Racemic nickel(II) pyridine-2-aldoximate complexes capped by 2,2-bipyridine and 1,10-phenanthroline: syntheses, structures and magnetic properties

Two Ni(II) pyridine-2-aldoximate complexes, Ni(pao)₂(bpy) (1) and Ni(pao)₂(phen) (2) (pao⁻=pyridine-2-aldoximate, bpy=2,2^′-bipyridine, phen=1,10-phenanthroline), were synthesized via the deprotonation of NiCl₂(Hpao)₂ in methanol followed by the addition of bidentate ligands of 2,2^′-bipyridine and 1,10-phenanthroline. Crystallization in CHCl₃ gave block-type crystals of 1 and 2 in high yields. The mononuclear structure surrounded by three bidentate ligands, i.e., two pao⁻ and one bpy or phen, was revealed by X-ray crystallography: 1 crystallizes in monoclinic space group P2₁/c with cell dimensions of a=13.457(3) Å, b=14.493(3) Å, c=19.104(4) Å, β=108.681(3)°, Z=4, and 2 crystallizes in monoclinic space group P2₁/n with cell dimensions of a=14.235(5) Å, b=12.018(4) Å, c=20.696(7) Å, β=110.304(4)°, Z=4. 1 and 2 each have two oximate groups (pao⁻), with an NO-trans arrangement around the Ni^II ion. Complexes 1 and 2 are racemic, namely, each molecule has a chiral center of Δ or Λ, thereby forming NO-trans-Δ and -Λ geometries in the solid state. Magnetic measurements revealed a paramagnetic S=1 spin state with a positive zero-field splitting parameter.     

Polymorphism and weak antiferromagnetic interactions in dibromo[(−)-sparteine-N,N]copper(II)

Two polymorphic crystal structures of the title compound, dibromo[(−)-sparteine-N,N^′]copper(II), 1, were determined. The structures of two isomorphs of 1, 1a [orthorhombic, P2₁2₁2₁, a=11.0463(9) Å, b=11.9839(15) Å and c=12.7835(19) Å] and 1b [orthorhombic, P2₁2₁2₁, a=7.6779(9) Å, b=12.0927(14) Å and c=18.090(2) Å], are composed of the same basic structural unit, Cu(C₁₅H₂₆N₂)Br₂. The bond distances in the molecular structures of 1a and 1b are identical to each other within the esds. However, there are slight differences in the bond angles around the Cu(II) center and considerable differences in their packing structure. Crystal 1a exhibits weak anti-ferromagnetism (J=−1.89 cm⁻¹) as opposed to the magnetically isolated paramagnetism observed for the analogous dichloro[(−)-sparteine]copper(II), 2. The results of a magneto-structural investigation of 1a and 2, and other supporting evidence, suggest that the pathway for the weak antiferromagnetic super-exchange in 1a might be through a Cu-Br ? Br-Cu contact.     

Effect of outer sphere anions on the structure and color of nitrosylpentaamminechromium complex

Three kinds of crystalline compounds containing the nitrosylpentaamminechromium complexes [Cr(NO)(NH₃)₅]²⁺(A) were obtained: chloride ACl₂ (red-orange), chloride perchlorate ACl(ClO₄) (brown), and perchlorate A(ClO₄)₂ (green). The cause of the color change of the complex A with the change of outer sphere anions was sought using X-ray structural data of ACl₂, ACl(ClO₄), and A(ClO₄)₂. Crystal data: ACl₂, orthorhombic, space group Cmcm, a=10.0236 (9) Å, b=9.098 (3) Å, c=10.357(1) Å, V=944.5 (5) ų, Z=4; ACl(ClO₄), tetragonal, space group P4/nmm, a=7.6986 (8) Å, c=9.9566(8) Å, V=590.1 (1) Å^3,Z=2; A(ClO₄)₂, orthorhombic, space group Pnma, a=15.760 (2) Å, b=11.480(2) Å, c=7.920 (2) Å, V=1432.9 (4) ų, Z=4. The complex cation in ACl₂ has a distorted octahedral structure with a linear CrNO moiety. The short CrN (nitrosyl) distance of 1.692 (7) Å indicates the presence of multiple bonding between the chromium atom and the nitrogen atom in the nitrosyl group. The interatomic distances and angles within the complex cations hardly change with the change of the counter anions, while the distances between the complex cations in each crystal increase in the order ACl₂<ACl(ClO₄)<A(ClO₄)₂. The bulky perchlorate anions seems to separate the complex cations, while smaller chloride anions are not large enough to separate them. The distance (3.213(5) Å) between O(NO) and N(NH₃ in the adjacent complex cation) is rather short in the crystal of ACl₂, and there are six hydrogen bonds, where the NO group is surrounded by four NH₃ ligands. The distance (4.002(5) Å) between O(NO) and N(NH₃) is much longer in the crystal of A(ClO₄)₂, indicating the presence of no hydrogen bonding. In the crystal of ACl(ClO₄) the distance (3.452(4) Å) between O(NO) and N(NH₃) is in between those of ACl₂ and A(ClO₄)₂. The presence of hydrogen bonding between O(NO) and N(NH₃ in the adjacent complex cation) seems to cause the color change with the change of outer sphere anions.     

Hydrogen-halide versus alkyl-halide oxidative addition in dimethyl platinum(II) complexes: Crystal structure of [PtBr2(bpy)]

Dimethyl platinum(II) complexes [PtMe₂(NN)] {NN = bu₂bpy (4,4′-di-tert-butyl-2,2′-bipyridine) (1a), bpy (2,2′-bipyridine) (1b), phen (1,10-phenanthroline) (1c)} reacted with commercial 3-bromo-1-propanol in the presence of 1,3-propylene oxide to afford cis, trans- [PtBrMe₂{(CH₂)₃OH}(NN)] (NN = bu₂bpy (2a), bpy (2b), phen (2c)). On the other hand, [PtMe₂(NN)] (1a)-(1b) reacted with the trace of HBr in commercial 3-bromo-1-propanol to give [PtBr₂(NN)] (NN = bu₂bpy (3a), bpy (3b)). The reaction pathways were monitored by ¹H NMR at various temperatures. Treatment of 1a-1b with a large excess of 3-bromo-1-propanol at −80 °C gave the corresponding methyl(hydrido)platinum(IV) complexes [PtBr(H)Me₂(NN)] (NN = bu₂bpy (4a), bpy (4b)) via the oxidative addition of dimethyl platinum(II) complexes with HBr. The complexes [PtBr(H)Me₂(NN)] decomposed by reductive elimination of methane above −20 °C for bu₂bpy and from −20 to 0 °C for bpy analogue to give methane and platinum(II) complexes [PtBrMe(NN)] (5a)-(5b) and then decomposed at about 0 °C to yield [PtBr₂(NN)] and methane. When the reactions were performed at a molar ratio of Pt:RX/1:10, the corresponding complexes [PtBrMe(NN)] (5a)-(5b) were also obtained. The crystal structure of the complex 3b shows that platinum adopts square planar geometry with a twofold axis through the platinum atom. The Pt…Pt distance (5.164 Å) is considerably larger than the interplanar spacing (3.400 Å) and there is no platinum-platinum interaction.     

Structures from powders: Diflorasone diacetate

Diflorasone diacetate, a steroid anti-inflammatory drug (marketed as Diacort^® or Florone^® by Pfizer) and used in the treatment of skin disorders, can be prepared as anhydrous form, DD1 (as deposited in the US pharmacopoeia), or as a monohydrated phase, DDW. Heating the DDW form above 90 °C, a mixture of DD1 and of a new anhydrous polymorph, DD2 is obtained. Further heating of this mixture, or of pure DD1, up to 230 °C (only a few degrees before melting!), generates an elusive anhydrous DD3 polymorph. Their crystal structures, determined uniquely from laboratory powder diffraction data, show the isomorphous character of the DDW and DD1 forms, while the DD2 and DD3 polymorphs crystallize with markedly different unit cells. Crystals of the DD1, DD2 and DDW forms are orthorhombic, P2₁2₁2₁, a = 29.386(1) Å; b = 10.4310(9) Å, c = 8.1422(7) Å, V = 2495.8(3) Å³ for DD1; a = 15.2639(10) Å; b = 11.7506(7) Å, c = 13.8931(11) Å, V = 2491.9(3) Å³ for DD2; a = 30.311(2) Å; b = 10.6150(9) Å, c = 7.9337(7) Å, V = 2552.7(4) Å³ for DDW; while the lattice parameters for the monoclinic P2₁DD3 species are a = 11.5276(10) Å; b = 13.8135(11) Å, c = 7.8973(7) Å, β = 103.053(6)°, V = 1225.0(2) Å³. These compounds have also been fully characterized by thermo analytical methods, as well by ¹³C, ¹⁹F, and ¹H NMR spectroscopy.     

Syntheses, structures, and properties of novel one dimensional copper cyanide coordination polymers

Three new one-dimensional copper coordination polymers have been prepared and fully characterized by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and magnetic susceptibility measurements. The structure of [Cu(CN)₂(bpy)] (1) (bpy = 2,2-bipyridyl) (monoclinic P2₁/c, a = 8.9761(7) Å, b = 16.731(1) Å, c = 8.0224(6) Å, β = 114.437(1)°) consists of Cu(II) metal centers coordinated by three cyanide ligands and chelated by one bpy to form the monomers Cu(CN)₃(bpy) with distorted square pyramidal geometry. Each monomer shares two cyanide ligands with two adjacent monomers to form infinite -Cu(II)-CN-Cu(II)-CN-Cu zigzag chains along the c-axis. The one-dimensional structure of [Cu(CN)(bpy)] (2) (hexagonal P3₂, a = 14.4883(6) Å, b = 12.921(1) Å) is built of tetrahedral Cu(CN)₂bpy metal complexes in which Cu(I) metal centers are coordinated by one nitrogen and one carbon from two different CN ligands, and two nitrogens from one bpy. The two CN ligands act as bridging ligands between adjacent monomers to form helical chains along the 3₂ screw axis. The crystal structure of [Cu₂Cl(CN)(bpy)] (3) (orthorhombic Pbca, a = 17.853(2) Å, b = 6.9724 (9) Å, c = 18.7357 (9) Å) consists of two monomers, CuCl₂(CN) and Cu(bpy)(CN) that share a cyanide ligand to form Cu₂Cl₂(CN)(bpy) dimers. The dimers link to each other by sharing Cl ligands leading to the formation of infinite Cu-Cl-Cu chain decorated by the complex Cu(CN)(bpy). Variable-temperature magnetic measurement shows an overall ferromagnetic behavior for compound 1. The magnetic pathway of compound 1 is through the cyanide bridge connecting apical and equatorial positions of adjacent copper (II) ions.     

Diastereoisomerically pure pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2-bipyridine: structural, electrochemical and spectral studies

Pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2^′-bipyridine of composition [(bpy)₂Ru(pzdc)Ru(bpy)₂](ClO₄) · H₂O (1) and [(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2) have been obtained in high yield and have been separated to their homochiral (ΛΛ/ΔΔ) rac (1a, 2a) and heterochiral (ΛΔ/ΔΛ) meso (1b, 2b) diastereoisomers. The distinctive structural features of these diastereoisomers have been characterized by 1-D and 2-D ¹H NMR spectroscopy. The X-ray crystal structure of rac-[(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2a) has been determined. The electrochemical and electronic spectral studies have established that there remain difference in properties and hence difference in intermetallic communication between the diastereoisomeric forms in each case.     

Neighbouring metal induced oxidative addition at the iron centre amongst the iron-arylpyridylphosphine complexes

Complexes of the type (η⁴-BuC₅H₅)Fe(CO)₂(P) (P = PPh₂Py 3, PPhPy₂4, PPy₃5; Py = 2-pyridyl) were satisfactorily prepared. Upon treatment of 3 with M(CO)₃(EtCN)₃ (M = Mo, 6a; W, 6b), the pyridyl N-atom could be coordinated to the metal M, which then eliminates a CO ligand from the Fe-centre and induced an oxidative addition of the endo-C-H of (η⁴-BuC₅H₅). This results in a bridged hydrido heterodimetallic complex [(η⁵-BuC₅H₄)Fe(CO)(μ-P,N-PPh₂Py)(μ-H)M(CO)₄] (M = Mo, 7a, 81%; W, 7b, 76%). The reaction of 4 or 5 with 6a,b did not give the induced oxidative addition, although these complexes contain more than one pyridyl N-atom. The reaction of 4 with M(CO)₄(EtCN)₂ (M = Mo, 9a; W, 9b) produced heterodimetallic complexes [(η⁴-BuC₅H₅)Fe(CO)₂(μ-P:N,N′-PPhPy₂)M(CO)₄] (M = Mo, 10a, 81%; W, 10b, 83%). Treatment of 5 with 6a,b gave [(η⁴-BuC₅H₅)Fe(CO)₂(μ-P:N,N′,N″-PPy₃)M(CO)₃] (M = Mo, 12a, 96%; W, 12b, 78%).     

Synthesis and characterization of three geometric isomers of ruthenium(2,2-bipyridyl)(salicylaldehyde)2

A new synthesis of Ru^II(bpy)(sal)₂ (1) (bpy=2,2^′-bipyridyl, sal=salicylaldehyde) has been developed and the separation and characterization of all three geometric isomers have been completed. The isomers are denoted 1a (phenolic oxygens trans), 1b, (aldehyde oxygens trans), and 1c (aldehyde oxygen trans to phenolic oxygen). All three isomers have been characterized by ¹H NMR, high resolution FAB-MS, UV-Vis, and cyclic voltammetry. Additionally, 1a has been characterized by solid-state UV-Vis and a single-crystal X-ray structural study. The solid-state packing of the Ru^II(bpy)(sal)₂ molecules in the structure of 1a displays intermolecular π-π interactions between bpy ligands of adjacent molecules. The bpy interactions form infinite π-stacks with alternating short stacking distances of 3.437 and 3.402 Å.     

Structure and spectroscopic studies of cis-bis(bipyridine) ruthenium(II) complexes of phenylcyanamide ligands

New ruthenium(II) complexes with cyanamide ligands, cis-[Ru(bpy)₂(Ipcyd)₂] (1) and [Ru(bpy)₂(OHpcyd)₂] (2) (bpy = 2,2′-bipyridine, Ipcyd = 4-iodophenylcyanamide anion, OHpcyd = 4-(3-hydroxy-3-methylbut-1-ynil)phenylcyanamide), have been prepared and characterized by UV-Vis, IR and ¹H NMR spectroscopies as well as electrochemical technique (CV). The complex cis-[Ru(bpy)₂(Ipcyd)₂] (1) crystallized with empirical formula of C₃₄H₂₄I₂N₈Ru in a monoclinic crystal system and space group of P2₁/c with a = 11.769(7) Å, b = 24.188(12) Å, c = 11.623(2) Å, β = 91.63(3)°, V = 3308(3) ų and Z = 4.     

Two cadmium-thiocyanate coordination polymers with organic cations: Synthesis, crystal structures and luminescent properties

Two new inorganic-organic hybrid polymers [ClBzQl]₂[Cd(SCN)_3.5Br_0.5]·0.25H₂O (1) and [ClBzMePy][Cd(SCN)₃] (2) (ClBzQl = 1-(4′-Cl-benzyl)quinolinium cation and ClBzMePy = 1-(4′-Cl-benzyl)-2-methylpyridinium cation) have been synthesized and characterized by IR, UV, elemental analysis and X-ray crystallography. Crystal structure analyses show that two polymers belong to the monoclinic space group P2/n (1) and P2₁/c (2) with a = 18.548(2) Å, b = 9.526(1) Å, c = 20.689(2) Å, β = 94.008(1)°, V = 3646.6(5) Å³ for 1, and a = 11.195(2) Å, b = 16.415(3) Å, c = 10.751(2) Å, β = 102.930(3)°, V = 1925.7(7) Å³ for 2. The Cd atom exhibits a distorted octahedral coordination geometry for 1 and 2. For 1, a pair of 1,1-μ-SCN⁻ anions and a pair of 1,3-μ-SCN⁻ anions are alternately bridge adjacent Cd centers to form infinite polymeric chains. For 2, adjacent Cd atoms are linked by three 1,3-μ-SCN⁻ anions to form infinite [Cd(SCN)₃⁻]_∞ polymeric chains. The luminescent properties of the two polymers in the solid state at room temperature were investigated.     

Palladium(II), platinum(II), ruthenium(II) and mercury(II) complexes of potentially tridentate Schiff base ligands of (E, N, O) type (E = S, Se, Te): Synthesis, crystal structures and applications in Heck and Suzuki coupling reactions

Schiff bases of 2-hydroxybenzophenone (HBP) (C₆H₅)(2-HOC₆H₄)CN(CH₂)_nEAr (L1/L2: E = S, Ar = Ph, n = 2/3; L3/L4: E = Se, Ar = Ph, n = 2/3; L5/L6: E = Te, Ar = 4-MeOC₆H₄, n = 2/3) and their complexes [PdCl(L-H)] (L = L1−L6; 1, 2, 3, 5, 7, 11), [PtCl(L3-H/L5-H)] (4/8), [PtCl₂(L4/L6)₂] (6/12), [(p-cymene)RuCl(L5/L6)]Cl (9/13) and [HgBr₂(L5/L6)₂] (10/14) have been synthesized and characterized by proton, carbon-13, selenium-77 and tellurium-125 NMR, IR and mass spectra. Single crystal structures of L1, 1, 3, 4, 5 and 7 were solved. The Pd-E bond distances (Å): 2.2563(6) (E = S), 2.3575(6)−2.392(2) (E = Se); 2.5117(5)−2.5198(5) (E = Te) are near the lower end of the bond length range known for them. The Pt-Se bond length, 2.3470(8) Å, is also closer to the short values reported so far. The Heck and Suzuki reaction were carried out using complexes 1, 3, 5 and 7 as catalysts under aerobic condition. The percentage yields for trans product in Heck reaction were found upto 85%.     

Mononuclear single helices of lanthanum(III) and europium(III). Metal dependent diastereomeric excess

Using the 1:2 condensate of benzildihydrazone and 2-acetylpyridine as a tetradentate N donor ligand L, LaL(NO₃)₃ (1) and EuL(NO₃)₃ (2), which are pale yellow in colour, are synthesized. While single crystals of 1 could not be obtained, 2 crystallises as a monodichloromethane solvate, 2·CH₂Cl₂ in the space group Cc with a = 11.7099(5) Å, b = 16.4872(5) Å, c = 17.9224(6) Å and β = 104.048(4)°. From the X-ray crystal structure, 2 is found to be a rare example of monohelical complex of Eu(III). Complex 1 is diamagnetic. The magnetic moment of 2 at room temperature is 3.32 BM. Comparing the FT-IR spectra of 1 and 2, it is concluded that 1 also is a mononuclear single helix. ¹H NMR reveals that both 1 and 2 are mixtures of two diastereomers. In the case of the La(III) complex (1), the diastereomeric excess is only 10% but in the Eu(III) complex 2 it is 80%. The occurrence of diastereomerism is explained by the chiralities of the helical motif and the type of pentakis chelates present in 1 and 2.     

Diverse dimensionalities and structures in copper coordination polymers incorporating substituted aliphatic dicarboxylate ligands and 4,4′-bipyridine

Hydrothermal synthesis has afforded a series of divalent copper coordination polymers with substituted glutarate ligands and the rigid rod tether 4,4′-bipyridine (bpy): {[Cu(Hdmg)₂(bpy)]·H₂O}_n (1, dmg = 3,3-dimethylglutarate), {[Cu₂(dmg)(bpy)₂](ClO₄)]_n (2), [Cu₂(emg)₂(bpy)]_n (3, emg = 3-ethyl, 3-methylglutarate) and [Cu₂(cda)₂(bpy)]_n (4, cda = 1,1-cyclopentanediacetate). All materials were characterized by single-crystal X-ray diffraction. Compound 1 manifests μ₂-oxygen bridged [Cu₂(Hdmg)₄] “X”-patterns connected into a ribbon motif by bpy linkers. On the other hand, 2 possesses mixed-valence [Cu^ICu^IICu^IICu^I] tetrameric clusters bridged by dmg ligands and pillared into an 8-connected body-centered cubic (bcu) cationic lattice by bpy linkers. Compounds 3 and 4 are structurally very similar, displaying chain motifs with {Cu₂(CO₂)₄} paddlewheels connected by dicarboxylates, in turn conjoined into (4,4)-grid coordination polymer layers by bpy tethers. Variable temperature magnetic data indicate the presence of very strong antiferromagnetic coupling within the {Cu₂(CO₂)₄} paddlewheels in the latter two complexes, with g = 2.30(2) and J = −352(3) cm⁻¹ for 3 and g = 2.35(2) and J = −352(5) cm⁻¹ for 4. Significant structural contrasts are evident when compared to previously reported divalent copper/4,4′-bipyridine coordination polymers with unsubstituted or 2-methyl substituted glutarate ligands.     

Synthesis, characterisation and natural abundance Os NMR spectroscopy of hydride bridged triosmium clusters with chiral diphosphine ligands

Treatment of [Os₃(μ-H)₂(CO)₁₀] with the chiral diphosphines BINAP, tolBINAP [(R)-2,2′-bis(di-4-tolylphosphino)-1,1′-binaphthyl], DIOP [(4R,5R)-(−)-O-isopropenylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane] affords [Os₃(μ-H)₂(CO)₈(μ-L)] (L = BINAP (1), tolBINAP (2), DIOP (4)) in high yield. The X-ray structures for 1, 2 and 4 are reported, and structural and spectroscopic comparisons are made between these clusters and [Os₃(μ-H)₂(CO)₈(μ-L)] (L = dppm (5), dppe (6), dppp (7)) which were synthesised similarly. Compounds 5 to 7 were previously synthesised by hydrogenation of 1,2-[Os₃(CO)₁₀(μ-L)] but the route from [Os₃(μ-H)₂(CO)₁₀] is preferable. The H-bridged Os?Os distances are similar in 1, 2 and 4 indicating that these species are formally unsaturated 46-electron clusters. The P?P distances vary from 4.24 to 4.30 Å in 1 and 2, respectively, to 4.53 Å in 4 and there are related changes in the angles associated with the ligand set around the H-bridged osmium atoms. Introduction of the diphosphine ligands completely suppresses the ability to add CO, to insert acetylene to form a μ-η¹,η²-vinyl compound, and to exchange hydride ligands with styrene-d₈, which are reactions characteristic of [Os₃(μ-H)₂(CO)₁₀]. Clusters 2 and 5-7 were also used to examine the potential of natural abundance ¹⁸⁷Os NMR spectroscopy through techniques based on inverse detection by HMQC, HSQC and HMBC spectroscopy.     

Cu(II) complexes with square pyramidal (N2S)CuCl2 chromophore: Jahn-Teller distortion and subsequent effect on spectral and structural properties

One monomeric neutral Cu(II) complex [(pmtpm)CuCl₂] (1) is reported by Lindoy and Livingstone [8]. Two new complexes namely, μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu(Cl)}₂ μ-Cl](ClO₄) (2) and a bis μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu}₂(μ-Cl)₂](ClO₄)₂ (3) derived from a tridentate Schiff base ligand, 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine (pmtpm) were synthesized and characterized by various spectroscopic methods and by X-ray crystallography. (N₂S)CuCl₂ chromophore(s) of distorted square pyramidal coordination geometries around Cu(II) ion(s) have been observed for all the complexes 1-3. The equatorial sites of the square plane comprise two N and a thioether S donor atoms of the pmtpm ligand as well as one Cl⁻ ion (terminal in 1 and 2, and bridging in 3) while the remaining axial site is occupied by a terminal Cl⁻ ion (for 1) or a bridging Cl⁻ ion (for 2 and 3). The equatorial Cu-Cl distances are much shorter [1: 2.2511(4) Å, 2: 2.2307(12) Å, 3: 2.2513(12) Å] than the axial Cu-Cl distances [1: 2.4394(4) Å, 2: 2.5597(9) Å, 3: 2.7037(12) Å]. The correlation of an axial Cu-Cl bond elongation with a lower g_|| value in the solid state EPR spectrum and a blue shifted ligand field transition in the solid and solution phase absorption spectrum has been observed.     

Syntheses, structures, and magnetic properties of two new μ-alkoxo-μ-pyrazolato bridged dicopper(II) complexes

The syntheses, structures, and magnetic properties of two new μ-alkoxo-μ-pyrazolato heterobridged compounds, [Cu ^II₂(L¹-F)(μ-prz)] (1) and [Cu ^II₂(L¹-2OMe) (μ-prz)] · 0.5 CH₃CN (2) (prz=pyrazolato; H₂L¹-F=1,3-bis(3-fluorosalicylideneamino)-2-propanol; H₂L¹-2OMe=1,3-bis(4,6-dimethoxy salicylideneamino)-2-propanol) have been reported. Compound 1 crystallizes in triclinic space group with a=8.6392(10) Å, b=10.6431(9) Å, c=11.6809(13) Å, α=85.972(8)°, β=71.492(9)°, and γ=72.221(9)°, while the unit cell parameters of 2 are as follows: space group: monoclinic C2/c, a=28.2948(5) Å, b=7.3033(2) Å, c=26.3933(5) Å, and β=96.243(1)°. The variable-temperature magnetic susceptibility measurements reveal that the metal centers in both the compounds are antiferromagnetically coupled with J=−200 cm⁻¹ for 1 and J=−175 cm⁻¹ for 2. The magnetic behaviors have been explained on the basis of two opposing factors, complementarity and countercomplementarity of magnetic orbitals.     

Structural studies on 1:1 and 2:1 adducts of silver(I) cyanide with alkanediamine ligands

The crystal structures of two 1:1 ligand-silver(I) cyanide complexes, [Ag(CN)(en)] (en = ethane-1,2-diamine) (1) and [Ag(CN)(pn)] (pn = propane-1,2-diamine) (2), and of two 2:1 ligand-silver(I) cyanide compounds, [(AgCN)₂ · tn] (tn = propane-1,3-diamine) (3) and [(AgCN)₂ · bn] (bn = butane-1,4-diamine) (4), were determined from single-crystal X-ray diffraction data, collected at 173 K. In 1 and 2, mononuclear AgCN complexes are formed, in which silver(I) is coordinated by one cyanide and one chelating alkanediamine donor ligand. However, in the dinuclear adducts of 3 and 4, two AgCN units are connected by one alkane-1,n-diamine bridging ligand (n = 3, 4). The resulting molecules of 1-4 are cross-linked via N-H?N hydrogen bonds. Apart from these intermolecular contacts, comparatively short Ag(I)-Ag(I) distances of 3.182(1) Å (in 1), 3.267(1) Å (in 2), 3.023(2) Å (in 3) and 3.050(2) Å (in 4) occur.     

Structural, photophysical and electrochemical studies of [RuN6] complexes having polypyridine and azole mixed-donor sites

The mixed-ligand ruthenium(II) complexes [(phen)₂Ru(pzbzimH₃)](ClO₄)₂·3H₂O (1), [(phen)₂Ru(bzimH)₂](ClO₄)₂·3H₂O (2) and [(bpy)₂Ru(bpybzimH₂)](ClO₄)₂ (3), where phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine, pzbzimH₃ = pyrazole-3,5-bis(benzimidazole), bzimH = benzimidazole and bpybzimH₂ = 6,6′-bis(benzimidazole-2-yl)-2,2′-bipyridine have been synthesized and spectroscopically characterized. The X-ray structures of the three compounds have been determined which show that relative to the polypyridine ligands (phen or bpy) two donor nitrogens of the second ligand occupy cis position. In case of 3, bpybzimH₂ ligand is coordinated in puckered form where its bpy unit acts in a monodentate fashion. The electrochemical properties, absorption and emission spectral characteristics and lifetimes of luminescence decay of the complexes have been compared. Deprotonation of the azole NH moieties of the complexes lead to substantial lowering of redox potentials of the Ru^II/Ru^III couple as well as the MLCT and emission band energies. Spectrophotometric and spectrofluorometric titrations of complexes 1 and 3 have been carried out in 3:2 acetonitrile-water as a function of pH over the range 3.5-12.0 and the pK values have been determined. The kinetic parameters for the decay of the ³MLCT excited states of 1 at different pH at 298 K have been evaluated.     

One-dimensional azido-bridged chiral copper(II) coordination polymers: Syntheses, structures and magnetic studies

Two new one-dimensional azido-bridged chiral copper(II) coordination polymers, [(μ-1,1,3-N₃)₂{Cu₂(R-L)₂(N₃)₂}]_n (1) (R-L = R-2-(N-(2-hydroxybutyl)carbaldimino) pyridine) and [(μ-1,1,3-N₃)₂{Cu₂(S-L)₂(N₃)₂}]_n (2) (S-L = S-2-(N-(2-hydroxybutyl)carbaldimino)pyridine) have been synthesized and structurally characterized. Complexes 1 and 2 crystallize in the monoclinic chiral space group P2₁. For 1, with a = 6.9565(17) Å, b = 20.675(5) Å, c = 9.859(2) Å, β = 105.944(5)° and Z = 2. In the case of compound 2, a = 6.9650(17) Å, b = 20.705(5) Å, c = 9.878(2) Å, β = 105.941(4)° and Z = 2. Both complexes consist of one-dimensional chiral structures in which the copper(II) ions with a distorted octahedral geometry are interlinked by the unusual μ-1,1,3 azido ligands. Circular dichroism spectra demonstrate that 1 and 2 are a pair of enantiomers. Their magnetic properties have been studied. Fitting of the susceptibility data for 1 and 2 using the Bleany-Bowers expression derived from the isotropic spin-exchange Hamiltonian H = −2JS₁S₂ leads to the parameters g = 2.21, J = −2.06 cm⁻¹, zJ′ = −0.0309 cm⁻¹ and R = 4.0 × 10⁻⁴.