Coordinated Aqua Ligands Research Articles

Hydrogen-bond directed 2D cyanide-bridged coordination polymer assembled from a new pentacyanidecobalt(III) building block and a bicompartimental Schiff-base manganese(III) compound: Synthesis, structures and magnetic properties

Abstract With a new pentacyanidecobalt(III) precursor K2[Co(CN)5(CH3CN)] and a bicompartimental Schiff base manganese(III) compound, a new two-dimensional cyanide-bridged Co(III)-Mn(III) coordination polymer constructed by hydrogen-bond interactions has been successfully synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals this cationic cyanide-bridged tetranuclear complex is self-complementary through coordinated aqua ligands from one complex and the free O4 compartments from the neighboring complex, giving interesting 2D supramolecular structure. Investigation over magnetic susceptibility reveals the overall weak antiferromagnetic coupling between the adjacent Mn(III) ions.

The geometry of the silver 1,1′-dibenzyl-2,2′-biimidazole complexes

The argentophilic interactions and interactions of weakly coordinated nitrate and water with silver metal were studied by investigating the reaction of 1,1′-dibenzyl-2,2′-biimidazole (Bn2bim) with silver nitrate. Three new silver complexes [Ag4(Bn2bim)4(NO3)2]·4(CH3CH2OH)·2(NO3)·0.5(H2O) (1), [Ag4(Bn2bim)4(H2O)4]·4(NO3) (2) and [Ag4(Bn2bim)4(NO3)4]·6(CH2Cl2)·2(H2O) (3) were synthesized and characterized. Complexes 1-3 have rare tetranuclear twisted closed cyclic structure with four bridging biimidazoles and variable nitrate/water ratio. The interactions between the nitrate ligand and Ag as well as water ligands and Ag are considered to be weak due to the ease of exchanging them. The structure 1 consists of a discrete tetranuclear complex with two short Ag⋯Ag distances of 3.0984(10)Å and 3.1994(10)Å, which indicates argentophilic interactions. The complex 2 forms linear assemblies of tetranuclear moieties via hydrogen bonding through weakly coordinated aqua ligand and NO3− counteranions. Crystallization from a mixture of dichloromethane and n-hexane led to an exchange of H2O ligands to nitrates and formation of a new discrete tetranuclear complex 3. Unlike 1, the more open structures of 2 and 3 did not show any argentophilic interactions. The two shortest Ag⋯Ag distances for complexes 2 and 3 were 4.6508(8)Å and 4.9517(5)Å and 4.5810(5)Å–5.0050(5)Å respectively. The overall energetics and the effect of the H2O molecules and the nitrate anions on the geometries of the Ag complexes were studied by computational DFT methods.

A mononuclear, mixed (salicylato) (nicotinamide) complex of Zn(II) with penta- and hexa-coordination sites: a novel framework structure

The title compound, diaqua(bissalicylato-κO)(bisnicotinamide-κN)zinc(II)][bis(triaqua (monosalicylato-κO)(mononicotinamide-κN)zinc(II)salicylate, includes three Zn(II) ions, four nicotinamide ligands, six salicylate ligands and eight coordinated aqua ligands in the asymmetric unit in complex structure. The geometry around one of the Zn(II) ions is a slightly distorted octahedron, of which the equatorial plane is formed by two carboxylate oxygens and two aqua oxygens, while the axial positions are occupied by two pyridyl nitrogen atoms. The other Zn(II) ions adopt fivefold coordinations with one carboxylate oxygen atom from salicylate ligand, one N atom from nicotinamide ligand and three oxygen atoms from aqua ligands. In addition, there are two salicylate anions in the unit cell that are not coordinated. They provide charge balance as counter-ions in the complex framework.

LnIII2MnIII2 heterobimetallic “butterfly” complexes displaying antiferromagnetic coupling (Ln = Eu, Gd, Tb, Er)

The isostructural heterometallic complexes [Ln(III)(2)Mn(III)(2)O(2)(ccnm)(6)(dcnm)(2)(H(2)O)(2)] (Ln = Eu (1Eu), Gd (1Gd), Tb (1Tb), Er (1Er); ccnm = carbamoylcyanonitrosomethanide; dcnm = dicyanonitrosomethanide) have been synthesised and structurally characterised. The in situ transition metal promoted nucleophilic addition of water to dcnm, forming the derivative ligand ccnm, plays an essential role in cluster formation. The central [Ln(III)(2)Mn(III)(2)(O)(2)] moiety has a "butterfly" topology. The coordinated aqua ligands and the NH(2) group of the ccnm ligands facilitate the formation of a range of hydrogen bonds with the lattice solvent and neighbouring clusters. Magnetic measurements generally reveal weak intracluster antiferromagnetic coupling, except for the large J(MnMn) value in 1Gd. There is some evidence for single molecule magnetic (SMM) behaviour in 1Er. Comparisons of the magnetic properties are made with other recently reported butterfly-type {Ln(III)(x)M(III)(4-x) (d-block)} clusters, x = 1, 2; M = Mn, Fe.

Zinc, cobalt and copper coordination polymers with different structural motifs from picolyl-triazole hybrid ligands

A series of one-dimensional coordination polymers, viz. [ZnCl2L1]n (1a: 1a-I and 1a-II), [ZnCl2L2]n (1b), [ZnCl2L3]n (1c), {[Co(L1)2(OH2)2]·(ClO4)2·(H2O)2}n (2a), {[Co(L2)2(OH2)2]·(ClO4)2·(H2O)2}n (2b), {[Cu(L1)2(OH2)2]·(ClO4)2·(H2O)2}n (3a), {[Cu(L2)2(OH2)]·(ClO4)2·(H2O)·(MeOH)}n (3b), and {[Cu(L3)2(OH2)]·(ClO4)2·(H2O)2}n (3c), and a three-dimensional coordination polymer [Cu2I2L3]n (4c) have been synthesized by self-assembly of 4-picolyl substituted 1,2,3-triazoles, viz.1-(4-picolyl)-4-butyl-1H-1,2,3-triazole (L1), 1-(4-picolyl)-4-pentyl-1H-1,2,3-triazole (L2) and 1-(4-picolyl)-4-hexyl-1H-1,2,3-triazole (L3), with appropriate metal salts. These coordination polymers have been characterized by single-crystal and powder X-ray diffraction (XRD) and thermogravimetric analyses (TGA). Complexes 3a–c have been subject to EPR analysis. Complexes 1a–c are 1D coordination polymers formed by singly bridging L1–L3 using their picolyl and 3-positioned nitrogen. Their modes of propagation (zig-zag, helical and wave-like) vary with the length of the alkyl pendant at the 4-position on the triazole moiety. Centro-symmetric polymers 2a and 2b are formed by doubly bridging spacers as 1D chains of 18-membered metallocycles fused at octahedral Co(II) centers with coordinated aqua ligands with extensive water–ClO4− H-bonding. Cu(II) complex 3a (space groupP21/n) is isostructural with 2a, but 3b and 3c crystallize with a chiral space group (P21) with square pyramidal Cu(II) doubly bridged by L2 and L3 to give 1D macrocyclic chiral chains. The spacer in 4c shows uniquely high coordination ability by engaging the donor functions of the nitrogen, not only at the picolyl and 3-position but also at the 2-position of the triazole. The resultant 3D polymer network is neutral and solvate free and has higher symmetry (space groupI41/a) than 4a and 4b. The spontaneous resolution of 3b and 3c is traced to the configurational characteristics of the four ligands and its transfer to the crystal network through space chiral packing. The 1D coordination polymers 1 are thermally most stable, whereas the MeOH-solvated and hydrated perchlorate salt 3b decomposes violently upon heating. Variable temperature photoluminescence (VT-PL) measurements revealed strong low energy (LE) rt emissions for 4a and 4b but not for 4c. The high energy (HE) emissions of 4a–c however increase significantly as temperature decreases. The remarkable variety of structural motifs in these coordination polymers is the result of (a) flexible bonding modes of the picolyl–triazole hybrid ligands, (b) different metal geometry options, (c) halide participation as bridging or capping ligands, (d) possibility of hydrate or solvate coordination and (e) extensive H-bonding involving anionic perchlorate methanol solvate as well as hydrates that are coordinated directly (viz. primary) and indirectly (viz. secondary) to the metal.

Two Cyanide-Bridged Heterometallic One-Dimensional Chain Complexes Constructed by Hydrogen Bond Interactions: Synthesis, Crystal Structures, and Magnetic Properties

Two trinuclear cyanide-bridged heterometallic Ni(II)– Mn(III) complexes {[Mn(L1)(H2O)]2[Ni(CN)4]} 2H2O (1) and {[Mn(L2)(H2O)]2[Ni(CN)4]} (2) (L1 = N,N-ethylene-bis(3-methoxysalicylideneiminate; L2 = N,N-ethylene-bis(3-ethoxysalicylideneiminate) have been obtained by using [Ni(CN)4]2− and two manganese(III) compounds containing bicompartimental Schiff base ligands as assembling segments. X-ray diffraction reveals that the two cyanide-bridged trinuclear complexes are self-complementary through intermolecular O–H…O hydrogen bond interactions formed by a coordinated aqua ligand from one molecule and the four phenolic oxygen atoms from the neighboring one, giving a supramolecular one-dimensional chain structure. Investigation of the magnetic susceptibilities of these two complexes reveals the overall weak antiferromagnetic interactions between the adjacent Mn(III) ions.

Supramolecular assembly of new heteropolymetalic molecules based on tetraiminodiphenolate macrocycle and hexacyanometallate anions: Magnetostructural and spectroscopic properties

Herein we report on the synthesis, single crystal X-ray structure, spectroscopic and magnetic properties of [{Cu 2(tidf)(H 2O)} 2(μ-CN) 2Fe(CN) 4]·6H 2O ( 1), [Cu 2(tidf)(H 2O) 2][Ni(CN) 4] (2) and [Cu 2(tidf)(H 2O) 2][Fe(CN) 5NO]·H 2O (3) (tidf = a Robson type macrocyclic ligand obtained on condensation of 2,6-diformyl-4-methylphenol and 1,3-diaminopropane). Complex (1) is pentanuclear; two paramagnetic dicopper(II) units are linked by a hexacyanoferrate(II) ion through two cyano-bridges. All compounds exhibit extensive, three-dimensional, supramolecular structures supported by classic hydrogen bonding between the coordinated aqua ligands, water molecules and cyano groups. Magnetism as a function of the temperature of complexes 1–3 is consistent with a strong antiferromagnetism with exchange parameters 2J estimated −783(29), −913(2), −905(1), respectively.

Solution studies of dinuclear polyamine-linked platinum-based antitumour complexes

The aquation profiles of two novel dinuclear polyamine-linked, platinum-based antitumour complexes [{trans-PtCl((15)NH(3))(2)}(2){μ-((15)NH(2)(CH(2))(6)(15)NH(2)(CH(2))(6)(15)NH(2))}](3+) (BBR3007, 1,1/t,t-6,6, 1) and [{trans-PtCl((15)NH(3))(2)}(2){μ-((15)NH(2)(CH(2))(6)(15)NH(2)(CH(2))(2)(15)NH(2)(CH(2))(6)(15)NH(2))}](4+) (BBR3610, 1,1/t,t-6,2,6, 1') have been probed using 2D [(1)H, (15)N] HSQC NMR spectroscopy. Reported herein are the rate constants for the hydrolysis of 1 and 1', as well as the acid dissociation constants of the coordinated aqua ligands in their aquated derivatives. The aquation and anation rate constants for the single step aquation model in 15 mM NaClO(4) (pH 5.4) at 298 K are, for 1, k(1) = 7.2 ± 0.1 ×10(-5) s(-1), k(-1) = 0.096 ± 0.002 M(-1) s(-1) and, for 1', k(1) = 4.0 ± 0.2 × 10(-5) s(-1), k(-1) = 1.4 ± 0.1 M(-1) s(-1). The effect of the linker backbone (Pt(tetra(m)mine vs. polyamine) was evaluated by comparison with previous data for the trinuclear complex [{trans-PtCl(NH(3))(2)}(2)(μ-trans-Pt(NH(3))(2){NH(2)(CH(2))(6)NH(2)}(2))](4+) (1,0,1/t,t,t or BBR3464). The pK(1) for 1,0,1/t,t,t (3.44) is closest to that of 1 (3.12), while the pronounced difference for 1' (4.54), means that 1' is the least aquated of the three complexes at equilibrium. pK(a) values of 5.92 were calculated for the aquated forms of both 1 and 1', which are 0.3 pK units higher than for either 1,0,1/t,t,t, or the dinuclear 1,1/t,t. The higher pK(a) values for both polyamine-linked compounds may be attributed to the formation of macrochelates between the central NH(2) groups and the {PtN(3)O} coordination sphere of the aquated species.

Understanding the role of the flexible bridging linker through kinetics and mechanistic study of Pt(ii) amphiphiles derived from a bis(2-pyridylmethyl)amine chelate head group

The substitution of aqua ligands of mononuclear Pt(II) complexes of the general form [Pt(H(2)O)(N,N-bis(2-pyridylmethyl)-N(CH(2))(n)-CH(3); -NC(CH(3))(3); -NH](CF(3)SO(3))(2), n = 1 (bpea); 2 (bppa); 3 (bpba); 5 (bpha), 9 (bpda) -NC(CH(3))(3) (bpbta) and -NH (bpma) by thiourea nucleophiles was investigated under pseudo first-order conditions as a function of concentration and temperature using the stopped-flow technique and UV-vis spectroscopy. The substitution reactions occur via two separate reaction steps, each fitting to a single exponential curve. In the two reaction steps, the thiourea nucleophiles first substitute the coordinated aqua ligand followed by ring opening via dechelation of one of the pyridyl units. The mode of activation for both steps remains associative in nature and the observed rate constants can be fitted to the equation k(obs(1st/2nd)) = k(2(1st/2nd))[Nu]. Appending a primary alkyl hydrocarbon group on the trans-N donor atom of the chelate head group marginally increases the rate of substitution of the aqua leaving group due to the weaker trans-influence of its alkyl amine donor group. However, when a tert-butyl group is the pendant group, reactivity increases by a factor of about two, reiterating the inductive nature of the flow of electron density from the tailing groups towards the Pt(II) metal centres. A comparison of the reactivities of the studied complexes with their dinuclear analogues bridged by alkyl diamines has demonstrated that the electronic effect of the alkyl diamine bridge on the overall reactivity of the multinuclear Pt(II) complexes is weak and insignificant when compared to steric effects due to the constraining bridge.

Catena-Poly[[[tetraaquacadmium(II)]-μ-3,3′-[p-phenylenebis(oxymethylene)]bis(1-pyridinioacetate)] dinitrate hemihydrate

In the title polymeric coordination complex, {[Cd(C22H20N2O6)(H2O)4](NO3)2·0.5H2O}n, obtained from the self-assembly of the flexible double betaine 3,3′-[p-phenyl­enebis(oxymethyl­ene)]bis­(1-pyridinioacetate) with cadmium nitrate, both the octa­hedrally coordinated CdII cation and the substituted betaine ligand lie on inversion centres. The chains constructed through the trans-related acetate groups of the ligand are inter-connected via O—H⋯O hydrogen bonds involving coordinated aqua ligands, the nitrate anions and the partial-occupancy (0.25) water mol­ecule of solvation, forming a three-dimensional structure.

Hydrogen-Bond Directed Cyanide-Bridged Molecular Magnets Derived from Polycyanidemetalates and Schiff Base Manganese(III) Compounds: Synthesis, Structures, and Magnetic Properties

A series of six new cyanide-bridged heterometallic complexes including two tetranuclear T-like Fe(III)Mn(III)(3) compounds, {[Mn(L(1))(H(2)O)](3)[Fe(CN)(5)(1-CH(3)im)]}ClO(4) x 1.5 H(2)O (1) and {[Mn(L(2))(H(2)O)](3)[Fe(CN)(5)(1-CH(3)im)]}ClO(4) x 3 H(2)O (2); two heptanuclear cage-shaped M(III)Mn(III)(6) (M = Fe, Cr) compounds, {[Mn(L(2))(H(2)O)](6)[Fe(CN)(6)]}[Fe(CN)(6)] x 6 CH(3)OH (3) and {[Mn(L(2))(H(2)O)](6)[Cr(CN)(6)]}[Cr(CN)(6)] x 6 CH(3)OH (4); and two two-dimensional M-Mn(III) networks, {[H(3)O][Mn(L(1))](2)[Fe(CN)(6)]} x 2 DMF (5) and {K[Mn(L(1))](2)[Cr(CN)(6)]} x 1.5 CH(3)CN x CH(3)OH (6) (L(1) = N,N-ethylene-bis(3-methoxysalicylideneiminate, L(2) = N,N-ethylene-bis(3-ethoxysalicylideneiminate) have been successfully assembled from three polycyanidemetalates containing five or six cyanide groups and two manganese(III) building blocks containing bicompartmental Schiff base ligands. The cyanide-bridged polynuclear complexes are self-complementary through a coordinated aqua ligand from one complex and the free O(4) compartment from the neighboring complex, giving supramolecular one-dimensional ladders and three-dimensional networks for 1 and 2 and for 3 and 4, respectively. Investigation over magnetic susceptibilities of the six complexes reveals the overall ferromagnetic interactions for complexes 1, 2, 3, and 5 and antiferromagnetic interaction for 4 and 6. Compounds 1-4 show some characteristics of metamagnet behavior at low temperatures due to the relatively strong intermolecular hydrogen-bonding interaction. The two complexes with two-dimensional structure exhibit three-dimensional antiferromagnetic ordering with typical metamagnetic behavior below 8.4 K for 5 and 11.5 K for 6, respectively. The present result appears to add new members to the very few examples of polynuclear clusters exhibiting 3D magnetic ordering relying on intermolecular interactions, to the best of our knowledge, which will be helpful for providing valuable information for the understanding and application of intermolecular hydrogen-bonding interactions in the molecular magnetic materials.

Syntheses, X-ray Structures, and Physicochemical Properties of Phenoxo-Bridged Dinuclear Nickel(II) Complexes: Kinetics of Transesterification of 2-Hydroxypropyl-p-nitrophenylphosphate

Four dinuclear nickel(II) complexes [Ni(II)(2)(L(1))(O(2)CMe)(2)(H(2)O)(2)][PF(6)].MeOH.3H(2)O (1), [Ni(II)(2)(L(1))(O(2)CMe)(2)(NCS)] (2), [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (3), and [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][BPh(4)].3MeOH.H(2)O (4) have been synthesized [HL(1): 2,6-bis[N-methyl-N-(2-pyridylethyl)amino]-4-methylphenol; HL(2): 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol]. Complexes 1, 3, and 4 are new while complex 2 was reported previously by Fenton and co-workers (the structure of 2 was presented but no physicochemical properties of this complex were reported; in this work such studies have been completed). X-ray crystallographic analyses of 1 and 4 reveal that each nickel(II) center is six-coordinate, terminally coordinated by two nitrogen donors [(pyridin-2-yl)ethylamine unit in 1 and 3-(pyridin-2-yl)pyrazole moiety in 4], and bridged by an endogenous phenolate ion. Each of the acetate ions in 1 adopts a eta(2)-coordination mode (chelating) whereas in 4 each is coordinated in a mu-eta(1):eta(1) syn-syn bridging mode. In 1 each Ni(II) center has water coordination whereas in 4 one Ni(II) center has a methanol and the other has water coordination. The X-ray structure of 3 could not be determined. The physicochemical properties (electronic spectroscopy and cyclic voltammetry) of the cation of 3 are identical to that of 4. Magnetic susceptibility measurements have revealed the occurrence of ferromagnetic coupling of spins of the nickel(II) centers in 2 [J = +9.80 cm(-1)]. The nickel(II) centers in 1 and 3 are antiferromagnetically coupled, but to different extents [J = -48.4 cm(-1) (1); J = -1.24 cm(-1) (3)]. The magnetic properties are correlated with the nature of bridges between the nickel(II) ions. The two coordinated aqua ligands in 1 and the aqua and methanol ligands in 3 have enabled these dinuclear nickel(II) complexes to function as catalysts in the hydrolysis of 2-hydroxypropyl-p-nitrophenylphosphate (HPNP). Complex 1 is more effective in the conversion of substrate to product (p-nitrophenolate ion) than 3, under identical experimental conditions. Pseudo first-order kinetic treatment has been done for complexes 1 and 3. Temperature-dependent measurements were done to evaluate kinetic/thermodynamic parameters for the hydrolysis/transesterification reaction of HPNP and to propose a mechanistic pathway. The activation parameters are DeltaH(++) = 64 kJ mol(-1), DeltaS(++) = -104 J mol(-1) K(-1) for 1 and DeltaH(++) = 68 kJ mol(-1), DeltaS(++) = -109 J mol(-1) K(-1) for 3. A mechanism consistent with the kinetic data is presented.

Bis[μ-1-(1,10-phenanthrolin-2-yl)-2-pyridone]bis{aqua[1-(1,10-phenanthrolin-2-yl)-2-pyridone]cadmium(II)} tetrakis(perchlorate)

In the title centrosymmetric binuclear complex, [Cd2(C17H11N3O)4(H2O)2](ClO4)4, the Cd(II) ion assumes a distorted octahedral geometry. There are pi-pi stacking interactions between the pyridine and 1,10-phenanthroline ring systems of adjacent ligands at the same Cd(II) centre. Intermolecular hydrogen bonds between the coordinated aqua ligand and the O atom of a keto group connect adjacent complex cations into extended chains. Hydrogen bonds also exist between the complex cations and the perchlorate anions. Compared with the fluorescence spectrum of the organic ligand, the complex displays strong fluorescent emission and an ipsochromic shift of the emission peaks, which may be attributed to the structural character.

Kinetics and mechanisms of the axial ligand substitution reactions of platinum(III) binuclear complexes with halide ions

The axial water ligand substitution reaction on the head-to-head (HH) and head-to-tail (HT) amidato-bridged cis-diammineplatinum(III) binuclear complexes, HH- and HT-[Pt2(NH3)4(m-amidato)2(OH2)2]4+ (amidato = α-pyridonato, a-pyrrolidonato, or pivalamidato), with halide ions (X = Cl ,Br ) in acidic aqueous solution reveals a consecutive 2-step kinetics under the pseudo first-order conditions of a large excess concentration of halide ion relative to that of the complex (Cx bCpt), corresponding to formation of the monohalo (step 1) and the dihalo complexes (step 2). The first substitution step of all the HH and HT diaqua dimers consists of two parallel reaction pathways: one is the simple substituion path of one of the coordinated aqua ligands with X, and the other is the replacement in the aquahydroxo complex which is the conjugate base of the diaqua dimer. In step 2, there are three reaction pathway patterns: the direct substitution path, the path via a coordinatively unsaturated intermediate, and the unusual path of OH replacement. Step 2 proceeds via either one or two paths of the three depending on the nature of the halide ion as well as the bridging ligand. On the other hand, the substitution reaction of the hydrogenphosphato-bridged lantern-type complex, [Pt2(m-HPO4)4(OH2)2]2 proceeds in 1-step at Cx bCpt, in which the first aqua ligand substitution to form the monohalo species is rate-determining and the monohalo species is in rapid equilibrium with the dihalo complex. The rate-determining step consists of parallel pathways similar to step 1 in the amidato-bridged complex systems.

X-ray crystal structures on the hydrolysis path of [{Ti(C 5Me 4R)F 3} 2]: Water adduct [{Ti(C 5Me 4Et)F 3} 2(H 2O)]·(H 2O), oxoaqua complex [Ti 7F 21O(C 5Me 4Et) 5(H 2O) 2] and oxo complex [Ti 8F 22O 2(C 5Me 4H) 6]·2CHCl 3

Sublimation of [{Ti(C 5Me 4Et)F 3} 2] in the presence of hydrated molecular sieves afforded crystals of dititanate [{Ti(C 5Me 4Et)F 3} 2(H 2O)]·(H 2O) ( 1·H 2O) with three bridging fluorines, terminally coordinated aqua ligand, and hydrogen-bonded non-coordinated water molecule. The crystallization of [{Ti(C 5Me 4R)F 3} 2] (R = Et, H) from solutions with H 2O:Ti ratio below one afforded mixed fluoro-oxo organotitanate clusters [Ti 7F 21O(C 5Me 4Et) 5(H 2O) 2] ( 2) and [Ti 8F 22O 2(C 5Me 4H) 6]·2CHCl 3 ( 3·2CHCl 3), respectively. The clusters could be considered as intermediates in the hydrolysis process of [{Ti(C 5Me 4R)F 3} 2]. The quantum–mechanical calculation reveal that monodentate-bonded ligand in complex 1 is energetically favoured over the more intriguing bidentate bridging one. The calculated geometry of model compound [{Ti(C 5H 5)F 3} 2(H 2O)]·(H 2O) closely resembles the 1·H 2O compound.

Catena-Poly[[[diaquabis(pyridine-4-carboxamide-κN)copper(II)]-μ2-squarato-κO1:O3] dihydrate

The asymmetric unit of the title compound, {[Cu(C4O4)(C6H6N2O)2(H2O)2].2H2O}n, consists of one pyridine-4-carboxamide (isonicotinamide or ina) ligand, one-half of a squarate dianion, a coordinated aqua ligand and a solvent water molecule. Both the CuII and the squarate ions are located on inversion centers. The CuII ions are octahedrally surrounded by four O atoms of two water molecules and two squarate anions, and by two N atoms of the isonicotinamide ligands. The crystal structure contains chains of squarate-1,3-bridged CuII ions. These chains are held together by N-H...O and O-H...O intermolecular hydrogen-bond interactions, forming an extensive three-dimensional network.

Synthesis and Characterization of Potassium Complexes Containing Terminal η2‐Pyrazolato Ligands

AbstractThe potassium complexes [K(η2‐3,5‐R2pz)(η6‐18‐crown‐6)] (R = Ph, tBu; pz = pyrazolato) were prepared by treatment of 3,5‐diphenylpyrazole or 3,5‐di‐tert‐butylpyrazole with potassium hydride in the presence of 18‐crown‐6. These complexes contain η6‐18‐crown‐6 and terminal η2‐pyrazolato ligands, and constitute the first examples of group 1 metal complexes with this pyrazolato ligand coordination mode. In contrast to [K(η2‐3,5‐Ph2pz)(η6‐18‐crown‐6)] and [K(η2‐3,5‐tBu2pz)(η6‐18‐crown‐6)], the aqua complex [K(η2‐3,5‐Me2pz)(H2O)(η6‐18‐crown‐6)] was obtained when 3,5‐dimethylpyrazole was treated with potassium hydride and 18‐crown‐6 in the presence of a small amount of water. [K(η2‐3,5‐Me2pz)(H2O)(η6‐18‐crown‐6)] contains an η2‐pyrazolato ligand that is bent towards being co‐facial with the best plane of the 18‐crown‐6 ligand, to allow hydrogen bonding between the pyrazolato ligand nitrogen atoms and the coordinated aqua ligand. The hydrogen bonding thus confers a novel terminal π‐facial η2‐bonding mode to the pyrazolato ligand. All compounds were characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Triaqua(2,2′-bipyridine)(thiophene-2,5-dicarboxylato)manganese(II) 4,4′-bipyridine hemisolvate trihydrate

The title compound, [Mn(C6H2O4S)(C10H8N2)(H2O)3]·0.5C10H8N2·3H2O or [Mn(tdc)(bpy)(H2O)3]·3H2O·0.5(bpyn) (tdc is thio­phene-2,5-di­carboxyl­ate, bpy is 2,2′-bi­pyridine and bpyn is 4,4′-bi­pyridine), crystallizes in space group P\overline 1. Complex molecules are linked into one-dimensional chains, running along the b axis, by hydrogen bonds between the coordinated aqua ligands and uncoordinated carboxyl­ate groups of tdc. Double-stranded chains consist of two of the one-dimensional chains and uncoordinated centrosymmetric bpyn mol­ecules, connected by hydrogen bonds between N atoms of the bpyn mol­ecules and coordinated aqua ligands. These double chains are further assembled into layers parallel to the ab plane, which extend into three-dimensional networks via hydrogen bonds between the coordinated and uncoordinated water molecules, and O atoms of tdc.

Photobehavior of aqueous uranyl ion and photo-oxygenation of isobutane using light from the visible region

The photochemical and photophysical behavior of the aqueous uranyl ion [UO2(H2O)5]2+ has been studied under the influence of visible light and with added perchloric acid over the range of 0.01–4 M. In the presence of 2-methylpropane (isobutane), photo-oxygenation of isobutane occurs to yield, as the major product, 2-methyl-2-propanol (tert-butyl alcohol) along with lesser amounts of 2-methyl-2-propene (isobutene) and other C1–C8 products. The quantum yield for formation of tert-butyl alcohol is independent of light intensity at the irradiation wavelength of 415 nm and of uranyl concentration, but it increases from 0.016 ± 0.001 at 0.01 M HClO4 (pH 2) to 0.13 ± 0.01 at 4 M HClO4. The emission spectrum from the electronically excited uranyl ion and the associated quantum yields have been measured in the presence and absence of isobutane, as a function of added perchloric acid. While in both cases the shape of the spectrum remains invariant, the quantum yields increase with increasing perchloric acid concentration. The strong dependence on added perchloric acid is interpreted within the context of the presence and interconversion of two electronically excited species, an acid form, *[UO2(H2O)5]2+, and a base form, *[UO2(H2O)n(OH)]+. It is proposed that both forms react with isobutane to give a tert-butyl radical, and that oxidation of coordinated aqua ligands occur, the latter generating a hydroxyl radical whose reaction with isobutane rapidly leads also to a tert-butyl radical. The reaction of this alkyl radical with ground-state [UO2(H2O)5]2+ then gives rise to the stable tert-butyl alcohol product and reduced forms of uranyl ion. Based upon the values of the quantum yields and of excited-state lifetime measurements reported in the literature, a comprehensive mechanism has been developed in a quantitative manner to provide calculated values of the rate constants for the individual mechanistic steps. The calculated rate constants provide a basis to calculate the values of quantum yields for emission and chemical reaction, as well as for lifetimes, that agree very satisfactorily with the experimental values over a 400-fold concentration change in added perchloric acid.Key words: photo-oxidation, photo-oxygenation, uranyl ion, isobutane, tert-butyl alcohol, lifetime, quantum yield, acid–base dissociation.

Flexible square supramolecular rings with hydrogen-bonded bushing in solid-state oxalurate complexes: versatility of the oxalurate ligand in covalent and noncovalent binding.

Isotypic pseudooctahedral complexes of Co, Ni, and Cu with two chelating oxalurate ligands and two water molecules, trans-[M(oxalurate)(2)(H(2)O)(2)], have been synthesized and isolated by a novel progressive crystallization technique. Diffraction analyses reveal that the three complexes form isotypic solid-state structures in which the molecular connectivity and complex network of noncovalent interactions are qualitatively identical throughout the series. The oxalurate groups form unbounded chains through two different self-recognition patterns-a typical DA-AD motif and an unusual DDA'-A'DD form (D = hydrogen bond donor, A' = double acceptor). The unsymmetrical oxalurate group possesses the topological properties necessary to form aggregates of higher symmetry, and the "M(oxalurate)(2)" fragments form a rhombic 2-D motif with hydrogen-bonded corners and with hydrogen-bond acceptors directed to the inside of the cyclic aggregate. The 2-D net is stacked to form a channeled 3-D structure, in which the coordinated aqua ligands form the principal interlayer interactions. The slanted channels are occupied by the axial waters and by waters of crystallization, which are hydrogen bonded to the channel walls to form an ordered bushing. The extensive 3-D hydrogen-bonded superstructure is flexible enough to accommodate the distortion produced by the Jahn-Teller effect in the copper compound without requiring a qualitative structural change. The bonds affected by Jahn-Teller distortion in the Cu complex [Cu-O = 2.3788(15) A] are significantly longer than their analogues in the Co and Ni complexes [Co-O = 2.175(2), Ni-O = 2.094(9) A].