Styrene polymerization using nickel(II) complexes as catalysts

Styrene polymerization is investigated with neutral and cationic Ni(II) complexes, i.e. Ni(bipy)Me₂, 1, Ni(bipy)Br₂, 2, Ni(phen)Br₂, 3, or Ni(Me₂phen)Br₂, 4, Ni(acac)₂, 5, (bipy = 2,2′-bipyridine, phen = phenanthroline, Me₂phen = 2,9-dimethyl-1,10-phenanthroline, acac = acetylacetonate), activated by [NHMe₂Ph][B(C₆F₅)₄] or B(C₆F₅)₃ as cocatalysts, in the presence of AlMe₃. The influence on the polystyrene features and the reaction kinetics of the nickel complex and boron activator, the Al/Ni or B/Ni molar ratios as well as the monomer concentration are studied. Catalytic systems derived from 2, 3 or 5 and [NHMe₂Ph][B(C₆F₅)₄] at a Ni:B:Al ratio of 1:1:5 are the most efficient at room temperature.     

Two bis-[1-(aryliminomethyleny)-2-oxy-naphthalen] nickel catalysts for the polymerization of methyl methacrylate

Two bis-(1-arylliminomethylenyl-2-oxy-naphthalen) nickel complexes (aryl = 2-methylphenyl, complex 1; aryl = 2,6-diisoproylphenyl, complex 2) were reacted with alkylaluminium in presence of equimolar PPh₃ and tested as catalysts in methyl methacrylate (MMA) polymerization. The two nickel catalysts can initiate polymerization of MMA with good to high activity, the highest activity reaching 1.1 × 10⁵ g PMMA/(mol Ni · h) by less bulky complex 1 at 0.8 mol/L of MMA, 400 of Al/Ni ratio and 0 °C. In addition, the structures of nickel complexes and polymerization conditions, such as monomer concentration, polymerization temperature and Al/Ni molar ratio on catalytic activity of polymerization have great influences on catalytic activity and product properties.     

Zirconium complexes with versatile β-diketiminate ligands: Synthesis, structure, and ethylene polymerization

A series of zirconium complexes (2c, 2d, 2f, 2g, 2h, 2i) containing symmetrical or unsymmetrical β-diketiminate ligands were synthesized by the reaction of ZrCl₄ · 2THF with lithium salt of the corresponding ligand in 1:2 molar ratio. X-ray crystal structures reveal that complexes 2d and 2g adopt distorted octahedral geometry around the zirconium center. These complexes showed moderate activities for ethylene polymerization, when methylaluminoxane (MAO) was used as cocatalyst. The steric and electronic effects of the substituents at the phenyl rings had considerable influence on the catalytic activities of the metal complex, as well as the molecular weights and molecular weight distributions (MWD) of produced polymers. Introduction of electron-withdrawing CF₃ group to phenyls in the ligand led to a significant increase of catalytic activities, and complex 2f (p-CF₃) exhibited the highest catalytic activity of 7.45 × 10⁵ g PE/mol-Zr · h among the investigated complexes. Complexes 2a-d could produce ultra-high molecular weight polyethylenes (UHMWPE) that were hardly dissolvable in decahydronaphthalene or 1,2-dichlorobenzene under the molecular weight measurement conditions. Nevertheless, polyethylenes with broad MWD could be afforded by complexes 2g-i, which was probably due to the introduction of bulky unsymmetrical ligands leading to the formation of multi active species under polymerization conditions. High-temperature ¹³C NMR data indicate the linear structure of obtained polyethylenes.     

Manganese complexes as models for manganese-containing pseudocatalase enzymes: Synthesis,structural and catalytic activity studies

Manganese complexes of the type [TpMn(X)] and [TpMn(μ-N₃)(μ-X)MnTp] (X = acetylacetonate, acac; picolinate, pic and Tp = Tp^Ph,Me for acac, Tp = Tp^ipr2 for pic complexes) having Tp^Ph,Me (hydrotris(3-phenyl,5-methyl-pyrazol-1-yl)borate)/Tp^ipr2 (hydrotris(3,5-diisopropyl-pyrazol-1-yl)borate) as a supporting ligand have been synthesized and structurally characterized. IR and X-ray structures suggest that complexes 7 and 9 are binuclear with azido and bidentate ligands (acac/pic) bridging, whereas complexes 6 and 8 are mononuclear with a 5-coordinated metal center. In complex 9 the picolinate is coordinated as tridentate in a η₃-fashion, but in complex 7 acac behaves as bidentate, whereas azide is coordinated in a bridging bidentate μ-1,3-manner in both 7 and 9. Since the coordination geometry of the manganese ions in complex 9 is very similar to the active site structure of manganese-containing pseudocatalase, we have tested the catalytic activity of the same towards the disproportionation of hydrogen peroxide. The catalytic results indicated that complex 9 has reasonably good catalase activity and may be suitable, structurally as well as functionally, as a model for the pseudocatalase enzyme.     

2-Oxazoline/benzoxazole-1,10-phenanthrolinylmetal (iron, cobalt or nickel) dichloride: Synthesis, characterization and their catalytic reactivity for the ethylene oligomerization

Series of 2-benzoxazole-1,10-phenanthrolines (L1-L4) and 2-oxazoline-1,10-phenanthrolines (L5-L8) were synthesized and used as tridentate N^N^N ligands in coordinating with metal (nickel, cobalt or iron) chlorides. Their metal complexes, nickel(II) (Ni1-Ni8), cobalt(II) (Co1-Co8) and iron(II) (Fe1-Fe8), were characterized by elemental and IR spectroscopic analyses. The molecular structures of the ligand L2 and the complexes Ni3, Co1, Co3 and Fe2 have been determined by the single-crystal crystallography. The nickel complex Ni3 and iron complex Fe2 display an octahedral geometry, whereas cobalt complex Co1 is with a distorted bipyramidal geometry and Co3 as square pyramidal geometry. At 10 atm ethylene, all the complexes showed good activities in ethylene dimerization upon activation with appropriate aluminum cocatalysts; the nickel complexes gave the activity up to 3.11 × 10⁶ g mol⁻¹(Ni) h⁻¹ upon activation with diethylaluminum chloride (Et₂AlCl), meanwhile the cobalt and iron complexes showed activities up to 1.51 × 10⁶ g mol⁻¹(Co) h⁻¹ and 1.89 × 10⁶ g mol⁻¹(Fe) h⁻¹, individually, upon activation with modified methylaluminoxane (MMAO).     

Nickel (II) complexes with β-enaminoketonato chelate ligands: Synthesis, solid-structure characterization and reactivity toward the addition polymerization of norbornene

Based on two β-enaminoketonato ligands [ArNC(CH₃)C(H)C(CF₃)OH] (L₁, Ar = 2,6-Me₂C₆H₃; L₂, Ar = 2,6-i-Pr₂C₆H₃), their mono(β-enaminoketonato)nickel (II) complexes [(ArNC(CH₃)C(H)C(CF₃)O)Ni(Ph)(PPh₃)] (1, Ar = 2,6-Me₂C₆H₃; 3, Ar = 2,6-i-Pr₂C₆H₃) and bis(β-enaminoketonato)nickel (II) complexes [(ArNC(CH₃)C(H)C(CF₃)O)₂Ni] (2, Ar = 2,6-Me₂C₆H₃; 4, Ar = 2,6-i-Pr₂C₆H₃) have been synthesized and characterized. The molecular structures of complex 1, 2 and 4 have been confirmed by single-crystal X-ray analyses. After being activated with methylaluminoxane (MAO) these catalytic precursors 1-4 could polymerize norbornene to afford addition-type polynorbornene (PNB). Interestingly, catalytic activities and PNB productivity were greatly enhanced due to the introduction of strong electron-withdrawing group - trifluoro methyl into the ligands. Catalytic activities, polymer yield, M_w and M_w/M_n of PNB have been investigated under various reaction conditions.     

Novel octahedral nickel(II) dithiocarbamates with bi- or tetradentate N-donor ligands: X-ray structures of [Ni(Bzppzdtc)(phen)2]ClO4 · CHCl3 and [Ni(Bz2dtc)2(cyclam)]

A series of novel octahedral nickel(II) dithiocarbamate complexes involving bidentate nitrogen-donor ligands (phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine) or a tetradentate ligand (cyclam = 1,4,8,11-tetraazacycloteradecane) of the composition [Ni(BzMetdtc)(phen)₂]ClO₄ (1), [Ni(Pe₂dtc)(phen)₂]ClO₄ (2), [Ni(Bzppzdtc)(phen)₂]ClO₄ · CHCl₃ (3), [Ni(Bzppzdtc)(phen)₂](SCN) (4), [Ni(BzMetdtc)(bpy)₂]ClO₄ · 2H₂O (5), [Ni(Pe₂dtc)(cyclam)]ClO₄ (6), [Ni(BzMetdtc)₂(cyclam)] (7), [Ni(Bz₂dtc)₂(cyclam)] (8) and [Ni(Bz₂dtc)₂(phen)] (9) (BzMetdtc = N,N-benzyl-methyldithiocarbamate(1-) anion, Pe₂dtc = N,N-dipentyldithiocarbamate(1-) anion, Bz₂dtc = N,N-dibenzyldithiocarbamate(1-) anion, Bzppzdtc = 4-benzylpiperazinedithiocarbamate(1-) anion), have been synthesized. Spectroscopic (electronic and infrared), magnetic moment and molar conductivity data, and thermal behaviour of the complexes are discussed. Single crystal X-ray analysis of 3 and 8 confirmed a distorted octahedral arrangement in the vicinity of the nickel atom with a N₄S₂ donor set. They represent the first X-ray structures of such type complexes. The catalytic influence of complexes 2, 3, 6, and 7 on graphite oxidation was studied and discussed.     

Nickel(II) complexes bearing phosphinooxazoline ligands: Synthesis, structures and their ethylene oligomerization behaviors

A series of Ni(II) complexes 4a-f ligated by the unsymmetrical phosphino-oxazolines (PHOX) were synthesized and characterized by elemental analysis and IR spectroscopy, and the structures of complexes 4c-4e were confirmed by the X-ray crystallographic analysis. All derivatives showed distorted tetrahedron geometry by the nickel center and coordinative atoms. Upon activation with methylaluminoxane (MAO) or Et₂AlCl, these complexes exhibited considerable to high activity of ethylene oligomerization. The ligands environments and reaction conditions significantly affect their catalytic activities, while the highest oligomerization activity (up to 1.18 × 10⁶ g · mol⁻¹(Ni) · h⁻¹) was observed for 4d at 20 atm of ethylene. Incorporation of 2-4 equivalents of PPh₃ as auxiliary ligands in the 4a-f/MAO catalytic systems led to higher activity and longer catalytic lifetime.     

Nickel (II) complexes bearing 2-ethylcarboxylate-6-iminopyridyl ligands: synthesis, structures and their catalytic behavior for ethylene oligomerization and polymerization

A series of nickel (II) complexes (L)NiCl₂ (7-9) and (L)NiBr₂ (10-12) were prepared by the reactions of the corresponding 2-carboxylate-6-iminopyridine ligands 1-6 with NiCl₂ · 6H₂O or (DME)NiBr₂ (DME = 1,2-dimethoxyethane), respectively. All the complexes were characterized by IR spectroscopy and elemental analysis. Solid-state structures of 7, 8, 10, 11 and 12 were determined by X-ray diffraction. In the cases of 7, 8 and 10, the ligands chelate with the nickel centers in tridentate fashion in which the carbonyl oxygen atoms coordinate with the metal centers, while the carbonyl oxygen atoms are free from coordinating with the nickel centers in 11 and 12. Upon activation with methylaluminoxane (MAO), these complexes are active for ethylene oligomerization (up to 7.97 × 10⁵ g mol⁻¹ (Ni) h⁻¹ for 11 with 2 equivalents of PPh₃ as auxiliary ligand) and/or polymerization (1.37 × 10⁴ g mol⁻¹ (Ni) h⁻¹ for 9). The ethylene oligomerization activities of 7-12 were significantly improved in the presence of PPh₃ as auxiliary ligands. The effects of the coordination environment and reaction conditions on the ethylene catalytic behaviors have been discussed.     

Synthesis, characterization and ethylene oligomerization studies of nickel complexes bearing 2-imino-1,10-phenanthrolines

A series of nickel (II) complexes ligated by 2-imino-1,10-phenanthrolines were synthesized and characterized by elemental and spectroscopic analysis as well as by single-crystal X-ray crystallography. X-ray crystallographic analysis reveals complexes 3, 5, 7 and 11 as the five-coordinated distorted trigonal-bipyramidal geometry. Upon activation with Et₂AlCl, these complexes exhibited considerably high activity for ethylene oligomerization (up to 3.76 × 10⁷ g mol⁻¹(Ni) h⁻¹ for 12 with 10 equiv. of PPh₃). The ligand environment and reaction conditions significantly affect the catalytic activity of their nickel complexes.     

Oxovanadium(IV) and (V) complexes of acetylpyridine-derived semicarbazones exhibit insulin-like activity

Reaction of 2-acetylpyridine semicarbazone (H2APS), 3-acetylpyridine semicarbazone (H3APS) and 4-acetylpyridine semicarbazone (H4APS) with [VO(acac)₂] (acac = acetylacetonate) gave [VO(H2APS)(acac)₂] (1), [VO(H3APS)(acac)₂] (2) and [VO(4APS)(acac)(H₂O)] · 1/2H₂O (3). Oxidation of complex 1 in acetonitrile gave [VO₂(2APS)] (4). The crystal structures of complexes 1 and 4 have been determined. Complexes 1–3 were able to enhance glucose uptake and to inhibit glycerol release from adipocytes, which indicate their potential to act as insulin-mimics.     

Synthesis and characterization of N-(2-pyridyl)benzamide-based nickel complexes and their activity for ethylene oligomerization

A series of N-(2-pyridyl)benzamides (1)-(11) and their nickel complexes, [N-(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide (12)-(16) and (aryl)[N-(2-pyridyl)benzamido](triphenylphosphine)nickel(II) (17)-(24), were synthesized and characterized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17, 19 and 23 is each has a six-membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12-16/MAO systems is up to 3.3 × 10⁴ g mol⁻¹ h⁻¹ whereas for 17-24/MAO systems it is up to 4.94 × 10⁵ g mol⁻¹ atm⁻¹ h⁻¹. The influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh₃/Ni molar ratio on catalytic activity was investigated.     

Rhodium(I) complexes with 1′-(diphenylphosphino)ferrocenecarboxylic acid as active and recyclable catalysts for 1-hexene hydroformylation

The rhodium complex trans-[Rh(CO)(Hdpf-κP)(dpf-κ²O,P)] (1), (Hdpf = 1′-(diphenylphosphino)ferrocenecarboxylic acid) was used as an efficient and recyclable catalyst for 1-hexene hydroformylation producing ca. 80% of aldehydes at 10 atm CO/H₂ and 80 °C. After the reaction, unchanged complex 1 was separated from the reaction mixture and used again three times with the same catalytic activity. The effect of modifying ligands, phosphines and phosphites, on the reactivity of 1 was investigated. The active catalytic systems containing 1 or trans-[Rh(CO)(L)(dpf-κ²O,P)] (2) were formed in situ from acetylacetonato rhodium(I) precursors [Rh(CO)₂(acac)] (3) or [RhL(CO)(acac)] (4) and Hdpf or Medpf (L = phosphine, Medpf = methyl ester of Hdpf).     

β-Diketiminate complexes of Group 4: active complexes for the isomerization of α-olefins and the polymerization of propylene towards elastomeric polypropylene

The β-diketiminate lithium ligand [{N(SiMe₃)C(Ph)}₂CH][Li] reacted with Group 4 metal salts (Ti and Zr) to yield the complexes [{N(SiMe₃)C(Ph)}₂CH]₂TiCl₂ (5) and [{N(SiMe₃)C(Ph)}₂CH][N(SiMe₃)C(Ph)NC(Ph)CH(SiMe₃)]ZrCl₂ (6). The crystal structure of 6 shows that one of the two ketamidinate ligands undergoes an isomerization to the corresponding substituted benzamidinate. A mechanism for the catalyzed isomerization of the β-diketiminate ligand is presented. Complex 5 was found to be active in the polymerization of propylene, producing remarkably high-molecular weight (>100,000 g mol⁻¹) elastomeric polymer, whereas the zirconium complex was found inactive. Complex 5, and surprisingly complex 6, were found to be active catalysts, in the presence of MAO (methylalumoxane), for the isomerization of aliphatic olefins (1-octene, allylbenzene). Each complex catalyzed the olefins by different mechanisms. Kinetic studies for the isomerization of allylbenzene by complex 5 show that the reaction rate follows a first order in both catalyst and olefin concentrations with ΔH^‡=14.7(4) kcal mol⁻¹ and ΔS^‡=−33(1) e.u. These findings support the epimerization mechanism of the last inserted monomer that is proposed for as the primary cause for the elastomeric properties of polypropylene produced by this complex. In addition, we show how complementary isomerization studies of α-olefins shed light on the polymerization mechanism.     

Novel nickel(II) and copper(II) complexes with phenoxy-imidazole ligands: Syntheses, crystal structures and norbornene addition polymerization

The novel nickel(II) (1) and copper(II) (2) complexes bearing 2′-(4′,6′-di-tert-butylhydroxy-phenyl)-1,4,5-triphenyl imidazole ligand have been synthesized and characterized. The molecular structure analyses of complexes 1 and 2 indicated that Ni(II) centre in 1 adopts a distorted tetrahedral coordination geometry with a dihedral angle of 85.2° between Ni(1)O(1)N(1) plane and Ni(1)O(1A)N(1A) plane, while the Cu(II) centre in 2 represents a distorted square planar coordination geometry with a cis-N₂O₂ arrangement of the donor atoms, the dihedral angle being 32° between Cu(1)O(1)N(1) plane and Cu(1)O(1A)N(1A) plane. After activation with methylaluminoxane (MAO), both Ni(II) and Cu(II) complexes can be used as catalysts for the addition polymerization of norbornene (NB). The polynorbornenes (PNBs) are produced with very high polymerization activity (10⁸ g PNB mol⁻¹ Ni h⁻¹) for Ni(II) complex and moderate catalytic activity (10⁵ g PNB mol⁻¹ Cu h⁻¹) for Cu(II) complex, respectively. The high molecular weight polynorbornenes (10⁶) are obtained for complexes 1 and 2. Moreover, the distinct effects of polymerization temperature and Al/M ratio on catalytic activities and molecular weights of polymers are discussed.     

Effect of the β-diketonate ligand on the spin states of [Ni(β-dkt)2(NH2-quin)] complexes

Three new complexes [Ni(β-dkt)₂(NH₂-quin)] {β-dkt = 2,2,6,6-tetramethylheptane-3,3-dionate (tmhd) 1, hexafluoroacetylacetonate (hfac) 2, 1,3-diphenylpropanedionate (dbm) 3} have been prepared by reacting [Ni(β-dkt)₂(H₂O)₂] with 8-aminoquinoline (NH₂-quin). [Ni(tmhd)₂(NH₂-quin)] is found to be solvatochromic exhibiting a square planar geometry in CH₂Cl₂, acetone, and acetonitrile with the tmhd ligand acting unusually as a counteranion while in THF and DMSO the complex is octahedral. In contrast, 2 and 3 are octahedral in all solvents. Single crystal X-ray diffraction studies reveal octahedral nickel centres with a cis arrangement of the β-diketonates. The molecular packing consists of hydrogen bonded dimers which in the case of 2 and 3 are connected to one another via π···π and C-H?π interactions, respectively. Cyclic voltammetry shows 1 and 3 oxidise irreversibly at 0.46 and 1.17 V, respectively.     

Coordination compounds of N,N′-olefin functionalized imidazolin-2-ylidenes

N-Heterocyclic carbene ligands (NHC) were metalated with Pd(OAc)₂ or [Ni(CH₃CN)₆](BF₄)₂ by in situ deprotonation of imidazolium salts to give the N-olefin functionalized biscarbene complexes [MX₂(NHC)₂] 3-7 (3: M = Pd, X = Br, NHC = 1,3-di(3-butenyl)imidazolin-2-ylidene; 4: M = Pd, X = Br, NHC = 1,3-di(4-pentenyl)imidazolin-2-ylidene; 5: M = Pd, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 6: M = Ni, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 7: M = Ni, X = I, NHC = 1-methyl-3-allylimidazolin-2-ylidene). Molecular structure determinations for 4-7 revealed that square-planar complexes with cis (5) or trans (4, 6, 7) coordination geometry at the metal center had been obtained. Reaction of nickelocene with imidazolium bromides afforded the η⁵-cyclopentadienyl (η⁵-Cp) monocarbene nickel complexes [NiBr(η⁵-Cp)(NHC)] 8 and 9 (8: NHC = 1-methyl-3-allylimidazolin-2-ylidene; 9: NHC = 1,3-diallylimidazolin-2-ylidene). The bromine abstraction in complexes 8 and 9 with silver tetrafluoroborate gave complexes [NiBr(η⁵-Cp)(η³-NHC)] 10 and 11. The X-ray structure analysis of 10 and 11 showed a trigonal-pyramidal coordination geometry at the nickel(II) center and coordination of one N-allyl substituent.     

Vinyl addition polymerization of norbornene catalyzed by β-iminoamine Ni(II) complexes/methylaluminoxane systems

Two nickel(II) complexes (A and B) bearing β-iminoamine ligands, [2-(ArNCH)-C₆H₄-NMe₂] (La, Ar = 2,6-i-Pr₂C₆H₃; Lb, Ar = 2,6-Me₂C₆H₃), were synthesized and characterized by elemental analyses and ¹H NMR. X-ray crystal structure of complex B reveals that the six-membered chelate ring adopts a envelope conformation, with nickel(II) atom deviating from the plane of backbone aromatic ring by 1.164 Å. In the presence of methylaluminoxane (MAO), both complexes showed moderate activities of 10⁵ g mol_Ni⁻¹ h⁻¹ for norbornene polymerization. β-iminoamine Ni(II)/MAO catalysts gave unimodal polymers (M_w, 3.16-8.02 × 10⁵ g/mol) with a relatively narrow MWD (M_w/M_n, 1.59-2.14), indicative of single-site catalyst behavior. The obtained polymers are vinyl-type polynorbornenes (PNBs), which are soluble in common solvents such as toluene, cyclohexane and dichlorobenzene.     

Incorporation of a tripodal ligand with a (N,O,O)-donor set into a new family of nickel and cobalt spin clusters

The reaction of Ni(OAc)₂, NiX₂ (X = Cl, Br) or CoCl₂ with the proligand 2-amino-2-methyl-1,3-propanediol (ampdH₂) affords a new family of tetranuclear complexes. The syntheses of [Ni₄(OAc)₄(ampdH)₄] (1) and [M₄X₄(ampdH)₄] (M = Ni, X = Cl, 2; M = Ni, X = Br, 3; M = Co, X = Cl, 4) are reported, together with the single crystal X-ray structures of 1, 2 and 4 and the magnetochemical characterization of 1, 3 and 4. Each member of this family of complexes displays a low symmetry structure that incorporates a {M₄O₄} core unit based on a distorted cubane. Magnetic measurements reveal ferromagnetic exchange interactions for 1, 3 and 4. These give rise to S = 4 ground state spins for the tetranuclear Ni complexes and an anisotropic effective S′ = 2 ground state for the Co complex.     

Transition metal complexes with thiosemicarbazide-based ligands. Part LIV. Nickel(II) complexes with pyridoxal semi- (PLSC) and thiosemicarbazone (PLTSC). Crystal and molecular structure of [Ni(PLSC)(H2O)3](NO3)2 and [Ni(PLTSC-H)py]NO3

This paper describes the synthesis of the first Ni(II) complexes with pyridoxal semicarbazone (PLSC), viz. Ni(PLSC)Cl₂ · 3.5H₂O (1), [Ni(PLSC)(H₂O)₃](NO₃)₂ (2), Ni(PLSC)(NCS)₂ · 4H₂O (3), [Ni(PLSC-2H)NH₃] · 1.5H₂O (4), as well as two new complexes with pyridoxal thiosemicarbazone (PLTSC), [Ni(PLTSC-H)py]NO₃ (5) and [Ni(PLTSC-H)NCS] (6). Complexes 1–3 are paramagnetic and have most probably an octahedral structure, for complex 2 this was proved by X-ray diffraction analysis. In contrast, complexes 4–6 are diamagnetic and have a square-planar structure, and in the case of complex 5 this was also confirmed by X-ray structural analysis. In all cases the Schiff bases are coordinated as tridentate ligands with an ONX (X = O, PLSC; X = S, PLTSC) set of donor atoms. With the complexes involving the neutral form of PLSC and the monoanionic form of PLTSC, the PL moiety is in the form of a zwitterion. In addition to the above-mentioned techniques, all the complexes were characterized by measuring their molar conductivities, UV–Vis and partial IR spectra.