Search

The complex [Co(tn) 2 pyCl]Y (tn = 1,3 diamino propane, Y = 2ClO 4 or ZnCl 4 ) has been re-examined and its visible absorption and 13 C NMR spectral data are consistent with the assignment of cis and not trans stereochemistry. The structure of [Co(tn) 2 pyCl] ZnCl 4 · H 2 O has been determined by X-ray structure analysis, showing that the complex is cis and the two six-membered Cotn rings adopt the chair conformation, but the two chairs are not identical.

Some complex chlorides of vanadium(II), A 2 [VCl 4 (CH 3 CO 2 H) 2 ], where A = NMeH 3 , C(NH 2 ) 3 (guanidinium) and C 4 H 12 N 2 (pyrazinium), have been isolated from vanadium(II) chloride in acetic acid and characterized by magnetic and spectroscopic measurements. By controlled aerial oxidation of the vanadium(II) complexes or directly from VCl 3 , a series of hexachlorovanadates (III), A 4 [VCl 6 ]Cl, has been prepared in which A = NMeH 3 , NMe 2 H 2 , NEtH 3 , NPr n H 3 and NBzH 3 . A single crystal X-ray investigation has been carried out on the methylammonium salt. There are two independent VCl 6 octahedra in the structure. Both are regular, with VCl distances in the range 2.380(2)–2.401(2) A and the internal ClVCl angles all within 0.5° of 90°. The complexes [Hpy] 3 [VCl 6 ], [NBu n H 3 ] 2 [VCl 5 ] and [NMeH 3 ] 4 [VBr 6 ]Br have also been isolated. From VCl 3 and the alkylammonium chloride in acetic acid or propionic acid as appropriate, the salts A 2 [VCl 5 (CH 3 CO 2 H)] (A = NMe 2 H 2 and A 2 [VCl 5 [C 2 H 5 CO 2 H)] (A = NPr n H 3 and NBu n H 3 ) have been obtained.

Reaction of [ReCl3(MeCN)(PPh3)2] with the planar pentadentate diacetylpyridinebis(benzoylhydrazone) ligands DAPBH2 and DAP-Me-BH2 and triethylamine in isopropanol under reflux gave the dark brown seven-coordinate complexes [ReCl(L)PPh3], containing the doubly deprotonated pentadentate ligand [L = DAPB(2−)(1); L = DAP-Me-B(2−) (2)]. Complex 1 has been characterized by crystallography. The central rhenium atom in 1 is seven-coordinate, with pentagonal bipyramidal geometry with the axial positions being occupied by the chloride ion and the triphenylphosphine ligand. The DAPB coordinates in a pentadentate manner in the equatorial plane of the complex and the five donor atoms of the doubly deprotonated DAPB(2−) ligand form an approximately planar pentagon. The rhenium atom is slightly displaced out of the ligand plane towards the phosphorus atom. Reaction of 2 with Ag[BF4] in CH2Cl2 at room temperature gave a black complex of stoichiometry [Re(DAP-Me-B)(PPh3)][BF4] (3). Reaction of [MoCl4(MeCN)2] with DAP-Me-BH2 and Et3N in dry CH2Cl2 under reflux gave deep green [MoCl2(DAP-MeB2)] (4), formulated as a seven-coordinate molybdenum(II) complex containing the doubly deprotonated pentadenate DAP-MeBH2 ligand in the equatorial plane of the complex. The Mossbauer spectra of the complexes [FeCl2(DAPBH2)]·H2O (5) and [FeCl(DAPMe-B)(H2O)] (6) were investigated as a function of temperature. The spectrum of 5 was consistent with high-spin seven-coordinate iron(II) and 6 was shown to contain two distinct iron(III) sites; possible structures are discussed.

The crystal structures of the complexes of 3,3-dimethyl- 2,2′-bipyridine (L), cis-[W(CO)4L], cis-[MO(CO)4L] · C4H6 and cis-[Cr(CO)4L] · C6H6 have been determined by X-ray diffraction. These structures show that repulsion between the methyl groups is principally responsible for the geometric distortion in each complex. Within the ligand, L, the two pyridine rings suffer distortion, in opposite directions, to pseudo-boat conformations so as to optimize metal—nitrogen binding. The benzene solvent molecules are arranged in a layer structure alternating with units of the metal complex. The metal complex molecule is beyond van der Waals contact with the benzene solvent molecule in each case.

The telluroamines 1-(NMe2)-2-(TeAr)-4-MeC6H3 (1) (Ar = 4-MeOC6H4 or 4-EtOC6H4) react with mercury(II) halides forming adducts of composition HgX2 · 1 (X = Cl or Br). The IR, far-IR (up to 50 cm−1), 1H and 13C NMR spectra of the mercury(II) complexes indicate that the ligands (1) behave as monodentate donors, coordinating through tellurium only. The complexes seem to be dimers of the composition [1 · XHg(μ-X)2HgX · 1]. The crystal structure of the adduct obtained from mercury(II) bromide has been determined. It reveals that the NMe2 group does not coordinate with mercury(II) and the complex is a dimer in which two somewhat asymmetrical bromine bridges are present between the mercury atoms. The coordination environment of each mercury is almost tetrahedral [91.25(3)–118.40(4)°]. The HgBr bridging bond lengths are 2.755(1) and 2.710(1) A.

The syntheses of several novel diazenido-, hydrazido- and imido- complexes of technetium are described. These precursors which contain technetium—nitrogen multiple bonds are derived directly from the appropriate organohydrazine or amine in good yield. Some of the chemistry has been extended to the metastable isotope 99mTc (γ, t 1 2 = 6 h) in highly dilute aqueous media to give single species in high radiochemical purity. These preparations are applicable to the synthesis of new technetium radiopharmaceuticals and should provide for the development of a whole new range of technetium-based diagnostic agents in nuclear medicine.

X-Ray crystallographic studies on [NEt4]2[Cr2[(O2CC2H5)4(NCS)2] show that the Cr–Cr separation (2.467A) in the dinuclear anion is one of the longest known. The thiocyanato groups are N-bonded, and the results emphasize the known sensitivity of the quadruple Cr–Cr bond to the nature of the axial ligands. The compound crystallises in the tetragonal space group P4/mnc with two molecules per unit cell, the dimensions of which are a = b = 9.785(1), c = 21.186(2) A. Magnetic investigations from room to liquid nitrogen temperature on the tetra-μ-propionato complex and on [NMe4]2 [Cr2(O2CCH3)4(NCS)2] show that both complexes have been obtained free from paramagnetic chromium(III) impurities. Their weak paramagnetic susceptibilities (Xcr is approx. 200 x 10−6 cm3 mol−1 at 295 K and 50 x 10−6cm3mol−1 at 90 K) are inherent, and are ascribed to temperature independent paramagnetism at low temperature plus para-magnetism arising from slight population of the triplet state (2J ⋍ 700 cm−1, g = 2, Nα = 50 x 10−6cm3mol−1) at higher temperatures.

The complexes trans-[Mo(SR)2)(diphos)2] (A) [R = alkyl, C6F5 or C6H4X-4, where X = H, F, Cl, CH3, NH2 or OCH3; diphos = Ph2PCH2CH2PPh2 (dppe) or (C6H4CH3-3)2PCH2CH2P(C6H4CH3-3)2 (dmtpe)] have been prepared by treatment of trans-[Mo(N2)2(diphos)2] with RSH. trans-[Mo(SBun)2(dppe)2] crystallizes in the monoclinic space group C2/c with a = 25.605(5) A, b = 12.055(2) A, c = 19.637(4) A, β = 107.08(2)° and final R = 0.041. The molecule is centrosymmetric with Mos = 2.363(1) A and MoRaverage = 2.511(1) A. Compounds (A) are diamagnetic and the 31P NMR chemical shifts and Eox 1 2 values of (A, R = C6H4X-4) show a linear dependence upon the Hammett σ function for X. Chemical oxidation (FeCl3 or CuCl2) followed by anion exchange gives the complexes [Mo(SR)2(dppe)2][BPh4], whose ESR spectra show a rhombic signal in frozen solution having hyperfine splitting which is solvent-dependent.

N-nitroso-N-alkylhydroxylamines have been prepared by hydrolysis of the mixture obtained by reaction of nitric oxide with Grignard reagents, and stabilized as their copper(II) or iron(III) complexes, Cu(RN2O2)2 and Fe(RN2O2)3, where R is, for example, Me, Et, Pri, Buiso, Ph, n-C8H17 or n-C12H25. The complexes have been characterized by analytical, magnetic and spectroscopic measurements. By single-crystal X-ray methods Cu(PriN2O2)2 has been found to be trans-planar and Fe(PrnN2O2)3 has a facial octahedral structure; in each complex the NO bond lengths are equal with no significant variation between the copper and iron complexes.

Reaction of [Fe(CO)2(OCMe2)(η5-C5H5)][PF6] with 1 equivalent of L (L = H2NNHCSNH2 or R′R″CNNHCSNH2 where R′= R″ = Me; R′ = H, R″ = Ph; R′= H, R″ = p-NO2Ph; R′= Me, R″= p-MePh; R′R″ = C5H10) in CHCl3 at 50°C gave good yields of [Fe(CO)2L(η5-C5H5)][PF6] by displacement of the acetone. The crystal structure of [Fe(CO)2(PhCHNNHCSNH2)(η5-C5H5)][PF6] was determined by single crystal X-ray diffraction studies refined to R = 0.067 for 1389 reflections above background. The coordination geometry about the iron may best be described in terms of a “piano stool” or pseudo-octahedral structure. The C5H5− ligand occupies three sites in the octahedron with the carbonyls and the sulphur atom of the thiosemicarbazone in the other three sites. The Mossbauer isomer shifts of these compounds have values which lie between that of [Fe(CO)3(η5-C5H5)]− and those for [Fe(CO)2X(η5-C5H5)] showing the thiosemicarbazone sulphur to be a poorer π-acceptor than CO and a better π-acceptor than the halides. The similarity of the spectroscopic data for all the compounds suggests that they all have the same structure. The monodentate S-bonded nature of the thiosemicarbazide in solutions of [Fe(CO)2(NH2NHCSNH2)(η5-C5H5)][PF6] is confirmed by its reaction with benzaldehyde to give the compound [Fe(CO)2(PhCHNNHCSNH2)(η5-C5H5)][PF6].

The new compound Cr(thiourea)2(NCS)2 contains trans-planar units stacked along the a-axis of the unit cell so that the chromium ions lie in infinite chains. In this first example of chains of directly interacting paramagnetic metal ions, the CrCr separation is 3.97 A which leads to weak antiferromagnetism but does not provide a conducting pathway. In contrast, the molecules in Cr(OPD)2(NCS)2, where OPD is o-phenylenediamine, prepared during investigations aimed at producing planar Cr2+ complexes by template reactions, do not stack and contain thiocyanate bridges. The new complexes Cr(OPD)Cl2 and [Cr(OPD)6]Cl2 have been prepared. The latter has been used in reactions with acetylacetone aimed at producing planar chromium(II)-tetra-azamacrocyclic complexes, but a new metal-free octa-azamacrocycle has been obtained.

The chromium(II) complex [CrI2(depe)2], where depe is 1,2-bis(diethylphosphino)ethane, is unusual in that it is high spin at room temperature, but on cooling undergoes a sharp transition to the low spin form at ca 170 K. Other complexes of chromium(II) halides and depe or 1,2-bis(dimethylphosphino)ethene (dmpe) are low spin. The structure of the high spin form of [CrI2(depe)2] has been determined.