Solid-state coordination chemistry of the oxomolybdate-organodiphosphonate/nickel-organoimine system: structural influences of the secondary metal coordination cation and diphosphonate tether lengths

The hydrothermal reactions of a molybdate source, a nickel(II) salt, tetra-2-pyridylpyrazine (tpyprz), and organodiphosphonic acids H(2)O(3)P(CH(2))(n)()PO(3)H(2) (n = 1-5) of varying tether lengths yielded a series of organic-inorganic hybrid materials of the nickel-molybdophosphonate family. A persistent characteristic of the structural chemistry is the presence of the [Mo(5)O(15)(O(3)PR)(2)](4)(-) cluster as a molecular building block, as noted for the one-dimensional materials [[Ni(2)(tpyprz)(2)]Mo(5)O(15)[O(3)P(CH(2))(4)PO(3)]]x6.65H(2)O (6x6.65H(2)O) and [[Ni(2)(tpyprz)(2)]Mo(5)O(15)[O(3)P(CH(2))(5)PO(3)]]x3.75H(2)O (8x3.75H(2)O), the two-dimensional phases [[Ni(4)(tpyprz)(3)][Mo(5)O(15)(O(3)PCH(2)CH(2)PO(3))](2)]x23H(2)O (3x23H(2)O) and [[Ni(3)(tpyprz)(2)(H(2)O)(2)](Mo(5)O(15))(Mo(2)O(4)F(2))[O(3)P(CH(2))(3)PO(3)](2)]x8H(2)O (5x8H(2)O), and the three-dimensional structures [[Ni(2)(tpyprz)(H(2)O)(3)]Mo(5)O(15)[O(3)P(CH(2))(3)PO(3))]]xH(2)O (4xH(2)O) and [[Ni(2)(tpyprz)(H(2)O)(2)]Mo(5)O(15) [O(3)P(CH(2))(4)PO(3)]]x2.25H(2)O (7x2.25H(2)O). In the case of methylenediphosphonic acid, the inability of this ligand to tether adjacent pentanuclear clusters precludes the formation of the common molybdophosphonate building block, manifesting in contrast a second structural motif, the trinuclear [(Mo(3)O(8))(x)(O(3)PCH(2)PO(3))(y)] subunit of [[Ni(tpyprz)(H(2)O)(2)](Mo(3)O(8))(2) (O(3)PCH(2)PO(3))(2)] (1) which had been previously observed in the corresponding methylenediphosphonate phases of the copper-molybdophosphonate family. Methylenediphosphonic acid also provides a second phase, [Ni(2)(tpyprz)(2)][Mo(7)O(21)(O(3)PCH(2)PO(3))]x3.5H(2)O (9x5H(2)O), which contains a new heptamolybdate cluster [Mo(7)O(21)(O(3)PCH(2)PO(3))](4)(-) and a cationic linear chain [Ni(tpyprz)](n)(4n+) substructure. The structural chemistry of the nickel-molybdophosphonate series contrasts with that of the corresponding copper-molybdophosphonate materials, reflecting in general the different coordination preferences of Ni(II) and Cu(II). Consequently, while the Cu(II)-organic complex building block of the copper family is invariably the binuclear [Cu(2)(tpyprz)](4+) subunit, the Ni(II) chemistry with tpyprz exhibits a distinct tendency toward catenation to provide [Ni(3)(tpyprz)(2)](6+), [Ni(4)(tpyprz)(3)](8+), and [Ni(tpyprz)](n)(4n+) building blocks as well as the common [Ni(2)(tpyprz)](4+) moiety. This results in a distinct structural chemistry for the nickel(II)-molybdophosphonate series with the exception of the methylenediphosphonate derivative 1 which is isostructural with the corresponding copper compound [[Cu(2)(tpyprz)(H(2)O)(2)](Mo(3)O(8))(2)(O(3)PCH(2)PO(3))] (2). The structural chemistry of the nickel(II) series also reflects variability in the number of attachment sites at the molybdophosphonate clusters, in the extent of aqua ligation to the Ni(II) tpyprz subunit, and in the participation of phosphate oxygen atoms as well as molybdate oxo groups in linking to the nickel sites.     

Multifunctional "clickates" as versatile extended heteroaromatic building blocks: efficient synthesis via click chemistry, conformational preferences, and metal coordination

Click chemistry has been utilized to access 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridines (BTPs) as versatile extended heteroaromatic building blocks for their exploitation in supramolecular chemistry, in particular foldamer and ligand design. In addition to their high-yielding synthesis using Cu(I)-catalyzed Huisgen-type 1,3-dipolar cycloaddition reactions the formed triazole moieties constitute an integral part of the BTP framework and encode both its pronounced conformational preferences as well as its chelating ability. A diverse set of symmetrical and non-symmetrical BTPs carrying electron-donating and -withdrawing substituents at both terminal aryl and the central pyridine moieties has efficiently been synthesized and could furthermore readily be postfunctionalized with amphiphilic side chains and porphyrin chromophores. In both solution and solid state, the BTP scaffold adopts a highly conserved horseshoe-like anti-anti conformation. Upon protonation or metal coordination, the BTP scaffold switches to the chelating syn-syn conformation. Iron and europium complexes have been prepared, successfully characterized by single-crystal X-ray diffraction analysis, and investigated with regard to their spin state and luminescent properties. The extended heteroaromatic BTP scaffold should prove useful for the design of responsive foldamer backbones and the preparation of new magnetic and emissive materials.     

The 1/1 and 2/1 approximants in the Sc-Mg-Zn quasicrystal system: triacontahedral clusters as fundamental building blocks

Single-crystal structures are reported for Sc(3)Mg(0.18(1))Zn(17.73(3)), the 1/1 approximant crystal (AC), and Sc(11.18(9))Mg(2.5(1))Zn(73.6(2)), the 2/1 AC, in the corresponding icosahedral quasicrystal (i-QC) system. The 1/1 AC crystallizes in space group Im, a = 13.863(2) A, Z = 8, and the 2/1 AC, in Pa, a = 22.412 (2) A, Z = 8. The latter, which is valuable in pointing the way to the QC structure, is the best ordered and refined 2/1 example to date. The fundamental building blocks in both ACs are triacontahedral clusters centered by smaller multiply endohedral Tsai-type arrays; the former are condensed through body-centered-cubic packing in the 1/1 and primitive cubic packing in the 2/1 AC. Novel prolate rhombohedra centered by Sc-Sc dimers are also generated between triacontahedra in the 2/1 AC.     

Nickel(II) and cobalt(II) coordination compounds of dichloroguanidinopyrimidines

Summary New coordination compounds of Ni^II and Co^II with dichloropyrimidinoguanidine (L) have been obtained and characterized by physico-chemical and spectroscopic methods. The complexes have the general formulae: [ML₃](ClO₄)₂, [ML₂(SO₄)], [ML₂(NCS)₂], (M = Ni or Co), [NiL₂(ClO₄)₂] and [CoL₂](ClO₄)₂. The ligands are bonded to the metal ion via one nitrogen atom from the pyrimidine heterocyclic ring and one from the guanidine group.     

Rare tetranuclear mixed-valent [Mn(II)2Mn(IV)2] clusters as building blocks for extended networks

We report the synthesis of a series of mixed valence Mn(II/IV) tetranuclear clusters [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(EtOH)(6)Br(2)]Br(2) (), [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(H(2)O)(2)Cl(4)].2EtOH.H(2)O (.2EtOH.H(2)O), [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(heedH(2))(2)](ClO(4))(4) (), [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(MeCN)(2)(H(2)O)(2)(bpy)(2)](ClO(4))(4) () and [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(bpy)(2)Br(4)].2MeOH (.2MeOH). Clusters are constructed from the tripodal ligand N,N-bis(2-hydroxyethyl)ethylene diamine (heedH(2)) and represent rare examples of tetranuclear Mn clusters possessing the linear trans zig-zag topology, being the first Mn(II/IV) mixed-valent clusters of this type. The molecular clusters can then be used as building blocks in tandem with the (linear) linker dicyanamide ([N(CN)(2)](-), dca(-)) for the formation of a novel extended network {[Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(H(2)O)(2)(MeOH)(2)(dca)(2)]Br(2)}(n) (), which exhibits a rare form of the 2D herring bone topology.     

Benzoquinolateplatinum(II) complexes as building blocks in the synthesis of Pt-Ag extended structures

The reaction between (NBu(4))[Pt(bzq)(C(6)F(5))(2)] (1, bzq = 7,8-benzoquinolate) and AgClO(4) in a 1 : 1 molar ratio, in acetone, gives the polymer [{Pt(bzq)(C(6)F(5))(2)}Ag](n) (2). The reaction of 2 with equimolecular amounts of PPh(3) and SC(4)H(8) (tht) produces the bimetallic complexes [{Pt(bzq)(C(6)F(5))(2)}AgL] (L = PPh(3) (3), tht (4)). For L = py, decomposition takes place and [Pt(bzq)(C(6)F(5))py] (5) is obtained. All these complexes have been characterized by X-ray diffraction. The most interesting features of complexes 2-4 is the presence of Pt-Ag bonds, with Pt-Ag distances of ca. 2.75 ?. Besides, the silver centres establish short η(1) bonding interactions with the C(ipso) of the bzq ligands, with distances Ag-C of ca. 2.45 ?. Complex 2 is a one-dimensional infinite chain in which the fragments "Pt(bzq)(C(6)F(5))(2)(-)" and Ag(+) alternate. On the other hand, complexes 1 and 3-5 show intermolecular pairing through π···π interactions between the aromatic rings of the bzq ligand, having interplanar separations of ca. 3.5 ?. Complex 2 dissolves in donor solvents (acetone, THF) as discrete bimetallic solvated fragments [{Pt(bzq)(C(6)F(5))(2)}AgS(n)] (S = solvent), similar to complexes 3 and 4. The persistence of the Pt-Ag bond in 2-4, supported by multinuclear NMR spectroscopy, causes a significant blue-shift in the lowest-lying absorption in relation to 1. This fact is attributed (TD-DFT) to a remarkable modification of the orbitals contributing to the HOMO, which changes the character of the transition from (1)LC/(1)MLCT in 1 to admixture (1)L'LCT/(1)MLCT in the bimetallic complexes. The low energy feature (490-530 nm) of 2 in solid state is attributed to CT from the Pt fragments to the Ag centers. Complexes 2-4 are only emissive in rigid media (solid and glasses). In the solid state, the metallic chain 2 exhibits a bright orange emission (560 nm, 298 K; 590 nm, 77 K), assigned to an excited state involving charge transfer from the platinum fragment with a remarkable contribution of C(6)F(5) (Ar(f)) rings to the Pt-Ag bond ((3)LMM'CT/(3)L'M'CT). However, 3 and 4 exhibit in solid state at 298 K a vibronic band, which is clearly resolved in two close non-equilibrated bands at 77 K in 3, tentatively ascribed to a mixture of (3)MLCT/(3)L'LCT transitions modified by the formation of the Pt-Ag bond. In glassy solution (77 K) 2-4 display a vibronic emission ascribed primarily to (3)LC character.     

meta-Phenylene-bridged double Schiff base copper(II) complexes as building blocks for 1D coordination polymers: Synthesis,crystal structure and magnetic properties

The new double Schiff-base ligands H₆ipa-hyhb and H₆ipa-hyhh were synthesized by condensation of a 4,6-diformylresorcinol derivative (ipa) with 4-hydroxy-butanoic acid hydrazide (hyhb) and 6-hydroxy-hexanoic acid hydrazide (hyhh). The reaction with copper(II) perchlorate in the presence of an appropriate co-ligand (Him = imidazole, Hpz = pyrazole) leads to the novel coordination polymers {[Cu₂(H₄ipa-hyhb)(Hpz)₂](ClO₄)₂}_n (1), {[Cu₂(H₄ipa-hyhb)(Him)₂](ClO₄)₂}_n (2), and {[Cu₂-(H₄ipa-hyhh)(Hpz)₂](ClO₄)₂}_n (3). These coordination polymers are composed of primary building blocks with the general formula [Cu₂(H₄ipa-X)(L)₂]²⁺ (X = hyhb, hyhh; L = Him, Hpz) which are linked by coordination of the hydroxyl groups of the ligand side chains at the apical position of copper(II) centers of adjacent building blocks. The resulting chains possess different topologies and therefore different supramolecular structures due to the variation in length of the ligand alkyl side chains. For the complexes 1 and 2 double hydroxyalkyl-bridged distorted ladder like chains are formed. Whereas in case of complex 3 single hydroxyalkyl-bridged chains are obtained which assemble to hydrogen bonded double chains. In the case of 1 and 2 these chains are cross-linked by hydrogen bonding interactions with the perchlorate counterions, whereas for 3 additional π–π stacking interaction are observed. The temperature-dependent magnetic measurements indicate weak antiferromagnetic interactions with coupling constants J = −26.1 cm⁻¹ (1), J = −28.2 cm⁻¹ (2), and J = −26.5 cm⁻¹ (3). The magnetic exchange interaction is solely the result of a coupling within the dinuclear complex moieties through the central resorcinol moiety.     

Rh(III) porphyrins as building blocks for porphyrin coordination arrays: from dimers to heterometallic undecamers

The coordination chemistry of a Rh(III) porphyrin building block was investigated with a view to the construction of heterometallic arrays of porphyrins. The Rh(III) porphyrin was found to coordinate methanol in the solid state and weakly in CDCl(3) solution. Crystallization afforded five coordinate pi stacked Rh(III) porphyrins. The distribution of products from reaction of Rh(III) porphyrin with DABCO, 4,4'-bipyridine, and 4,4'-bipyrimidine could be displaced toward dimeric species by silica gel column chromatography or recrystallization which served to remove excess ligand. Weak coordination to nitriles was observed, although it was sufficiently strong to organize a dimeric complex of 5,5'-dicyano-2,2'-bipyridine in the solid state. Complexes with 4,4'-bipyrimidine and 5,5'-dicyano-2,2'-bipyridine possess uncoordinated chelating nitrogen atoms. Larger heterometallic porphyrin arrays were assembled using a combination of Sn(IV) and Rh(III) porphyrin coordination chemistry. A Sn(IV) porphyrin acted as a core around which were coordinated two isonicotinate groups, carboxylic acid functionalized porphyrins, or porphyrin trimer dendrons. Rh(III) porphyrins were coordinated to pyridyl groups at the periphery of these entities. In this way an eleven porphyrin array, with four different porphyrin metalation states, was assembled. The diamagnetic nature of both the Rh(III) and Sn(IV) porphyrins, the slow ligand exchange kinetics on the NMR time scale, and tight ligand binding permitted the porphyrin arrays to be analyzed by two-dimensional (1)H NMR techniques.     

Neutral pyridyl-functionalized C,N-ortho-chelated aminoaryl platinum(II) corner building blocks for application in coordination reactions

Two homoleptic pyridyl-functionalized C,N-ortho-chelating aminoaryl platinum(II) complexes, cis-[Pt(eta(2)-C,N)] (3a,b), were prepared via an unconventional method involving the initial synthesis of a bromide-functionalized C,N-chelating aminoaryl platinum(II) precursor complex 8, to which subsequently pyridyl groups were attached via a Suzuki-Miyaura C-C coupling reaction. The electron-donating properties of the pyridyl nitrogen atoms of the resulting complexes (3a,b) were used in complexation reactions with monocationic NCN-pincer (NCN = [C6H3(CH2NMe2)(2-)2,6]-) platinum(II) (11a) and palladium(II) (12a) nitrate complexes [M(NCN)(NO3)], thereby obtaining four trimetallic coordination complexes 16-19. The difference in the pyridine-metal coordination behavior between platinum and palladium was studied by varying the ratios of the reagents and by variable-temperature NMR experiments. IR and Raman analyses of 11a and 12a were performed to determine the coordination behavior of the nitrate counteranion, and it was found that both NO3- and H2O coordinate to the metal centers. The crystal structure determinations of free pyridyl complex 3a, [Pt(NCN)(NO3)] (11a), and [Pt(NCN)(NO3)].(H2O) (11b), as well as the crystal structure of trisplatinum coordination complex 16, are reported.     

The structural organization of oligonuclear cobalt(II,III) and cobalt(III) carboxylates

The review deals with the topology of homonuclear carboxylate complexes of cobalt(II, III) and cobalt(III) whose structures are built from the monocarboxylate anions RCOO^– (R is a radical containing no electron-donating substituents), water, and its deprotonated forms.     

Construction of polyoxometalate-based inorganic-organic compounds using silver(I) double helicates as secondary building blocks

Two polyoxometalate-based silver(I) compounds including a three-dimensional porous crystalline array and a double-helicate bisupporting cluster were achieved using metal-organic helicates and Keggin [PMo(12)O(40)](3-) as secondary building blocks.     

Increasing nuclearity of secondary building units in porous cobalt(II) metal-organic frameworks: variation in structure and H2 adsorption

Reaction of Co(NO(3))(2)·6H(2)O with H(2)L [H(2)L = pyridine-4-(phenyl-3',5'-dicarboxylic acid)] under different reaction conditions gives three closely-related metal-organic framework polymers, {[Co(2)(L)(2)(DMF)]·n(solv)}(∞) (1), {[Co(L)]·2DMF}(∞) (2) and {[Co(3)(L)(3)(DMF)(0.5)(H(2)O)(1.5)]·n(solv)}(∞) (3). Variation in reaction conditions thus has a decisive impact on the materials isolated, producing frameworks based upon either binuclear (1, 2) or trinuclear (3) cobalt cluster nodes. Analysis of their crystal structures shows that all three contain considerable solvent-accessible volumes, an indication of porosity that is confirmed for desolvated 1 and 3, which can store up to 2.75 and 2.33 wt% of H(2) at 78 K and 20 bar, respectively.     

Tetrahedral and octahedral coordination for cobalt(II) complexes of N-isopropyl-2-pyrrolidinone

Complexes of the formulas [Co(NIPP)₄](ClO₄)₂ and [Co(NIPP)₆](ClO₄)₂ have been synthesized and isolated (NIPP = N-isopropyl-2-pyrrolidinone). IR spectra and conductance data are presented as proof that perchlorate coordination in [Co(NIPP)₄](ClO₄)₂ does not occur. Vibrational spectra indicate that coordination occurs through the NIPP carbonyl oxygen for both complexes. Spectral parameters obtained from the electronic spectra and magnetic moments indicate tetrahedral and octahedral coordination for [Co(NIPP)₄](ClO₄)₂ and [Co(NIPP)₆](ClO₄)₂, respectively. The powder X-ray diffraction data appear to support the assignments of these two geometries. The crystal-field prediction that Δ(T_d)/Δ(O_h) = 0.44 is in reasonably good agreement with the experimental results.     

Synthesis,structural characterization and properties of one-dimensional coordination polymers of cobalt(II)- and nickel(II)-phosphonate complexes with 2,2′-bipyridine as a secondary ligand component: Observation of both cis and trans conformations of a diphosphonic acid

Two new isomorphous cobalt and nickel phosphonates [M^II(2,2′-bipy)₂LH₄]_n[LH₂]_n, M = Co (compound 1), M = Ni (compound 2) were hydrothermally synthesized from p-xylylenediphosphonic acid (LH₄) and the corresponding metal salts with 2,2′-bipyridine as secondary ligand component. Both the compounds 1 and 2 are characterized by routine elemental analyses, IR-, electronic-spectral analyses, thermogravimetric studies and unambiguously characterized by single crystal X-ray crystallography. The structures were refined in monoclinic space group C2/c. The crystal structure consists of 1D [M(2,2′-bipy)₂LH₄]²⁺ chains and [LH₂]²⁻ anions. The flexibility of non-rigid ligand p-xylylenediphosphonic acid (LH₄) tends to adopt a rare cis conformation in the crystal structure to meet the coordination requirement of the metal center from the usual trans conformation. The hydrogen bonding in the crystal structure leads to cylindrical tubes that extend via p-xylylenediphosphonic acid resulting in a 2D supramolecular sheet throughout the crystal. Compounds 1 and 2 are additionally characterized by thermogravimetric studies.     

Encapsulated transition metal catalysts comprising peripheral Zn(II)salen building blocks: template-controlled reactivity and selectivity in hydroformylation catalysis

Encapsulated phosphane ligands can be easily constructed through coordinative interactions between Zn(II)-salphen complexes and pyridylphosphane templates; the template has a pronounced impact on the catalyst structure and consequently on the performance in the hydroformylation of 1-octene.     

Dual coordination modes of ethylene-linked NP2 ligands in cobalt(II) and nickel(II) iodides

Here we report the syntheses and crystal structures of a series of cobalt(II) and nickel(II) complexes derived from (R)NP2 ligands (where R = OMe(Bz), H(Bz), Br(Bz), Ph) bearing ethylene linkers between a single N and two P donors. The Co(II) complexes generally adopt a tetrahedral configuration of general formula [(NP2)Co(I)(2)], wherein the two phosphorus donors are bound to the metal center but the central N-donor remains unbound. We have found one case of structural isomerism within a single crystal structure. The Co(II) complex derived from (Bz)NP2 displays dual coordination modes: one in the tetrahedral complex [((Bz)NP2)Co(I)(2)]; and the other in a square pyramidal variant, [((Bz)NP2)Co(I)(2)]. In contrast, the Ni(II) complexes adopt a square planar geometry in which the P(Et)N(Et)P donors in the ligand backbone are coordinated to the metal center, resulting in cationic species of formula [((R)NP2)Ni(I)](+) with iodide as counterion. All Ni(II) complexes exhibit sharp (1)H and (31)P spectra in the diamagnetic region. The Co(II) complexes are high-spin (S = 3/2) in the solid state as determined by SQUID measurements from 4 to 300 K. Solution electron paramagnetic resonance (EPR) experiments reveal a high-spin/low-spin Co(II) equilibrium that is dependent on solvent and ligand substituent.     

Syntheses and structural characterization of transition metal(II) coordination polymers containing 4,4′-dipyridyldisulfide

The reactions of Zn(NO₃)₂ · 6H₂O and FeSO₄ · 7H₂O with 4-PDS (4-PDS = 4,4′-dipyridyldisulfide) and NH₄SCN in CH₃OH afforded the complexes [Zn(NCS)₂(4-PDS)]_n (1) and [Fe(NCS)₂(4-PDS)₂ · 4H₂O]_n (2), respectively, while the reaction of CoCl₂ · 6H₂O with 4-PDS in CH₃OH gave the complex {[Co(4-PDS)₂][Cl]₂ · 2CH₃OH}_n, (3). These complexes have been characterized by spectroscopic methods and their structures determined by X-ray crystallography. The 4-PDS ligands in 1 are coordinated to the metal centers through the nitrogen atoms to form 1-D zigzag-chains, and the distorted tetrahedral coordination geometry at each zinc center is completed by a pair of N-bonded thiocyanate ligands. Compound 2 has a 1-D channel-chain structure and each octahedral Fe(II) metal center is coordinated by four 4-PDS ligands and two trans N-bonded thiocyanate ligands. Weak SS interactions in complex 1 link the 1-D chains into 2-D molecular sheets. In complex 2, the channel chains are interlinked through SS interactions to form molecular sheets, which interpenetrate through the SS interactions to form 3-D structures with large cavities that are occupied by the water molecules. Compound 3 also has a 1-D channel-chain structure with each square-planar Co(II) metal center coordinated by four 4-PDS ligands. Multiple C–HCl hydrogen bonds and SO interactions in 3 link the 1-D chains into 2-D structures.