Zinc, cadmium, and mercury complexes of a pyridyloxy-substituted cyclotriphosphazene: syntheses, structures, and fluxional behavior.

The synthesis and characterization of the fluxional, d(10) cyclotriphosphazene complexes, [MLCl(2)] (M = Zn, Cd, and Hg; L = spiro-[(1,1'-biphenyl)-2,2'-dioxy]tetrakis(4-methyl-2-pyridyloxy)cyclotriphosphazene), are described. Single-crystal X-ray structures show that the zinc complex has crystallized into two crystal forms: one as a tetrahedral species, with a N(2)Cl(2) donor set in which a geminal pair of the pendant pyridyloxy nitrogen atoms binds to the zinc, and the other as a trigonal-bipyramidal (tbp) one, with an N(3)Cl(2) donor set. The third nitrogen atom comes from the phosphazene ring and the two pyridyl ligands are non-geminal. The asymmetric unit of the cadmium complex contains three structurally distinct molecules. One molecule has a tbp structure similar to that of the zinc complex. The second molecule has a six-coordinate, distorted octahedral geometry around the cadmium center with a N(4)Cl(2) donor set, with three of the nitrogen donor atoms coming from the pendant pyridyloxy arms. The third site contains a tbp complex and a distorted octahedral species with a relative occupancy of 3:1. The identification of these three different forms in the one crystal suggests that the energy difference between the tbp and distorted octahedral isomers is not large. Quantitative analysis of the (1)H NMR and variable-temperature (31)P NMR spectra of the zinc, cadmium, and mercury complexes in a CD(2)Cl(2) solution, coupled with the X-ray structural results, shows that an associative fluxional mechanism (ΔS(++) < -65 J mol(-1) K(-1)) is operating.

Toward an iron(II) spin-crossover grafted phosphazene polymer.

Two new cyclotriphosphazene ligands with pendant 2,2':6',2″-terpyridine (Terpy) moieties, namely, (pentaphenoxy){4-[2,6-bis(2-pyridyl)]pyridoxy}cyclotriphosphazene (L(1)), (pentaphenoxy){4-[2,6-terpyridin-4-yl]phenoxy}cyclotriphosphazene (L(2)), and their respective polymeric analogues, L(1P) and L(2P), were synthesized. These ligands were used to form iron(II) complexes with an Fe(II)Terpy(2) core. Variable-temperature resonance Raman, UV-visible, and Mössbauer spectroscopies with magnetic measurements aided by density functional theory calculations were used to understand the physical characteristics of the complexes. By a comparison of measurements, the polymers were shown to behave in the same way as the cyclotriphosphazene analogues. The results showed that spin crossover (SCO) can be induced to start at high temperatures by extending the spacer length of the ligand to that in L(2) and L(2P); this combination provides a route to forming a malleable SCO material.

Structural trends in a series of bulky dialkylbiarylphosphane complexes of CuI.

CuI complexes containing the bulky dialkylbiarylphosphane 2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl (tBuXPhos, L) and an ancillary ligand (Cl-, Br-, I-, MeCN, ClO4- or SCN-) have been structurally characterized, namely, chlorido[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I), [CuCl(C29H45P)], 1, bromido[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I), [CuBr(C29H45P)], 2, [2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]iodidocopper(I), [CuI(C29H45P)], 3, (acetonitrile-κN)[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I) hexafluoridophosphate, [Cu(CH3CN)(C29H45P)]PF6, 4, [2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP](perchlorato-κO)copper(I), [Cu(ClO4)(C29H45P)], 5, and di-µ-thiocyanato-κ2S:N;κ2N:S-bis{[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I)}, [Cu2(NCS)2(C29H45P)2], 6. Iodide complex 3 shows significant CuI-arene interactions, in contrast to its chloride 1 and bromide 2 counterparts, which is attributed to the weaker interaction between the iodide ion and the CuI centre. When replacing iodide with an acetonitrile (in 4) or perchlorate (in 5) ligand, the reduced interaction between the CuI atom and the ancillary ligand results in stronger CuI-arene interactions. No CuI-arene interactions are observed in dimer 6, due to the tricoordinated CuI centre having sufficient electron density from the coordinated ligands.

Excited states of Ru(II) and Re(I) bipyridyl complexes attached to cyclotriphosphazenes: a synthetic, spectroscopic, and computational study.

A series of new cyclotriphosphazene ligands substituted with pendant 2,2'-bipyridyl moieties, namely, bis[(1,1'-biphenyl)-2,2'-dioxy](2,2'-bipyridyl-3,3'-dioxy)cyclotriphosphazene (L(1)), bis[(1,1'-biphenyl)-2,2'-dioxy][bis{4-(2,2'-bipyridin)-4-yl-phenyoxy}]cyclotriphosphazene (L(2)), (pentaphenoxy)[4-(2,2'-bipyridin)-4-yl-phenyoxy]cyclotriphosphazene (L(3)), and (pentaphenoxy) [4-{6-phenyl(2,2'-bipyridin)-4-yl}-phenoxy]cyclotriphosphazene (L(4)), has been used to synthesize the ruthenium(II) and rhenium(I) complexes, [(L)Ru(bpy)(2)](PF(6))(4) (L = L(1) or L(3)), [(L(2)) {Ru(bpy)(2)}(2)](PF(6))(4), [(L)Re(CO)(3)Cl] (L = L(1), L(3) or L(4)), and [(L(2)) {Re(CO)(3)Cl}(2)]. Single crystal X-ray structures of [(L(1))Re(CO)(3)Cl] and [(L(4))Re(CO)(3)Cl] show the bipyridyl component of the cyclotriphosphazene substituted ligands is bound to the Re(I) giving a distorted octahedral "N(2)C(3)Cl" coordination sphere in both cases. Density functional theory (DFT) methods were employed to model the ground-state vibrational properties of the molecules, and their accuracies verified using vibrational spectroscopy. Electronic transitions were identified using UV-visible and resonance Raman spectroscopic techniques, aided by time-dependent (TD) DFT methods. Transient resonance Raman spectra of the excited states of the compounds were acquired and found to be comparable to those reported for studied metal bipyridyl units lacking the cyclotriphosphazene substituents. The cyclotriphosphazene unit has little effect on the properties of the metal bipyridyl chromophore.

Metal-metal communication in copper(II) complexes of cyclotetraphosphazene ligands.

Copper(II) chloride and bromide react with the pyridyloxy-substituted cyclotetraphosphazene ligands, octakis(2-pyridyloxy)cyclotetraphosphazene (L(1)), and octakis(4-methyl-2-pyridyloxy)cyclotetraphosphazene (L(2)), to form the dimetallic complexes, [L(CuX2)2] (L = L(1), X = Br; L = L(2), X = Cl or Br), and [{L(1)(CuCl2)2}n]. Single crystal X-ray crystallography shows the complex [{L(1)(CuCl2)2}n] to be a coordination polymer propagated by interligand "Cu(mu-Cl)2Cu" bridges whereas [L(2)(CuCl2)2] forms discrete dimetallic cyclotetraphosphazene-based moieties. The variable temperature magnetic susceptibility data for [{L(1)(CuCl2)2}n] are consistent with a weak antiferromagnetic exchange interaction between the copper(II) centers occurring via the bridging chloride ions. [L(2)(CuCl2)2] and [L(CuBr2)2] (L = L(1) and L(2)) exhibit normal Curie-like susceptibilities. The abstraction of a chloride ion, using [Ag(MeCN)4](PF6), from each copper site in [L(2)(CuCl2)2], affords the new complex, [L(2)(CuCl)2](PF6)2, in which the two copper(II) ions are separated by "N-P=N-P=N" phosphazene bridges. Electron spin resonance and variable temperature magnetic measurements indicate the occurrence of weak antiferromagnetic coupling between the unpaired electrons on the copper(II) centers. Density Functional Theory (DFT) calculations on the [L(2)(CuCl)2](2+) dication and the related cyclotriphosphazene complex, [L(4)(CuCl2)2] (L(4) = hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene), have identified "electron-density-bridge" molecular orbitals which involve Cu 3d orbitals overlapping with the non-bonding N-based molecular orbitals on the phosphazene rings as the pathway for this interaction.

Conformationally rigid chelate rings in metal complexes of pyridyloxy-substituted 2,2'-dioxybiphenyl-cyclotetra- and cyclotriphosphazene platforms.

Divalent metal halides react with pyridyloxy-substituted 2,2'-dioxybiphenyl-cyclotri- and cyclotetraphosphazene ligands to form the complexes, [MLX2] [M=Co or Cu; L=(2,2'-dioxybiphenyl)tetrakis(2-pyridyloxy)cyclotriphosphazene (L1) or (2,2'-dioxybiphenyl)tetrakis(4-methyl-2-pyridyloxy)cyclotriphosphazene (L2); X=Cl or Br], [ZnLCl2] [L=bis(2,2'-dioxybiphenyl)bis(2-pyridyloxy)cyclotriphosphazene (L3) or bis(2,2'-dioxybiphenyl)bis(4-methyl-2-pyridyloxy)cyclotriphosphazene (L4)], [MLCl2] [M=Cu or Hg; L=tris(2,2'-dioxybiphenyl)bis(2-pyridyloxy)cyclotetraphosphazene (L5)] and [Cu2LCl4] (L=trans-bis(2,2'-dioxybiphenyl)tetrakis(2-pyridyloxy)cyclotetraphosphazene (L6)]. Single-crystal X-ray structures show the L2 ligand complexes to have a N3Cl2 five-coordinate, trigonal-bipyramidal donor set with the phosphazene ring and pendant pyridyloxy nitrogens binding to the metal ions. The coordinated L2 ligand in the complex, [CoL2Cl2], slowly hydrolyses in acetonitrile with the loss of a pyridine pendant arm to form a dimetallic species, which has been characterized by crystallography as [{CoL2aCl}]2.4MeCN (L2a=[N3P3(biph)(OPy)3(O)]-, biph=2,2'-dioxybiphenyl, OPy=2-oxopyridine). The ligands, L3, L4, L5, and L6, bind to the metal halides via gem-substituted pyridyloxy nitrogens only. The resulting rigid eight-membered chelate rings all have distorted boat conformations, which force distorted-tetrahedral N2Cl2 coordination environments onto the metal ions. The spectroscopic (ESR and electronic) and magnetic properties of the complexes are reported.

Conformational flexibility in 2,2'-Dioxybiphenyl-chloro-cyclotetraphosphazenes and its relevance to polyphosphazene analogues.

The reaction of the cyclotetraphosphazene, [N4P4Cl8], with the difunctional reagent, 2,2'-biphenol, in the presence of potassium carbonate in acetone produced the spiro-substituted derivatives, 2,2'-dioxybiphenylhexachlorocyclotetraphosphazene, bis(2,2'-dioxybiphenyl)tetrachloro-cyclotetraphosphazene, and tris(2,2'-dioxybiphenyl)dichlorocyclotetraphosphazene. Both cis and trans geometrical isomers of the bis compound are observed. Although chromatographic separation of these was unsuccessful, a sample of the trans isomer was obtained by fractional crystallization. The compounds all show non-first-order 31P NMR spectra which were simulated to extract the spectral parameters. Single-crystal X-ray structures of both the trans bis and the tris compounds show that the cyclophosphazene rings exhibit conformational flexibility which gives rise to different crystalline forms being obtained from the same solvent systems. Crystals of trans-bis(2,2'-dioxybiphenyl)tetrachloro-cyclotetraphosphazene were obtained in two different space groups: Pnna (orthorhombic) and P21/n (monoclinic). In the orthorhombic structure, the dominant (72%) conformation of one phosphazene ring is a chair form, and the other (28%) resembles a boat. While for the monoclinic structure, the ring is virtually flat with an oval shape. In both cases the dioxybiphenyl groups are found in R and S configurations in the same molecule and are pi stacked in columns (Pnna) or involved in pi-pi or pi-H interactions (P21/n), thus anchoring the phosphorus atoms of the cyclotetraphosphazenes but still allowing flexibility in the ring conformations. Three crystalline modifications of tris(2,2'-dioxybiphenyl)dichloro-cyclotetraphosphazene were obtained: two in space group P (triclinic), which contained two molecules of dichloromethane in the unit cell, and one solvent-free form in space group P21/n (monoclinic). The cyclophosphazene rings exhibit puckered conformations with the trans-dioxybiphenyl moieties having opposing RS or SR conformations. DFT calculations were carried out on each of the phosphazene ring conformations in trans-bis(2,2'-dioxybiphenyl)tetrachlorocyclotetraphosphazene identified from the X-ray diffraction analysis. It is concluded that intermolecular interactions (i.e., pi-pi or pi-H) between the dioxybiphenyl groups is a factor that modifies the nature of the potential energy surface between the different conformers. The flexibility of the phosphazene ring is supported computationally through the calculated low-energy barriers and experimentally through the highly disordered phosphazene ring conformations observed in the solid state. The results on 2,2'-dioxybiphenyl-substituted cyclotetraphosphazenes provide evidence that microcrystalline domains in their 2,2'-dioxybiphenyl-substituted polyphosphazene analogues will be generated by similar pi-pi and pi-H interactions.

Gold(I) and platinum(II) complexes with a new diphosphine ligand based on the cyclotriphosphazene platform.

A new diphosphine ligand assembled on the cyclotriphosphazene platform forms linear chelate and dimetallic bridged complexes with Au(I) and a cis-chelate complex with Pt(II).

Polymer building blocks: self-assembly of silver(I) cyclotriphosphazene cationic columns.

The multimodal ligand hexakis(2-pyridyloxy)cyclotriphosphazene (L) and its 4-methyl-2-pyridyloxy analogue (MeL) react with Ag(I) to afford {[AgL]+}infinity supramolecular cationic columns via self-assembly, with the anions occupying the intercolumnar channels. In contrast, the reaction of MeL with Cu(I) yields a dimetallic Cu(II) complex containing mu-OH and mu-4-methyl-2-pyridyloxylato bridges.

Copper(II) chloride complexes with multimodal ligands based on the cyclotriphosphazene platform.

The reaction of hexakis(2-pyridyloxy)cyclotriphosphazene (L) and hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene (MeL) with copper(ii) chloride afford the complexes [CuLCl(2)], [(CuCl(2))(2)(MeL)], [CuLCl]PF(6) and [Cu(MeL)Cl]PF(6). The single-crystal X-ray structure of [CuLCl(2)] shows the copper ion to be in a square based pyramidal distorted trigonal bipyramidal (SBPDTBP) environment (tau= 0.47) with L acting as a kappa(3)N donor, coordinating via the nitrogen atoms from two non-geminal pyridyloxy pendant arms, a nitrogen atom in the phosphazene ring and two chloride ions. In the dimetallic complex, [(CuCl(2))(2)(MeL)], the geometry about both (symmetry related) copper(ii) centres is also SBPDTBP (tau= 0.57) with a 'N(3)Cl(2)' donor set. In the monocation of [CuLCl]PF(6), L acts as a kappa(5)N donor, bonding to the copper(ii) centre through the nitrogen atoms of four pyridyloxy pendant arms, a phosphazene ring nitrogen atom and a chloride ion to give an elongated rhombic octahedral coordination sphere. The phosphazene ring atoms remain virtually coplanar in all three structures as a consequence of the phenoxy-hinge, which links the pyridine pendant donors to the cyclotriphosphazene platform, allowing the formation of six-membered chelate rings. The spectroscopic (mass spectral, EPR and electronic) and magnetic properties of the complexes are discussed. The EPR and variable temperature magnetic susceptibility results for the dicopper complex, [(CuCl(2))(2)(MeL)], point to a very weak electronic interaction between the metal atoms.

A phenolate-induced trans influence: crystallographic evidence for unusual asymmetric coordination of an alpha-diimine in ternary complexes of iron(III) possessing biologically relevant hetero-donor N-centered tripodal ligands.

Three mononuclear ternary complexes of iron(III) with an alpha-diimine (bipy or phen) and a derivative of N,N-bis(2-hydroxybenzyl)glycinate (L3-) have been synthesized and characterized by magnetic susceptibility measurements, electron paramagnetic resonance (EPR) spectroscopy, vibrational spectroscopy, and electronic absorption spectroscopy. Single-crystal X-ray structure determinations of the pseudo-octahedral complexes [Fe(bipy)L] x MeCN [L = (3,5-Br2)-L3- or (5,3-Cl,Me)-L3-] revealed a considerable and consistent distortion in the coordination of bipy to iron(III) attributable largely to electronic effects. In both crystal structures, the Fe-N(pyridyl) bond trans to the phenolate oxygen is 0.133 A longer than the other one positioned trans to the tertiary amine nitrogen, a relatively weaker donor. This coordination behavior of bipy is of structural interest and has not been observed previously for iron(III). The electronic and EPR spectra of the compounds [Fe(L'-L')L] x MeCN (L'-L' = bipy or phen) are consistent with the spin state of the central metal atom (S = 5/2). The charge-transfer transitions arising from the strong interactions of the phenolate moieties with the ferric ion have been identified as phenolate (p(pi)) --> iron(III) (d(pi*)) (lambda(max) approximately 500 nm, epsilon approximately 3000 M(-1) cm(-1)) and phenolate (p(pi)) --> iron(III) (d(sigma*) (lambda(max) approximately 320 nm, epsilon approximately 5200 M(-1) cm(-1)). The presence of the phenolate moieties in the quadridentate hetero-donor tripodal ligands, H3L, lends these iron(III) ternary complexes the potential to model the specific metal-coordination, metal-substrate interactions, and physicochemical behaviors of several iron-tyrosinate proteins.

Structural and spectroscopic studies on mercury(II) tribenzylphosphine complexes.

The tribenzylphosphine (PBz3) complexes of mercury(II), [Hg(PBz3)2](BF4)2, [Hg(PBz3)2(NO3)2] and [HgX(NO3)(PBz3)](X = Cl, Br, I and SCN), have been synthesised and their structures determined by single-crystal X-ray crystallography. [Hg(PBz3)2](BF4)2 contains [Hg(PBz3)2]2+ cations with linear P-Hg-P coordination, the first example of a truly two-coordinate [Hg(PR3)2]2+ complex. The mercury coordination in [Hg(PBz3)2(NO3)2] can be described as distorted tetrahedral, with a significant deviation of the P-Hg-P angle from linearity as a result of coordination of the nitrate groups. Nitrate coordination is also observed in [HgX(NO3)(PBz3)](X = Cl, Br, I), resulting in significantly non-linear P-Hg-X coordination. The thiocyanate complex is a centrosymmetric thiocyanate-bridged dimer with distorted trigonal-pyramidal mercury coordination to the P atom of PBz3, to the S and N atoms of two bridging thiocyanate groups, and to the O atom of one nitrate group. For all the nitrato complexes, secondary mercury-nitrate interactions (Hg-O 2.7-3.1 A) effectively raise the coordination number of the Hg(II) centres to six. High-resolution 31P solid-state NMR spectra of the six tribenzylphosphine mercury(II)-complexes, obtained by combining magic-angle spinning, proton dipolar decoupling and proton-phosphorus cross-polarization (CP-MAS), have been recorded. The spectra of [Hg(PBz3)2](BF4)2 and [HgX(NO3)(PBz3)](X = Cl, Br, I and SCN) exhibit a single line, due to species that contain non-magnetic isotopes of mercury, and satellite lines, due to 1J(31P-199Hg) coupling. The asymmetric unit of [Hg(PBz3)2(NO3)2] contains two molecules with four phosphorus environments, resulting in two AB spectra with 2J(31P-31P) coupling, due to species that contain non-magnetic isotopes of mercury, and satellite lines consisting of two ABX spectra, due to 1J(31P-199Hg) coupling. These spectra have been analysed to yield all of the chemical shifts and coupling constants involved. A remarkable increase in 1J(31P-199Hg) is observed from [Hg(PBz3)2](BF4)2 to [Hg(PBz3)2(NO3)2] as a consequence of the incorporation of the nitrate group into the Hg coordination sphere in the latter case. Several of the spectra also exhibit broader satellites due to the presence of scalar spin-spin coupling between 31P and the quadrupolar 201Hg nucleus. Slow-spinning methods have been used to analyze the spinning-sideband intensities of the NMR spectra, in order to obtain the 31P shielding anisotropy and asymmetry parameters Deltasigma and eta. The 199Hg and 31P NMR shielding tensors of PMe3 models of the above six compounds have been calculated using relativistic density functional theory. The 31P results are in good agreement with experiment and assist in the assignment of some of the signals.