Branko Kaitner

High metal coordination numbers in group 15 organometallics: crystal structures of triphenylbismuthbis(trifluoroacetate) and triphenylantimonybis(trifluoroacetate)

Abstract Crystals of Ph3Bi(OCOCF3)2 have been shown by X-ray diffractometry to be made up of isolated molecules in which the coordination at bismuth is intermediate between trigonal bipyramidal, with apipcal monodentate CF3COO groups and pentagonal bipyramidal with equatorial bidentate CF3COO groups. In the case of Ph3Sb(OCOCF3)2 there is essentially trigonal bipyramidal coordination at antimony, with apical CF3COO groups, and with a quite different conformation from that found for the bismuth compound.

Axial additions in nickel(II) complexes of (5SR,7RS,12RS,14SR)-tetra-methyl-1,4,8,11-tetra-azacyclotetradecane (Lα) and crystal-structure analysis of the planar orange and octahedral violet perchlorate salts NiLα,(ClO4)2

Reduction of the nickel(II) complex of C-meso-5,7,12,14-tetramethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene with NaBH4 gives predominantly the nickel(II) complex of the title ligand, Lα. Both orange (1) and violet (2) isomers of NiLα(ClO4)2 have been characterised and structures established by X-ray crystallography. Crystals of (1) are monoclinic, space group P21/c with two formula units in a unit cell of dimensions a= 8.244(1), b= 8.656(1), c= 16.701(1)A, and β= 110.28(1)°. Crystals of (2) are triclinic, space group P with two formula units in a cell of dimensions a= 10.645(1), b= 8.298(1), c= 14.198(2)A, α= 121.36(1), β= 94.61(1), and γ= 82.77(1)°. Both structures were solved by the heavy-atom method and refined by full-matrix least-squares calculations. For (1), R= 0.036 for 2 434 observed reflections; for (2). R= 0.043 for 1 924 observed reflections. Orange complex (1) contains ionic perchlorate with the closest Ni ⋯ O contact 2.808(5)A. In the centrosymmetric square-planar cation the Ni–N distances are 1.964(3) and 1.974(3)A. The purple complex (2) contains two independent discrete half molecules (2a) and (2b) lying on inversion centres in the asymmetric unit, both with axially bound perchlorate. Principal distances are Ni–O 2.235(3) and 2.221(2)A and Ni–N 2.063(2)–2.081 (2)A. The metal complexes have the trans III arrangement of the chiral nitrogen centres, with the four methyl groups equatorial. The complex [NiLα]2+ undergoes axial additions with unidentate ligands (H2O, Br–, Cl–, NCS–, N3–, NO2–, O2CMe–) and trans-[NiLX2]n+ have been prepared and characterised. Infrared and d–d spectra are reported. The equilibrium [NiLα]2++ 2H2O ⇌[NiLα(OH2)2]2+has been studied over a temperature range, yielding K= 5.06 at 25 °C with ΔH⊖=–22.1 kJ mol–1 and ΔS⊖=–60.6 J K–1 mol–1.

Synthesis and structure of stable indium and gallium complexes of (R)-1,4,7-tris(2′-methylcarboxymethyl)-triazacyclononane

Abstract The title ligand forms stable neutral complexes with gallium and indium and the structure of the latter has been studied by X-ray crystallography.

STEREOCHEMISTRY OF COMPLEXES WITH N-ALKYLATED AMINO ACIDS. VIII. CRYSTAL STRUCTURE AND CONFORMATIONAL ANALYSIS OF AQUABIS(L-N,N-DIMETHYLTHREONINATO)COPPER(II) DIHYDRATE

Abstract The structure of blue, monoclinic (space group P21) crystals of aquabis(L-N,N-dimethylthreoninato)copper(II) dihydrate was determined by X-ray diffraction and refined to R = 0.030. The coordination around the copper(II) atom is distorted square-pyramidal with threonine N and O atoms in trans orientations (Cu-O 1.930(3) and 1.926(3)A, Cu-N 2.042(3) and 2.055(3)A, O-Cu-O 163.9, N-Cu-N 164.0°) and apical water (Cu-O(W) 2.206 A). The shape of the coordination polyhedron was reasonably well reproduced with molecular mechanics calculations, yielding root-mean-square deviations of ten valence angles around copper to 4.5°. The calculated strain energy of the crystal conformation is about 21 kJ mol− higher than the energy of the most stable conformer. This was tentatively attributed to the additional stabilization of molecular conformation by intermolecular hydrogen bonds in the solid state.

Stereochemistry of Complexes with N-Alkylated Amino Acids. v. Crystal Structure, Molecular Mechanics Calculations and Conformational Analysis of Bis(L-N,N-Diethyl-α-Alaninato)Aquacopper(II)

Abstract The crystal structure of the blue orthorhombic (space group C2221) modification of bis(L.-N,N-diethyl-α-alaninato)aquacopper was solved by X-ray methods and refined to R = 0.043. The complex has twofold crystallographic symmetry and coordination around the copper(II) atom is distorted square-pyramidal with the water molecule axial. Principal dimensions are Cu-Ow 2.260(4), Cu-O 1.922(2), Cu-N 2.075(4)A, O-Cu-O 175.6(1), N-Cu-N 159.9(2), Ow-Cu-O 92.2(1), Ow-Cu-N 100.0(1)°. The conformation of the unique chelate ring is very similar to that found in (D-N,N-diethylalaninato)(L-N,N-diethylalaninato)copper(II). The shape of the coordination polyhedron was reasonably well reproduced with theoretical calculations (molecular mechanics), yielding differences between calculated and measured angles around copper of from 1.3 to 5.2[ddot]. The calculated strain energy of the crystal conformation is about 4 kJ mol−1 higher than the energy of the most stable conformer. This fact was tentatively attributed to the...

Reversible ethylene coordination in (η2-C2H4)Pt(PCy3)2

Abstract The complex (η2-C2H4)Pt(PCy3)2 (I) exists in the equilibrium (η2-C2H4)Pt(PCy3)2⇌Pt0(PCy3)2+C2H4 in solution, involving the reversible coordination of ethylene to the platinum(0) centre. Two dimensional 31P NMR spectroscopy provides evidence for exchange between the two platinum(0) species. The X-ray crystallographic analysis of (I)·1/2C6H14 provides evidence for weak coordination of the ethylene moiety in the solid state. I lies on a two-fold crystallographic axis which passes through Pt and the mid-point of the olefin Cue5fbC bond; principal dimensions include Ptue5f8P 2.284(1), Ptue5f8C(olefin) 2.137(7), Cue5fbC 1.440(7) A, Pue5f8Ptue5f8P 116.33(7)°, Cue5f8Ptue5f8C 39.4(2)°. These results are interpreted in terms of possible bonding modes.

Stereochemistry of Complexes with N-Alkylated Amino Acids. IV. Crystal Structure of Disordered D,L-BIS(N,N-Diethyl-α-Alaninato)Copper(II); Molecular Mechanics Calculations and Conformational Analysis of Copper(II) N,N-Diethylalaninates

Abstract The crystal structure of a new, red, triclinic modification of (D,L-N,N-diethyl-α-alaninato)copper(II) was solved by X-ray diffraction methods and refined to R = 0.035. The structure contains discrete molecules disordered over two sites in a 72:28 ratio with the copper atom on an inversion centre. The copper, oxygen and nitrogen atoms and one carbon atom are common to both molecules while six carbon atoms are disordered over two sites. The coordination around the copper atom is irregular square-planar with oxygen and nitrogen atoms necessarily trans. Interatomic distances [Cu-O 1.910(2)A and Cu-N 2.033(2)A] are comparable with those found in related crystal structures. The two independent molecules A and B (which are disordered about an inversion centre) have identical conformations in the lattice, molecular mechanics calculations correctly predict the crystal (most stable) conformation of D,L-bis(N,N-diethyl-α-alaninato)copper(II); the conformation predicted for the L,L isomer appears to be a tr...

Synthesis, X-ray crystal structure, and cation transfer properties of a calix[4]arene tetraketone, a new versatile molecular receptor

Treatment of p-t-butylcalix[4]arene with bromoacetone–potassium carbonate yields a crystalline tetraketone which shows exceptionally high phase-transfer activity towards alkali metal cations in aqueous solutions; X-ray and n.m.r. analyses show that the receptor possesses a cone conformation in which the carbonyl groups are pre-organised for ion binding.

1,4,7-Triazacyclononane-1,4,7-triyltrimethylenetris-(phenylphosphinate) enforces octahedral geometry: crystal and solution structures of its metal complexes and comparative biodistribution studies of radiolabelled indium and gallium complexes

1,4,7-Triazacyclononane-1,4,7-triyltrimethylenetris(phenylphosphinate) formed C3-symmetric complexes with the divalent ions of Co. Ni, Cu and Zn and structurally similar complexes with the trivalent ions of Fe, Co, Ga and In. For each of the eight crystal structures examined, the ligand adopts the same rigid conformation and a single chiral diastereoisomer is formed (RRR or SSS at each stereogenic phosphorus centre). The geometry around the metal centre is slightly distorted octahedral. The copper(II) complex only undergoes a Jahn–Teller distortion below 100 K, and the pink cobalt(II) complex only slowly oxidises to the dark blue cobalt(III) complex. The chiral gallium(III) complex may be resolved by preparative HPLC, and its 1H NMR spectrum has been fully assigned with the aid of two-dimensional methods. The indium-111 and gallium-67 complexes have been examined in vivo and exhibit selective biliary clearance associated with their lipophilic nature.

Metallaheteroborane chemistry. Part 5. Synthesis of closo-[2,2-(PR3)2-1,2-SePtB10H10](R3= Et3, Bun3 or Me2Ph) and arachno-[9,9-(PMe2Ph)2-6,9-SePtB8H10] and their characterisation by nuclear magnetic resonance techniques: the crystal and molecular structures of closo-[2,2-(PEt3)2-1,2-SePtB10H10] and arachno-[9,9-(PMe2Ph2),-6,9-SePtB8H10]

The close compounds [2,2-(PR3)2-1,2-SePtB10H10], where R3= Et3(1) or Bun3(2), have been isolated in low-to-moderate yield from the reaction between cis-[PtCl2(PR3)2] and nido-[7-SeB10H11]– in tetrahydrofuran. Both closo-[2,2-(PMe2Ph)2-1,2-SePtB10H10](3) and arachno-[9,9-(PMe2Ph)2-6,9-SePtB6H10](4) were isolated from the reaction with R3= Me2Ph. N.m.r. spectroscopy confirms the general structures of the compounds, and variable-temperature 1H-{31P} experiments on (3) show the rotational metal-to-heteroborane bonding fluxionality to have ΔG328‡ca. 58 kJ mol–1. An X-ray diffraction study of compound (1) shows the orthorhombic crystals belong to the space group Fdd2, with Z= 16 and cell dimensions a= 55.052(6), b= 17.842(5), and c= 10.259(4)A, R= 0.042 for 2 551 observed reflections. Cage interatomic distances involving Pt or Se are Pt–Se 2.676(2), Pt–B 2.23(2)–2.32(2), and Se–B 2.08(2)–2.20(2)A. Crystals of (4) are orthorhombic, space group P21nm with a= 6.935(1),b= 10.048(2), and c= 17.413(2)A, R= 0.022 for 1 375 observed reflections. Interatomic distances include Pt–B 2.147(10)–2.230(7) and Se–B 2.062(15)–2.113(8)A. Both the X-ray crystallographic and n.m.r. results for (4) indicate this compound belongs to the arachno class. As a model for (4), the bonding of the PtP2 unit to the heteroborane SB8H10 ligand has been analysed in a frontier-orbital approach.