Vasile Lozan

Structural Study and Solution Integrity of Dioxomolybdenum(VI) Complexes with Tridentate Schiff Base and Azole Ligands

Four new molybdenum complexes (Mo VI O2(L 1 )(Him)) (1), (Mo VI O2(L 1 )(3-MepzH) (2), (Mo VI O2(L 2 )(3-MepzH)) (3), and ((Mo VI O2)2(µ-L 3 )(MeOH)2 )( 4) were synthesized and characterized by IR, NMR, ESI-MS, and single-crystal structure analysis (H2L 1 2-(salicylideneamino)-2-methyl-1-propanol, H2L 2 2-(3- methoxysalicylideneamino)-2-methyl-1-propanol, H4L 3 1,7- bis(salicylidene)dihydrazide malonic acid, Him imidazole and 3- MepzH 3-methylpyrazole). In all four structures the molyb- denum atom has a distorted octahedral coordination with the three meridional donor atoms from the Schiff base di- or tetraanion (L 1,2 ) 2 /(L 3 ) 4 and one oxo group occupying the sites of the equa- torial plane. The other oxo group and the azole or methanol mol- ecule occupy the apical sites. In 1-3 two centrosymmetrically related

Stabilisation of a paramagnetic BH4--bridged dinickel(II) complex by a macrodinucleating hexaaza-dithiophenolate ligand

The first paramagnetic borohydrido-bridged dinuclear nickel(II) complex, [(L)Ni(II)2(mu(1,3)-BH4)]+, stabilised by a sterically demanding hexaaza-dithiophenolate macrocycle, has been obtained by the reaction of [(L)Ni(II)2(micro-ClO4)]+ with N(n)Bu4BH4.

Coordination chemistry of dinucleating P2N2S ligands: preparation and characterization of cationic palladium complexes.

The thioethers (4-tert-butyl-2,6-bis((2-(diphenylphosphino)ethylimino)methyl)phenyl)(tert-butyl)sulfane (tBuL3) and (4-tert-butyl-2,6-bis((2-(diphenylphosphino)ethylamino)methyl)phenyl)(tert-butyl)sulfane (tBuL4) react readily with [Pd(NCMe)2Cl2] to give the dinuclear palladium thiophenolate complexes [(L3)Pd2(Cl)2]+ and [(L4)Pd2(micro-Cl)]2+ (HL3=2,6-bis((2-(diphenylphosphino)ethylimino)methyl)-4-tert-butylbenzenethiol, HL4=2,6-bis((2-(diphenylphosphino)ethylamino)methyl)-4-tert-butylbenzenethiol). The chlorides in could be replaced by neutral (MeCN) and anionic ligands (NCS-, N3-, I-, CN-) to give the dinuclear PdII complexes [(L3)Pd2(NCMe)2]3+, [(L3)Pd2(SCN)2]+, [(L3)Pd2(N3)2]+, [(L3)Pd2(I)2]+, and [(L3)Pd2(CN)2]+. The acetonitrile ligands in are readily hydrated to give the corresponding amidato complex [(L3)Pd2(NHCOMe)]2+. All complexes were isolated as perchlorate salts and studied by infrared, 1H, and 31P NMR spectroscopy. In addition, complexes [ClO4].EtOH, [ClO4]2, [ClO4], [ClO4].EtOH, and [ClO4]2.MeCN.MeOH have been characterized by X-ray crystallography. The dipalladium complex was found to catalyse the vinyl-addition polymerization of norbornene in the presence of MAO (methylalumoxane) and B(C6F5)3/AlEt3.

Preparation and characterization of CrIII, MnII, FeII, CoII and NiII complexes of a hexaazadithiophenolate macrocycle

The ligating properties of the 24-membered macrocyclic dinucleating hexaazadithiophenolate ligand (L(Me))2- towards the transition metal ions Cr(II), Mn(II), Fe(II), Co(II), Ni(II) and Zn(II) have been examined. It is demonstrated that this ligand forms an isostructural series of bioctahedral [(L(Me))M(II)2(OAc)]+ complexes with Mn(II) (2), Fe(II) (3), Co(II) (4), Ni(II) (5) and Zn(II) (6). The reaction of (L(Me))2- with two equivalents of CrCl2 and NaOAc followed by air-oxidation produced the complex [(L(Me))Cr(III)H2(OAc)]2+ (1), which is the first example for a mononuclear complex of (L(Me))2-. Complexes 2-6 contain a central N3M(II)(mu-SR)2(mu-OAc)M(II)N3 core with an exogenous acetate bridge. The Cr(III) ion in is bonded to three N and two S atoms of (L(Me))2- and an O atom of a monodentate acetate coligand. In 2-6 there is a consistent decrease in the deviations of the bond angles from the ideal octahedral values such that the coordination polyhedra in the dinickel complex 5 are more regular than in the dimanganese compound 2. The temperature dependent magnetic susceptibility measurements reveal the magnetic exchange interactions in the [(L(Me))M(II)2(OAc)]+ cations to be relatively weak. Intramolecular antiferromagnetic exchange interactions are present in the Mn(II)2, Fe(II)2 and Co(II)2 complexes where J = -5.1, -10.6 and approximately -2.0 cm(-1) (H = -2JS1S2). In contrast, in the dinickel complex 5 a ferromagnetic exchange interaction is present with J = +6.4 cm(-1). An explanation for this difference is qualitatively discussed in terms of the bonding differences.

Ternary complexes composed of naphthalene diimides and binucleating metallocavitands: preparation, characterisation and structure of [(Ni2L)2(NDI)][BPh4]2

The synthesis and physical properties of the ternary complex 3(2+), prepared by reaction of a naphthalene diimide dicarboxylate 2 with the binucleating dinickel(II) cavitand 1, are discussed. The complex 3(2+) is characterised by cyclic voltammetry which shows a wealth of metal-centred and diimide-based processes at -1.62, -1.04 and 0.15 V vs Fc/Fc+. Absorption and fluorescence spectroscopy of 3(2+) in CH2Cl2 compared to the components 4+ and 5, respectively, are used to characterise the complex further. In particular there is a substantial quenching (approximately 95%) of the diimide fluorescence upon complexation. X-Ray crystallography has been used to characterise complex 3(2+) in the solid state. Of particular interest is the supramolecular structure in which the naphthalene diimide is included between the two metallocavitand hemispheres.

Macrocyclic Nickel(II) Complexes Coligated by Hydrosulfide and Hexasulfide Ions: Syntheses, Structures, and Magnetic Properties of [NiII2L(μ-SH)]+ and [{LNiII2}2(μ-S6)]2+

The borohydride complex [Ni(II)2L(mu-BH4)]+ (3) where L(2-) represents a sterically demanding hexaaza-dithiophenolate ligand reacts rapidly with elemental sulfur in acetonitrile at ambient temperature to produce the cationic complexes [Ni(II)2L(mu-SH)]+ (4) and [(Ni(II)2L) 2(mu-S6)]2+ (6). Both complexes were isolated as ClO4(-) or BPh4(-) salts and characterized by IR and UV/vis spectroscopy and X-ray crystallography. Complex 4 (also accessible from [Ni(II)2L(ClO4)]+ (5) and Na2S.9H2O) features an unprecedented N3Ni(II)(mu-SR)2(mu-SH)Ni(II)N3 core structure, the hydrosulfide ligand being deeply buried in the binding-cavity of the bowl-shaped [Ni(II)2L]2+ complex. In 6, a helical S6(2-) chain, with a structure reminiscent to that of plastic sulfur, is almost completely encapsulated by two [Ni(II)2L]2+ subunits. In contrast to other triply sulfur-bridged N3Ni(II)(SR)3Ni(II)N3 structures whose ground states are typically of S = 0, 4 reveals an S = 2 ground-state which is attained by a ferromagnetic exchange interaction between the two Ni(II) (S = 1) ions ( J = 18 cm (-1), H = -2JS1S2). Intradimer ferromagnetic exchange interactions are also present in 6 ( J = 23 cm (-1)). A qualitative explanation for this difference is offered.

Trapping of a Thiolate→Dibromine Charge‐Transfer Adduct by a Macrocyclic Dinickel Complex and Its Conversion into an Arenesulfenyl Bromide Derivative

Stuck on sulfur: The first transition-metal complexes with S-Br units are surprisingly stable. Solid 3 is stable for at least six months and under vacuum solid 2 does not lose Br(2). The formation of the first structurally characterized transition-metal arenesulfenyl bromide complex 3 occurs with a change of the spin ground state from S = 2 to S = 0.

Synthesis, structure, computational modeling, and biological activity of two novel bimesitylene derivatives

Tetrazole- and nitrile-containing bimesitylene derivatives with potential use in coordination chemistry were synthesized and characterized, and their structural particularities are discussed. For the bimesitylene bistetrazole derivative, geometry optimization was carried out by quantum-chemical calculations using density functional theory together with vibrational frequencies, natural bond orbitals, and highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) calculations. The newly synthesized bimesitylene derivatives were also evaluated for their antimicrobial activity against three different reference strains, namely Escherichia coli, Staphylococcus aureus, and Candida albicans.

Structure and Bonding in Nickel-Thiolate-Iodine Charge-Transfer Complexes.

The dinuclear nickel complexes [Ni2 L(μ-O2 CR)](ClO4 ) [R=Me (4), R=OMe (6)], where L2- is a 24-membered macrocyclic N6 S2 ligand, react readily with excess I2 in MeCN solution at 4 °C to form stable mono-(I2 ) and bis-(I2 ) charge-transfer (CT) adducts of the type [Ni2 L(μ-O2 CR)(I2 )n ]+ (n=1 or 2) containing linear RS-I-I linkages. Three new CT compounds, namely, [Ni2 L(OAc)(I2 )](I2 )(I3 ) (5), [Ni2 L(O2 COMe)(I2 )](I5 )⋅MeCN (7⋅MeCN), and [Ni2 L(O2 COMe)(I2 )2 ](I5 )⋅MeCN (8⋅MeCN) as well as the triiodide salt [Ni2 L(OAc)](I3 ) (9) were synthesized and fully characterized. A common feature of the CT adducts is a polyiodide matrix, which surrounds the individual complex molecules, stabilized by secondary I⋅⋅⋅I interactions with the CT linkages. The scatter in both the RS-I (2.6 to 3.0 Å) and the I-I bond lengths (2.7 to 3.0 Å) is indicative of both a variable strength of the RS- →I2 bond and a varying degree of charge transfer. An analysis of the structural parameters was undertaken accompanied by DFT calculations to quantify the donating ability of the bridging thiolate functions and to shed more light on the bonding in this rare sort of charge-transfer complexes. The stability of the CT complexes and the results of preliminary transport measurements are also reported.

Preparation and Characterization of Macrocyclic Dinickel Complexes Coligated by Tetrazolate Ligands

The dinuclear nickel(II) complex [Ni2LCl]+ (1), where (L)2− represents a 24-membered macrocyclic hexamine-dithiophenolate ligand, reacts readily with 5-R-tetrazolate ligands to give the complexes [Ni2L(RCN4)]+, where R = H (2), Me (3), Ph (4). The new complexes were either isolated as perchlorate or tetraphenylborate salts and fully characterized by elemental analysis, UV/Vis, and IR spectroscopy. The structures of 2[BPh4] · MeCN, 3[BPh4] · 2MeCN, and 4[BPh4] ·MeCN were determined by X-ray crystallography, showing that all tetrazolate units are in a 2,3-bridging mode to generate dioctahedral N3Ni(μ-S)2(μ-N4CR)NiN3 core structures. The RCN4− groups interact less strongly with the [Ni2L]2+ fragment than pyrazolate ligands (CH)3N2 − as reflected in the longer Ni-N distances.