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Abstract: X-ray crystallographic analyses revealed that the Pd–P and Pd–X bond lengths of [PdX2(P–P)] complexes (X− =Cl, Br and I and P–P=Ph2P(CH2) n PPh2; n =1: dppm, 2: dppe, 3: dppp, 4: dppb) are: Pd–P (dppm, dppe)Pd–X (dppp, dppb). The oxidation potentials values, E ½(ox), of the shorter Pd–P and longer Pd–X bond lengths in the dppm and dppe complexes are high and reflect strong dxy (dπ (Pd)) interaction with (dσ∗ (Pd)) and that this interaction is less dependent on X−. The longer Pd–P and shorter Pd–X bonds for the dppp and dppb complexes reflect that the (dσ∗ (Pd)) interaction is largely dependent on X−. The reduction potential, E ½(red), which reflects the (dσ∗ (Pd) LUMO energy, and the oxidation potential, E ½(ox), which reflects the (dxy (dπ (Pd) HOMO energy were, determined. The E ½(red) and E ½(ox) values indicate the σ-bonding properties and π-interaction in the system, respectively. Good linear relationships were observed between the potentials difference [E ½(ox)− E ½(red)] and the ligand-field transition energy (dπ (dxy )→dσ∗ ()) in the series of dihalogenopalladium(II) complexes. The linear relationship shows that the energies of the d–d transitions and ΔE(Redox) of the dppm and dppe complexes are less dependent on X− whilst those of the dppp and dppb are largely X− dependent. [Copyright &y& Elsevier]

Three metal(III)-tripodal tridentate phosphine complexes of the formula [MCl(acac)(tdmme)]PF6, where M=Cr, Co or Rh; acac=pentane-2,4-dionate; tdmme=1,1,1-tris(dimethylphosphinomethyl)ethane, were prepared and their molecular and crystal structures and spectroscopic properties examined. All the complexes crystallized in an isomorphous space group P212121, which is indicative of spontaneous resolution of the enantiomeric pair. The Cr&z.sbnd;P bond lengths in [CrCl(acac)(tdmme)]PF6 (average 2.437 A˚) are remarkably longer than the corresponding Co&z.sbnd;P (average 2.201 A˚) and Rh&z.sbnd;P (average 2.252 A˚) ones. The longer and therefore the weaker Cr&z.sbnd;P bonds may explain the relatively weak trans influence of the &z.sbnd;PMe2 group in [CrCl(acac)(tdmme)]PF6; among the three MIII complexes, the elongation of M&z.sbnd;O bond lengths in [MCl(acac)(tdmme)]PF6 from those in [M(acac)3] has been found to be CrIII (0.016 A˚)

Abstract: A series of cobalt(III) complexes containing 2-cyanoethylphosphines, [Co(acac)2{P(CH2CH2CN) n Ph3– n }2]BF4 {acac=2,4-pentanedionate; n =1 (1), 2 (2), and 3 (3)} have been prepared, and their molecular and crystal structures have been determined. The X-ray diffraction study revealed that these complexes are the trans isomers in the crystals. The Co–P bond lengths are little affected by the number of 2-cyanoethyl substituents on the P atom, which is consistent with a small change of the σ-donicity among these phosphines. The trans configuration of these complexes is maintained in solution, as revealed by 1H NMR spectroscopy. The 2-cyanoethylphosphines could not form stable cis-isomers of [Co(acac)2{P(CH2CH2CN) n Ph3– n }2]+, like the corresponding methylphosphines (PMe n Ph3– n ). This fact probably results from a strong electron-withdrawing property of a terminal cyano group of phosphine substituent. In the UV–Vis absorption spectra of complexes 1–3, the LMCT transition band is observed in the range of 20500–24000cm−1, which is comparable to the analogous PMe n Ph3– n complexes, but their intensity is characteristically weaker than that of the corresponding PMe n Ph3– n complexes. [Copyright &y& Elsevier]

Abstract: The synthesis and magnetic characterization of pyrazolato-bridged dinuclear complexes [{M(NCS)(4-Phpy)}2(μ-bpypz)2] (Hbpypz=3,5-bis(2-pyridyl)-pyrazole; 4-Phpy=4-phenylpyridine; M=Co2+ (1) and Fe2+ (2)) are described together with the X-ray crystal analysis of the cobalt complex. The structure of 1 shows that the desired coordination has been achieved with the cobalt atoms being coordinated to two bpypz to form the dimer. The X-ray diffraction patterns show 1 and 2 to be isomorphous at room temperature. 2 displays a single spin-crossover transition between the [HS–HS] and [LS–LS] states with T c =150K. [Copyright &y& Elsevier]