Exchange and Double-Exchange Phenomena in Linear Homo- and Heterotrinuclear Nickel(II,III,IV) Complexes Containing Six μ2-Phenolato or μ2-Thiophenolato Bridging Ligands

Increasing the electron donation in a dinucleating ligand family: molecular and electronic structures in a series of CoIICoII complexes

We have developed a family of dinucleating ligands with varying terminal donors to generate dinuclear peroxo and high-valent complexes and to correlate their stabilities and reactivities with their molecular and electronic structures as a function of the terminal donors. It appears that the electron-donating ability of the terminal donors is an important handle for controlling these stabilities and reactivities. Here, we present the synthesis of a new dinucleating ligand with potentially strong donating terminal imidazole donors. As CoII ions are sensitive to variations in donor strength in terms of coordination number, magnetism, UV-Vis-NIR spectra, redox potentials, we probe the electron donation ability of this new ligand in CoIICoII complexes in comparison to the parent CoIICoII complexes with terminal pyridine donors and we synthesize the analogous CoIICoII complexes with terminal 6-methylpyridines and methoxy-substituted pyridines. The molecular structures show indeed strong variations in coordination numbers and bond lengths. These differences in the molecular structures are reflected in the magnetic properties and in the d-d transitions demonstrating that the molecular structures remain intact upon dissolution. The redox potentials are analyzed with respect to the electron donation ability and are the only handle to observe an effect of the methoxy-substituted pyridines. All data taken together show the following order of electron donating ability for the terminal donors: 6-methylpyridines ≪ pyridines < methoxy-substituted pyridines ≪ imidazoles.

Direct and remote control of electronic structures and redox potentials in μ-oxo diferric complexes

Non-heme diiron enzymes activate O2 for the oxidation of substrates in the form of peroxo FeIII2 or high-valent FeIV2 intermediates. We have developed a dinucleating bis(tetradentate) ligand system that stabilizes peroxo and hydroperoxo FeIII2 complexes with terminal 6-methylpyridine donors, while the peroxo FeIII2 intermediate is reactive with terminal pyridine donors presumably via conversion to a fluent high-valent FeIV2 intermediate. We present here a derivative with electron-donating methoxy substituents at the pyridine donors and its diferric complexes with an {FeIIIX(μ-O)FeIIIX} (X- = Cl-, OAc-, and OH-) or an {FeIII(μ-O)(μ-OAc)FeIII} core. The complex-induced oxidation of EtOH with H2O2 provides μ-OAc-, and in acetone, the complex with mixed OH-/OAc- exogenous donors is obtained. Both reactivities indicate a reactive fluent peroxo FeIII2 intermediate. The coupling constant J and the LMCT transitions are insensitive to the nature of the directly bound ligands X- and reflect mainly the electronic structure of the central {FeIII(μ-O)FeIII} core, while Mössbauer spectroscopy and d-d transitions probe the local FeIII sites. The remote methoxy substituents decrease the potential for the oxidation to FeIV by ∼100 mV, while directly bound OH- in {FeIII(OH)(μ-O)FeIII(OH)} with a short 1.91 Å FeIII-OOH bond decreases the potential by 590 mV compared to {FeIII(OAc)(μ-O)FeIII(OAc)} with a 2.01 Å FeIII-OOAc bond. Interestingly, this FeIII-OH bond is even shorter (1.87 Å) in the mixed OH-/OAc- complex but the potential is the mean value of the potentials of the OH-/OH- and OAc-/OAc- complexes, thus reflecting the electron density of the central {FeIII(μ-O)FeIII} core and not of the local FeIII-OH unit.

Reactivities and Electronic Structures of μ-1,2-Peroxo and μ-1,2-Superoxo CoIIICoIII Complexes: Electrophilic Reactivity and O2 Release Induced by Oxidation

Peroxo complexes are key intermediates in water oxidation catalysis (WOC). Cobalt plays an important role in WOC, either as oxides CoOx or as {CoIII(μ-1,2-peroxo)CoIII} complexes, which are the oldest peroxo complexes known. The oxidation of {CoIII(μ-1,2-peroxo)CoIII} complexes had usually been described to form {CoIII(μ-1,2-superoxo)CoIII} complexes; however, recently the formation of {CoIV(μ-1,2-peroxo)CoIII} species were suggested. Using a bis(tetradentate) dinucleating ligand, we present here the synthesis and characterization of {CoIII(μ-1,2-peroxo)(μ-OH)CoIII} and {CoIII(μ-OH)2CoIII} complexes. Oxidation of {CoIII(μ-1,2-peroxo)(μ-OH)CoIII} at -40 °C in CH3CN provides the stable {CoIII(μ-1,2-superoxo)(μ-OH)CoIII} species and activates electrophilic reactivity. Moreover, {CoIII(μ-1,2-peroxo)(μ-OH)CoIII} catalyzes water oxidation, not molecularly but rather via CoOx films. While {CoIII(μ-1,2-peroxo)(μ-OH)CoIII} can be reversibly deprotonated with DBU at -40 °C in CH3CN, {CoIII(μ-1,2-superoxo)(μ-OH)CoIII} undergoes irreversible conversions upon reaction with bases to a new intermediate that is also the decay product of {CoIII(μ-1,2-superoxo)(μ-OH)CoIII} in aqueous solution at pH > 2. Based on a combination of experimental methods, the new intermediate is proposed to have a {CoII(μ-OH)CoIII} core formed by the release of O2 from {CoIII(μ-1,2-superoxo)(μ-OH)CoIII} confirmed by a 100% yield of O2 upon photocatalytic oxidation of {CoIII(μ-1,2-peroxo)(μ-OH)CoIII}. This release of O2 by oxidation of a peroxo intermediate corresponds to the last step in molecular WOC.

Oxidative C–C/C–X coupling in organometallic nickel complexes: insights from DFT

NiIII and NiIV-center complexes prefer direct reductive elimination than reacting through five-coordinate intermediates. 32+ complex in the presence of Cl− undergoes Cl–Csp2 elimination preferably over Cl–Csp3 and Csp3–Csp2 elimination.

Syntheses, structures, and magnetic properties of a series of Mn-M-Mn trinuclear complexes with different spin configurations

A series of trinuclear complexes, [MnII2Y^III(L)₂(HL)₂(NO₃)₃][Y^III(NO₃)₅]·7H₂O (1'), [MnII2Gd^III(HL)₄(NO₃)₄]₂[MnII2Gd^III(L)(HL)₃(NO₃)₄][Gd^III(NO₃)₅]₄·2(o-Xy)·12H₂O (2') and [MnII3(L)(HL)₂(NO₃)₄](NO₃)·1.25(p-Xy) (3'), were synthesized using a β-diketone ligand HL (HL = 1,3-bis(pyridin-2-yl)propane-1,3-dione). X-ray structural analyses revealed that each complex has a trinuclear core with an Mn(II)-M-Mn(II) arrangement (M = Y^III (1), Gd^III (2), and Mn^II (3)). In 1' with a diamagnetic Y(III) ion, negligible antiferromagnetic interactions between terminal Mn(II) ions are operative. On the other hand, 2' shows ferromagnetic interactions between Mn(II) and Gd(III) ions, affording a spin ground state of S_T = 17/2. The homometallic Mn(II)₃ complex of 3' has an S_T = 5/2 spin ground state resulting from the antiferromagnetic interactions between neighboring Mn(II) ions. The maximum magnetic entropy change (-ΔS_m) of 1'-3' was estimated to be 12.3, 24.8, and 8.0 J kg^-1 K^-1, respectively.

Synthesis, Structure, and Magnetic Properties of Linear Trinuclear CuII and NiII Complexes of Porphyrin Analogues Embedded with Binaphthol Units

A porphyrin analogue embedded with (S)-1,1′-bi-2-naphthol units was synthesized without reducing optical purity of the original binaphthol unit. This new macrocyclic ligand provides the hexaanionic N4O4 coordination environment that enables a linear array of three metal ions. That is, it provides the square planar O4 donor set for the central metal site and the distorted square planar N2O2 donor set for the terminal metal sites. In fact, a CuII3 complex with a Cu(1)–Cu(2) distance of 2.910 Å, a Cu(1)–Cu(2)–Cu(1′) angle of 174.7°, and a very planar Cu2O2 diamond core was obtained. The variable-temperature 1H-NMR study of the CuII3 complex showed increasing paramagnetic shifts for the naphthyl protons as temperature increased, which suggests strong antiferromagnetic coupling of CuII ions. The temperature dependence of the magnetic susceptibility indicated antiferromagnetic coupling both for the CuII3 complex (J = −434 cm−1) and for the NiII3 complex (J = −49 cm−1). The linear (L)M(µ-OR)2M(µ-OR)2M(L) core in a rigid macrocycle cavity made of aromatic components provides robust metal complexes that undergo reversible ligation at the apical sites of the central metal.

Ligand architecture for triangular metal complexes: a high oxidation state Ni3 cluster with proximal metal arrangement

A new multidentate tetraanionic ligand platform for supporting trinuclear transition metal clusters has been developed. Two trisphenoxide phosphinimide ligands bind three Ni centers in a triangular arrangement. The phosphinimide donors bridge in μ3 fashion and the phenoxides complete a pseudo-square planar coordination sphere around each metal center. Electrochemical studies reveal two pseudo-reversible oxidation events at notably low potentials (-0.80 V and +0.05 V). The one electron oxidized species was characterized structurally, and it is assigned as a NiIII-containing cluster.

A tetranuclear nickel cluster isolated in multiple high-valent states

We report a series of high-valent tetranuclear nickel clusters isolated from the chemical oxidation of an all Ni(ii) ([Ni₄]) neutral cluster. Electrochemical analysis of [Ni₄] reveals three reversible sequential oxidations at 0.248 V (1e^-), 0.678 V (1e^-), and 0.991 V (2e^-) vs. Fc/Fc⁺ corresponding to mono-, di-, and tetra-oxidized species, [Ni₄]⁺, [Ni₄]²⁺, [Ni₄]⁴⁺, respectively. Using spectroscopic, crystallographic, magnetometric, and computational techniques, we assign the primary loci of oxidations to the Ni centers in each case, thus resulting in the isolation of the first tetranuclear all-Ni(iii) cluster, [Ni₄]⁴⁺.

Solution and solid state structures and magnetism of a series of linear trinuclear compounds with a hexacoordinate LnIII and two terminal NiII centers

Reported are the syntheses, structures and magnetic properties, also by NMR spectroscopy in solution, of a series of 13 linear trinuclear 3d-4f compounds with a lanthanide(iii) surrounded by two Ni^II ions, NiLn^III, where the central Ln^III is hexacoordinate. For three of the crystal structures, an additional H₂O molecule is coordinated to the central Ln^III ion, leading to a monocapped trigonal prismatic structure. However, NMR spectroscopy indicates that in solution, these complexes also have a hexacoordinate Ln^III center. The solution magnetic anisotropies, determined by NMR spectroscopy, indicate that the axial components of the anisotropies are relatively small and that the Dy^III derivative might therefore not exhibit single molecule magnetism. The axial anisotropies determined by NMR spectroscopy are in good agreement with the expectations based on the distorted trigonal prismatic ligand field.

Competing ferro- and antiferromagnetic interactions in a hexagonal bipyramidal nickel thiolate cluster

A new hexagonal bipyramidal Ni8 cluster is reported and its magnetic behaviour is analyzed. The molecular structure consists of a hexagonal wheel capped by two additional apical Ni(2+) ions. This structure supports ferromagnetic superexchange interactions between adjacent Ni(2+) ions in the wheel and an antiferromagnetic superexchange interaction between the wheel and apical Ni(2+) ions.

Synthesis of open-shell, bimetallic Mn/Fe trinuclear clusters

Concomitant deprotonation and metalation of hexadentate ligand platform (tbs)LH6 ((tbs)LH6 = 1,3,5-C6H9(NHC6H4-o-NHSiMe2(t)Bu)3) with divalent transition metal starting materials Fe2(Mes)4 (Mes = mesityl) or Mn3(Mes)6 in the presence of tetrahydrofuran (THF) resulted in isolation of homotrinuclear complexes ((tbs)L)Fe3(THF) and ((tbs)L)Mn3(THF), respectively. In the absence of coordinating solvent (THF), the deprotonation and metalation exclusively afforded dinuclear complexes of the type ((tbs)LH2)M2 (M = Fe or Mn). The resulting dinuclear species were utilized as synthons to prepare bimetallic trinuclear clusters. Treatment of ((tbs)LH2)Fe2 complex with divalent Mn source (Mn2(N(SiMe3)2)4) afforded the bimetallic complex ((tbs)L)Fe2Mn(THF), which established the ability of hexamine ligand (tbs)LH6 to support mixed metal clusters. The substitutional homogeneity of ((tbs)L)Fe2Mn(THF) was determined by (1)H NMR, (57)Fe Mössbauer, and X-ray fluorescence. Anomalous scattering measurements were critical for the unambiguous assignment of the trinuclear core composition. Heating a solution of ((tbs)LH2)Mn2 with a stoichiometric amount of Fe2(Mes)4 (0.5 mol equiv) affords a mixture of both ((tbs)L)Mn2Fe(THF) and ((tbs)L)Fe2Mn(THF) as a result of the thermodynamic preference for heavier metal substitution within the hexa-anilido ligand framework. These results demonstrate for the first time the assembly of mixed metal cluster synthesis in an unbiased ligand platform.

Metal atom lability in polynuclear complexes

The asymmetric oxidation product [((Ph)L)Fe3(μ-Cl)]2 [(Ph)LH6 = MeC(CH2NHPh-o-NHPh)3], where each trinuclear core is comprised of an oxidized diiron unit [Fe2](5+) and an isolated trigonal pyramidal ferrous site, reacts with MCl2 salts to afford heptanuclear bridged structures of the type ((Ph)L)2Fe6M(μ-Cl)4(thf)2, where M = Fe or Co. Zero-field, (57)Fe Mössbauer analysis revealed the Co resides within the trinuclear core subunits, not at the octahedral, halide-bridged MCl4(thf)2 position indicating Co migration into the trinuclear subunits has occurred. Reaction of [((Ph)L)Fe3(μ-Cl)]2 with CoCl2 (2 or 5 equivalents) followed by precipitation via addition of acetonitrile afforded trinuclear products where one or two irons, respectively, can be substituted within the trinuclear core. Metal atom substitution was verified by (1)H NMR, (57)Fe Mossbauer, single crystal X-ray diffraction, X-ray fluorescence, and magnetometry analysis. Spectroscopic analysis revealed that the Co atom(s) substitute(s) into the oxidized dimetal unit ([M2](5+)), while the M(2+) site remains iron-substituted. Magnetic data acquired for the series are consistent with this analysis revealing the oxidized dimetal unit comprises a strongly coupled S = 1 unit ([FeCo](5+)) or S = 1/2 ([Co2](5+)) that is weakly antiferromagnetically coupled to the high spin (S = 2) ferrous site. The kinetic pathway for metal substitution was probed via reaction of [((Ph)L)Fe3(μ-Cl)]2 with isotopically enriched (57)FeCl2(thf)2, the results of which suggest rapid equilibration of (57)Fe into both the M(2+) site and oxidized diiron site, achieving a 1:1 mixture.

Interplay of magnetic exchange interactions and Ni-S-Ni bond angles in polynuclear nickel(II) complexes

The ability of bridging thiophenolate groups (RS(-)) to transmit magnetic exchange interactions between paramagnetic Ni(II) ions is examined. Specific attention is paid to complexes with large Ni-SR-Ni angles. For this purpose, dinuclear [Ni(2)L(1)(mu-OAc)I(2)][I(5)] (2) and trinuclear [Ni(3)L(2)(OAc)(2)][BPh(4)](2) (3), where H(2)L(1) and H(2)L(2) represent 24-membered macrocyclic amino-thiophenol ligands, are prepared and fully characterized by IR- and UV/Vis spectroscopy, X-ray crystallography, static magnetization M measurements and high-field electron spin resonance (HF-ESR). The dinuclear complex 2 has a central N(3)Ni(2)(mu-S)(2)(mu-OAc)Ni(2)N(3) core with a mean Ni-S-Ni angle of 92 degrees . The macrocycle L(2) supports a trinuclear complex 3, with distorted octahedral N(2)O(2)S(2) and N(2)O(3)S coordination environments for one central and two terminal Ni(II) ions, respectively. The Ni-S-Ni angles are at 132.8 degrees and 133.5 degrees . We find that the variation of the bond angles has a very strong impact on the magnetic properties of the Ni complexes. In the case of the Ni(2)-complex, temperature T and magnetic field B dependencies of M reveal a ferromagnetic coupling J=-29 cm(-1) between two Ni(II) ions (H=JS(1)S(2)). HF-ESR measurements yield a negative axial magnetic anisotropy (D<0) which implies a bistable (easy axis) magnetic ground state. In contrast, for the Ni(3)-complex we find an appreciable antiferromagnetic coupling J'=97 cm(-1) between the Ni(II) ions and a positive axial magnetic anisotropy (D>0) which implies an easy plane situation.

Stabilization of Unusual Substrate Coordination Modes in Dinuclear Macrocyclic Complexes

The steric protection offered by the macrobinucleating hexaazaditiophenolateligand (L) allows for the preparation of the first stable dinuclear nickel(II) borohydride bridged complex, which reacts rapidly with elemental sulphur producing a tetranuclear nickel(II) complex [{(L)Ni2}2(μ-S6)]2+ bearing a helical μ4-hexa- sulfide ligand. The [(L)CoII 2]2+ fragment have been able to trap a monomethyl orthomolybdate in the binding pocket. Unusual coordination modes of substrate in dinuclear macrocyclic compounds was demonstrated.

Isotropic and Antisymmetric Double-Exchange, Zero-Field, Zeeman, and Hyperfine Splittings in Trinuclear Valence-Delocalized [Cu37+] Clusters

Valence delocalization in the [Cu3(7+)] trimer is considered in the model of the double-exchange coupling, in which full delocalization corresponds to the migration of the single d(x2-y2) hole and relatively strong isotropic double-exchange coupling. Strong double exchange results in the pairing of the individual spins in the delocalized trimer even at room temperature. The model explains the delocalized singlet 1A1 ground state in the planar Cu3(mu3-O) core by strong double exchange with positive double-exchange parameter t(0), whereas the delocalized triplet ground state of the [Cu3(7+)] trimer, which was observed in the Cu3(mu3-S)2 cluster, may be explained by the double exchange with relatively weak positive t(0): 0 < t(0) < 2J (degenerate 3E ground state) or negative t(0) (triplet 3A2 ground state). An analysis of the splitting of the delocalized degenerate 3E term requires inclusion of the antisymmetric double-exchange interaction, which takes into account the spin-orbit coupling in the double-exchange model. The cluster parameter KZ of the antisymmetric double-exchange coupling is proportional to t(0) and anisotropy of the g factor Deltag(parallel)[Cu(II)], KZ << t(0). Antisymmetric double exchange is relatively large in the [Cu3(7+)] cluster with the d(x2-y2) magnetic orbitals lying in the Cu3 plane [Cu3(mu3-O) core], whereas for the d(x2-y2) magnetic orbitals lying in the plane perpendicular to Cu3, antisymmetric double-exchange coupling is weak [Cu3(mu3-S)2 cluster]. The antisymmetric double-exchange coupling results in the linear zero-field splitting DeltaK = 2[equation: see text]KZ (approximately t(0)) of the delocalized degenerate 3E term that leads to strong anisotropy of the Zeeman splittings in the external magnetic field and a complex electron paramagnetic resonance (EPR) spectrum. The delocalized model of hyperfine interaction explains the hyperfine structure [10 hyperfine lines with the relative intensities 1:3:6:10:12:12:10:6:3:1 and the interval a/3] of the EPR transitions in the triplet states that was observed in the EPR spectra of the Cu3(mu3-S)2 cluster.

Preparation and characterization of dinuclear Pd(ii) complexes of binucleating tetraaza-thiophenolate ligands

The thioethers 4-tert-butyl-2,6-bis((2-(dimethylamino)ethylimino)methyl)phenyl(tert-butyl)sulfane (tBu-L3) and 4-tert-butyl-2,6-bis((2-(dimethylamino)ethylimino)methyl)phenyl(tert-butyl)sulfane (tBu-L4) react with PdCl2(NCMe)2 to give the dinuclear palladium thiophenolate complexes [(L3)Pd2Cl2]+ (2) and [(L4Pd2(mu-Cl)]2+ (3) (HL3= 2,6-bis((2-(dimethylamino)ethylimino)methyl)-4-tert-butylbenzenethiol, HL4 = 2,6-bis((2-(dimethylamino)ethylamino)methyl)-4-tert-butylbenzenethiol). The chloride ligands in could be replaced by neutral (NCMe) and anionic ligands (NCS-, N3-, CN-, OAc-) to give the diamagnetic Pd(II) complexes [(L3)Pd2(NCMe)2]3+ (4), [(L3)Pd2(NCS)2]+ (5), [(L3)Pd2(N3)2]+ (6), [{(L3)Pd2(mu-CN)}2]4+ (7) and [(L3)Pd2(OAc)]2+ (9). The nitrile ligands in and in [(L3)Pd2(NCCH2Cl)2]3+ are readily hydrated to give the corresponding amidato complexes [(L3)Pd2(CH3CONH)]2+ (8) and [(L3)Pd2(CH2ClCONH)]2+ (10). The reaction of [(L3)Pd2(NCMe)2]3+ with NaBPh4 gave the diphenyl complex [(L3)Pd2(Ph)2]+ (11). All complexes were either isolated as perchlorate or tetraphenylborate salts and studied by IR, 1H and 13C NMR spectroscopy. In addition, complexes 2[ClO4], 3[ClO4]2, 5[BPh4], 6[BPh4], 7[ClO4]4, 9[ClO4]2, 10[ClO4]2 and 11[BPh4] have been characterized by X-ray crystallography.

Ferro- and antiferromagnetic interactions in face-sharing trioctahedral NiIIMnIINiIIand NiIIFeIIINiIIcomplexes with the same 1–5/2–1 spin system

Two heterotrinuclear complexes, [Mn(II)(Ni(II)L)2].2CH3OH (where H3L = 1,1,1-tris(N-salicylideneaminomethyl)ethane) and [Fe(III)(Ni(II)L)2]NO3.C2H5OH, consisting of three face-sharing octahedra have been prepared; although these complexes have closely related structures and have the same 1-5/2-1 spin system, they show completely different magnetic interactions between the adjacent metal ions: ferromagnetic (Ni(II)-Mn(II)) and antiferromagnetic (Ni(II)-Fe(III)).

Preparation and characterization of CrIII, MnII, FeII, CoIIand NiIIcomplexes 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.

Synthesis, Structure, and Stereochemistry of Trinuclear Metal Complexes Formed from the Phosphorus-Based Achiral Tripodal Ligand {P(S)[N(Me)NCHC6H4-o-OH]3} (LH3): Luminescent Properties of L2Cd3·2H2O

Neutral trinuclear metal complexes L2Cd3 x 2H2O, L2Mn3 x MeOH, and L2Zn3 x MeOH were isolated in the reaction between the phosphorus-centered achiral tris(hydrazone) P(S)[N(Me)N=CHC6H(4)-o-OH]3 (LH3) and the corresponding divalent metal ions. The trinuclear complexes contain two equivalent terminal metal ions (M(t)) and a central metal ion (M(c)). The ligand encapsulates M(t) in a facial N3O3 coordination environment. From the coordination sphere of the two terminal metal ions a pair of phenolic oxygen atoms further coordinate to the central metal ion. The coordination requirements of M(c) are completed by the solvents of coordination. The achiral trianionic tripodal ligand (L)3- induces chirality in the metal complexes. This results in a delta (clockwise) or lambda (anticlockwise) configuration for the terminal metal ions. The enantiomeric complexes 2-4 (delta-delta or lambda-lambda) crystallize as racemic compounds. The supramolecular structures of 2-4 reveal chiral recognition in the solid-state; every molecule with the delta-delta configuration interacts stereospecifically, through C-H...S=P bonds, with two lambda-lambda molecules to generate a one-dimensional polymeric chain. Photophysical studies of the diamagnetic trinuclear complexes reveal that the tricadmium complex is luminescent in the solid state as well as in solution. In contrast LH3 and L2Zn3 x MeOH are nonluminescent.

A phosphorus supported multisite coordinating tris hydrazone P(S)[N(Me)N=CH-C6H4-o-OH]3 as an efficient ligand for the assembly of trinuclear metal complexes: synthesis, structure, and magnetism

A phosphorus supported multisite coordinating ligand P(S)[N(Me)N=CH-C(6)H(4)-o-OH](3) (2) was prepared by the condensation of the phosphorus tris hydrazide P(S)[N(Me)NH(2)](3) (1) with o-hydroxybenzaldehyde. The reaction of 2 with M(OAc)(2).xH(2)O (M = Mn, Co, Ni, x = 4; M = Zn, x = 2) afforded neutral trinuclear complexes [P(S)[N(Me)N=CH-C(6)H(4)-o-O](3)](2)M(3) [M = Mn (3), Co (4), Ni (5), and Zn (6)]. The X-ray crystal structures of compounds 2-6 have been determined. The structures of 3-6 reveal that the trinculear metal assemblies are nearly linear. The two terminal metal ions in a given assembly have an N(3)O(3) ligand environment in a distorted octahedral geometry while the central metal ion has an O(6) ligand environment also in a slightly distorted octahedral geometry. In all the complexes, ligand 2 coordinates to the metal ions through three imino nitrogens and three phenolate oxygens; the latter act as bridging ligands to connect the terminal and central metal ions. The compounds 2-6 also show intermolecular C-H...S=P contacts in the solid-state which lead to the formation of polymeric supramolecular architectures. The observed magnetic data for the (s = 5/2)3 L(2)(Mn(II))(3) derivative, 3, show an antiferromagnetic nearest- and next-nearest-neighbor exchange (J = -4.0 K and J' = -0.15 K; using the spin Hamiltonian H(HDvV) = -2J(S(1)S(2) + S(2)S(3)) - 2J'S(1)S(3)). In contrast, the (s = 1)(3) L(2)(Ni(II))(3) derivative, 5, displays ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions (J = 4.43 K and J' = -0.28 K; H = H(HDvV)+ S(1)DS(1) + S(2)DS(2)+ S(3)DS(3)). The magnetic behavior of the L(2)(Co(II))(3) derivative, 4, reveals only antiferromagnetic exchange analogous to 3 (J = -4.5, J' = -1.4; same Hamiltonian as for 3).