Synthesis of Iron and Cobalt Complexes of a Ferrocene-Linked Diphosphinoamide Ligand and Characterization of a Weak Iron-Cobalt Interaction.

A ferrocene-based bis(phosphinoamine) fc(NHP(i)Pr2)2 has been deprotonated and used in salt metathesis reactions to form dimeric complexes ([fc(NP(i)Pr2)2]M)2 (M = Fe, Co). A novel coordination environment for Co(II) is observed including a weak but significant Fe-Co interaction, which was characterized using X-ray crystallography, Mössbauer spectroscopy, and VT-magnetometry. Density functional theory (DFT) calculations including natural bond order analysis provides further support for the interaction and suggests a combination of Fe → Co and Co → Fe interactions.

Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Proradical Ligands.

The geometric and electronic structure of a doubly oxidized bimetallic Co complex containing two redox-active salen moieties connected via a 1,2-phenylene linker was investigated and compared to an oxidized monomeric analogue. Both complexes, namely, CoL(1) and Co2L(2), are oxidized to the mono- and dications, respectively, with AgSbF6 and characterized by X-ray crystallography for the monomer and by vis-NIR (NIR = near-infrared) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) magnetometry, and density functional theory (DFT) calculations for both the monomer and dimer. Both complexes exhibit a water molecule coordinated in the apical position upon oxidation. [CoL(1)-H2O](+) displays a broad NIR band at 8500 cm(-1) (8400 M(-1) cm(-1)), which is consistent with recent reports on oxidized Co salen complexes (Kochem, A. et al., Inorg. Chem., 2012, 51, 10557-10571 and Kurahashi, T. et al., Inorg. Chem., 2013, 52, 3908-3919). DFT calculations predict a triplet ground state with significant ligand and metal contributions to the singularly occupied molecular orbitals. The majority (∼75%) of the total spin density is localized on the metal, highlighting both high-spin Co(III) and Co(II)L(•) character in the electronic ground state. Further oxidation of CoL(1) to the dication affords a low-spin Co(III) phenoxyl radical species. The NIR features for [Co2L(2)-2H2O](2+) at 8600 cm(-1) (17 800 M(-1) cm(-1)) are doubly intense in comparison to [CoL(1)-H2O](+) owing to the description of [Co2L(2)-2H2O](2+) as two non-interacting oxidized Co salen complexes bound via the central phenylene linker. Interestingly, TD-DFT calculations predict two electronic transitions that are 353 cm(-1) apart. The NIR spectrum of the analogous Ni complex, [Ni2L(2)](2+), exhibits two intense transitions (4890 cm(-1)/26 500 M(-1) cm(-1) and 4200 cm(-1)/21 200 M(-1) cm(-1)) due to exciton coupling in the excited state. Only one broad band is observed in the NIR spectrum for [Co2L(2)-2H2O](2+) as a result of the contracted donor and acceptor orbitals and overall CT character.

Fe(III) bipyrrolidine phenoxide complexes and their oxidized analogues.

Fe(III) complexes of the symmetric (2S,2'S)-[N,N'-bis(1-(2-hydroxy-3,5-di-tert-butylphenylmethyl))]-2,2'-bipyrrolidine (H2L(1)) and dissymmetric (2S,2'S)-[N,N'-(1-(2-hydroxy-3,5-di-tert-butylphenylmethyl))-2-(pyridylmethyl)]-2,2'-bipyrrolidine (HL(2)) ligands incorporating the bipyrrolidine backbone were prepared, and the electronic structure of the neutral and one-electron oxidized species was investigated. Cyclic voltammograms (CV) of FeL(1)Cl and FeL(2)Cl2 showed expected redox waves corresponding to the oxidation of phenoxide moieties to phenoxyl radicals, which was achieved by treating the complexes with 1 equiv of a suitable chemical oxidant. The clean conversion of the neutral complexes to their oxidized forms was monitored by UV-vis-NIR spectroscopy, where an intense π-π* transition characteristic of a phenoxyl radical emerged ([FeL(1)Cl](+•): 25,500 cm(-1) (9000 M(-1) cm(-1)); [FeL(2)Cl2](+•): 24,100 cm(-1) (8300 M(-1) cm(-1)). The resonance Raman (rR) spectra of [FeL(1)Cl](+•) and [FeL(2)Cl2](+•) displayed the characteristic phenoxyl radical ν7a band at 1501 and 1504 cm(-1), respectively, confirming ligand-based oxidation. Electron paramagnetic resonance (EPR) spectroscopy exhibited a typical high spin Fe(III) (S = 5/2) signal for the neutral complexes in perpendicular mode. Upon oxidation, a signal at g ≈ 9 was observed in parallel mode, suggesting the formation of a spin integer system arising from magnetic interactions between the high spin Fe(III) center and the phenoxyl radical. Density functional theory (DFT) calculations further supports this formulation, where weak antiferromagnetic coupling was predicted for both [FeL(1)Cl](+•) and [FeL(2)Cl2](+•).

High pressure study of a highly energetic nitrogen-rich carbon nitride, cyanuric triazide.

Cyanuric triazide (CTA), a nitrogen-rich energetic material, was compressed in a diamond anvil cell up to 63.2 GPa. Samples were characterized by x-ray diffraction, Raman, and infrared spectroscopy. A phase transition occurring between 29.8 and 30.7 GPa was found by all three techniques. The bulk modulus and its pressure derivative of the low pressure phase were determined by fitting the 300 K isothermal compression data to the Birch-Murnaghan equation of state. Due to the strong photosensitivity of CTA, synchrotron generated x-rays and visible laser radiation both lead to the progressive conversion of CTA into a two dimensional amorphous C=N network, starting from 9.2 GPa. As a result of the conversion, increasingly weak and broad x-ray diffraction lines were recorded from crystalline CTA as a function of pressure. Hence, a definite structure could not be obtained for the high pressure phase of CTA. Results from infrared spectroscopy carried out to 40.5 GPa suggest the high pressure formation of a lattice built of tri-tetrazole molecular units. The decompression study showed stability of the high pressure phase down to 13.9 GPa. Finally, two CTA samples, one loaded with neon and the other with nitrogen, used as pressure transmitting media, were laser-heated to approximately 1100 K and 1500 K while compressed at 37.7 GPa and 42.0 GPa, respectively. In both cases CTA decomposed resulting in amorphous compounds, as recovered at ambient conditions.

Heterobimetallic coordination polymers based on the [Pt(SCN)4]2- and [Pt(SeCN)4]2- building blocks.

New complexes and the first coordination polymers containing [Pt(SCN)4](2-) of the type [M(L)x][Pt(SCN)4] (where L = 2,2'-bipyridine (bipy), x = 2, M = Co(II), Ni(II), Cu(II); L = ethylenediamine (en), x = 2, M = Ni(II), Cu(II); L = N,N,N',N'-tetramethylethylenediamine (tmeda), x = 1, M = Cu(II); L = 2,2';6',2″-terpyridine (terpy), x = 1, M = Mn(II), Co(II); L = 1,10-phenanthroline (phen), x = 2, M = Pb(II)) were prepared by reacting the appropriate metal-ligand cations with K2[Pt(SCN)4] and structurally characterized. [M(bipy)2Pt(SCN)4]2·2MeOH (M = Co (1), Cu (4)) consist of supramolecular tetranuclear distorted squares containing two [M(bipy)2](2+) and two [Pt(SCN)4](2+) units. [Cu(bipy)2(NCS)]2[Pt(SCN)4] (6) is a double salt of the [Pt(SCN)4](2-) anion and two [Cu(bipy)(NCS)](+) cations. [Cu(en)2Pt(SCN)4] (7, 8) are 1-D coordination polymers that are coordinated in either cis or trans fashion at the [Pt(SCN)4](2-) unit, for 7 and 8, respectively. Complexes [Cu(en)2Pt(SeCN)4] (9) and [Ni(en)2Pt(SCN)4] (10) are similar to 8 and 7, respectively, but complex 9 (prepared using ((n)Bu4N)2[Pt(SeCN)4]) also presents intermolecular Se-Se interactions which resulted in an increased dimensionality. Compounds [M(terpy)Pt(SCN)4] (M = Mn (11), Co (13)) involve 2-D sheets of [M(terpy)](2+) and [Pt(SCN)4](2-) units, whereas [Mn(terpy)2][Pt(SCN)4] (12) is a double salt of one [Mn(terpy)2](2+) unit and one [Pt(SCN)4](2-). [Cu(tmeda)Pt(SCN)4] (14) contains a five-coordinate Cu(2+) metal center coordinated to one tmeda ligand and three different [Pt(SCN)4](2-) units, resulting in 2-D sheets. [Pb(phen)2Pt(SCN)4] (15) contains an 8-coordinate Pb(2+) metal center coordinated to two phen ligands and four [Pt(SCN)4](2-), generating a 3-D network in the solid state. Structural correlations were established between the ancillary ligand, the choice of metal, the structure of the [Pt(SCN)4](2-) building block, and the resulting dimensionality of the coordination polymers.

Linking high anisotropy Dy3 triangles to create a Dy6 single-molecule magnet.

A unique Dy(III)(6) complex is created by linking of two Dy(III)(3) triangles, in which intramolecular ferromagnetic interactions and single-molecule magnetic behaviour have been observed.

Two-dimensional networks of lanthanide cubane-shaped dumbbells.

The syntheses, structures, and magnetic properties are reported for three new lanthanide complexes, [Ln(III)(4)(mu(3)-OH)(2)(mu(3)-O)(2)(cpt)(6)(MeOH)(6)(H(2)O)](2) (Ln = Dy (1.15MeOH), Ho (2.14MeOH), and Tb (3.18MeOH)), based on 4-(4-carboxyphenyl)-1,2,4-triazole ligand (Hcpt). The three complexes were confirmed to be isomorphous by infrared spectroscopy and single-crystal X-ray diffraction. The crystal structure of 1 reveals that the eight-coordinate metal centers are organized in two cubane-shaped moieties composed of four Dy(III) ions each. All metal centers in the cubane core are bridged by two mu(3)-oxide and two mu(3)-hydroxide asymmetrical units. Moreover, each cubane is linked to its neighbor by two externally coordinating ligands, forming the dumbbell {Dy(III)(4)}(2) moiety. Electrostatic interactions between the ligands of the triazole-bridged dimers form an extended supramolecular two-dimensional arrangement analogous to a metal-organic framework with quadrilateral spaces occupied by ligands from axial sheets and by four solvent molecules. The magnetic properties of the three compounds have been investigated using dc and ac susceptibility measurements. For 1, the static and dynamic data corroborate the fact that the {Dy(III)(4)} cubane-shaped core exhibits slow relaxation of its magnetization below 5 K associated with a single-molecule magnet behavior.

Stabilization of different redox levels of a tridentate benzoxazole amidophenoxide ligand when bound to Co(iii) or V(v).

A tridentate benzoxazole-containing aminophenol ligand NNOH2 was coordinated to Co and V metal centers and the electronic structure of the resultant complexes characterized by both experimental and theoretical methods. The solid state structure of the Co complex exhibits a distorted octahedral geometry with two tridentate ligands bound in meridional fashion, and coordination-sphere bond lengths consistent with a Co(iii) oxidation state. EPR and magnetic data support a S = 1/2 ground state, and a formal electronic description of Co(iii)(NNOAP)(NNOISQ) where NNOAP corresponds to an amidophenoxide and NNOISQ to the iminosemiquinone redox level. However, the metrical parameters are similar for both ligands in the solid state, and DFT calculations support delocalization of the ligand radical over both ligands, affording an intermediate ligand redox level Co(iii)(NNO1.5-)(NNO1.5-). The vanadyl complex exhibits a distorted octahedral geometry in the solid state consistent with a V(v) metal center and amidophenoxide (NNOAP), acetylacetonate and oxo ligands. The ligand metrical parameters are consistent with significant amidophenoxide to V(v) π donation. Overall, our results highlight the roles of electron transfer, delocalization, and π bonding in the metal complexes under study, and thus the complexity in assignment of the electronic structure in these systems.

Synthesis, structure and light scattering properties of tetraalkylammonium metal isothiocyanate salts.

A series of ammonium and tetraalkylammonium metal isothiocyanate salts of the type Q(y)[M(NCS)x] (M = Cr(III), x = 6, y = 3, Q = NH4(+), Me4N(+), Et4N(+), n-Bu4N(+); M = Mn(II), x = 6, y = 4, Q = Me4N(+); M = Mn(II), x = 5, y = 3, Q = Et4N(+); M = Fe(III), x = 6, y = 3, Q = Me4N(+), Et4N(+), n-Bu4N(+); M = Co(II), x = 4, y = 2, Q = n-Bu4N(+); M = Eu(III), Gd(III), Dy(III), x = 6, y = 3, Q = Bu4N(+)) has been synthesized and structurally characterized. The octahedral Cr(III) salts are isostructural to previously and newly reported Fe(III) salts. The Ln(III)-containing anions are also octahedral. For Mn(II), although the Me4N(+) salt is octahedral, the Et4N(+) salt [Mn(NCS)5](3-) possesses a distorted trigonal bipyramidal geometry. For (Et4N)3[Fe(NCS)6] and (n-Bu4N)3[Fe(NCS)6], a solid-state size-dependent change in colour from red to green was observed and was attributed to a light scattering phenomenon in the crystalline samples.

Synthesis, characterization and catalytic activity of copper(II) complexes containing a redox-active benzoxazole iminosemiquinone ligand.

A tridentate benzoxazole-containing aminophenol ligand HL(BAP) was synthesized and complexed with Cu(II). The resulting Cu(II) complexes were characterized by X-ray, IR, UV-vis-NIR spectroscopies, and magnetic susceptibility studies, demonstrating that the ligand is oxidized to the o-iminosemiquinone form [L(BIS)](-) in the isolated complexes. L(BIS)Cu(II)Cl exhibits a distorted tetrahedral geometry, while L(BIS)Cu(II)OAc is square pyramidal. In both solid state structures the ligand is coordinated to Cu(II)via the benzoxazole, as well as the nitrogen and oxygen atoms from the o-iminosemiquinone moiety. The chloride, or acetate group occupies the fourth and/or fifth positions in L(BIS)Cu(II)Cl and L(BIS)Cu(II)OAc, respectively. Magnetic susceptibility measurements indicate that both complexes are diamagnetic due to antiferromagnetic coupling between the d(9) Cu(II) centre and iminosemiquinone ligand radical. Electrochemical studies of the complexes demonstrate both a quasi-reversible reduction and oxidation process for the Cu complexes. While L(BIS)Cu(II)X (X = Cl) is EPR-silent, chemical oxidation affords a species with an EPR signal consistent with ligand oxidation to form a d(9) Cu(II) iminoquinone species. In addition, chemical reduction results in a Cu(II) centre most likely bound to an amidophenoxide. Mild and efficient oxidation of alcohol substrates to the corresponding aldehydes was achieved with molecular oxygen as the oxidant and L(BIS)Cu(II)X-Cs2CO3 as the catalyst.

Non-innocent ligand behaviour of a bimetallic Cu complex employing a bridging catecholate.

The geometric and electronic structure of a bimetallic Cu Schiff-base complex and its one-electron oxidized form have been investigated. The two salen units in the neutral complex 1 are linked via a bridging catecholate function, and the coupling between the two Cu(II) d(9) centres was determined to be weakly antiferromagnetic on the basis of solid-state magnetic studies (J = -3 cm(-1)), and variable-temperature electron paramagnetic resonance (EPR) (J = -3 cm(-1)). Theoretical calculations (DFT) were in agreement with the experimental results (J = -7 cm(-1)), and provided insight into the coupling mechanism for the neutral system. One-electron oxidation provided [1](+) which was observed to have limited stability in solution. The oxidized complex was determined to be a ligand radical species in solution, with the electron hole potentially localized on the redox-active dioxolene, the phenolate ligands, or delocalized over the entire ligand system. Electrochemical experiments and UV-vis-NIR spectroscopy, in combination with density functional theory (DFT) calculations, provided insight into the locus of oxidation and the degree of delocalization in this system. The ligand radical for [1˙](+) was determined experimentally to be localized on the dioxolene bridge with a small amount of spin density on the outer phenolate moieties predicted by the calculations. This assignment was aided via comparison to data for the Ni analogue (Inorg. Chem., 2011, 50, 6746). The resonance Raman spectrum of [1˙](+) (λ(ex) = 413 nm) in CH(2)Cl(2) solution clearly exhibited a new band at 1308 cm(-1) in comparison to 1, supporting semiquinone formation. Variable-temperature EPR on the three-spin system [1˙](+) did not provide definitive information on the coupling interaction, possibly due to a very small difference in energy between the S = 3/2 and S = 1/2 states and/or a very small zero-field splitting, in combination with significant line-broadening. The data is consistent with a description of the overall electronic structure of [1˙](+) as a bimetallic Cu(II) complex with a bridge-localized semiquinone ligand radical species.

Synthesis, characterisation and computational studies on a novel one-dimensional arrangement of Schiff-base Mn3 single-molecule magnet.

The syntheses, structures and magnetic properties are reported for three new manganese complexes containing the Schiff-base ((2-hydroxy-3-methoxyphenyl)methylene)isonicotinohydrazine (H(2)hmi) ligand. Complex [Mn(II)(H(2)hmi)(2)(MeOH)(2)Cl(2)] (1) was obtained from the reaction of H(2)hmi with MnCl(2) in a MeOH-MeCN mixture. Addition of triethylamine to the previous reaction mixture followed by diethyl ether diffusion yielded a dinuclear manganese [Mn(III)(2)(hmi)(2)(OMe)(2)](infinity).2MeCN.2OEt(2) (2) compound. Upon increasing the MnCl(2)/H(2)hmi ratio, the mixed valence complex [Mn(III)(2)Mn(II)(hmi)(2)(OMe)(2)Cl(2)](infinity).MeOH (3) was obtained. Dc and ac magnetic measurements were carried out on all three samples. The ac susceptibility and field dependence of the magnetisation measurements confirmed that complex 3 exhibits a single-molecule magnet behaviour with an effective energy barrier of 8.1 K and an Arrhenius pre-exponential factor of 3 x 10(-9) s.