L.S. Gelfand

Nicotinic and isonicotinic acid n-oxide interactions with 3d metal perchlorates[1]

Interactions of nicotinic or isonicotinic acid N-oxides (N-nicOH and N-inicOH, respectively) with 3d metal (II) perchlorates in ethanol-triethyl orthoformate lead, in most cases, to partial substitution of perchlorate with nicotinate (N-nicO) or isonicotinate(N-inicO) N-oxide anionic groups. These reactions led to the isolation of the following new metal complexes: Ni(N-inicOH)3(ClO4)2·3H2O: the only true adduct of the series, apparently polynuclear, with both unidentate terminal and bidentate bridging N-inicOH, bridging O2ClO2 ligands, ionic ClO4− and lattice water. Complexes with exclusively anionic ligands of the type (ClO4) (MMn, Cu for LN-nicO; MCu for LN-inicO), with both terminal and bridging L, ionic and unidentate coordinated perchlorate, and aqua ligands. The rest of the complexes are of the mixed ligand type, i.e.: [H2O)2(O3ClO)M(N-nic)2M(N-nicOH)(OH2)2] (ClO4) (MCo, Ni), with bridging N-nicO, terminal N-nicOH,-OClO3 and aqua ligands, and ionic ClO4−; M4(N-inicOH) (N-inicO)5 (ClO4)3. 4H2O (MMn, Co, Zn), polynuclear with exclusively bridging organic ligands, terminal aqua and bidentate perchlorato groups, and ionic ClO4−; and, Zn4(N-nicOH)N-nicO)5(ClO4)3. 10H2O, probably tetrameric, with four bridging and one terminal N-nicO groups, and terminal N-nicOH, aqua and =O2ClO2 ligands, as well as ionic ClO4−. With the exception of the latter complex, which is hexacoordinated, the new metal complexes appear to be pentacoordinated. The likely structural types proposed for these compounds were based on the overall spectral and magnetic evidence obtained.

2,6-lutidine N-oxide complexes with metal chlorides

Abstract Complexes of 2,6-lutidine N-oxide (N-lutO or L) with a number of metal chlorides were prepared and characterized by means of spectral (ir and electronic), magnetic and conductance studies. Cr(III) and Al(III) yielded hexacoordinated complexes, which are most probably of the type [ML2Cl2(OH2)2] Cl·nH2O, involving both coordinated and anionic Cl groups, aquo ligands and lattice water. ML2Cl2 complexes isolated appear to be binuclear, chloride-bridged, penta-coordinated of the type [ClL2MCl2ML2Cl] for M = Mn, Ni, and monomeric, trans-square planar for M = Pd, Pt. FeCl2 formed a 2:3 complex (Fe2L3Cl4), which seems to involved both terminal and bridging chloro ligands, and coordination number five. A trans-arrangement of the N-lutO ligands in the above complexes is considered as most likely, in view of the obvious steric interactions between ligands of this type, occupying coordination sites, cis to each other. Finally, a second NiCl2 complex prepared, comprising coordinated methanol, is probably binuclear, chloride-bridged, hexacoordinated, of the type [ClL(CH3OH)2NiCl2Ni(CH3OH)2LCl].

Isonicotinate n-oxide complexes with dipositive 3d metal ions [1]

Abstract Divalent 3d metal complexes with isonicotinate N-oxide (N-inicO), of the type M(N-inicO)2·xH2O (M = Mn·Zn; x = 6 for M = Fe, Co, Ni, Zn; x = 5 for M = Mn; x = 2 for M = Cu), were prepared by reaction of (N-inicO)NH4 with the corresponding metal(II) acetates or ferrous ammonium sulfate in water. Desiccation of the preceding complexes over P4O10, under a vacuum of 10−4 torr, led to partial dehydration, affording the following lower hydrates: x = 5for M =Ni; x = 1.5 for M = Co, Zn;x = 1 for M = Cu; x = 0.5 for M = Mn, Fe. Characterization of the new metal complexes, based on spectral and magnetic studies, and the insolubility of all the complexes in water and organic solvents, led to their formulation as polynuclear of the following types: Hexa- and penta-hydrates; hexa-coordinated, [M(N-inicO)2(OH2]n·mH2O (m = 4n for M = Fe, Co,Ni, Zn; m = 3n for M = Mn, Ni), with the N- incO ligands forming single bridges between adjacent metal ions and functioning as bidentate, coordinating through the NO and one of the carboxylate oxygens; part of the non-coordinated COO oxygens are hydrogen-bonded to water, which is present in the form of both aqua ligands and lattice H2O. The lower hydrates of the type [(N-inicO2M-(OH2)-M(N-inicO)2)]n· bridging acqua ligand per two metal ions, as well as bidentate bridging N-inicO, being pentacoordinated of the type [(N-inocO)2M-(OH2)-M(N-inico)2]n· mH2O (m = O for M = Mn, Fe; m = 2n for M= CO, Zn). The dihydrate Cu(II) complex appears to be square-planar of the type [Cu(N-inicO)2]n·2nH2O, with bidentate bridging N-inicO ligands and exclusively lattice and H-bonded water. The corresponding monohydrate ([Cu(N-inicO)2]n·nH2O) probably contains both tetra-and penta-coordinated Cu2+ ions, with some N-inicO ligands acting at bidentate and some as tridentate (coordinating through the NO and the two COO oxygens) bridging. N-inicO is a 1igand of about the same strength as picolinate- and nicotinate-N-oxides.

Transition metal acetate reactions with nicotinic and isonicotinic acid N-oxides

Abstract Reactions of M(II) acetates (M = Mn, Co, Ni, Cu, Zn) with nicotinic or isonicotinic acid N-oxides (N-nicOH and N-inicOH, respectively), in ethanol-triethyl orthoformate solution, lead to partial substitution of acetate with nicotinate (N-nicO) or isonicotinate (N-inicO) N-oxide anionic groups. Complexes of the following types were precipitated during these reactions: Mn 2 (N-nicO)(CH 2 COO) 3 ·6H 2 O; M(N-nicOH)(N-nicO)(CH 3 COO)·xH 2 O (x = 0 for M = Co, Zn; x = 2 for M = Ni); Cu 2 (N-nicOH)(N-nicO) 2 (CH 3 COO) 2 ; and M 2 (N-inicOH)(N-inicO) 2 (CH 3 COO) 2 ·xH 2 O (x = 1 for M = Mn, Zn; x = 2 for M = Cu; x = 4 for M = Co, Ni). Bi- or poly-nuclear structures were proposed for these complexes, on the basis of characterization studies. The N-nicO and N-inicO ligands appear to be invariably bridging, and the acetato groups terminal (bidentate chelating in most cases). The neutral N-nicOH and N-inicOH ligands were found to act in certain cases as terminal, unidentate, NO oxygen-bonded, and in other cases as bridging, bidentate, coordinating through the N-O and CO oxygens. The Mn(II), Co(II) and Ni(II) complexes are normal high-spin compounds of these metal ions. Cu 2 (N-inicOH)(N-inicO) 2 (CH 3 COO) 2 ·2H 2 O also exhibits normal magnetic behaviour at 305-80°K. However, its analogue with the N-nicOH and N-nicO ligands shows a μ eff decrease of 0.2 μB over the same temperature range, owing to antiferromagnetic exchange between adjacent Cu 2+ ions, in a highly cross-linked polynuclear structure.

Picolinic acid N-oxide interactions with 3d metal perchlorates [1]

Abstract Interactions of picolinci acid N-oxide(LH) with 3d metal perchlorated in ethanol-triethyl orthoformate lead to the partial or complete substitution of perchlorate with anionic picolinate N-oxide(L) groups. Complexes of the following types were isolated and characterized: [ML(LH)(OH 2 ) 2 ](ClO 4 ) (M = Mn, Zn), with both L and LH functioning as bidentate chelating O,O-ligands, coordinating through the NO and one of the COO oxygens; [CrL 2 (LH)(OH 2 )] (ClO 4 )·4H 2 O, [FeL(LH) 2 (OH 2 ) 2 ](ClO 4 )·2H 2 O, [ML(LH)(OH 2 ) 3 ](ClO 4 ·H 2 O (M = Co, Ni; x = 0 for M = Co; x = 2 for M = Ni), with bidentate chelating L and unidentate NO oxygen-bonded LH ligands; [FeL 2 (OH 2 ) 3 ](ClO 4 )·H 2 O, with one bidentate chelating and one unidentate NO oxygen-bonded L ligand (all the preceding new complexes are low symmetry hexacoordinated); and the previously reported square-planar [CuL 2 ] bis-chelate.

TRANSITION METAL TETRAFLUOROBORATE INTERACTIONS WITH 2,6‐LUTIDINE N‐OXIDE

Abstract The interactions of transition metal tetrafluoroborates with 2,6-lutidine N-oxide(L) in organic solvents were studied, under various conditions. A number of adducts of the types [CrL 6 ](BF 4 ) 3 , [ML 4 ](BF 4 ) 2 (M = Fe, Cu, Zn, Cd), [CoL 4 (FBF 3 )](BF 4 )·H 2 O and [L 3 NiL 2 NiL 3 ](BF 4 ) 4 were isolated and characterized. In most cases, these compounds are similar to the corresponding metal perchlorate complexes (including the square-planar Fe 2+ complex, which is partially spin-paired (S = 1; μ eff = 3.55 μB)). The only differences are that the new Co 2+ complex involves coordinated FBF 3 , while the 4:1 Co(ClO 4 ) 2 analog contains exclusively ionic ClO 4 , and that, whereas the diamagnetic, square-planar [NiL 4 ] (ClO 4 2 complex remains unchanged for a long time before dimerizing to the paramagnetic [L 3 NiL 2 NiL 3 ](ClO 4 ) 4 , with the [NiL 4 ](BF 4 ) 2 analog the monomeric species is unstable, dimerizing within a few hours. These differences were attributed to the significantly smaller steric hindrance exerted by BF 4 relative to ClO 4 . In addition to the preceding adducts, a number of products of the types [L 3 CoF 2 CoL 3 ] (BF 4 ) 2 , [(F 2 BF 2 )L(ROH)MF 2 M(ROH)L(F 2 BF 2 )] (R = CH 3 for M = Mn; R = C 2 H 5 for M = Ni) and MnLF(BF 4 )·4MnF 2 were isolated. Formation of MF(BF 4 ) or MF 2 is accompanied by elimination of BF 3 ·L from the initially formed adducts. This reaction seems to be favored when the initial adducts of L with M(BF 4 ) 2 involves coordinated tetrafluoroborato ligands [1].

Hexakis(tris(hydroxymethyl)phosphine oxide)metal(II) and (III) perchlorates [1]

Abstract Complexes of tris(hydroxymethyl)phosphine oxide (thpo) with various metal perchlorates were prepared by interaction of ligand and salt in triethyl orthoformate. Characterization of the new complexes by means of spectral, magnetic and conductance studies led to their formulation as [M(thpo) 6 ](ClO 4 ) n (M = Mg 2+ , Cr 3+ , Mn 2+ , Fe 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Nd 3+ ; n = 2 or 3), involving low symmetry hexacoordinated complex cations and exclusively ionic perchlorate. Thpo acts as a unidentate ligand, coordinating through the PO oxygen. The tendency of thpo to form 6:1 cationic metal complexes, in contrast to other phosphine oxides, which yield 4:1 or 5:1 complexs with the same metal perchlorates, is attributed to its lower ligand-field strength. The metal-thpo bonds are weaker than the corresponding bonds in the complexes of other phosphine oxides. This leads to a less sterically crowded environment around the central metal ion, and allows the accommodation of six thpo molecules in the first coordination sphere.

Cobalt(II) and nickel(II) perchlorate complexes with 2,6-lutidine n-oxide

Abstract Two new Co(ClO4)2 complexes with 2,6-lutidine N-oxide(L) have been prepared and characterized as [CoL3(O2ClO2)](ClO4) and [CoL5](ClO4)2. Both these compounds involve pentacoordinated complex cations, the former comprising three L groups and one bidentate perchlorato ligand, and the latter five L ligands, in the inner coordination sphere of Co2+. IR and electronic spectral data for the new Co(II) complexes lend additional support to our previous assignment of [CoL4](ClO4)2 as a spin-free square-planar cationic complex. Interaction of Ni(ClO4)2 with L, in the presence of NaBφ4(φ = C6H5), leads to the precipitation of a product analyzing as Ni2L8(ClO4)3(Bφ4). Two isomeric forms of this product exist, as was also the case with NiL4(ClO4)2 (reported elsewhere), viz. a violet, diamagnetic, monomeric, square-planar species, which is presumably a 1:1 mixture of [NiL4](ClO4)2 and [NiL4](ClO4)(Bφ4), and a light green pentacoordinated, L-bridged dimer, which is of the high-spin type. The diamagnetic isomer is rather unstable, being rapidly converted to the paramagnetic isomer, immediately after filtration in the atmosphere. However, under inert conditions, this conversion does not proceed to completion; in fact, when the violet isomer is stored in an evacuated desiccator, while still wet, it is gradually converted to an indefinitely air-stable khaki product, which is apparently a mixture of the two isomers.

Main group metal(II) tetrafluoroborate interactions with 2,6-lutidine N-oxide

Abstract Combination of a predried methanolic solution of M(BF4)2 (M = Mg, Ca, Sn, Pb) with 2,6-lutidine N-oxide (L) at ambient temperature results in the precipitation of ML4(BF4)2 (M = Mg, Ca) or MLF(BF4) (M = Sn, Pb). The new Mg2+ and Ca2+ adducts appear to be pentacoordinated of the [ML4(FBF3)](BF4) type, involving both ionic and coordinated BF4 groups. The Sn2+ and Pb2+ complexes are presumably produced by elimination of one molecule of the BF3L complex from the initially formed adduct of M(BF4)2 with L. These complexes seem to be tricoordinated monomers of the [MLF(FBF3)] type, with the first coordination sphere of the Sn2+ or Pb2+ ion occupied by one fluoro, one -FBF3 and one L ligand.

Copper(II) chloride adducts with nicotinic and isonicotinic acid N-oxides

Abstract CuL n Cl 2 complexes are formed by interaction of nicotinic (n = 4) or isonicotinic (n = 1) acidd N-oxide and CuCl 2 solutions in ethanol-triethylorthofromate. The 1:4 CuCl 2 adduct with nicotinic acid N-oxide seems to be a dimer of the [L 3 ClCuL 2 CuClL 3 ]Cl 2 type, with both terminal and briging, exclusively NO oxygen-bonded ligand groups. This compound exhibits a subnormal ambient temperature magnetic moment (1.20 βB) and temperature-dependent paramagnetic behavior. The 1:1 CuCl 2 adduct with isonicotinic acid N-oxide is apparently polymeric ([CuLcl 2 ] x ), with the ligand functioning as tridentate, bridging, coordinating through all three (NO and COO) of its oxygens. This formulation is supported by the magnetic evidence, i.e. , normal ambient temperature μ eff of 2.06 μB, and measurable antiferromagnetic exchange at lower temperatures.