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Treatment of the N-heterocyclic chlorophosphine precursor (PPP)Cl (1) with two equivalents of nickelocene (NiCp2) affords the phosphorus-bridged dimer [(μ-PPP)Ni2Cp2]Cl (2). In contrast, an equimolar mixture of 1 and NiCp2 in the presence of PPh3 generates a different product, (PP(C5H5)P)NiCl2 (3), in which a cyclopentadienyl anion has migrated to the N-heterocyclic phosphenium center. The phosphorus-bound Cp ring in complex 3 has undergone a [1,5]-hydride shift to afford a vinylic C5H5− ring, and can be subsequently deprotonated to produce [(PP(C5H4)P)NiCl] (4).

Recent work has revealed substantial differences in the structure, spectroscopic properties, and reactivity of heterobimetallic Zr/Co complexes of the general form XZr(R′NPR2)3CoY (R′ = iPr, 2,4,6-trimethylphenyl, 3,5-dimethylphenyl; R = Ph, iPr; X, Y = halides or neutral donor ligands) as a function of nitrogen and phosphorus donor atom substituents. To probe the electronic differences between these ligands, a series of Mo(CO)5(R2PNHR′) complexes has been synthesized (R = Ph, R′ = iPr (2a); R = iPr, R′ = iPr (2b), 2,4,6-trimethylphenyl (2c), 3,5-dimethylphenyl (2d), 4-methylphenyl (2e), 4-trifluoromethylphenyl (2f), 4-methoxyphenyl (2g)). Thermolysis of Mo(CO)6 with the corresponding phosphinoamine ligands 1a–1g affords 2a–2g. The infrared carbonyl stretching frequencies of these complexes have been compared to probe the effects of phosphorus and nitrogen substituents on the electronic properties of the phosphinoamine ligands.

The chromium(III) tris(phosphinoamide) precursor Cr(iPrNPiPr2)3 (1) has been used to synthesize Cr/Rh and Cr/Ir heterobimetallic complexes. Treatment of [MCl(COD)]2 with 1 affords the open shell S = 3/2 complexes ClCr(μ-iPrNPiPr2)2M(η2-iPrNPiPr2) (M = Rh (2), Ir (3)). Instead of simple coordination of the late transition metal fragment to the C3-symmetric tris(phosphinoamide) binding pocket, the preference of RhI and IrI for a square planar environment leads to a chloride/amide ligand exchange process. Complexes 1–3 have been structurally characterized using X-ray crystallography, revealing short Cr–Rh and Cr–Ir distances (2.6095(3) A (2); 2.6064(4) A (3)) indicative of metal–metal bonds. A computational investigation of the electronic structures of 2 and 3 reveals substantial metal–metal orbital overlap, but the high spin nature of the CrIII center leads to population of metal–metal antibonding orbitals and relatively weak metal–metal bonding. The effects of the metal–metal interaction on the redox properties of the CrIII center are investigated using cyclic voltammetry.

This manuscript describes the preparation of a new PN(H)SiO(H) pincer-type ligand that is based on the diarylamine backbone and links together phosphine, amine, and silanol donor sites. Treatment of PN(H)SiO(H) with Pd(acac)2, (COD)PdCl2, or Pd(OAc)2 resulted in the formation of (κ2-PNSiO(H))Pd(acac) (3), (κ2-PN(H)SiO(H))PdCl2 (4), and (κ3-PNSiO(H))PdOAc (5), in which the supporting ligand displays different degrees of coordination and protonation. In complex 5, the PNSiO(H) ligand functions as a tridentate phosphine-amido-silanol pincer ligand, with additional strong hydrogen bonding between the silanol OH and one of the oxygens of the Pd-bound acetate. Complex 5 cleanly exchanged acetate for a triflate upon treatment with Me3SiOTf, yielding (κ3-PNSiO(H))PdOTf (6). Analogous treatment with Me3SiCl did not lead cleanly to the expected (κ3-PNSiO(H))PdCl (7), but instead ultimately to (κ2-PN(H)SiO(SiMe3))PdCl2 (8). The dianionic PNSiO ligand was accessed by reactions of 5 with base in the presence of pyridine or PMe3 to give (κ3-PNSiO)Pd(py) (9) and (κ3-PNSiO)Pd(PMe3) (10), respectively. Solid-state structures of 5 and 9 were established by single-crystal X-ray diffractometry and revealed square-planar geometry about Pd with tridentate coordination of the pincer ligand.

The coordination chemistry of a diphosphine pincer ligand incorporating an N-heterocyclic phosphenium cation (PPP+) and its halophosphine precursors [PP(X)P] has been explored using copper(I) reagents. In contrast to the P–X bond cleavage observed when other low valent transition metals are used, simple coordination compounds [PP(X)P]CuY (X = Y = Cl (1); X = Cl, Y = I (2); X = Y = I (3)) are formed when halophosphine precursors are treated with CuY starting materials. Exposure of the N-heterocyclic iodophosphine complex 3 to THF results in ring-opening insertion to form the alkoxyphosphine complex [PP(O-CH2CH2CH2CH2-I)P]CuI (4). Since this reaction does not occur with the chlorophosphine compounds 1 and 2, it is proposed that iodide dissociation exposes the electrophilic metal-bound phosphenium cation to allow THF coordination and subsequent ring-opening. The electrophilicity of the N-heterocyclic phosphenium is also apparent when the halide-free ligand precursor [PPP][BPh4] is employed: CuCl reacts with [PPP][BPh4] to form [PP(Ph)P]CuCl (5), the product of phenyl group abstraction from [BPh4]−. A similar arylphosphine product [PP(Mes)P]CuCl (6, Mes = 2,4,6-trimethylphenyl) is obtained via transmetallation between [PP(Cl)P] and mesitylcopper(I). The isolation of complexes 4–6 provide indirect evidence for the formation of an electrophilic copper–phosphenium intermediate {[PPP]CuCl}+.

A series of copper halide complexes have been prepared employing 2-pyridone as a ligand. The compounds [CuBr 2 (2-pyridone) 2 ] 2 ( 1 ), [CuCl 2 (2-pyridone) 2 ] 2 ( 2 ), [CuCl 2 (2-pyridone)] 2 ( 3 ), [CuCl 2 (2-pyridone) 3 ] ( 4 ), and [CuCl 2 ·2H 2 O] 2 [(2-pyridone) 2 ] ( 5 ) were prepared and their structures and magnetic properties studied. Compounds 1 and 2 are dimeric species with the Cu(II) ions bridged by a pair of O-atoms from 2-pyridone molecules. Compound 3 is also a dimer, but in this case bridged by a pair of chloride ions. Only compound 4 is monomeric with fairly well isolated copper(II) ions, while compound 5 is a coordination polymer with the Cu(II) ions linked into chains via pairs of bridging chloride ions. Analysis of the magnetic data reveals that 1 and 2 exhibit significant antiferromagnetic interactions, while 4 is very weakly antiferromagnetic. Compounds 3 and 5 show weak ferromagnetic interactions. Data for 1 and 2 were fit to the antiferromagnetic dimer model with a Curie–Weiss correction to account for interdimer interactions: 1 , J = −41.7(1) K, θ = −0.8(1) K; 2 , J = −38.2(1) K, θ = −0.7(1) K. Data for 3 were fit to the ferromagnetic dimer model with a Curie–Weiss correction for interdimer interactions:); 2 , J = 9.4(6), θ = −3.2(3). Interactions in both 4 and 5 were sufficiently weak that data were fit only to the Curie–Weiss expression resulting in θ -values of −0.50(7) and 0.58(4) K respectively.

The crystal structure of a fifth polymorph of malonic acid has been determined by single crystal X-ray diffraction. The unit cell parameters, crystal structure and calculated powder diffraction lines for the new polymorph (monoclinic, Z ′ = 3) are distinctly different from those of the reported forms. There are both similarities as well as differences in the arrangement of molecules in the crystal lattice in all the forms. The molecules, in all the polymorphs, interact through the formation of O–H⋯O hydrogen bonded dimers by –COOH group with significant differences between the forms within this packing pattern.

Reaction of 3-amino-1,2,4-triazine (3-atz) or 2-aminopyrazine (2-apz) with Cu(hfac)2·xH2O led to the formation of the monometallic and trimetallic complexes Cu(hfac)2(3-atz)2 (1), Cu3(hfac)6(3-atz)2 (2), Cu(hfac)2(2-apz)2 (3) and Cu3(hfac)6(2-apz)2 (4). The azine molecules behave as both monodentate and bridging bidentate ligands. The Cu(II) ions exhibit a range of coordination geometries. In 1 and 3, the complex is distorted octahedral with the Jahn–Teller axis lying along one of the O–Cu–O axes. In 2 and 4, the central Cu(II) ion is also distorted octahedral with the Jahn–Teller axis lying along the N–Cu–N axis, while the terminal Cu(II) ions are five-coordinate. Structure analysis reveals that addition of the amino-substituent makes the ligands more coordinating, leading to shorter Cu N bonds. In the case of 4, this results in a stronger magnetic superexchange pathway and the complex exhibits antiferromagnetic behavior at low temperatures.

A new orthorhombic polymorph of silver malonate (II) has been synthesized and structurally characterized. Compound II crystallizes in space group Pnma, with a = 12.8180(11), b = 9.2479(8), c = 4.0219(3) A; V = 476.75(7) A3; Z = 4; ρcalc = 4.427 g cm−3. Full-matrix least-squares refinement converged to R1 = 0.0099 (I > 2σ(I), 765 data) and wR2 = 0.0264 (F2, 785 data, 51 parameters). The familiar eight-membered Ag2(RCO2)2 ring, characteristic of most silver(I) carboxylate complexes, has a Ag–Ag distance of 2.977(1) A. Puckered sheets in the crystal ab plane are connected along c to form a three-dimensional coordination polymer. The density of II is >30% higher than that of the monoclinic polymorph (I), first characterized in 1981. A survey of the density ratios of polymorphs in the Cambridge Structural Database indicates that virtually all of the pairs of entries having a density ratio >1.2 involve at least one form with significant void volume, as estimated using PLATON. However, neither I nor II have significant void volume, which suggests that the silver malonate polymorphs represent one of the largest density differences observed to date for a polymorphic pair. To date, it has not been possible to prepare I in our laboratories.

New PCP ligands in which the phosphine donor arms are connected to the central aromatic ring via NH moieties and their (PCP)PdCl complexes have been prepared. One such (PCP)PdCl complex was characterized by X-ray diffractometry in the solid state. The (PCP)PdCl complexes are exceptionally robust towards oxygen and water despite the presence of P–N bonds.

Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with M(NO 3 ) 2 · x H 2 O (M=Mn, Co, Ni, Zn) in acetonitrile solutions produced a linear polymer [Mn(μ-C 6 H 5 C 4 O 3 )(C 6 H 5 C 4 O 3 )(H 2 O) 3 ] n ( 1 ) and a series of isomorphous monomeric complexes [M(C 6 H 5 C 4 O 3 ) 2 (H 2 O) 4 ] [M=Co ( 2 ), Ni ( 3 ), Zn ( 4 )]. The complex 1 contains octahedral manganese with each metal centre being bridged μ-1,3 by a phenylsquarate ligand to two neighbouring metal atoms and further coordinated to a pendant phenylsquarate ligand group and three aqua ligands. The isomorphous monomeric complexes 2 – 4 all contain two phenylsquarate ligand groups oriented trans to each other, but with the substituent phenyl group on the ligand oriented cis to the ligating oxygen atom. The coordination polyhedron in each of these monomers is completed by four aqua ligands. The polymeric manganese complex shows no significant antiferromagnetic coupling and no semiconductivity.

Heating 3,5-dihalo-4-aminobenzoylchlorides affords the analogous solid polybenzamides. X-Ray structure determinations of 3,5-dichloro-, 3,5-dibromo- and 3,5-diiodo-4-aminobenzoylchlorides reveal that all three structures contain infinite hydrogen-bonded chains of monomers in a head-to-tail arrangement (graph set notation C(8)), with amine-to-carbonyl carbon atom distances

Sodium propynoate, Na(O2CC≡CH) 1, was synthesized from propynoic acid and sodium hydroxide in methanol solution. Irradiation of solid 1 with 60Co γ-rays (654 kGy dose) leads to an amorphous dark-colored acetylenic polymer in high yield. An X-ray structure determination of compound 1 shows that the sodium ion is five-coordinate, with a square-pyramidal geometry. The five-coordinate local moiety is part of an unusual two-dimensional polymer in the crystal bc plane. Crystal packing of the two-dimensional, solid-state polymers leads to a bilayer motif, and the relatively short metal–metal distance of 3.575 A promotes close packing of the organic tails with parallel acetylene moieties and a very short –C≡C–···–C≡C– contact of 3.29 A along the crystallographic b direction. Crystal data for 1: orthorhombic, space group Pna21, a=19.837(6), b=3.575(1), and c=5.232(1) A; V=371.0 A3; Z=4; R=0.0262; Rw=0.0327 for 427 data for which I>1.96σ(I).

The crystal structures of 272 metal carboxylates were surveyed with regard to the prevalence of bilayer formation. Bilayers affect the chemical and physical properties of solids. In particular, solid-state reactivity may be greatly enhanced by the presence of 2-dimensional metal coordination polymers in a bilayer motif. Bilayer formation is common (≈60% of 2-D coordination polymers) for aliphatic 3-carbon acidate salts and complexes, and is dominant (92%) for salts and complexes of ≥4-carbon aliphatic acids. For aromatic unsubstituted acids, the percentage is remarkably low (32% of all structures in the class—most are 1-D coordination polymers), while addition of a spacer group between the carboxyl group and the aromatic portion leads to >90% bilayer/2-D coordination polymer formation. The above points and other subtle features are illustrated in this contribution, and strategies for planning the production of possible bilayer materials are proposed.

The solid state phase behavior of hydroquinone 1 with bis-(N,N-diethyl)bicyclo[2.2.2]octane-1,4-dicarboxamide ( 4 ) and with bis-(N,N-dimethyl)bicyclo[2.2.2]octane-1,4-dicarboxamide ( 5 ) has been investigated. A 1:1 complex, 6 , exists with hydroquinone and the diethyl derivative 4 . A 1:2 complex, 7 , and a 2:1 complex, 8 , is formed with hydroquinone and the dimethyl derivative, 5 . X-ray structure determinations of these cocrystals have been performed and the role of the alkyl side chains in the crystal packing is discussed.

We have observed an unusual example of cobalt-mediated cyclization of 4-pyridinecarboxaldehyde and 2-nitroaniline to afford 2-(4-pyridyl)benzimidazole under hydro(solvo)thermal conditions. Reaction of Co(NO 3 ) 2 ·6H 2 O with 4-pyridinecarboxaldehyde and 2-nitroaniline in ethanol at 120°C gave a cobalt(II) coordination compound, Co[2-(4-pyridyl)benzimidazole] 2 (H 2 O) 2 (NO 3 ) 2 , 1 . In contrast, when the hydro(solvo)thermal reaction was carried out between Co(NO 3 ) 2 ·6H 2 O and isonicotinic acid in the presence of 2-nitroaniline at 110°C, a one-dimensional Co(II) coordination polymer with the formula of [Co(isonicotinate)(4-pyridiniumcarboxylate)(H 2 O)(NO 3 )] ∞ , 2 , resulted. The X-ray single crystal structures of both 1 and 2 are described. Interestingly, the isonicotinic acid in 2 exists as a 4-pyridiniumcarboxylate tautomer, and the pyridinium hydrogen atom forms a very strong hydrogen bond to the carboxylate oxygen of the 4-pyridiniumcarboxylate on an adjacent metal center. 1 forms a three-dimensional polymeric network through hydrogen bonding interactions, while 2 exists as a 2-D bilayer polymeric network through hydrogen bonding interactions.

A new cocrystalline salt, 5-bromo-2-aminopyridinium propynoate 7, has been synthesized. Inspection of the crystal structure reveals that the packing differs markedly from that of the chemically analogous species 2-aminopyridinium propynoate 1. While 1 undergoes a thermally-induced Michael addition reaction in the solid state, compound 7 is thermally stable. The lack of similarity between the crystal structures of 1 and 7 may arise from a set of favorable, infinite Br⋯Br interactions (3.82–3.84 A). Short contacts between acetylenic carbon atoms are also characterized and discussed.

Synthesis and characterization of two coordination complexes of 2,4′-bipyridine, Co(2,4′-bipyridine) 2 (NO 3 ) 2 (H 2 O) ( 1 ), and Cd(2,4′-bipyridine) 2 (NO 3 ) 2 (H 2 O) 2 ( 2 ), are described. Complex 1 was obtained by reacting Co(NO 3 ) 2 · 6H 2 O and 2,4′-bipyridine in a mixture of water and ethanol at room temperature, while 2 was synthesized from Cd(NO 3 ) 2 · 4H 2 O and 2,4′-bipyridine under hydro(solvo)thermal conditions at 90°C. In both complexes the metal centers only coordinate to the 4-pyridyl nitrogen atoms of the 2,4′-bipyridine ligands, with the rest of the coordination sites occupied by nitrate groups and water molecules. In 1 , the 2-pyridyl nitrogen atoms of the 2,4′-bipyridine ligands form intermolecular hydrogen bonds with both hydrogen atoms of the coordinated water molecule, resulting in a two-dimensional (2-D) polymeric network. In 2 , all the hydrogen atoms of the two coordinated water molecules are engaged in intermolecular hydrogen bonding with the 2-pyridyl nitrogen atoms of the 2,4′-bipyridine ligands and the oxygen atoms of the coordinated nitrate group; a 2-D hydrogen-bonded polymeric network is also obtained. Complexes 1 and 2 are the first coordination complexes of 2,4′-bipyridine to be characterized by X-ray crystallography.

The tricyclic triamine core27 of martinellic acid (2) has been prepared stereospecifically in eight steps from 2-hydroxymethylaniline in 11% overall yield. The key steps are the addition of 2-hydroxymethylaniline to vinylcyclopropane14 to prepare cycloaddition precursor19 in only two steps and an intramolecular [3+2] azomethine ylide cycloaddition reaction to produce tetracycle20 with>9:1 diastereoselectivity. Download : Download full-size image

Enamides 3a-c and 6 crystallize in α-packing modes with short intermolecular distances of 3.7–4.0 A between alkene carbon atoms of adjacent molecules related by a center of symmetry. Irradiation at 350 nm of these crystalline tertiary phenylethenyl enamides affords head-to-tail dimers 8a-c and 9, respectively, in 87–92% yield, in marked contrast to the E to Z isomerization that is the exclusive reaction upon solution irradiation of enamides 3a and 6.

The solid state phase behavior of hydroquinone 1 with bis-(N,N-diethylamino)terephthalamide 2 and with bis-(N,N-dimethylamino)terephthalamide 3 has been investigated. Stoichiometric cocrystals have been prepared of the identified stable complexes. X-ray structure determinations of these cocrystals have been performed. The role of the alkyl side chains in the crystal packing geometry is discussed.

The structure of acetatodimethylthallium 2 has been used as a model in an attempt to predict and ‘engineer’ a phase of dimethyl(propynoato)thallium 3 which would be reactive in the solid state. Upon irradiation with X-rays or 60Co γ-rays, 3 is indeed converted to the corresponding deep-brown polypropynoate. The crystal structure of 3 contains, as expected, an infinite set of short contacts (3.454 A) between acetylene moieties; the presence of such a chain is a requirement for a propynoate material to be sensitive to ionizing radiation. However, the crystal structures of 2 and 3 are quite different owing to subtle changes in CH⋯O hydrogen bonding, Crystals of 3, (CH3)2Rl(O2CC≡CH), belong to the orthorhombic system, space group Pnma, a = 7.316(4), b = 11.268(6), c = 9.033(5) A ; Z = 4 . Full-matrix least-squares refinement of positional and displacement parameters for all nonhydrogen atoms, using 338 data for which |Fo| > 3.92σ(|Fo|), led to R = 0.059 and Rw = 0.068.

Motivated by the Haldane conjecture, the powder susceptibilities of two nickel complexes (1: NiCl2L2, with LP(CH2CH2CN)3; 2: bis(propiolato)tetraaquonickel(II)) have been investigated as part of a search for new S=1 antiferromagnetic linear chains. The effective moments of both complexes correspond to high-spin S=1 Ni(II) ions at room temperature but decrease rapidly below 20 K. Analysis of the data showed the decreases to correspond to the effects of single-ion anisotropy and not magnetic exchange. The susceptibilities of 1 and 2 can be described as resulting from single-ion anisotropy parameters D/k=7 and 8.5 K, respectively, with the ms=0 single state low for both complexes. Neither 1 nor 2 can be considered a magnetic linear chain.

The crystal and molecular structure of a fragment of a face-to-face metallocene polymer, the [2,3]-oligomer( 2a , n = 2) of 1,8-diferrocenylnaphthalene( 1a ), has been determined in order to better define the structural features of the polymer. The molecular structure of this compound shows the same form and magnitude of molecular distortions as those found in the monomeric unit 1a . An unusual feature of the oligomer is the cis arrangement of the two naphthalene nuclei, which brings several of the carbon centers on each naphthalene ring in close proximity. These structural aspects are discussed in the context of possible structures for the related polymer.

The crystal structure of Co(NCS) 2 [4-vinylpyridine] 4 has been determined by X-ray diffraction methods. The complex crystallizes in space group Pbca , with a = 32.293(15) A, b = 11.416(6) A, c = 17.033(10) A , and Z = 8. Full-matrix least-squares refinement of positional and thermal parameters for all atoms (H atoms fixed at calculated positions), with 1458 reflections ( F >; 3.92 σ (F) ) led to R = 0.075 and R w = 0.079. The trans -octahedral complex consists of four vinylpyridine ligands, arranged in a propeller-shape, and two isothiocyanate ligands. Powder diffraction of Co(NCS) 2 (4-vinylpyridine) 2 indicates an isomeric cell, with a = 13.77 A . The analogous Ni(II) complexes are isomorphous with the Co(II) complexes, suggesting that the yellow–green complex Ni(NCS) 2 (4-vpy) 2 , previously thought to be polymeric, is in fact tetrahedral.

The usefulness of simultaneous polymerization and crystallization as a preparative tool for transition metal polymers is established; syntheses of both stable and metastable mixed-metal (M=Ni,Co) polymers are described. The metastable polymers show solid-state reactivity as well as room-temperature photochromism. (Author)