Syntheses of novel exo and endo isomers of ansa-substituted fluorophosphazenes and their facile transformations into spiro isomers in the presence of fluoride ions

Reactions of the dilithiated diols RCH2P(S)(CH2OLi)2 [R = Fc (1), Ph (2) (Fc = ferrocenyl)] with N3P3F6 in equimolar ratios at -80 degrees C result exclusively in the formation of two structural isomers of ansa-substituted compounds, endo-RCH2P(S)(CH2O)2[P(F)N]2(F2PN) [R = Fc (3a), Ph (4a)] and exo-RCH2P(S)(CH2O)2[P(F)N]2(F2PN) [R = Fc (3b), Ph (4b)], which are separated by column chromatography. Increasing the reaction temperature to -40 degrees C results in more of the exo isomers 3b and 4b at the expense of the endo isomers. The formation of the ansa-substituted compounds is found to depend on the dilithiation of the diols, as a reaction of the silylated phosphine sulfide FcCH2P(S)(CH2OSiMe3)2 (5) with N3P3F6 in the presence of CsF does not yield either 3a or 3b but instead gives the spiro isomer [FcCH2P(S)(CH2O)2 PN](F2PN)2 (6) as the disubstitution product of N3P3F6. The ansa isomers 3a and 3b are transformed into the spiro compound 6 in the presence of catalytic amounts of CsF at room temperature in THF, while 4a and 4b are transformed into the spiro compound [PhCH2P(S)(CH2O)2PN](F2PN)2 (7) under similar conditions. The novel conversions of ansa-substituted phosphazenes into spirocyclic phosphazenes were monitored by time-dependent 31P NMR spectroscopy. The effect of temperature on a transformation was studied by carrying out reactions at various temperatures in the range from -60 to +33 degrees C for 3b. In addition, compounds 3a, 3b, 4a, and 6 were structurally characterized. In the case of the ansa compounds, the nitrogen atom flanked by the bridging phosphorus sites was found to deviate significantly from the plane defined by the five remaining atoms of the phosphazene ring.     

Ansa versus spiro substitution of cyclophosphazenes: is fluorination essential for ansa to spiro transformation of cyclophosphazenes?

Fluorinated ansa substituted cyclophosphazenes endo-FcCH(2)P(S)(CH(2)O)(2)[P(F)N](2)(F(2)PN) [Fc = ferrocenyl] (1) and exo-FcCH(2)P(S)(CH(2)O)(2)[P(F)N](2)(F(2)PN) (2) readily transform to the spirocyclic compound [FcCH(2)P(S)(CH(2)O)(2)PN](F(2)PN)(2) (3) not only in the presence of CsF but also with non-fluorinated bases such as Cs(2)CO(3), K(2)CO(3), KOBu(t), Et(3)N, DABCO, DBN, and DBU. The analogous tetrachloro ansa compound exo-FcCH(2)P(S)(CH(2)O)(2)[P(Cl)N](2)(Cl(2)PN) (5), however, did not transform to the chlorinated spiro compound (6) in the presence of these bases. With excess of CsF, P-Cl bonds of 5 were found to undergo fluorination leading to the formation of 2, which transformed to spirocyclic compound 3. Time dependent (31)P NMR spectroscopy was used to monitor this transformation. Crystal structure studies on the ansa substituted compounds 4 and 5 have shown weak bonding interactions involving C-H...Cl, C-H...O, and C-H...S interactions.     

1,3-Diaxial steric effects and intramolecular hydrogen bonding in the conformational equilibria of new cis-1,3-disubstituted cyclohexanes using low temperature NMR spectra and theoretical calculations

The conformational equilibria of 3-X-cyclohexanol [X=F (1), Cl (2), Br (3), I (4), Me (5), NMe(2) (6) and MeO (7)] and of 3-X-methoxycyclohexane [X=F (8), Cl (9), Br (10), I (11), Me (12), NMe(2) (13) and MeO (14)] cis isomers were determined from low temperature NMR spectra and PCMODEL calculated coupling constants. The energy differences between aa and ee conformers were obtained from these data (DeltaG(J)(av) and DeltaG(PC)(av), respectively) and also by the additivity principle from data for the monosubstituted cyclohexanes (DeltaG(Ad)). H-1 and H-3 hydrogen vicinal coupling constants and DeltaG(J)(av) values showed that the diequatorial conformer is predominant in the conformational equilibrium of the compounds studied at low temperature. However, DeltaG(PC)(av) data show that compounds 6 and 7 constitute an exception, since they are almost equally populated by ee and aa at room temperature, due to stabilization of their aa conformer by an intramolecular hydrogen bond. DeltaG(Ad) values, obtained according to the additivity principle, show a better agreement for compounds 2 and 3, since the 1,3-diaxial steric effect is counterbalanced by the formation of an intramolecular hydrogen bond (IAHB). For the remaining compounds, DeltaG(Ad) values underestimate the energy differences, since the 1,3-diaxial steric effect, between X and OH or OCH(3), is absent in the monosubstituted compounds used as references. Moreover, the DeltaG(PC)(av), calculated from the coupling constants, obtained through the PCMODEL program, are rather smaller than the DeltaG(J)(av) values, since the program does not have parameters for the effect, observed in this report, of a substituent at gamma position on coupling constants values for the hydrogen under consideration.     

Syntheses and experimental studies on the relative stabilities of spiro, ansa, and bridged derivatives of cyclic tetrameric fluorophosphazene

Reactions of (CF2CH2OSiMe3)2 and CF2(CF2CH2OSiMe3)2 with N4P4F8 (1) in a 1:2.5 molar ratio resulted in the formation of monospiro compounds [(CF2CH2O)2PN](F2PN)3 (2) and [CF2(CF2)CH2O)2PN](F2PN)3 (4) as well as the intermolecular bridged compounds F7N4P4OCH2CF2CF2CH2OP4N4)F7 (3) and F7N4P4OCH2CF2CF2CF2CH2OP4N4F7 (5). An equimolar reaction of dilithiated 1,3-propanediol with 1 resulted in the 1,3-ansa-substituted compound CH2(CH2O)2[P(F)N]2(F2PN)2 (6) as the major product in good yield. However, an analogous reaction of the dilithiated 1,3-propanedithiol with 1 gave only the spirocyclic compound CH2(CH2S)2(PN)(F2PN)3 (8). The molecular structures of 2 and 6 were determined by single-crystal X-ray diffraction. In the presence of catalytic amounts of CsF in THF, the bridged compound 3 was converted to the spirocyclic compound 2 while the 1,3-ansa compound 6 under similar conditions transformed into the monospiro-substituted compound CH2(CH2O)2 (PN)(F2PN)3 (7). These transformations were monitored by time-dependent 19F and 31P NMR studies.     

Interpretation of indirect nuclear spin-spin coupling tensors for polyatomic xenon fluorides and group 17 fluorides: results from relativistic density-functional calculations

Significant improvements have been made recently in the calculation of NMR indirect nuclear spin-spin coupling tensors (J). In particular, the relativistic zeroth-order regular approximation density-functional theory (ZORA-DFT) approach holds great promise for the calculation of spin-spin coupling constants for a variety of chemical systems containing heavy nuclei. In the present work, the ZORA-DFT method is applied to the calculation of the complete reduced coupling tensors, K, for a range of chlorine-, bromine-, iodine-, and xenon-containing species: K(Cl,F) for ClF(2)(+), ClF(3), ClF(4)(+), ClF(5), ClF(6)(-), and ClF(6)(+); K(Br,F) for BrF(3), BrF(6)(-), and BrF(6)(+); K(I,F) for IF(4)(+) and IF(6)(+); K(Xe,F) for XeF(+), XeF(2), XeF(3)(+), XeF(4), XeF(5)(-), XeF(5)(+), and XeF(7)(+). These species represent a wide variety of geometrical bonding arrangements. Agreement between the calculated coupling constants and available experimental data is excellent, and the absolute sign of the coupling constants is provided. It is shown that (1)K(iso) may be positive or negative even within the same molecule, e.g., K(Cl,F)(iso) may be of either sign, depending on the local environment. Periodic trends in (1)K(iso) for isovalent and isostructural molecules are evident. The spin-spin coupling anisotropies, Delta K, and the orientations of the K tensors are also determined. The success of the calculations is a direct result of employing reliable geometries and considering both scalar and spin-orbit relativistic effects. The dependence of K(Cl,F)(iso) and K(Xe,F)(iso) on the local molecular and electronic structure is discussed in terms of the paramagnetic spin-orbit (PSO) and combined Fermi-contact spin-dipolar (FC+SD) coupling mechanisms. The PSO term depends strongly on the number of valence shell electron lone pairs on the central heavy atom, and the FC+SD contribution increases with the Cl[bond]F or Xe[bond]F bond length for a given series of compounds. This interpretation allows for the successful rationalization of the existing experimental data.     

Preparation of the first examples of ansa-spiro substituted fluorophosphazenes and their structural studies: analysis of C-H...F-P weak interactions in substituted fluorophosphazenes

The reactions of fluorophosphazenes, endo ansa FcCH(2)P(S)(CH(2)O)(2)[P(F)N](2)(F(2)PN) (1) (Fc = ferrocenyl) and spiro [RCH(2)P(S)(CH(2)O)(2)PN](F(2)PN)(2) (R = Fc (2), C(6)H(5) (3)], with dilithiated diols have been explored. The study resulted in the formation of the first examples of ansa-spiro substituted fluorinated cyclophosphazenes as well as a bisansa substituted fluorophosphazene. The bisansa compound [1,3-[FcCH(2)P(S)(CH(2)O)(2)]][1,5-[CH(2)(CH(2)O)(2)]]N(3)P(3)F(2) (4) was found to be nongeminaly substituted with both the ansa rings in cis configuration, which is in stark contrast to the observations on cyclic chlorophosphazenes where geminal bisansa formation has been observed. The ansa-spiro compounds (5-7) underwent the ansa to spiro transformation leading to dispiro compounds in the presence of catalytic amounts of CsF at room temperature. Two of the ansa-spiro compounds, endo-[3,5-[FcCH(2)P(S)(CH(2)O)(2)]][1,1-[CH(2)(CH(2)O)(2)]]N(3)P(3)F(2) (5) and endo-[3,5-[FcCH(2)P(S)(CH(2)O)(2)]][1,1-[FcCH(2)P(S)(CH(2)O)(2)]]N(3)P(3)F(2) (6), were structurally characterized, and the crystal structures indicate boat-chair conformation as well as crown conformation for the eight-membered ansa rings. Weak C-H.F-P interactions observed in the crystal structures of the ansa-spiro substituted fluorophosphazene derivatives have been analyzed and compared with C-H.F-P interactions of other fluorinated phosphazenes and thionyl phosphazenes.     

Ab initio study of complexes with two cations as N-H donors to F-: structures and spin-spin coupling constants across N-H-F hydrogen bonds

A systematic ab initio study has been carried out to determine the MP2/6-31+G(d,p) structures and EOM-CCSD coupling constants across N-H-F-H-N hydrogen bonds for a series of complexes F(H(3)NH)(2)(+), F(HNNH(2))(2)(+), F(H(2)CNH(2))(2)(+), F(HCNH)(2)(+), and F(FCNH)(2)(+). These complexes have hydrogen bonds with two equivalent N-H donors to F(-). As the basicity of the nitrogen donor decreases, the N-H distance increases and the N-H-F-H-N arrangement changes from linear to bent. As these changes occur and the hydrogen bonds between the ion pairs acquire increased proton-shared character, (2h)J(F)(-)(N) increases in absolute value and (1h)J(H)(-)(F) changes sign. F(H(3)NH)(2)(+) complexes were also optimized as a function of the N-H distance. As this distance increases and the N-H...F hydrogen bonds change from ion-pair to proton-shared to traditional F-H...N hydrogen bonds, (2h)J(F)(-)(N) initially increases and then decreases in absolute value, (1)J(N)(-)(H) decreases in absolute value, and (1h)J(H)(-)(F) changes sign. The signs and magnitudes of these coupling constants computed for F(H(3)NH)(2)(+) at short N-H distances are in agreement with the experimental signs and magnitudes determined for the F(collidineH)(2)(+) complex in solution. However, even when the N-H and F-H distances are taken from the optimized structure of F(collidineH)(2)(+), (2h)J(F)(-)(N) and (1h)J(H)(-)(F) are still too large relative to experiment. When the distances extracted from the experimental NMR data are used, there is excellent agreement between computed and experimental coupling constants. This suggests that the N-H-F hydrogen bonds in the isolated gas-phase F(collidineH)(2)(+) complex have too much proton-shared character relative to those that exist in solution.     

Characterizing hydrogen bonding and proton transfer in 2:1 FH:NH3 and FH:collidine complexes through one- and two-bond spin-spin coupling constants across hydrogen bonds

Ab initio equation-of-motion coupled cluster singles and doubles calculations have been carried out on a variety of 2:1 FH:NH(3) complexes (F(b)H(b):F(a)H(a):NH(3)) to investigate the effects of structural changes on one- and two-bond spin-spin coupling constants across F(a)-H(a)-N and F(b)-H(b)-F(a) hydrogen bonds and to provide insight into experimentally measured coupling constants for 2:1 FH:collidine (2:1 FH:2,4,6-trimethylpyridine) complexes. Coupling constants have been computed for 2:1 FH:NH(3) equilibrium structures and proton-transferred perpendicular and open structures at 2:1 FH:NH(3), FH:pyridine, and FH:collidine geometries. (2h)J(Fa)(-)(N), (1)J(Fa)(-)(Ha), and (1h)J(Ha)(-)(N) exhibit expected dependencies on distances, angles, and the nature of the nitrogen base. In contrast, one- and two-bond coupling constants associated with the F(b)-H(b)-F(a) hydrogen bond, particularly (2h)J(F)()b(-)(F)()a, vary significantly depending on the F-F distance, the orientation of the hydrogen-bonded pair, and the nature of the complex (HF dimer versus the anion FHF(-)). The structure of the 2:1 FH:collidine complex proposed on the basis of experimentally measured coupling constants is supported by the computed coupling constants. This study of the structures of open proton-transferred 2:1 FH:NH(3), FH:pyridine, and FH:collidine complexes and the coupling constants computed for 2:1 FH:NH(3) complexes at these geometries provides insight into the role of the solvent in enhancing proton transfer across both N-H(a)-F(a) and F(b)-H(b)-F(a) hydrogen bonds.     

Synthesis, crystal structures and magnetic properties of bis(μ-dialkoxo)-bridged linear trinuclear copper(II) complexes with aminoalcohol ligands: a theoretical/experimental magneto-structural study

The bis(μ-dialkoxo)-bridged trinuclear copper(II) complexes [Cu(3)(ap)(4)(ClO(4))(2)EtOH] (1), [Cu(3)(ap)(4)(NO(3))(2)] (2), [Cu(3)(ap)(4)Br(2)] (3) and [Cu(3)(ae)(4)(NO(3))(2)] (4) (ae = 2-aminoethanolato and ap = 3-aminopropanolato) have been synthesised via self-assembly from chelating aminoalcohol ligands with the corresponding copper(II) salts. The complexes are characterised by single-crystal X-ray diffraction analyses and variable temperature magnetic measurements. The crystal structures of complexes 1-4 consist of slightly bent linear or linear trinuclear [Cu(3)(aa)(4)](2+) (aa = aminoalcoholato) units to which the perchlorate, nitrate or bromide anions are weakly coordinated. The adjacent trinuclear units of 1-4 are connected together by hydrogen bonds and bridging nitrate or bromide anions resulting in the formation of 2D layers. Magnetic studies of 1, 2 and 4 show that J values vary from -379 to +36.0 cm(-1) as the Cu-O-Cu angle (θ) and the out-of-plane shift of the carbon atom of the bridging alkoxo group (τ) vary from 103.7 to 94.4° and from 0.9 to 35.5°, respectively. Magnetic exchange coupling constants calculated by DFT methods are of the same nature and magnitude as the experimental ones. For complexes 1, 2 and 4, which have complementarity effects between the θ and τ angles (small θ values are associated with large τ values and vice versa), an almost linear relationship between the calculated J values with θ angles could be established, thus supporting that the θ and τ angles are the two key structural factors that determine the magnetic exchange coupling for such a type of compounds. Complex 3 does not obey this linear correlation because of the existence of counter-complementarity effects between these angles (small θ values are associated with small τ values and vice versa). It is of interest that the theoretical calculations for the magnetic exchange interaction between next-nearest neighbours indicate that the usual approximation in experimental studies of neglecting the magnetic coupling between the next-nearest neighbours in linear trinuclear complexes could lead to considerable errors, especially when J(1) and J(2) are of the same order of magnitude as J(3).     

A theoretical study of the NMR spin-spin coupling constants of the complexes [(NC)(5)Pt-Tl(CN)(n)](n-) (n = 0-3) and [(NC)(5)Pt-Tl-Pt(CN)(5)](3-): a lesson on environmental effects

The molecular geometries and the nuclear spin-spin coupling constants of the complexes [(NC)(5)Pt-Tl(CN)(n)](n-), n = 0-3, and the related system [(NC)(5)Pt-Tl-Pt(CN)(5)](3-) are studied. These complexes have received considerable interest since the first characterization of the n = 1 system by Glaser and co-workers in 1995 [J. Am. Chem. Soc. 1995, 117, 7550-7551]. For instance, these systems exhibit outstanding NMR properties, such as extremely large Pt-Tl spin-spin coupling constants. For the present work, all nuclear spin-spin coupling constants J(Pt-Tl), J(Pt-C), and J(Tl-C) have been computed by means of a two-component relativistic density functional approach. It is demonstrated by the application of increasingly accurate computational models that both the huge J(Pt-Tl) for the complex (NC)(5)Pt-Tl and the whole experimental trend among the series are entirely due to solvent effects. An approximate inclusion of the bulk solvent effects by means of a continuum model, in addition to the direct coordination, proves to be crucial. Similarly drastic effects are reported for the coupling constants between the heavy atoms and the carbon nuclei. A computational model employing the statistical average of orbital-dependent model potentials (SAOP) in addition to the solvent effects allows to accurately reproduce the experimental coupling constants within reasonable limits.     

Structures, energies, and spin-spin coupling constants of methyl-substituted 1,3-diborata-2,4-diphosphoniocyclobutanes: four-member B-P-B-P rings B2P2(CH3)(n)H(8-n), with n = 0, 1, 2, 4

An ab initio study has been carried out to determine the structures, relative stabilities, and spin-spin coupling constants of a set of 17 methyl-substituted 1,3-diborata-2,4-diphosphoniocyclobutanes B(2)P(2)(CH(3))(n)H(8-n), for n = 0, 1, 2, 4, with four-member B-P-B-P rings. The B-P-B-P rings are puckered in a butterfly conformation, in agreement with experimental data for related molecules. Isomers with the CH(3) group bonded to P are more stable than those with CH(3) bonded to B. If there is only one methyl group or if two methyl groups are bonded to two different P or B atoms, isomers with equatorial bonds are more stable than those with axial bonds. However, when two methyl groups are present, the gem isomers are the most stable for molecules B(2)P(2)(CH(3))(2)H(6) with P-C and B-C bonds, respectively. Transition structures present barriers to the interconversion of two equilibrium structures or to the interchange of axial and equatorial positions in the same isomer. These barriers are very low for the isomer with two methyl groups bonded to B in axial positions for the isomer with four axial bonds and for the isomer with geminal B-C bonds at both B atoms. Coupling constants (1)J(B-P), (1)J(P-C), (1)J(B-C), (2)J(P-P), and (3)J(P-C) are capable of providing structural information. They are sensitive to the number of methyl groups present and can discriminate between axial, equatorial, and geminal bonds, although not all do this to the same extent. The one-bond coupling constants (1)J(B-P), (1)J(P-C), and (1)J(B-C) are similar in equilibrium and transition structures, but (3)J(P-C) and (2)J(P-P) are not. These coupling constants and those of the corresponding fluoro-derivatives of the 1,3-diborata-2,4-diphosphoniocyclobutanes demonstrate the great sensitivity of phosphorus coupling to structural and electronic effects.     

An "S"-shaped pentanuclear CuII cluster derived from the metal-assisted hydrolysis of pyCOpyCOpy: structural, magnetic and spectroscopic studies

Reaction of [Cu2(O2CMe)4(H2O)2] with 2,6-di-(2-pyridylcarbonyl)-pyridine (pyCOpyCOpy or dpcp) in MeCN-H2O 10:1, led to the pentanuclear copper(II) complex [Cu5(O2CMe)6{pyC(O)(OH)pyC(O)(OH)py}2] () which crystallizes in the triclinic P1 space group. The copper(II) atoms are arranged in an "S"-shaped configuration, and are bridged by the doubly deprotonated bis(gem-diol) form of the ligand, pyC(O)(OH)pyC(O)(OH)py2-. Magnetic susceptibility data indicate the interplay of both ferro- and antiferromagnetic intramolecular interactions stabilizing an S=3/2 ground state. Fitting of the data according to a next-nearest-neighbour model {H=-[J1(S1S2+S1'S2')+J2(S2S3+S3'S2')+J3(S1S3+S3'S1')+J4(S2S2')]} yields exchange coupling constants J1=+39.7 cm(-1), J2=-15.9 cm(-1), J3=-8.3 cm(-1) and J4=+4.3 cm(-1), leading to an S=3/2 ground state. X-Band EPR spectroscopy indicates a zero-field splitting of the ground state with |D3/2|=0.38 cm(-1).     

Syntheses and reactions of the fluorinated cyclic thionylphosphazene NSO(Ar)[NPF(2)]2(Ar = 4-t-BuC(6)H(4)-) with difunctional reagents

The S-aryl substituted thionylphosphazene (Cl(2)PN)(2)[4-t-BuC(6)H(4)(O)SN] (1) was prepared by Friedel-Craft's reaction of NSOCl(NPCl(2))(2) with tert-butylbenzene. When it reacted with excess KSO(2)F at 110 degrees C, the P-Cl bonds of 1 were fluorinated, yielding the tetrafluorothionylphosphazene, (F(2)PN)(2)[4-t-BuC(6)H(4)(O)SN] (2). An equimolar reaction of 2 with dilithiated 1,3-propanediol in THF at -78 degrees C resulted in the formation of the ansa-substituted compound CH(2)(CH(2)O)(2)[FPN](2)[4-t-BuC(6)H(4)(O)SN] (3). The crystal structures of 2 and 3 were determined. In 3 the ansa ring is trans on the PNS heterocycle with respect to the aryl group. Reaction of 2 with the disiloxane (CF(2)CH(2)OSiMe(3))(2), in the presence of catalytic amounts of CsF in THF at 90 degrees C, resulted in the formation of the dispiro compound [(CF(2)CH(2)O)(2)PN](2)[4-t-BuC(6)H(4)(O)SN] (4). Compounds 1-4 were characterized by IR, NMR ((1)H, (13)C, (19)F, (31)P), mass spectral, and elemental analyses.     

An octanuclear complex containing the [Fe3O]7+ metal core: structural, magnetic, Mössbauer, and electron paramagnetic resonance studies

A new asymmetrically coordinated bis-trinuclear iron(III) cluster containing a [Fe(3)O](7+) core has been synthesized and structurally, magnetically, and spectroscopically characterized. [Fe(6)Na(2)O(2)(O(2)CPh)(10)(pic)(4)(EtOH)(4)(H(2)O)(2)](ClO(4))(2).2EpsilontOH (1.2EpsilontOH) crystallizes in the P space group and consists of two symmetry-related {Fe(3)O](7+) subunits linked by two Na(+) cations. Inside each [Fe(3)O](7+) subunit, the iron(III) ions are antiferromagnetically coupled, and their magnetic exchange is best described by an isosceles triangle model with two equal (J) and one different (J ') coupling constants. On the basis of the H = -2SigmaJ(ij)S(i)S(j) spin Hamiltonian formalism, the two best fits to the data yield solutions J = -27.4 cm(-1), J ' = -20.9 cm(-1) and J = -22.7 cm(-1), J ' = -31.6 cm(-1). The ground state of the cluster is S = (1)/(2). X-band electron paramagnetic resonance (EPR) spectroscopy at liquid-helium temperature reveals a signal comprising a sharp peak at g approximately 2 and a broad tail at higher magnetic fields consistent with the S = (1)/(2) character of the ground state. Variable-temperature zero-field and magnetically perturbed M?ssbauer spectra at liquid-helium temperatures are consistent with three antiferromagnetically coupled high-spin ferric ions in agreement with the magnetic susceptibility and EPR results. The EPR and M?ssbauer spectra are interpreted by assuming the presence of an antisymmetric exchange interaction with |d| approximately 2-4 cm(-1) and a distribution of exchange constants J(ij).     

(3h)J((15)N-(31)P) spin-spin coupling constants across N[bond]H....O[bond]P hydrogen bonds

Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) calculations have been performed to evaluate three-bond (15)N-(31)P coupling constants ((3h)J(N[bond]P)) across N[bond]H....O[bond]P hydrogen bonds in model cationic and anionic complexes including NH(4)(+):OPH, NH(4)(+):OPH(3), NH(3):(-)O(2)PH(2), NFH(2):(-)O(2)PH(2), and NF(2)H:(-)O(2)PH(2). Three-bond coupling constants can be appreciable when the phosphorus is P(V), but are negligible with P(III). (3h)J(N[bond]P) values in complexes with cyclic or open structures are less than 1 Hz, a consequence of the nonlinear arrangement of N, H, O, and P atoms. For complexes with these structures, (3h)J(N[bond]P) may not be experimentally measurable. In contrast, complexes in which the N, H, O, and P atoms are collinear or nearly collinear have larger values of (3h)J(N[bond]P), even though the N[bond]P distances are longer than N[bond]P distances in cyclic and open structures. In linear complexes, (3h)J(N[bond]P) is dominated by the Fermi-contact term, which is distance dependent. Therefore, N[bond]P (and hydrogen-bonding N[bond]O) distances in these complexes can be determined from experimentally measured (15)N-(31)P coupling constants.     

Defective dicubane-like tetranuclear nickel(II) cyanate and azide nanoscale magnets

Four tetrameric nickel(II) pseudohalide complexes have been synthesized and structurally, spectroscopically, and magnetically characterized. Compounds 1-3 are isostructural and exhibit the general formula [Ni(2)(dpk·OH)(dpk·CH(3)O)(L)(H(2)O)](2)A(2)·2H(2)O, where dpk = di-2-pyridylketone; L = N(3)(-), and A = ClO(4)(-) for 1, L = NCO(-) and A = ClO(4)(-) for 2, and L = NCO(-) and A = NO(3)(-) for 3. The formula for 4 is [Ni(4)(dpk·OH)(3) (dpk·CH(3)O)(2)(NCO)](BF(4))(2)·3H(2)O. The ligands dpk·OH(-) and dpk·CH(3)O(-) result from solvolysis and ulterior deprotonation of dpk in water and methanol, respectively. The four tetramers exhibit a dicubane-like core with two missing vertexes where the Ni(II) ions are connected through end-on pseudohalide and oxo bridges. Magnetic measurements showed that compounds 1-4 are ferromagnetic. The values of the exchange constants were determined by means of a theoretical model based on three different types of coupling. Thus, the calculated J values (J(1) = J(2), J(3), and D) were 5.6, 11.8, and 5.6 cm(-1) for 1, 5.5, 12.0, and 5.6 cm(-1) for 2, 6.3, 4.9, and 6.2 cm(-1) for 3, and (J(1), J(2), J(3), and D) 6.9, 7.0, 15.2, and 4.8 cm(-1) for 4.     

A solid-state NMR investigation of single-source precursors for group 12 metal selenides; M[N(iPr2PSe)2]2 (M = Zn, Cd, Hg)

The first solid-state NMR investigation of dichalcogenoimidodiphosphinato complexes, M[N(R(2)PE)(2)](n), is presented. The single-source precursors for metal-selenide materials, M[N((i)Pr(2)PSe)(2)](2) (M = Zn, Cd, Hg), were studied by solid-state (31)P, (77)Se, (113)Cd, and (199)Hg NMR at 4.7, 7.0, and 11.7 T, representing the only (77)Se NMR measurements, and in the case of Cd[N((i)Pr(2)PSe)(2)](2)(113)Cd NMR measurements, to have been performed on these complexes. Residual dipolar coupling between (14)N and (31)P was observed in solid-state (31)P NMR spectra at 4.7 and 7.0 T yielding average values of R((31)P,(14)N)(eff) = 880 Hz, C(Q)((14)N) = 3.0 MHz, (1)J((31)P,(14)N)(iso) = 15 Hz, alpha = 90 degrees , beta = 26 degrees . The solid-state NMR spectra obtained were used to determine the respective phosphorus, selenium, cadmium, and mercury chemical shift tensors along with the indirect spin-spin coupling constants: (1)J((77)Se,(31)P)(iso), (1)J((111/113)Cd,(77)Se)(iso), (1)J((199)Hg,(77)Se)(iso), and (2)J((199)Hg,(31)P)(iso). Density functional theory magnetic shielding tensor calculations were performed yielding the orientations of the corresponding chemical shift tensors. For this series of complexes the phosphorus magnetic shielding tensors are essentially identical, the selenium magnetic shielding tensors are also very similar with respect to each other, and the magnetic shielding tensors of the central metals, cadmium and mercury, display near axial symmetry demonstrating an expected deviation from local S(4) symmetry.     

Temperature dependence of the crystal lattice organization of coordination compounds involving nitronyl nitroxide radicals: a magnetic and structural investigation

Four new mononuclear complexes of formula Cd(PN)(4)(NCS)(2) (A), Cd(PNN)(4)(N(3))(2) (B), Zn(PNN)(4)(N(3))(2) (C), and Zn(PNN)(2)(NCS)(2) (D), where PNN stands for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and PN for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl, were synthesized and structurally and magnetically characterized. The X-ray structures of compounds B and C were also determined at 90 K. Compounds A[bond]C crystallize in the triclinic space group P 1 macro (No. 2), and D crystallizes in the monoclinic space group P2(1)/m (No. 11). A[bond]C adopt a centrosymmetric distorted octahedral geometry in which the metal ions are bonded to four radical ligands through the nitrogen atom of the pyridyl rings and the azido or thiocyanato ligands occupy the apical positions. Compound D adopts a distorted tetrahedral geometry in which the zinc ion is bonded to two radicals and two thiocyanato ligands. As suggested by their magnetic behavior, the low-temperature X-ray structures of B and C show that these compounds undergo a clear structural change with respect to the room-temperature structures. The experimental magnetic behaviors were perfectly reproduced by a dimer model for A[bond]C and an alternating chain model for D while the sudden breaks observed in the chi(M)T versus T curves for B and C were well accounted for by the high- and low-temperature X-ray structures. For all these complexes the crystal structures favor significant overlap between molecular magnetic orbitals leading to rather strong intermolecular antiferromagnetic interactions.     

Energetics of halogen bonding of group 10 metal fluoride complexes

A study is presented of the thermodynamics of the halogen-bonding interaction of C(6)F(5)I with a series of structurally similar group 10 metal fluoride complexes trans-[Ni(F)(2-C(5)NF(4))(PCy(3))(2)] (2), trans-[Pd(F)(4-C(5)NF(4))(PCy(3))(2)] (3), trans-[Pt(F){2-C(5)NF(2)H(CF(3))}(PR(3))(2)] (4a, R = Cy; 4bR = iPr) and trans-[Ni(F){2-C(5)NF(2)H(CF(3))}(PCy(3))(2)] (5a) in toluene solution. (19)F NMR titration experiments are used to determine binding constants, enthalpies and entropies of these interactions (2.4 ≤ K(300) ≤ 5.2; -25 ≤ ΔH(o) ≤ -16 kJ mol(-1); -73 ≤ ΔS(o) ≤ -49 J K(-1) mol(-1)). The data for -ΔH(o) for the halogen bonding follow a trend Ni < Pd < Pt. The fluoropyridyl ligand is shown to have a negligible influence on the thermodynamic data, but the influence of the phosphine ligand is significant. We also show that the value of the spin-spin coupling constant J(PtF) increases substantially with adduct formation. X-ray crystallographic data for Ni complexes 5a and 5c are compared to previously published data for a platinum analogue. We show by experiment and computation that the difference between Pt-X and Ni-X (X = F, C, P) bond lengths is greatest for X = F, consistent with F(2pπ)-Pt(5dπ) repulsive interactions. DFT calculations on the metal fluoride complexes show the very negative electrostatic potential around the fluoride. Calculations of the enthalpy of adduct formation show energies of -18.8 and -22.8 kJ mol(-1) for Ni and Pt complexes of types 5 and 4, respectively, in excellent agreement with experiment.