Metal-centered ferrocene clusters from 5-ferrocenylpyrimidine and ferrocenylpyrazine

A series of metal-centered ferrocene compounds has been designed by using 5-ferrocenylpyrimidine (L1) and ferrocenylpyrazine (L2). These ligands, when combined with transition metal salts, produce mixed-metal polynuclear complexes with structural diversity. Reaction of L1 with M(SCN)(2) (M = Ni, Co) produces the pinwheel-like 4:1 complexes (L1)(4).M(SCN)(2), while reactions of L1 and L2 with Cu(NO(3))(2) give the 3:1 complex (L1)(3).Cu(NO(3))(2) and the 2:1 complex (L2)(2).Cu(NO(3))(2), respectively. Reactions of L1 and L2 with M(hfac)(2) (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate, M = Mn, Ni, Cu, Zn) produce 2:1 complexes (L)(2).M(hfac)(2) with cis and trans configurations, respectively. Crystal structures as well as solid-state electrochemical properties of these redox active complexes were investigated.     

Loops, chains, sheets, and networks from variable coordination of Cu(hfac)2 with a flexibly hinged aminoxyl radical ligand

One pair of reactants, Cu(hfac)(2) = M and the hinge-flexible radical ligand 5-(3-N-tert-butyl-N-aminoxylphenyl)pyrimidine (3PPN = L), yields a diverse set of five coordination complexes: a cyclic loop M(2)L(2) dimer; a 1:1 cocrystal between an M(2)L(2) loop and an ML(2) fragment; a 1D chain of M(2)L(2) loops linked by M; two 2D M(3)L(2) networks of (M-L)(n) chains cross-linked by M with different repeat length pitches; a 3D M(3)L(2) network of M(2)L(2) loops cross-linking (M-L)(n)-type chains with connectivity different from those in the 2D networks. Most of the higher dimensional complexes exhibit reversible, temperature-dependent spin-state conversion of high-temperature paramagnetic states to lower magnetic moment states having antiferromagnetic exchange within Cu-ON bonds upon cooling, with accompanying bond contraction. The 3D complex also exhibited antiferromagnetic exchange between Cu(II) ions linked in chains through pyrimidine rings.     

Synthesis, structure, and cooperative proton-electron transfer reaction of Bis(5,6-diethylpyrazinedithiolato)metal complexes (M = Ni, Pd, Pt)

New proton and electron donors, M(II)(HL)(2) (M = Ni, Pd, Pt; L = 5,6-diethylpyradzinedithiolate), as well as a proton and electron acceptor, Pt(IV)(L)(2), were prepared and characterized. The pH-dependent cyclic voltammetry of the M(II)(HL)(2) complexes revealed a favorable Gibbs free energy (K(com) > 1) for the proton and electron transfer reactions from M(II)(HL)(2) to M(IV)(L)(2); i.e., the equilibrium for the following reaction lies to the right: M(II)(HL)(2) + M(IV)(L)(2) <==>2M(III)(HL)(L).     

M...HNR interactions in imino-bound diaryltriazene complexes: structure and fluxionality

The nominally square-planar coordination of the d(8) complexes [MClL(1)L(2)(p-XC(6)H(4)NNNHC(6)H(4)X-p)](M = Rh, L(1)= L(2)= CO, X = H, Me, Et or F; M = Ir, L(1)= L(2)= CO, X = Me; M = Pd or Pt, L(1)= Cl, L(2)= PPh(3), X = Me; M = Pd, L(1)L(2)=eta(3)-C(3)H(5), X = Me), with the triazene N-bonded via the imine group, is supplemented by an axial M...H-N interaction involving the terminal amino group.     

Stepwise formation of "organometallic boxes" with half-sandwich Ir, Rh and Ru fragments

Octanuclear complexes with half-sandwich Ir, Rh and Ru fragments and tetra(4-pyridyl)porphyrin (L1) and oxalate (L2) spacer ligands [(Cp*M)4L1]2[L2]4 (M = Ir (6a) M = Rh (6b)), [((cymene)Ru)4(L1)]2[L2]4 were prepared and characterized.     

Anionic Fischer-type carbene complexes as bidentate (N,O) ligands

New polynuclear complexes, (L1)3M2 [M2 = Cr(III) (4a,4b), Fe(III) (5), Co(III) (8)], (L1)2M2(L2)2 [M2 = Co(II) (7), Ni(II) (9)], (L1)2M2(O)L2 [M2 = V(IV) (6)] and L1M2Cp2 [M2 = Ti(III) (10)] with L1 = (CO)5M1=C[C=NC(CH3)=CHS](O-)(M1 = Cr or W) and L2 = 4-methylthiazole or THF, are described. The molecular structures of these complexes determined by X-ray diffraction show that the Fischer-type carbene complexes act as bidentate ligands towards the second metal centre, coordinating through C(carbene)-attached O-atoms and imine N-atoms of the thiazolyl groups to form five-membered chelates with the oxygen atoms in the mer configuration. Isostructural complexes have similar characteristic band patterns in their far-IR spectra. Cyclic voltammetry of selected complexes reveals the oxidation of the carbene complex ligand between 1.01 and 1.29 V. Oxidation of the central metal (M2) takes place at 0.56 and 0.86 V for 7 and 9, respectively. Three stepwise reductions of Cr(III) to Cr(0) occur for 4a and 4b in the region -0.51 to -1.58 V. These new ligand types and other variants thereof should find application in ligand design with the first metal -- and other ligands attached thereto -- in the carbene complex ligand, playing an important role.     

Synthesis and crystal and electronic structures of the Na2(Sc4Nb2)(Nb6O12)3 octahedral niobium cluster oxide. Structural correlations between AnBM6L12(Z) series and Chevrel Phases

We report here the synthesis and crystal and electronic structures of the Na(2)(Sc(4)Nb(2))(Nb(6)O(12))(3) niobium oxide whose structure is related to that of Ti(2)Nb(6)O(12). It constitutes a new member of the larger A(n)()BM(6)L(12)(Z) families (A = monovalent cation located in tetrahedral cavities of units, B = monovalent or trivalent cations located in octahedral cavities of units, M = rare earth, Zr, or Nb, Z = interstitial except for M = Nb). The structural relationships between the A(n)BM(6)L(12)(Z) series (M(6)L(i)(12)L(a)(6) unit-based compounds with a M(6)L(i)(6)L(i-a)(6/2)L(a-i)(6/2) cluster framework) and Chevrel Phases (M(6)L(i)(8)L(a)(6) unit-based compounds with a M(6)L(i)(2)L(i-a)(6/2)L(a-i)(6/2) cluster framework) are shown in terms of M(6)L(18) and M(6)L(14) unit packing. Despite a topology similar to that encountered in Chevrel Phases, intercalation properties are not expected in the Nb(6)O(i)(6)O(i-a)(6/2)O(a-i)(6/2) cluster framework-based compounds. Finally, it is shown, from theoretical LMTO calculations, that a semiconducting behavior is expected for a maximum VEC of 14 in the Nb(6)O(i)(6)O(i-a)(6/2)O(a-i)(6/2) cluster framework.     

Nickel complexes of a bulky beta-diketiminate ligand

Nickel(II) chloride forms a complex with tetrahydrofuran, NiCl(2)(THF)(1.5), that can be used to prepare nickel chloride complexes of a bulky beta-diketiminate ligand L(Me). [L(Me)NiCl](2) and L(Me)NiCl(2)LiTHF(2), which have tetrahedral geometries in the solid state, are in equilibrium with three-coordinate L(Me)NiCl. Thermodynamic parameters for the equilibrium between [L(Me)NiCl](2) and L(Me)NiCl are DeltaH = 51(5) kJ/mol and DeltaS = 116(11) J/(mol.K). L(Me)NiCl forms a tetrahydrofuran complex with a binding constant of 1.2(2) M(-)(1) at 21 degrees C. The chloride complexes were used to generate a three-coordinate nickel(II)-amido complex. This amido complex, L(Me)NiN(SiMe(3))(2), is compared with L(Me)MN(SiMe(3))(2) (M = Mn, Fe, Co) (Panda, A.; Stender, M.; Wright, R. J.; Olmstead, M. M.; Klavins, P.; Power, P. P. Inorg. Chem. 2002, 41, 3909-3916). Trends in the metrical parameters of the three-coordinate L(Me)M(II) amido compounds are similar to the trends in three-coordinate L(tBu)M(II) chloride compounds (Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.; Lachicotte, R. J. J. Am. Chem. Soc. 2002, 124, 14416-14424).     

"Jumping crystals": oxygen-evolving metal-nitroxide complexes

The crystals of heterospin complexes [M(hfac)(2)L(2)] (where M = Cu, Ni, Co, or Mn; hfac = hexafluoroacetylacetonate; and L = nitronyl nitroxide, 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl) were found to make unusual jumping motions. Under ambient conditions, the jumping and various displacements of crystals lasted for several weeks. The mechanical motion was accompanied by the cracking and disintegration of crystals, and a solid [M(hfac)(2)(L(1))(2)] complex with the corresponding imino nitroxide 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-1-oxyl (L(1)) was detected. The jumping was accompanied by the spontaneous elimination of oxygen, the source of which was the nitronyl nitroxyl fragment of coordinated L. An X-ray study of [M(hfac)(2)L(2)] (where M = Cu, Ni, Co, or Mn) showed that the molecular structure of all [M(hfac)(2)L(2)] and their packing in the solid state were identical. The packing of [M(hfac)(2)L(2)] was concluded to be critical to the mechanical effect. In complexes with different stoichiometries or different sets of diamagnetic ligands ([Cu(hfac)(2)L](2), [Cu(hfac)(acac)L]·EtOH, [CuPiv(2)L(2)]·2CH(2)Cl(2), and [Cu(hfac)(2)L(2)Cu(2)Piv(4)]·3C(7)H(8) (where acac is acetylacetonate and Piv is trimethylacetate), or free L), the effect vanished when the packing changed.     

Catalytic dehydrogenation of dimethylamine borane by group 4 metallocene alkyne complexes and homoleptic amido compounds

Dehydrogenation of Me(2)NH·BH(3) (1) by group 4 metallocene alkyne complexes of the type Cp(2)M(L)(η(2)-Me(3)SiC(2)SiMe(3)) [Cp = η(5)-cyclopentadienyl; M = Ti, no L (2Ti); M = Zr, L = pyridine (2Zr)] and group 4 metal amido complexes of the type M(NMe(2))(4) [M = Ti (8Ti), Zr (8Zr)] is presented.     

Metal-to-ligand charge-transfer sensitisation of near-infrared emitting lanthanides in trimetallic arrays M2Ln (M=Ru, Re or Os; Ln=Nd, Er or Yb)

The new pro-ligand 4-methyl-4'-(carbonylamino(2-(tert-butoxycarbonylamino)ethyl))-2,2'-bipyridyl (L1) has been prepared and used to synthesise the complex fac-Re(I)Cl(CO)3(L1) 1 and the complex salts [M(II)(bipy)2(L1)](PF6)2 (M=RuII 8 or OsII 15). Deprotection with trifluoroacetic acid affords the amine-functionalised derivatives fac-Re(I)Cl(CO)3(L2) 2, [M(II)(bipy)2(L2)](PF6)2 (M=RuII 9 or OsII 16) which react with the dianhydride of diethylenetriamine pentaacetic acid (DTPA) to give the binuclear complex {fac-Re(I)Cl(CO)3}2(L3) 3 and the complex salts [{M(II)(bipy)2}2(L3)](PF6)4 (M = RuII 10 or OsII 17). The latter react with salts Ln(OTf)3 to afford a series of 12 heterotrimetallic compounds that contain a lanthanide (Ln) ion in the DTPA binding site; {fac-Re(I)Cl(CO)3}2(L3)LnIII (Ln=Nd 4, Er 5, Yb 6 or Y 7) and [{M(II)(bipy)2}2(L3)LnIII](PF6)(OTf)3 (M=RuII, Ln=Nd 11, Er 12, Yb 13 or Y 14; M=OsII, Ln=Nd 18, Er 19, Yb 20 or Y 21). All of these trimetallic species display absorption bands ascribed to metal-to-ligand charge-transfer (MLCT) excitations, and luminescence measurements show that these excited states can be used to sensitise near-infrared emission from LnIII (Ln=Nd, Er or Yb) ions. Single crystal X-ray structures of L1 and [RuII(bipy)2(L2H)](H2PO4)3.(CH3)2CO.0.8H2O were obtained, the latter revealing the presence of H2PO4- counter anions, the source of which is presumed to be hydrolysis of PF6- ions.     

Synthesis and structural characterisation of lithium and sodium 2,6-dibenzylphenolate complexes

The stoichiometric treatment of 2,6-dibenzylphenol (HOdbp) or 2,2"-dimethoxy-2,6-dibenzylphenol (HOdbpOMe) with n-butyllithium or sodium bis(trimethylsilyl)amide (the latter as a solution in THF) in Et2O or DME affords the dimeric alkali metal phenolates [{M(Odbp)(L)}2] (M = Li; L = Et2O (1), L = DME (2), M = Na; L = Et2O (5), L = DME (6)), [{Li(OdbpOMe)}2] (3) and [{M(OdbpOMe)(L)}2] (M = Li; L = DME (4), M = Na; L = THF (7), L = DME (8)). Complexes 3 and 7 exhibit -OdbpOMe methoxy coordination and all four sodium complexes (5-8) display pi-aryl contacts from one phenolate radial arm to each sodium centre. The attempted synthesis of {Na(odbp)}n by direct sodiation of HOdbp yields a small quantity of the 2-benzylphenolate [{Na(Ombp)(DME)}4] (9) (-Ombp = -OC6H4-2-CH2Ph), providing a rare example of benzyl C-C bond scission.     

Phenylthiyl radical complexes of gallium(III), iron(III), and cobalt(III) and comparison with their phenoxyl analogues.

Three hexadentate, asymmetric pendent arm macrocycles containing a 1,4,7-triazacyclononane-1,4-diacetate backbone and a third, N-bound phenolate or thiophenolate arm have been synthesized. In [L(1)](3)(-) the third arm is 3,5-di-tert-butyl-2-hydroxybenzyl, in [L(2)](3)(-) it is 2-mercaptobenzyl, and in [L(3)](3)(-) it is 3,5-di-tert-butyl-2-mercaptobenzyl. With trivalent metal ions these ligands form very stable neutral mononuclear complexes [M(III)L(1)] (M = Ga, Fe, Co), [M(III)L(2)] (M = Ga, Fe, Co), and [M(III)L(3)] (M = Ga, Co) where the gallium and cobalt complexes possess an S = 0 and the iron complexes an S = (5)/(2) ground state. Complexes [CoL(1)].CH(3)OH.1.5H(2)O, [CoL(3)].1.17H(2)O, [FeL(1)].H(2)O, and [FeL(2)] have been characterized by X-ray crystallography. Cyclic voltammetry shows that all three [M(III)L(1)] complexes undergo a reversible, ligand-based, one-electron oxidation generating the monocations [M(III)L(1)(*)](+) which contain a coordinated phenoxyl radical as was unambiguously established by their electronic absorption, EPR, and M?ssbauer spectra. In contrast, [M(III)L(2)] complexes in CH(3)CN solution undergo an irreversible one-electron oxidation where the putative thiyl radical monocationic intermediates dimerize with S-S bond formation yielding dinuclear disulfide species [M(III)L(2)-L(2)M(III)](2+). [GaL(3)] behaves similarly despite the steric bulk of two tertiary butyl groups at the 3,5-positions of the thiophenolate, but [Co(III)L(3)] in CH(2)Cl(2) at -20 to -61 degrees C displays a reversible one-electron oxidation yielding a relatively stable monocation [Co(III)L(3)(*)](+). Its electronic spectrum displays intense transitions in the visible at 509 nm (epsilon = 2.6 x 10(3) M(-)(1) cm(-)(1)) and 670sh, 784 (1.03 x 10(3)) typical of a phenylthiyl radical. The EPR spectrum of this species at 90 K proves the thiyl radical to be coordinated to a diamagnetic cobalt(III) ion (g(iso) = 2.0226; A(iso)((59)Co) = 10.7 G).     

Molecular and electronic structures of bis-(o-diiminobenzosemiquinonato)metal(II) complexes (Ni, Pd, Pt), their monocations and -anions, and of dimeric dications containing weak metal-metal bonds

Two series of square planar, diamagnetic, neutral complexes of nickel(II), palladium(II), and platinum(II) containing two N,N-coordinated o-diiminobenzosemiquinonate(1-) pi radical ligands have been synthesized and characterized by UV-vis and (1)H NMR spectroscopy: [M(II)((2)L(ISQ))(2)], M = Ni (1), Pd (2), Pt (3), and [M(II)((3)L(ISQ))(2)] M = Ni (4), Pd (5), Pt (6). H(2)[(2)L(PDI)] represents 3,5-di-tert-butyl-o-phenylenediamine and H(2)[(3)L(PDI)] is N-phenyl-o-phenylenediamine; (L(ISQ))(1-) is the o-diiminobenzosemiquinonate pi radical anion, and (L(IBQ))(0) is the o-diiminobenzoquinone form of these ligands. The structures of complexes 1, 4, 5, and 6 have been (re)determined by X-ray crystallography at 100 K. Cyclic voltammetry established that the complete electron-transfer series consisting of a dianion, monoanion, neutral complex, a mono- and a dication exists: [M(L)(2)](z)z = -2, -1, 0, 1+, 2+. Each species has been electrochemically generated in solution and their X-band EPR and UV-vis spectra have been recorded. The oxidations and reductions are invariably ligand centered. Two o-diiminobenzoquinones(0) and two fully reduced o-diiminocatecholate(2-) ligands are present in the dication and dianion, respectively, whereas the monocations and monoanions are delocalized mixed valent class III species [M(II)(L(ISQ))(L(IBQ))](+) and [M(II)(L(ISQ))(L(PDI))](-), respectively. One-electron oxidations of 1 and trans-6 yield the diamagnetic dications [cis-[Ni(II)((2)L(ISQ))((2)L(IBQ))](2)]Cl(2) (7) and [trans-[Pt(II)((3)L(ISQ))((3)L(IBQ))](2)](CF(3)SO(3))(2) (8), respectively, which have been characterized by X-ray crystallography; both complexes possess a weak M.M bond and the ligands adopt an eclipsed configuration due to weak bonding interactions via pi stacking.     

Unusual iron(II) and cobalt(II) complexes derived from monodentate arylamido ligands

The coordination chemistry of the N-substituted arylamido ligands [N(R)(C6H3R'2-2,6)] [R = SiMe3, R' = Me (L1); R = CH2But, R' = Pri (L2)] toward FeII and CoII ions was studied. The monoamido complexes [M(L1)(Cl)(tmeda)] [M = Fe (1), Co (2)] react readily with MeLi, affording the mononuclear, paramagnetic iron(II) and cobalt(II) methyl-arylamido complexes [M(L1)(Me)(tmeda)] [M = Fe (3), Co (4)]. Treatment of 2:1 [Li(L2)(THF)2]/FeCl2 affords the unusual two-coordinate iron(II) bis(arylamide) [Fe(L2)2] (5).     

A macrocyclic ligand able to bind gallium(III) by preorganized pendant arms; coordination and kinetic studies

The equilibria and kinetics of the binding of gallium(III) to 4-(N),10-(N)-bis[2-(3-hydroxo-2-oxo-2-H-pyridine-1-y1)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L) were investigated in acidic medium at ionic strength 1 M (NaClO4). Spectrophotometric titrations in the UV region revealed that L is able to bind Ga3+ also at high H+ concentration. The kinetic (stopped-flow) experiments are interpreted on the basis of three parallel reaction paths (i) M3+ + H2L2+ = M(H2L)5+ where M(H2L)5+ is in a steady state, (ii) M(OH)2+ + H2L2+ = M(HL)4+ + H2O and (iii) M(OH)2+ + HL+ = ML3+ + H2O. The first-order rate constants for conversion of the outer-sphere into the inner-sphere complexes are similar to those of the Ga(III)/tropolone system which is known to react according to the dissociative Id mechanism and to the relevant rate constants for water exchange at the metal ion. The effects of pH on the UV-Vis absorption, fluorescence emission properties and NMR spectral features on the Ga(III)/L system were also investigated. Spectrophotometric titrations in the UV region reveal that, in acid medium the prevailing species is M(HL)4+ whereas the chelate ML3+ prevails for [H+] < 0.01 M. The results indicate metal coordination at the oxygen atoms of the 3-hydroxo-2-oxopyridine residues.     

A potentiometeric study of protonation and complex formation of xylenol orange with alkaline earth and aluminum ions

Xylenol orange (XO) is one of the complexometric indicators, that can bind to metal cations at both their amino and acidic groups. In this study the protonation constants and distribution diagrams of XO were studied pH-metrically, and the corresponding six protonation constants were calculated. The complex formation between XO (L) and alkaline earth ions (M) was investigated and the formation constants of the resulting complexes ML, MHL, M(2)L and M(2)HL were determined. The stabilities of both ML and M(2)L complexes were found to vary in the order Mg(2+)> Ca(2+)> Sr(2+)> Ba(2+). Studying the complex formation between Al(3+) ion (M) and XO (L), it was observed that four complexed species with stoichiometries ML, ML(2), MHL and MH(2)L could be formed in solution. It was also found that the Al L(2) complex can act as a chelating agent for further complexation with two cations other than Al(3+) ion (i.e. Ba, L, Al, L, Ba, Mg, L, Al, L, Mg, and Mg, L, Al, L, Ba). The formation constants of the resulting mixed complexes were determined and their distribution diagrams were investigated.     

Large M4L4 (M = Al(III), Ga(III), In(III), Ti(IV)) tetrahedral coordination cages: an extension of symmetry-based design

As an extension to a rational design for the formation of self-assembled coordination cages, the syntheses for very large M4L4 tetrahedra based on a hexadentate 3-fold symmetric ligand (1,3,5-tris(4'-(2' ',3' '-dihydroxybenzamido)phenyl)benzene (H6L2)) are described. Four tetrahedral M4L2(4) assemblies (M = Al(III), Ga(III), In(III), Ti(IV)), with cavity sizes of around 450 A3, have been characterized by elemental analysis, NMR spectroscopy, and high-resolution electrospray mass spectrometry. Differences in chiral resolution and dynamic behavior of host-guest interactions with previously reported tetrahedral M4L(N)6 and M4L1(4) architectures are highlighted for the ligands 1,5-bis(2',3'-dihydroxybenzamido)naphthalene (H4L(N)) and 1,3,5-tris(2',3'-dihydroxybenzamido)benzene (H6L1). An even larger 3-fold symmetric ligand, 1,3,5-tris(4'-(2' ',3' '-dihydroxybenzamido)-1',1' '-biphenyl)benzene (H6L3) has been prepared but, due to increased flexibility and deviation from the intended 3-fold symmetry, does not undergo self-assembly to form the M4L3(4) structure.     

3d Metal complexes with 2-hydroxy-3-methoxybenzaliminopropyl and 4-hydroxy-3-methoxybenzaliminopropyl immobilized on aerosil as catalysts of ozone decomposition

The composition and structure of M(II) (Mn, Co, Cu) complexes with Schiff bases (L1 = 2-hydroxy-3-methoxybenzaliminopropyl, L2 = 4-hydroxy-3-methoxybenzaliminopropyl) immobilized on Aerosil and their catalytic activity in ozone decomposition were studied. The formation of pseudotetrahedral bisligand complexes M(L1)₂ and pseudooctahedral complexes M(L2)₂ on the modified surface of Aerosil was confirmed by IR and ESR spectroscopy and by diffuse reflectance spectroscopy (DSR). The catalytic activity of isostructural complexes in ozone decomposition varies in the order Mn > Co > Cu, and M(L₂)₂ complexes are more active than M(L1)₂.     

Spacially confined M2 centers (M = Fe, Co, Ni, Zn) on a sterically bulky binucleating support: synthesis, structures and ethylene oligomerization studies

Two new bulky aryl-bridged pyridyl-imine compartmental (pro)ligands, 2,6-{(2,6-i-Pr(2)C6H3)N=C(Me)C5H3N}2C6H3Y (Y = H L1, OH L2-H), have been prepared in moderate to good overall yields via a Stille-type cross-coupling approach. The molecular structure of L2-H reveals a transoid configuration within the pyridyl-imine units with a hydrogen-bonding interaction maintaining the phenol coplanar with one of the adjacent pyridine rings. The interaction of 2 equiv of MX2 with L1 in n-BuOH at 110 degrees C gives the binuclear complexes, [(L1)M2X4] (M = Fe, X = Cl (1a); M = Co, X = Cl (1b); M = Ni, X = Br (1c); M = Zn, X = Cl (1d)), in which the metal centers adopt distorted tetrahedral geometries and occupy the two pyridyl-imine cavities in L1. In contrast, deprotonation of L2-H occurs upon reaction with 2 equiv of MX2 to afford the phenolate-bridged species [(L2)M2(mu-X)X2] (M = Fe, X = Cl (2a); M = Co, X = Cl (2b); M = Ni, X = Br (2c); M = Zn, X = Cl (2d)). 1H NMR studies of diamagnetic 1d and 2d reveal that the limited rotation of the N-aryl groups in 1d is further impeded in 2d by steric interactions imparted by the two closely located N-aryl groups. Partial displacement of the bridging bromide in 2c results upon its treatment with acetonitrile to afford [(L2)Ni2Br3(NCMe)] [2c(MeCN)]; no such reaction occurs for 2a, 2b, or 2d. Upon activation with excess methylalumoxane (MAO), 1b, 1c, 2b, and 2c show some activity for alkene oligomerization forming low molecular-weight materials with methyl-branched products predominating for the nickel systems. Single-crystal X-ray diffraction studies have been performed on L2-H, 1c, 2b, 2c, 2c(NCMe), and 2d.