NMR coupling to (199)Hg(II).

The solution state coordination chemistry of Hg(ClO(4))(2) with tris[(2-(6-methylpyridyl))methyl]amine (TLA) was investigated in acetonitrile-d(3) by proton NMR. Although Hg(II) is a d(10) metal ion commonly associated with notoriously rapid exchange between coordination environments, as many as six ligand environments were observed to be in slow exchange on the chemical shift time scale at select metal-to-ligand ratios. One of these ligand environments was associated with extensive heteronuclear coupling between protons and (199)Hg and was assigned to the complex [Hg(TLA)](2+). The (5)J((1)H(199)Hg) = 8 Hz associated with this complex is the first example of five-bond coupling in a nitrogen coordination compound of Hg(II). The spectral complexity of related studies conducted in acetone-d(6) precluded analysis of coordination equilibria. Crystallographic characterization of the T-shaped complex [Hg(TLAH)(CH(2)COCH(3))](ClO(4))(2) (1) in which two pyridyl rings are pendant suggested that the acidity of acetone combined with the poor coordinating abilities of the neutral solvent adds additional complexity to solution equilibria. The complex crystallizes in the triclinic space group P1 macro with a = 9.352(2) A, b = 12.956(2) A, c = 14.199(2) A, alpha = 115.458(10) degrees, beta = 90.286(11) degrees, gamma = 108.445(11) degrees, and Z = 2. The Hg-N(amine), Hg-N(pyridyl), and Hg-C bond lengths in the complex are 2.614(4), 2.159(4), and 2.080(6) A, respectively. Relevance to development of (199)Hg NMR as a metallobioprobe is discussed.

Comparison of Heteronuclear Coupling Constants for Isostructural Nitrogen Coordination Compounds of (111/113)Cd and (199)Hg.

The complexation of Cd(II) by the tripodal ligand tris[(2-pyridyl)methyl]amine and dipodal ligand bis[(2-pyridyl)methyl]amine was investigated by solution-state NMR and X-ray crystallography. Cadmium coordination compounds exhibiting rarely observed solution-state NMR (1)H-(111/113)Cd satellites were characterized. The eight-coordinate complex [Cd(TMPA)(2)](ClO(4))(2).toluene (1) crystallizes in the triclinic space group P1 with a = 9.629(2) Å, b = 11.020(2) Å, c = 11.641(2) Å, alpha = 114.069(13) degrees, beta = 97.492(13) degrees, gamma = 91.034(14) degrees, and Z = 1. The average Cd-N(amine) distance is 2.53(4) Å and the average Cd-N(pyridyl) distance is 2.54(6) Å. The complex [Cd(BMPA)(NCCH(3))(OH(2))(OClO(3))][Cd(BMPA)(2)](ClO(4))(3).(CH(3)CN) (2) crystallizes in the triclinic space group P&onemacr; with a = 10.446(2) Å, b = 16.653(3) Å, c = 17.736(3) Å, alpha = 62.479(9) degrees, beta = 80.606(14) degrees, gamma = 84.66(2) degrees, and Z = 2. In the pseudo-octahedral monocation, the nitrogen-containing ligands occupy equatorial positions with Cd-N distances of 2.321(8), 2.283(7), and 2.263(8) Å for the amine, pyridyl (average) and acetonitrile nitrogens, respectively. Significant axial interactions occur with Cd-O bond distances of 2.313(7) Å (water) and 2.478(7) Å (perchlorate). In the pseudo-trigonal prismatic dication, the average Cd-N(amine) distances is 2.395(5) Å and the average Cd-N(pyridyl) distance is 2.362(8) Å. The solid-state structures and solution-state NMR trends were very similar to recently reported isovalent complexes of Hg(II), providing an exceptional opportunity to compare coupling constants of coordination compounds. Implications for the use of (111/113)Cd and (199)Hg NMR as metallobioprobes are discussed.

Correlation of a Solution-State Conformational Change between Mercuric Chloride Complexes of Tris[(2-(6-methylpyridyl))methyl]amine with X-ray Crystallographic Structures.

Solution-state NMR and X-ray crystallography were used to investigate the complexation of HgCl(2) by the potentially tetradentate ligand tris[(6-methyl-2-pyridyl)methyl]amine (TLA) in acetonitrile. A change in the ligand conformation as a function of the metal-to-ligand ratio could be indirectly monitored through large changes in (3)J((1)H(199)Hg) to the methylene protons at -40 degrees C. The solution-state NMR were correlated with two solid-state structures. The five-coordinate complex [Hg(TLA)Cl(2)] (1) crystallizes in the triclinic space group P&onemacr; with a = 8.663(3) Å, b = 11.539(4) Å, c = 13.739(3) Å, alpha = 80.81(2) degrees, beta = 75.84(2) degrees, gamma = 80.97(3) degrees, and Z = 2. The Hg-N(amine) distance of 2.505(7) Å for the tridentate ligand is the same as the average Hg-N(lutidyl) distance of 2.50(3) Å for the two bound lutidyl nitrogens. [Hg(TLA)Cl](2)(Hg(2)Cl(6)) (2) also crystallizes in P&onemacr; with a = 10.606(2) Å, b = 15.104(3) Å, c = 17.785(4) Å, alpha = 67.46(3) degrees, beta = 83.52(3) degrees, gamma = 80.29(3) degrees, and Z = 2. The ligand is tetradentate in the two crystallographically unique cations which are arranged in a dimer-like orientation. The average Hg-Cl distance is 2.37 (1) Å, and the average interionic Hg-Cl distance is 3.51(1) Å. The Hg- N(lutidyl) distances are of two types: two have an average distance of 2.36(3) Å, nearly the same as the Hg-N(amine) distance of 2.35(2) Å. The remaining four N(lutidyl) distances have an average distance of 2.56(5) Å.