Cyanide Ligands Research Articles

Poly[μ-cyano-μ-pyrazine-nickel(I)

The title compound, [Ni(CN)(C4H4N2)]n, was prepared by the hydro­thermal reaction of NiCl2, KCN and pyrazine. The NiII atoms are linked via cyanide ligands into a zigzag [NC–Ni–NC]∞ chain running parallel to [010]. These chains are further connected into a three-dimensional network by bridging pyrazine ligands, which have inversion symmetry. The coordination geometry around the NiII atom is distorted tetra­hedral, with one N and one C atom from the cyanide and two N atoms from the pyrazine ligands.

Conformational Mobility in the Active Site of a Heme Peroxidase

Conformational mobility of the distal histidine residue has been implicated for several different heme peroxidase enzymes, but unambiguous structural evidence is not available. In this work, we present mechanistic, spectroscopic, and structural evidence for peroxide- and ligand-induced conformational mobility of the distal histidine residue (His-42) in a site-directed variant of ascorbate peroxidase (W41A). In this variant, His-42 binds "on" to the heme in the oxidized form, duplicating the active site structure of the cytochromes b but, in contrast to the cytochromes b, is able to swing "off" the iron during catalysis. This conformational flexibility between the on and off forms is fully reversible and is used as a means to overcome the inherently unreactive nature of the on form toward peroxide, so that essentially complete catalytic activity is maintained. Contrary to the widely adopted view of heme enzyme catalysis, these data indicate that strong coordination of the distal histidine to the heme iron does not automatically undermine catalytic activity. The data add a new dimension to our wider appreciation of structure/activity correlations in other heme enzymes.

Cyanide Binding and Heme Cavity Conformational Transitions in Drosophila melanogaster Hexacoordinate Hemoglobin,

The reason for the presence of hemoglobin-like molecules in insects, such as Drosophila melanogaster, that live in fully aerobic environments has yet to be determined. Heme endogenous hexacoordination (where HisE7 and HisF8 axial ligands to the heme Fe atom are both provided by the protein) is a recently discovered mechanism proposed to modulate O(2) affinity in hemoglobins from different species. Previous results have shown that D. melanogaster hemoglobin 1 (product of the glob1 gene) displays heme endogenous hexacoordination in both the ferrous and ferric states. Here we present kinetic data characterizing the exogenous cyanide ligand binding process, and the three-dimensional structure (at 1.4 A resolution) of the ensuing cyano-met D. melanogaster hemoglobin. Comparison with the crystal structure of the endogenously hexacoordinated D. melanogaster hemoglobin shows that the transition to the cyano-met form is supported by conformational readjustment in the CD-D-E region of the protein, which removes HisE7 from the heme. The structural and functional features of D. melanogaster hemoglobin are examined in light of previous results achieved for human and mouse neuroglobins and for human cytoglobin, which display heme endogenous hexacoordination. The study shows that, despite the rather constant value for cyanide association rate constants for the ferric hemoproteins, different distal site conformational readjustments and/or heme sliding mechanisms are displayed by the known hexacoordinate hemoglobins as a result of exogenous ligand binding.

13C NMR Studies of the Electronic Structure of Low-Spin Iron(III) Tetraphenylchlorin Complexes

A series of low-spin six-coordinate (tetraphenylchlorinato)iron(III) complexes [Fe(TPC)(L)2]+/- (L = 1-MeIm, CN-, 4-CNPy, and (t)BuNC) have been prepared, and their (13)C NMR spectra have been examined to reveal the electronic structure. These complexes exist as the mixture of the two isomers with the (d(xy))2(d(xz), d(yz))3 and (d(xz), d(yz))4(d(xy))1 ground states. Contribution of the (d(xz), d(yz))4(d(xy))1 isomer has increased as the axial ligand changes from 1-MeIm, to CN(-) (in CD2Cl2 solution), CN- (in CD(3)OD solution), and 4-CNPy, and then to tBuNC as revealed by the meso and pyrroline carbon chemical shifts; the meso carbon signals at 146 and -19 ppm in [Fe(TPC)(1-MeIm)2]+ shifted to 763 and 700 ppm in [Fe(TPC)(tBuNC)2]+. In the case of the CN- complex, the population of the (d(xz), d(yz))4(d(xy))1 isomer has increased to a great extent when the solvent is changed from CD2Cl2 to CD3OD. The result is ascribed to the stabilization of the d(xz) and d(yz) orbitals of iron(III) caused by the hydrogen bonding between methanol and the coordinated cyanide ligand. Comparison of the 13C NMR data of the TPC complexes with those of the TPP, OEP, and OEC complexes has revealed that the populations of the (d(xz), d(yz))4(d(xy))1 isomer in TPC complexes are much larger than those in the corresponding TPP, OEC, and OEP complexes carrying the same axial ligands.

Trans-Dicyanotetrakis(2-isocyano-2,4,4-trimethylpentane)ruthenium(II)

In the centrosymmetric title compound, [Ru(CN)2(C9H17N)4], the central Ru atom is octahedrally coordinated by four isocyanide and two cyanide ligands in a trans configuration. The corresponding cis isomer, which is also produced in the reaction of Ru3(CO)12 with isooctylisocyanide, is not configurationally stable and slowly isomerizes into the trans isomer in solution.

Carbene Ligands in Diiron Complexes.

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The Vibrational Spectra of the Cyanide Ligand Revisited: Terminal Cyanides

A comparison is made between the vibrational characteristics of the carbonyl and cyanide ligands. There are significant differences; the latter has a smaller dipole moment and a larger quadrupole moment associated with the bond stretch. This quadrupole moment may be linked to the observation that the totally symmetric nu(CN) mode does not lie at the highest frequency for some cyanide complexes. There are problems with the pi-bonding model commonly used to interpret the nu(CN) data. For instance, for the first transition row hexacyanoanions, the spectra are almost independent of t2g occupancy but are very sensitive to the formal charge. It is suggested that the observed nu(CN) frequency shifts on complex formation are in large measure determined by the effective charge on the cation to which the cyanide group is attached, and a new model, the Internal Vibrational Stark Effect, is suggested to account for this. The model is supported by DFT calculations. Raman spectra of some cubic cyano species are reported, along with polarization and intensity data.

Magnetic and structural properties of a cyano-bridged 1D ruthenium(III)–nickel(II) coordination polymer

Reaction of [Ni(cyclam)](ClO 4) 2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) with Na[Ru(salen)(CN) 2] ( 2) (salen = ethylenebis(salicylimine)) generated the 1D coordination polymer [Ru(III)(salen)(CN) 2][Ni(II)(cyclam)](ClO 4) ( 1). X-ray diffraction studies of 1 revealed a structure consisting of alternating Ni(II) and Ru(III) ions bridged by cyanide ligands. The cyano C-terminus remained bound to the Ru(III) center while the perchlorate anion induced a deviation from linearity along the Ru–CN–Ni axis. Structural characterization of 2 disclosed a 2D framework where the sodium counterions bridge between [Ru(salen)(CN) 2] units. Magnetic measurements of 1 indicate ferromagnetic coupling between Ni(II) and Ru(III) with no long-range magnetic order above 3 K.

Supramolecular Self Assembly of [Cu(CN)4]3− Ions with Cationic {Ph3Sn+} Units in the Presence of Neutral Bidentate Ligands

The supramolecular interplay of the Ph 3 Sn+ unit and the [Cu(CN) 4 ]3− ion with either 4,4′-bipyridine (bpy), trans-1,2-bis(4-pyridyl)ethene (tbpe), 1,2-bis(4-pyridyl)ethane (bpe), pyrazine (pyz), or methylpyrazine (mepyz) as bidentate ligands in presence of H 2 O has been investigated for the first time. The products obtained have the general formula [(Ph 3 Sn) 3 Cu(CN)4·L·XH2O], where L is a bidentate ligand and X = 0–2. H 2 O molecules are usually coordinated to tin atoms and are involved in two significant O─H─N hydrogen bonds, wherein the nitrogen atoms belong either to the bidentate ligand or the M-coordinated cyanide ligands. The structures of these supramolecular coordination polymers were investigated by elemental analysis, X-ray powder diffraction, and IR, mass, and NMR spectra.

Fe(bpym)(CN)4]-: A New Building Block for Designing Single-Chain Magnets

We herein present the preparation, crystal structure, magnetic properties, and theoretical study of new heterobimetallic chains of formula {[Fe(III)(bpym)(CN4)]2M(II)(H2O)2}.6H2O [bpym = 2,2'-bipyrimidine; M = Zn (2), Co (3), Cu (4), and Mn (5)] which are obtained by using the building block PPh4[Fe(bpym)(CN)4].H2O (1) (PPh4+= tetraphenylphosphonium) as a ligand toward the fully solvated MII ions. The structure of complex 1 contains mononuclear [Fe(bpym)(CN)4]- anions. Compounds 2-5 are isostructural 4,2-ribbonlike bimetallic chains where the [Fe(bpym)(CN)4]- unit acts as a bis-monodenate ligand through two of its four cyanide ligands toward the M atom. Water hexamer clusters (4) and regular alternating fused six- and four-membered water rings with two dangling water molecules (2, 3, and 5) are trapped between the cyanide-bridged 4,2-ribbonlike chains. 1 and 2 behave as magnetically isolated low-spin iron(III) centers. 3 behaves as a single-chain magnet (SCM) with intrachain ferromagnetic coupling, slow magnetic relaxation, hysteresis effects, and frequency-dependent ac signals at T < 7 K). As expected for a thermally activated process, the nucleation field (Hn) in 3 increases with decreasing T and increasing v. Below 1.0 K, Hn becomes temperature independent but remains strongly sweep rate dependent. In this temperature range, the reversal of the magnetization may be induced by a quantum nucleation of a domain wall that then propagates due to the applied field. 4 and 5 are ferro- and ferrimagnetic chains respectively, with metamagnetic-like behavior (4). DFT-type calculations and QMC methodology provided a good understanding of the magnetic properties of 3-5.

Bis(N-ethylethylenediamine-κ2 N,N′)copper(II)–hexacyanocobaltate(III)–water (3/2/4): a two-dimensional ladder structure of a bimetallic assembly

The title compound, poly[[tetracyano-octa-μ-cyano-hexakis(N-ethylethylenediamine)tricopper(II)dicobaltate(III)] tetrahydrate], [Cu(C4H12N2)2]3[Co(CN)6]2·4H2O or {[Cu3Co2(CN)12(C4H12N2)6]·4H2O} n , was crystallized from an aqueous reaction mixture containing Cu(ClO4)2, N-ethylethylenediamine and K3[Co(CN)6] in a self-assembling process. The polymeric chains are extended through –CoIII–CN–CuII– linkages involving four or two cyanide ligands of the centrosymmetric [Co(CN)6]3− complex ions, forming a two-dimensional ladder structure. The CuII atoms, one of which also lies on an inversion centre, have a distorted octahedral coordination geometry, the degree of tetragonal Jahn–Teller distortion being T = 0.785 and 0.810 (T is the ratio of mean in-plane Cu—N bond lengths to axial Cu—N bond lengths). This local Jahn–Teller distortion results from the anisotropic features of this two-dimensional cyano-bridged structure.

Formation of pyridine from acetylenes and nitriles catalyzed by RuCpCl, CoCp, and RhCp derivatives – A computational mechanistic study

The mechanism of the catalytic formation of pyridines from the coupling of two alkynes and the nitriles N CR (R = H, Me, Cl, COOMe) with the fragments CpRuCl, CpCo, and CpRh has been investigated by means of DFT/B3LYP calculations. According to the proposed mechanism, the key reaction step is the oxidative coupling of two alkyne ligands to give metallacyclopentatriene (Ru, Rh) and metallacyclopentadiene (Co) intermediates. In the case of ruthenium, this process is thermodynamically clearly favored over the oxidative coupling between one alkyne and one nitrile ligand to afford an azametallacycle. This alternative pathway however cannot be dismissed in the case of Co and Rh. The rate determining step of the overall catalytic cycle is the addition of a nitrile molecule to the metallacyclopentatriene and metallacyclopentadiene intermediates, respectively, which has to take place in a side-on fashion. Competitive alkyne addition leads to benzene formation. Thus, also the chemoselectivity of this reaction is determined at this stage of the catalytic cycle. In the case of the RuCpCl fragment, the addition of nitriles R–C N and acetylenes RC CH has been studied in more detail. For R = H, Cl, and COOMe the side-on addition of nitriles is kinetically more favored than alkyne addition and, in accordance with experimental results, pyridine formation takes place. In the case of R = Me nitrile addition could not be achieved and the addition of alkynes to give benzene derivatives seems to be kinetically more favored. Once the nitrile is coordinated facile C–C bond coupling takes place to afford an unusual five- and four-membered bicyclic ring system. This intermediate eventually rearranges to a very unsymmetrical azametallaheptatriene complex which in turn provides CpRuCl(κ 1-pyridine) via a reductive elimination step. Completion of the catalytic cycle is achieved by an exergonic displacement of the respective pyridine product by two acetylene molecules regenerating the bisacetylene complex.

Characterization of the Spontaneous “Aging” of the Heme Oxygenase from the Pathological BacteriumNeisseria meningitidisvia Cleavage of the C-Terminus in Contact with the Substrate. Implications for Functional Studies and the Crystal Structure

Solution 1H NMR spectroscopy and mass spectrometry are utilized to characterize the irreversible "aging" of native heme oxygenase from N. meningitidis, NmHO. 2D NMR characterization of the cyanide-inhibited substrate complex shows that the C-terminal interaction between Arg208His209 and the exposed pyrrole of the protohemin substrate in the "native" NmHO complex is lost in the "aging". Mass spectrometry and N-terminal sequencing of wild type and "aged" NmHO reveal that the "aging" process involves cleavage of the Arg208His209 dipeptide. The construction of the double deletion mutant without Arg208His209 and its NMR comparison as both the resting state substrate complex and its cyanide-inhibited complex with the "aged" NmHO reveal that cleavage of the C-terminal dipeptide is the only modification during the aging. Comparison of cyanide ligand binding constants reveal a factor approximately 1.7 greater CN- affinity in the native than "aged" NmHO. The rate of protohemin degradation and its stereoselectivity are unaffected by the C-terminal truncation. However, the free alpha-biliverdin yield in the presence of desferrioxamine is significantly increased in the "aged" NmHO and its deletion mutant relative to WT, arguing for a role of the NmHO C-terminus in modulating product release. The facile cleavage of Arg208His209 in the resting state complex, with a half-life of approximately 24 h at 25 degrees C, suggests that previous characterization of NmHO may have been carried out on a mixture of native and "aged" NmHO, and may account for the "lost" C-terminal residues in the crystal structures.

Diruthenium Dithiolato Cyanides: Basic Reactivity Studies and a Post Hoc Examination of Nature's Choice of Fe versus Ru for Hydrogenogenesis

The reaction of Ru2(S2C3H6)(CO)6 (1) with 2 equiv of Et4NCN yielded (Et4N)2[Ru2(S2C3H6)(CN)2(CO)4], (Et4N)2[3], which was shown crystallographically to consist of a face-sharing bioctahedron with the cyanide ligands in the axial positions, trans to the Ru-Ru bond. Competition experiments showed that 1 underwent cyanation >100x more rapidly than the analogous Fe2(S2C3H6)(CO)6. Furthermore, Ru2(S2C3H6)(CO)6 underwent dicyanation faster than [Ru2(S2C3H6)(CN)(CO)5]-, implicating a highly electrophilic intermediate [Ru2(S2C3H6)(mu-CO)(CN)(CO)5]-. Ru2(S2C3H6)(CO)6 (1) is noticeably more basic than the diiron compound, as demonstrated by the generation of [Ru2(S2C3H6)(mu-H)(CO)6]+, [1H]+. In contrast to 1, the complex [1H]+ is unstable in MeCN solution and converts to [Ru2(S2C3H6)(mu-H)(CO)5(MeCN)]+. (Et4N)2[3] was shown to protonate with HOAc (pKa = 22.3, MeCN) and, slowly, with MeOH and H2O. Dicyanide [3]2- is stable toward excess acid, unlike the diiron complex; it slowly forms the coordination polymer [Ru2(S2C3H6)(mu-H)(CN)(CNH)(CO)4]n, which can be deprotonated with Et3N to regenerate [H3]-. Electrochemical experiments demonstrate that [3H]- catalyzes proton reduction at -1.8 V vs Ag/AgCl. In contrast to [3]2-, the CO ligands in [3H]- undergo displacement. For example, PMe3 and [3H]- react to produce [Ru2(S2C3H6)(mu-H)(CN)2(CO)3(PMe3)]-. Oxidation of (Et4N)2[3] with 1 equiv of Cp2Fe+ gave a mixture of [Ru2(S2C3H6)(mu-CO)(CN)3(CO)3]- and [Ru2(S2C3H6)(CN)(CO)5]-, via a proposed [Ru2]2(mu-CN) intermediate. Overall, the ruthenium analogues of the diiron dithiolates exhibit reactivity highly reminiscent of the diiron species, but the products are more robust and the catalytic properties appear to be less promising.

Photoinduced synthesis and electrochemical properties of new ruthenium(mono)bipyridine dialkylcyanamide and propiononitrile complexes

Photochemical exchange of carbonyls was used to produce new ruthenium dialkylcyanamide and nitrile compounds [RuCl 2(bpy)(CO)(NCNMe 2)] ( 2), [RuCl 2(bpy)(CO)(NCNEt 2)] ( 3), and [RuCl 2(bpy)(CO)(NCEt)] ( 4) from trans(Cl)-[RuCl 2(bpy)(CO) 2] ( 1). The reaction energetics, steric effects and electronic effects induced by the dialkylcyanamide and nitrile ligands were studied using computational DFT methods and cyclic voltammetry. In all cases the photochemical exchange reaction favors rearrangement of the ligands and formation of the trans(Cl,L)-[RuCl 2(bpy)(CO)L] (L = NCNMe 2, NCNEt 2 or NCEt) isomer as the main products. The oxidation potential of the complexes decreases with the increase of the HOMO energy and of net electron-donor character of the ligands, the dialkylcyanamides (whose electrochemical Lever E L ligand parameter has been estimated) behaving as stronger net electron donors than propiononitrile or CO. The electronic effect of the dialkylcyanamide and nitrile ligands is also reflected into the HOMO–LUMO energy difference, which is slightly reduced compared to the original dicarbonyl compound 1. The computational results show that the geometry of the isomer plays also an important role in the determination of orbital energies.

Structures, magnetic properties, and XPS of cyanide-bridged Nd III/Sm III/Gd III–Cr III complexes

Synthesis, structural characterization, and spectroscopic and magnetic properties of three new cyano-bridged 3d–4f bimetallic complexes, Ln III(DMF) 4(H 2O) 3Cr III (CN) 6 · nH 2O (Ln = Nd, Sm, Gd), have been described. The Nd–Cr complex crystallizes in the monoclinic P2 1/ n space group with the following unit cell parameters: a = 20.063(7) Å, b = 8.967(4) Å, c = 18.023(6) Å, b = 96.12(3)°, V = 3224(2) Å 3, and Z = 4. The neodymium (III) ion, which adopts anti-prism eight-coordination environment, is linked to the [Cr III(CN) 6] 3− moiety through a bridging cyanide ligand with Nd–N = 2.550(4) Å and Nd–N–C = 164.4(4)°. The variable-temperature (0.5 T at 2–300 K) and variable-field (0–5 T at 2 and 5 K) magnetic measurements reveal that the weak interaction of Gd–Cr complexes differs from that of Nd–Cr and Sm–Cr ones mainly because of the lack of orbital angular momentum. The XPS and diffuse reflectance electronic spectra were also measured to discuss charge transfer transitions concerning π-backdonation from the viewpoint of magneto-optical functions.

An improved purification procedure for the soluble [NiFe]-hydrogenase of Ralstonia eutropha: new insights into its (in)stability and spectroscopic properties

Infrared (IR) spectra in combination with chemical analyses have recently shown that the active Ni-Fe site of the soluble NAD(+)-reducing [NiFe]-hydrogenase from Ralstonia eutropha contains four cyanide groups and one carbon monoxide as ligands. Experiments presented here confirm this result, but show that a variable percentage of enzyme molecules loses one or two of the cyanide ligands from the active site during routine purification. For this reason the redox conditions during the purification have been optimized yielding hexameric enzyme preparations (HoxFUYHI(2)) with aerobic specific H(2)-NAD(+) activities of 150-185 mumol/min/mg of protein (up to 200% of the highest activity previously reported in the literature). The preparations were highly homogeneous in terms of the active site composition and showed superior IR spectra. IR spectro-electrochemical studies were consistent with the hypothesis that only reoxidation of the reduced enzyme with dioxygen leads to the inactive state, where it is believed that a peroxide group is bound to nickel. Electron paramagnetic resonance experiments showed that the radical signal from the NADH-reduced enzyme derives from the semiquinone form of the flavin (FMN-a) in the hydrogenase module (HoxYH dimer), but not of the flavin (FMN-b) in the NADH-dehydrogenase module (HoxFU dimer). It is further demonstrated that the hexameric enzyme remains active in the presence of NADPH and air, whereas NADH and air lead to rapid destruction of enzyme activity. It is proposed that the presence of NADPH in cells keeps the enzyme in the active state.

Trans-Dichlorobis(piperidine-1-carbonitrile)platinum(II)

In the title centrosymmetric complex, trans-[PtCl2(C6H10N2)2], the PtII centre is coordinated by two piperidine-1-carbonitrile ligands and two chloro ligands, resulting in a typical square-planar geometry. The C—N distance between the nitrile and piperidine group [1.306 (4) Å] clearly indicates that this bond is not a pure single bond, being closer to a C=N double bond. This points to a noticeable contribution of the bipolar structure [Pt]—N−=C=N+R2 in the resonance hybrid of the push–pull nitrile ligand.

New members of the [Ru(diimine)(CN)4]2−family: structural, electrochemical and photophysical properties

A series of complexes of the type K(2)[Ru(NN)(CN)(4)] has been prepared, in which NN is a diimine ligand, and were investigated for both their structural and photophysical properties. The ligands used (and the abbreviations for the resulting complexes) are 3-(2-pyridyl)pyrazole (Ru-pypz), 2,2'-bipyrimidine (Ru-bpym), 5,5'-dimethyl-2,2'-bipyridine (Ru-dmb), 1-ethyl-2-(2-pyridyl)benzimidazole (Ru-pbe), bidentate 2,2':6',2'''-terpyridine (Ru-tpy). The known complexes with = 2,2'-bipyridine (Ru-bpy) and 1,10-phenathroline (Ru-phen) were also included in this work. A series of crystallographic studies showed that the [Ru(NN)(CN)(4)](2-) complex anions form a range of elaborate coordination networks when crystallised with either K(+) or Ln(3+) cations. The K(+) salts are characterised by a combination of near-linear Ru-CN-K bridges, with the cyanides coordinating to K(+) in the usual 'end-on' mode, and unusual side-on pi-type coordination of cyanide ligands to K(+) ions. With Ln(3+) cations in contrast only Ru-CN-Ln near-linear bridges occurred, affording 1-dimensional helical or diamondoid chains, and 2-dimensional sheets constituted from linked metallamacrocyclic rings. All of the K(2)[Ru(CN)(4)] complexes show a reversible Ru(II)/Ru(III) couple (ca.+0.9 V vs. Ag/AgCl in water), the exception being Ru-tpy whose oxidation is completely irreversible. Luminescence studies in water showed the presence of (3)MLCT-based emission in all cases apart from Ru-bpym with lifetimes of tens/hundreds of nanoseconds. Time-resolved infrared studies showed that in the (3)MLCT excited state the principal C-N stretching vibration shifts to positive energy by ca. 50 cm(-1) as a consequence of the transient oxidation of the metal centre to Ru(III) and the reduction in back-bonding to the cyanide ligands; measurement of transient decay rates allowed measurements of (3)MLCT lifetimes for those complexes which could not be characterised by luminescence spectroscopy. A few complexes were also examined in different solvents (MeCN, dmf) and showed much weaker emission and shorter excited-state lifetimes in these solvents compared to water.

Influence of the metal size in the structure of the complexes derived from a pentadentate [N3O2] hydrazone

The influence of the metal size in the nuclearity of the complexes derived from the hydrazone ligand 2,6-bis(1-salicyloylhydrazonoethyl)pyridine [H(4)daps] has been investigated. We have synthesised a series of new complexes [M(H(x)daps)] x yH(2)O, (x = 2,3; y = 0-3) with M = Ag (1), Cd (2), Al (3), Sn (4) and Pb (6), using an electrochemical procedure. The crystal and molecular structures have been determined for the mononuclear complexes [Sn(H(2)daps)(H(2)O)(2)] x 4H(2)O (5) and [Pb(H(2)daps)(CN)][Et(4)N] (7). Complex is the first neutral Sn(II) complex derived from a pentadentate hydrazone Schiff base ligand. Complex shows the lead coordinated to the hydrazone donor set and a cyanide ligand, being the first reported complex with the lead atom coordinated to a monodentate cyanide group. Additionally, we have synthesised the lead complex using chemical conditions, in the presence of sodium cyanide which allowed us to isolate the neutral complex [Pb(H(2)daps)] (8). Evaporation of these mother liquors led the novel compound [Pb(Hdaphs)(CH(3)COO)] (9). Complex 9 shows the initial ligand hydrolysed in one of the imine bonds giving rise to a new tetradentate ligand [H(2)daphs] coordinated to the lead atom and a bidentate acetate group. Moreover, the solution behaviour of the complexes has been investigated by (1)H, (113)Cd, (117)Sn and (207)Pb NMR techniques. In particular multinuclear NMR has provided new useful data to correlate factors such as oxidation state, coordination number and nature of the kernel donor atoms due to the new coordination found in complexes 5 and 7. The comparative study of the structures of the complexes derived from this pentadentate [N(3)O(2)] hydrazone ligand let us to conclude that the metal size is a key factor to control the nuclearity of the complexes derived from the ligand [H(4)daps].