Selective metal-assisted assembly of mesocates or helicates with tristhiosemicarbazone ligands

1 Selective metal-assisted assembly of mesocates or helicates with tristhiosemicarbazone ligands María J. Romero,a Miguel Martínez-Calvo,a Marcelino Maneiro,b Guillermo Zaragoza,c Rosa Pedridoa,*, and Ana M. González Noyaa,* a Departamento de Química Inorgánica, Facultade de Química, Campus Vida, Universidade de Santiago de Compostela, Santiago de Compostela, Galicia, E-15782, Spain. b Departamento de Química Inorgánica, Facultade de Ciencias, Campus Terra, Universidade de Santiago de Compostela, E-27002, Lugo, Spain. c Unidade de Difracción de Raios X, Edificio CACTUS, Universidade de Santiago de Compostela, Campus Sur, Santiago de Compostela, Galicia, E-15782, Spain. ABSTRACT The effect of the ligand and/or metal-related factors on the formation of tristhiosemicarbazone metallosupramolecular complexes has been studied in this work. The crystal structures of zinc(II) and lead(II) tristhiosemicarbazone mesocates and a hydrolyzed cadmium(II) helicate let us to better rationalize some factors involved on the selective formation of helicates or mesocates. 2 INTRODUCTION Among the large variety of discrete supramolecular species reported to date, helicates and mesocates are considered to be the simplest and most promising architectures 1 , 2 because of their wide range of possibilities in different areas of nanoscience related to biomedicine, 3 catalysis 4 and magnetic materials. 5 A helical assembly is inherently chiral as it contains two metal ions with identical (i.e. ΔΔ or ΛΛ) configurations. However if the resulting assembly contains the metal ions with opposite chirality (i.e. ΔΛ or ΛΔ) the helicate’s achiral partner, the meso-helicate (or mesocate) is formed. Thiosemicarbazones are highly versatile skeletons that have been widely used as ligands in coordination chemistry. 6 Besides they have been also employed in the areas of chemical biology and biomedicine. 7 Our research group has pioneered the use of these types of skeletons as precursors of different supramolecular arrays. Thus, we have reported mesocates, 8 , 9 helicates 10 , 11 and cluster thiosemicarbazone-derived helicates with singular functional architectures 12 and promising new functionalities. 13 The formation of mesocates instead of helicates appears to be controlled by a variety of factors, including the specific ligand design, 14 the temperature and solvent conditions 15 or the incorporation of a guest molecule. 16 To date, the great majority of the investigations performed to selectively obtain helicates/mesocates are based on structural features of the ligands. However, only a few partial studies have shown that different metal ions give rise to different supramolecular structures based on their coordination requirements.1a, 17 In 2012 we demonstrated that we can selectively obtain mesocate or helicate architectures following a simple metal ion recognition strategy using tetradentate bisthiosemicarbazone ligands.9 Thus, meso- 3 helical compounds were formed in the Co(II) and Zn(II) cases whereas Cd(II) ions gave rise to helical assemblies. As a continuation of those studies we have tried to examine whether the presence of a third thiosemicarbazone thread in the ligands would affect the discrete supramolecular structure of the assembled supramolecular species compared to those derived from the related bisthiosemicarbazones (Scheme 1).9,11, 18 Bearing our previous results in mind, we have designed the ligands H2LMe 1 and H2LPh 2, which have three [NS] thiosemicarbazone domains separated by a short arene spacer. Both ligands differ on the terminal methyl- and phenyl substituents in the thioamide moieity, respectively. To date, scarce metallosupramolecular structures derived from tristhiosemicarbazone ligands have been reported in literature. For example, a tristhiosemicarbazone ligand with tripodal structure has been employed to assemble a molecular Co(II) tetrahedron with application in photocatalytic reactions. 19 The most relevant structures obtained with other tris-bidentate ligands bearing a rigid spacer consist on supramolecular clusters 20 or polynuclear host complexes, 21 while other related tripodal ligands with a more flexible spacer give rise to mononuclear complexes. 22 It is worth noting that tristhiosemicarbazone helicate- or mesocate-type metal complexes have not been achieved yet. 4 Scheme 1. Bisthiosemicarbazone ligands H2LR (R= Me, Et, Ph, PhOMe and PhN) previously studied by us (a) and tristhiosemicarbazones H3LR (R = Me, 1; R= Ph, 2) employed in this work (b). Herein we report the selective assembly of dinuclear helical and meso-helical complexes through metal-ion recognition or ligand design by using the tristhiosemicarbazone ligands H3LMe 1 and H3LPh 2. The electrochemical reaction of 1 and 2 with zinc, cadmium and lead plates has been carried out in this work. These metal ions might coordinate to two or three ligand strands, hence acquiring tetrahedral or octahedral coordination environments. We have analyzed the crossed effect of several factors, such as the presence of a third arm in the thiosemicarbazone ligands, the metal ion size and the electronic configuration of the metal ion, on the selective formation of metallosupramolecular helicates or mesocates. 5 RESULTS AND DISCUSSION Ligands. The hexadentate thiosemicarbazone ligands 1 and 2 display three flexible bidentate [NS] domains separated by a rigid aromatic spacer (Scheme 1). They were synthesized by condensation reaction of 1,3,5-triacetylbenzene and the corresponding thiosemicarbazide in a molar ratio 1:3, as described in the Experimental section, and completely characterized with the usual techniques. Single crystals of the ligand H3LMe were obtained by slow evaporation of the mother liquors in ethanol and its structure was determined by X-ray diffraction. The crystal structure consists of discrete molecules of ligand solvated by a water molecule, 1·H2O (Figure 1). The bond distances and angles are within the expected range for thiosemicarbazone ligands (Table S1).9,10 The arrangement between the three thiosemicarbazone arms can be assigned as anti-open, syn-open and syn-close (Scheme S1) with all the imine bonds showing an E conformation. Additionally the imine nitrogen atoms of each ligand thread [N(3)/N(4)/N(7)] establish intramolecular classical hydrogen bonds with the thioamide NH groups [N(1)- H(1)/N(6)-H(6)/N(9)-H(9)] (Figure S1, Table S2). These and other weak interactions are likely to determine the opposite orientation of the Nimine/Sthioamide binding atoms in the free ligand and the crystal packing of 1 in the solid state (Figure S1). 6 Figure 1. Sticks diagram of the tristhiosemicarbazone ligand [H3LMe]·H2O (1·H2O). The water molecule has been omitted for clarity. As mentioned above, the donor atoms in the bidentate domains of ligand 1 (N3/S1, N4/S2, N7/S3) are oriented in opposite directions. Our previous experience on the coordination chemistry of tetradentate bisthiosemicarbazone ligands has shown that the assembly of helicates or meso-helicates occurs through conformational changes in the ligand.9, 23 Namely the coordination of a thiosemicarbazone bidentate domain Nimine/ Sthioamide to a metal ion requires a rotation about the thioamide N-CS bond in order to allow the imine nitrogen and sulfur atoms point towards the same metal centre.23 We have observed that the formation of meso-helicates from related tetradentate bisthiosemicarbazone ligands requires a further rotation at one of the imine bonds, which changes from the E conformation in the free ligand to the thermodynamically less stable Z conformation in the mesocate.9 However, the E conformation at the imine bonds in the ligand is preserved when a helicate is formed and therefore the assembly of these helical species should be energetically favored.9 7 In this work we have employed the electrochemical synthesis to obtain crystalline Zn(II), Cd(II) and Pb(II) supramolecular complexes with the methyl- and phenyl-substituted ligands 1 and 2, respectively. We have tried to deprotonate two or the three ligand arms by means of an exhaustive control of the reaction time during the electrochemical synthesis. The obtained results demonstrated that the resulting complexes always contain the dianionic ligands, with independence of the conditions employed. The X-ray diffraction technique allowed us to analyse whether the number of ligand arms, the tuning of the terminal substituents and the nature and preferences of the metal ion might influence the nature of the discrete supramolecular structure. Mesocates and helicates assembly. We initiated our studies with the Zn(II) ion which has a d10 electronic configuration. Differences in ligand-field stabilization energies (LFSE) are expected between metal ions with an incomplete or complete d electronic shell. In this case, the complete d10 shell of a Zn(II) ion leads to the same mean LFSE in tetrahedral and octahedral fields while other metal ions with the incomplete dn shell might exhibit a LFSE gain depending on the crystal field splitting. Previously we found that the series of bisthiosemicarbazone ligands H2LR (Scheme 1a) afforded meso-helical structures in the cases of two similar-sized ions, Co(II) and Zn(II), for all the final R substituents.9 These results demonstrated that the lack of LFSE or the size of the terminal group does not have any effect on the type of structure obtained. With these antecedents in mind, herein we have investigated whether the coordination of the tristhiosemicarbazone ligands 1 and 2 around Zn(II) ions would result on the assembly of helicates or mesocates. The electrochemical reaction of a zinc plate in the presence of ligands 1 8 or 2 in a conducting acetonitrile solution (see Experimental section) yielded the neutral metal complexes [Zn2(HLMe)2] (3) and [Zn2(HLPh)2] (4), respectively. The analytical and spectroscopic data (elemental analysis, MALDI-TOF MS, IR and 1H NMR spectroscopy) are in agreement with the formation of dimeric [Zn2(HLR)2] species. The coordination of ligands 1 or 2 to the Zn(II) ions in a dianionic mode was confirmed by the absence of the hydrazide NH signal from two thiosemicarbazone domains in the 1H NMR spectra of complexes 3 and 4. Besides a slight upfield shift of the hydrazide NH signal from the unbound arm was observed. Figure 2. Sticks diagram of the zinc(II) mesocate [Zn2(HLMe)2] 3. Slow evaporation of the mother liquors from the electrochemical synthesis of 3 afforded X-ray quality crystals of [Zn2(HLMe)2] 3, that was further analysed by X-ray diffraction (Figure 2, Table S3). The crystal structure of 3 reveals two ligand molecules coordinated to two zinc ions in a side-by-side coordination mode giving rise to a meso-helical structure. Despite the existence of three arms with potential [NS] binding sites, each ligand unit behaves in fact as a 9 bisthiosemicarbazone, with two [NS] binding domains that coordinate two metal centres, while the third [NS] domain remains unbound. Each zinc(II) ion is coordinated to an imine nitrogen atom and a sulfur atom from each ligand unit (Figure 2) and hence lies in a [N2S2] distorted tetrahedral coordination environment. In order to reach this tetrahedral kernel for each zinc(II) ion, the imine bond configuration at the two coordinated thiosemicarbazone arms changes from E/E in the free ligand H3LMe to E/Z in the mesocate 3. The Zn−S and Zn−N bond distances (ca. 2.3 and 2.0 Å, respectively; Table S3) are in good agreement with those observed in zinc thiosemicarbazone complexes.10, 24 The Zn···Zn distance of 7.018 Å in mesocate 3 is slighty shorter than the intermetallic distance observed in its analogue bisthiosemicarbazone zinc mesocate derived from 1,3-diacetylbenzene previously reported by us (Zn···Zn 7.158 Å).8 The crystal cell of mesocate 3 reveals the existence of intermolecular hydrogen bond interactions between the sulfur atoms and the thioamide NH groups. The hydrazide NH group in the unbound arm forms an intermolecular hydrogen bond with deprotonated hydrazide nitrogen belonging to a coordinated arm from a neighbour complex (Table S4). These weak interactions result in a lineal arrangement of mesocate molecules (Figure S7) and the formation of channels with the free protonated ligand arm oriented into their inner cavity (Figure S8). Our investigations on the ligand and metal-related factors was extended with d10 closed-shell metal ions with a large size, cadmium(II) and lead(II). Both metal ions can be also found in tetrahedral and octahedral environments. 16 bonds. The void created by the lead lone pair might favor the coordination of the imine nitrogen atoms with the same E/E conformation than in the free ligand. Additionally the two aromatic spacers adopt a "face-to-face" orientation (centroid-to-centroid distance is ca. 6.3 Å) and consequently the aromatic π-clouds would be almost perpendicular to the lead lone pairs. Figure 5. Comparison of the arrangement of the coordinated tristhiosemicarbazone ligands in the zinc(II) mesocate [Zn2(HLMe)2], 3 (a) and the lead(II) mesocate [Pb2(HLPh)2]·6CH3CN (8·6CH3CN) (b). View along the metals axis. The crystallographic studies carried out herein allowed us to identify significant differences with regards the conformation of the coordinated ligands, as mentioned above (Figure 5). The imine bonds adopt a Z/E conformation upon binding to Zn(II) ions in a meso-helical structure, however the stereochemically-active lone pair at the Pb(II) ions in the meso-helicate 8·6CH3CN seems to contribute towards a more thermodynamically favoured structure with an E/E conformation at the imine bonds alike the Cd(II) helicate 6*·3CH3CN. Besides the no coordination of the third arm in both mesocate and helicate species might be due to the rigid nature of the benzene spacer 17 in the ligands 1 and 2, as the coordination to a third metal ion could be hampered once two of the bidentate chelating arms are bound to two metal centers. The analysis of the experimental results demonstrated that the presence of more donor atoms in this type of ligands does not affect to: i) the discrete supramolecular helicate or mesocate nature of the complexes, therefore confirming that the assembly process is mainly driven by the metal ion nature; ii) the nuclearity of the particular helicate and mesocate is maintained as M2(HL)2 despite of the introduction of more donor atoms on the ligand structure; iii) the reaction time does not affect to the deprotonation degree of the ligand. The third arm remains protonated and uncoordinated in all cases, which is an unexpected but novel result. SUMMARY AND CONCLUSIONS We have reported the first cases of mesocate and helicates metallosupramolecular structures with tristhiosemicarbazone ligands. The coordination of these [NS] trisbidentate ligands to different metal ions demonstrates that the addition of a third thiosemicarbazone arm in a ligand tuned with a phenyl rigid spacer does not modify the resulting discrete supramolecular assembly, as tristhiosemicarbazone ligands behave in all cases alike bisthiosemicarbazones. The steric constraints due to the change from methyl- to phenylsubstituents in both ligands do not preclude the assembly of dinuclear mesocates/helicates. Moreover, the obtained results hence indicate that the metal-related factors (e.g. metal size) control the outcome of the self-assembly of helicate or mesocates. Thus, small-sized zinc ions give rise to mesocates whereas the bigger cadmium (II) afforded chiral helicates. In the particular case of Pb(II) we confirmed the prevalent role of the lone pair that prevents the isolation of helicates. 18 EXPERIMENTAL SECTION Materials and Methods. All solvents, 1,3,5-triacetylbenzene, 4-N-methyl-3-thiosemicarbazide, 4-N-phenyl-3-thiosemicarbazide, and the zinc, cadmium and lead metal plates (ca. 2x2 cm2) were purchased from commercial sources and were employed as received without any purification thereof. Elemental compositions of the compounds (C, H, N and S) were carried out on a FISONS EA model 1108 Analyzer. A Varian Mercury 300 spectrometer was employed to record the 1H and 13C/DEPT NMR spectra operating at room temperature. DMSO-d6 was used as deuterated solvent and the chemical shifts are reported as  (in ppm) and expressed relative to Me4Si (δ = 0 ppm). Infrared spectra were recorded from 4000 to 500 cm−1 on a BRUKER IFS-66V spectrophotometer using KBr discs. An API4000 Applied Biosystems mass spectrometer equipped with Triple Cuadrupole analyser was used to collect the positive electrospray ionisation mass data (ESI+), using standard spectroscopic-grade solvents. A Bruker Autoflex spectrometer, using DCTB as the matrix, was used to register the Matrix-assisted Laser Desorption Ionisation Time of Flight (MALDI-TOF) mass spectra. 19 Synthesis of Ligands [H3LMe] 1. 0.66 g (3.2 mmol) of 1,3,5-triacetylbenzene and 1.02 g (9.6 mmol) of 4-N-methyl-3- thiosemicarbazide were mixed and dissolved in absolute ethanol (75 mL). Then a catalytic amount of p-toluensulfonic acid was added to promote the iminic condensation. The reaction mixture was refluxed for 24 h, using a Dean-Stark trap to remove the released water. The resulting solution was evaporated (to a volume of ca. 20 mL) and cooled down to 4 oC until the formation of a white microcrystalline product was observed. This solid was filtered off, washed with diethyl ether (5 cm3) and then dried under vacuum. Yield: 1.15 g (77%); m.p. 275-277 oC; E. A. (Found: C, 46.4; H, 5.7; N, 26.8; S, 20.5; C18H27N9S3 required: C, 46.4; H, 5.8; N, 27.1; S, 20.7); ESI--MS (m/z) 464.1 [H3LMe-H]-; 1H NMR (DMSO-d6, ppm):  10.32 (s, NH, 3H), 8.67 (c, NH, 3H, J= 4.4 Hz), 8.23 (s, 3H), 3.04 (d, 9H, J= 4.4 Hz), 2.39 (s, 9H); 13C/DEPT NMR (DMSO-d6, ppm):  178.81 (C=S), 147.95 (C=N), 138.24 (Car), 125.55 (CHar), 31.25 (CH3), 14.89 (CH3); IR (KBr, cm-1): (NH) 3366, 3217, (C=N + C-N) 1555, 1493, (C=S) 1101, 889, (N-N) 1036. Crystals of 1·H2O suitable for X-ray crystallography were obtained by slow evaporation of the mother liquors. [H3LPh] 2. 0.31 g (1.5 mmol) of 1,3,5-triacetylbenzene and 0.77 g (4.5 mmol) of 4-N-phenyl-3- thiosemicarbazide were were mixed and dissolved in absolute ethanol (75 mL). A catalytic amount of p-toluensulfonic acid was added in to the mixture in order to favors the imine bond formation. Then the reaction was refluxed with a Dean-Stark trap during a period of 4 h to remove the released water. The volume of the resulting solution was concentrated to 20 mL. After that, the resulting pale yellow ligand was separated by filtration, washed with diethyl ether (5 cm3) and then dried using vacuum. Yield: 0.80 g (80%); m.p. >300 oC; E. A. (Found: C, 60.7; 20 H, 5.0; N, 19.4; S, 15.0; C33H33N9S3 required: C, 60.8; H, 5.1; N, 19.3; S, 14.8); ESI--MS (m/z) 650.2 [H2LPh-H]-; 1H NMR (DMSO-d6, ppm):  10.62 (s, NH,3H), 10.15 (s, NH, 3H), 8.41 (s, 3H), 7.48 (d, 6H, J= 7.4 Hz), 7.30 (ta, 3H, J1= 6.8 Hz, J2= 7.0 Hz), 7.18 (t, 3H, J1-2= 6.5 Hz), 2.48 (s, 9H); 13C/DEPT NMR (DMSO-d6, ppm):  177.60 (C=S), 149.66 (C=N), 139.61 (Car), 138.48 (Car), 128.57 (CHar), 126.57 (CHar), 126.25 (CHar), 125.83 (CHar), 15.64 (CH3); IR (KBr, cm-1): (NH) 3300, 3215, (C=N + C-N) 1593, 1541, 1497, (C=S) 1174, 751, (N-N) 1030. Synthesis of Complexes The zinc, cadmium and lead complexes were synthesized by an electrochemical procedure using acetonitrile as solvent. As typical example the synthetic procedure employed for the isolation of the complex [Zn2(HLMe)2] (3) is described below: The neutral zinc(II) complex 3 was prepared by an electrochemical procedure. The electrochemical cell can be summarised as follows: Pt(-)  H3LMe + CH3CN  Zn(+). The ligand H3LMe (0.1 g, 0.22 mmol) was dissolved in acetonitrile (ca. 80 cm3). A tiny amount of tetraethylammonium perchlorate was incorporated to the reaction media as supporting electrolyte. The resulting mixture was electrolysed under two different conditions: 10 mA and 19 V for 1 h 43 min to achieve trideprotonation of the ligand H3LMe and 10 mA and 19 V for 1 h 9 min to bideprotonate the ligand. The pale yellow powder was isolated by filtration, washed with a small volume of diethyl ether (10 mL) and dried under vacuum. CAUTION! Although we have not encountered any problem so far during the electrochemical synthesis perchlorate salts must be carefully manipulated as they are potentially explosive. 21 Both synthetic conditions gave rise to the same M2(HLR)2 stoichimetries (R= Me, Ph) for zinc, cadmium and lead ions. In addition, we must point herein that in the cases of the lead methylsubstituted complex and zinc, cadmium and lead phenyl-substituted complexes the quality of their 1H NMR spectra did not allow an accurate assignment of the signals. [Zn2(HLMe)2] 3: Yield: 0.095 g (82%); Ef = 0.4 mol F-1; E. A. (Found: C, 40.8; H, 4.8; N, 23.6; S, 18.2; C36H50N18S6Zn2 required: C, 40.9; H, 4.8; N, 23.8; S, 18.2; MALDI-TOF MS (m/z) 1059.2 [M2(HL)2+H]+, 1121.2 [M3(L)2+H]+; 1H NMR (300 MHz, DMSO-d6, ppm):  10.29 (m, 1H’1), 8.82 (s, 1H3), 8.42 (sa, 1H’2), 8.06 (s, 2H’3), 6.94 (c, 2H2), 3.03 (d, 3H’4), 2.79 (m, 6H4), 2.54 (s, 3H’5), 2.38 (s, 6H5); IR (KBr, cm-1): (NH) 3364, 3173, (C=N + C-N) 1541, 1495, (C=S) 1090, 885, (N-N) 1049. Colourless X-ray quality crystals of [Zn2(HLMe)2] 3 were collected after filtration of the initial precipitate obtained during the electrochemical synthesis followed by slow evaporation of the mother liquors. [Zn2(HLPh)2] 4: Yield: 0.096 g (61%); Ef = 0.6 mol F-1; E. A. (Found: C, 55.3; H, 4.2; N, 17.3; S, 13.3; C66H62N18S6Zn2 required: C, 55.4; H, 4.4; N, 17.6; S, 13.5; MALDI-TOF MS (m/z) 714.1 [M(HL)]+, 1431.2 [M2(HL)2+H]+, 1494.1 [M3(L)2]+; IR (KBr, cm-1): (NH) 3308, (C=N + C-N) 1595, 1527, 1481, (C=S) 1185, 750, (N-N) 1029. [Cd2(HLMe)2] 5: Yield: 0.11 g (87%); Ef = 0.5 mol F-1; E. A. (Found: C, 37.4; H, 4.5; N, 21.7; S, 16.7; C36H50N18S6Cd2 required: C, 37.5; H, 4.4; N, 21.9; S, 16.7; MALDI-TOF MS (m/z) 684.2 [M2(HL)+H]+, 1045.4 [M(HL)2+H]+, 1157.3 [M2(HL)2+H]+; 1H NMR (300 MHz, DMSO-d6, ppm):  10.20 (s, 1H’1), 8.63-7.50 (m, 4 [H’2+H3+H’3]), 6.88 (s, 2H2), 3.01 (d, 3H4), 2.83 (m, 6H’4), 2.52 (s, 3H’5), 2.35 (s, 6H5); IR (KBr, cm-1): (NH) 3363, (C=N + C-N) 1530, 1491, (C=S) 1084, 882, (N-N) 1053. 22 [Cd2(HLPh)2] 6: Yield: 0.081 g (69%); Ef = 0.5 mol F-1; E. A. (Found: C, 51.8; H, 4.0; N, 16.3; S, 12.3; C66H62N18S6Cd2 required: C, 52.0; H, 4.1; N, 16.5; S, 12.8; MALDI-TOF MS (m/z) 764.1 [M(HL)+H]+, 874.0 [M2(HL)]+, 1526.2 [M2(HL)2+H]+, 1635.1 [M3(L)2+H]+; IR (KBr, cm- 1): (OH) 3451, (NH) 3304, (C=N + C-N) 1594, 1526, 1494, (C=S) 1176, 750, (N-N) 1029. Colourless X-ray quality crystals of [Cd2(LPh’)2]·3CH3CN (6*·3CH3CN) were grown by slow evaporation of the mother liquors from the electrochemical synthesis. In this complex, the initial ligand H3LPh has underwent hydrolysis of one the imine bonds, and consequently a new bisthiosemicarbazone ligand H2LPh’ was formed. [Pb2(HLMe)2]·H2O 7: Yield: 0.14 g (93%); Ef = 0.6 mol F-1; E. A. (Found: C, 31.6; H, 3.9; N, 18.4; S, 14.0; C36H52N18O1S6Pb2 required: C, 31.8; H, 3.8; N, 18.5; S, 14.1; MALDI-TOF MS (m/z) 672.1 [M(HL)+H]+; IR (KBr, cm-1): (OH) 3426, (NH) 3362, (C=N + C-N) 1530, 1490, (C=S) 1093, 863, (N-N) 1051. [Pb2(HLPh)2] 8: Yield: 0.140 g (74%); Ef = 0.6 mol F-1; E. A. (Found: C, 46.0; H, 3.5; N, 14.4; S, 11.0; C66H62N18S6Pb2 required: C, 46.2; H, 3.6; N, 14.7; S, 11.2; MALDI-TOF MS (m/z) 1064.1 [M2(HL)]+; 1H NMR (300 MHz, DMSO-d6, ppm):  7.65 (s, 1H3), 8.42 (sa, 1H’2), 8.06 (s, 2H’3), 6.94 (c, 2H2), 3.03 (d, 3H’4), 2.79 (m, 6H4), 2.54 (s, 3H’5), 2.38 (s, 6H5);IR (KBr, cm- 1): (NH) 3388, (C=N + C-N) 1599, 1521, 1492, (C=S) 1178, 749, (N-N) 1028. X-ray quality crystals of [Pb2(HLPh)2]·6CH3CN (8·6CH3CN) were grown by slow evaporation of the mother liquors after filtration of the initial precipitate obtained in the electrochemical synthesis. Crystal Structure Determinations. Colourless crystals of 1·H2O, 3 and 8·6CH3CN and yellow prismatic crystals of 6*·3CH3CN respectively, were obtained as indicated before. The crystals were mounted on a glass fibre and directly used for data collection. Crystal data collection was 23 performed at a 100(2) K temperature using a BRUKER APPEX-II diffractometer with a CCD area detector, using graphite monochromated MoK(α) radiation (λ = 0.71073 Å). The reflection data file was generated from the raw frame data and then treated with BRUKER SAINT. 31 An empirical absorption correction (SADABS) 32 was applied to the collected reflections. The structures of the ligand and the complexes were solved by using the SIR-97 program 33 and refined by full-matrix least-squares techniques against F2 using SHELXL-97 program package. 34 All non-hydrogen atoms were assigned with positional and anisotropic displacement parameters. The hydrogen atoms were (placed in calculated positions) included as fixed contributions riding on attached atoms with isotropic thermal parameters (1.2-1.5 times those of their carrier atoms). Criteria of a satisfactory complete analysis were the ratios of "rms" shift to standard deviation less than 0.001 was taken and no significant features were observed in the final difference maps. The molecular graphics include in the manuscript and the SI files were prepared with the MERCURY program. 35 The most relevant crystal data of the ligand 1·H2O is listed in SI whereas the crystal data details for the complexes 3, 6*·3CH3CN and 8·6CH3CN are located in the main text. Important bond distances and angles are summarized in Tables S1, S3, S5 and S7 while hydrogen bond parameters are listed in Table S2, S4; S6 and S8. CCDC 1847154–1847157, contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via ww.ccdc.cam.ac.uk/data_request.cif. ASSOCIATED CONTENT Supporting Information 24 ‡ Electronic Supplementary Information (ESI) available: Synthetic schemes and procedures, NMR spectra, crystallographic data for 1·H2O, 3, 6*·3CH3CN, and 8·6CH3CN. ORTEP and crystal packing figures, main bond distances and angles, and hydrogen bond parameters. The Supporting Information is available free of charge (PDF) at DOI: 10.1021/xxxxx AUTHOR INFORMATION Corresponding Authors * Email: [email protected] * Email: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Conflicts of interest There are no conflicts of interest to declare. Notes § Crystal data for [Zn2(HLMe)2]·3: (C36H50N18S6Zn2), Mw = 1058.04 g/mol, crystal dimensions: 0.12  0.08  0.07 mm3, monoclinic, P21/n, a = 11.3615(7), b = 13.8470(8), c = 16.5088(8) Å, α = 90,  = 101.413(3), γ = 90°, V = 2545.9(2) Å3, Z = 2,  = 1.234 mm−1, F(000) = 1096. Radiation  (Mo-K) = 0.7107 Å, T = 100(2) K, reflections collected/unique 22093/3651 (Rint = 25 0.108), R (all data) = 0.1078, wR (all data) = 0.1632, GOF = 1.016, max/min residual density 0.696/ -0.516 e.Å-3. CCDC 1847155. §§ Crystal data for [Cd2(LPh’)2]·3CH3CN (6*·3CH3CN): (C58H57N15O2S4Cd2), Mw = 1349.23 g/mol, crystal dimensions: 0.14 × 0.10 × 0.03 mm3, monoclinic, P21/n, a = 13.1135(7), b = 27.6972(14), c = 16.3410(9) Å, α = 90,  = 101.070(2), γ = 90°, V = 5824.7(5) Å3, Z = 4,  = 0.930 mm−1, F(000) = 2744. Radiation  (Mo-K) = 0.7107 Å, T = 100(2) K, reflections collected/unique 55889/7116 (Rint = 0.142), R (all data) = 0.1066, wR (all data) = 0.1185, GOF = 1.014, max/min residual density 0.673/ –0.590 e.Å-3. CCDC 1847156. §§§ Crystal data for [Pb2(HLPh)2]·6CH3CN (8·6CH3CN): (C78H80N24S6Pb2), Mw = 1960.48 g/mol, crystal dimensions: 0.41 × 0.04 × 0.03 mm3, triclinic, P -1, a = 11.9075(19), b = 13.050(2), c = 14.468(2) Å, α = 99.666(10),  = 103.061 (10), γ = 105.777(9)°, V = 2043.5(6) Å3, Z = 1,  = 4.33 mm−1, F(000) = 976. Radiation  (Mo-K) = 0.7107 Å, T = 100(2) K, reflections collected/unique 37984/7486 (Rint = 0.138), R (all data) = 0.0964, wR (all data) = 0.1348, GOF = 1.011, max/min residual density 3.11/ –1.75 e.Å-3. CCDC 1847157. ACKNOWLEDGMENTS Financial support from the Xunta de Galicia (GRC2014/025 and METALBIO ED431D 2017/01) and MINECO (CTQ2017-90802-REDT) is acknowledged. REFERENCES ( 1 ) See for example (a) Piguet, C.; Bernardinelli, G.; Hopfgartner, G. Helicates as Versatile Supramolecular Complexes. Chem. Rev. 1997, 97, 2005–2062; (b) Swiegers, G. F.; Malefetse, T. 32 ( 24 ) Christlieb, M.; Cowley, A. R.; Dilworth, J. R.; Donnelly, P. S.; Paterson, B. M.; Struthers, H. S. 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