Two novel three-dimensional coordination polymers based on metal clusters: Hydrothermal syntheses, crystal structures and luminescence

Two novel coordination polymers with interesting supramolecular architecture, [Zn₂(OH)(BTC)(bix)] (1) and [Cd₂(CDC)₂(bix)₂] (2) (H₃BTC = 1,3,5-benzenetricarboxylic acid, H₂CDC = trans-1,4-cyclohexanedicarboxylic acid and bix = 1,2-bis(imidazol-1-ylmethyl)benzene) have been obtained via hydrothermal reaction and characterized by elemental analysis, IR and single-crystal X-ray diffraction. Complex 1 features a 3D network with one of the scarce (3,8)-connected (4³)₂(4⁶.6¹⁸.8⁴) topology based on the rare CdI₂-type layer constructed from secondary building units (SBUs) of zinc clusters. While 2 exhibits a scarcely reported eight-connected 3⁶.4¹⁶.5⁶ net with dinuclear cadmium clusters as secondary building units. The luminescent properties of 1 and 2 along with the bix ligand in the solid state were investigated.     

Syntheses, structures and photoluminescent properties of two zinc(II) coordination polymers based on aromatic polycarboxylate and 1,4-bis(imidazol-1-ylmethyl)benzene

Hydrothermal reaction of Zn(NO₃)₂·6H₂O with benzene-1,2,3-tricarboxylic acid (H₃BTC) or 5-bromoisophthalic acid (H₂BIPA) in the presence of 1,4-bis(imidazol-1-ylmethyl)benzene (bix) produced two novel coordination polymers [Zn₂(OH)(BTC) (bix)]·H₂O (1) and Zn(BIPA)(bix) (2), which were characterized by single-crystal X-ray diffraction, elemental analysis, IR and thermoanalysis. Complex 1 is a novel example of the 2D (3,4)-connected nets with (4²·6)(4²·6³·8) topology. In 2, the BIPA and bix ligands linked the Zn(II) atoms into a deeply corrugated 2D sheet. The corrugated 2D sheets polycatenate each other in a parallel manner yielding a rare 2D → 3D parallel polycatenation net. Thermal and luminescent properties of two complexes have also been investigated.     

Syntheses, structures and properties of copper(II) and cobalt(II) metal-organic frameworks based on R-isophthalate (R = -CH3 or -C(CH3)3) and 1,1′-(1,4-butanediyl)bis(imidazole) ligands

Three new complexes [Cu₂(mip)₂(bbi)]_n (1), {[Cu₂(tbip)₂(bbi)₂(H₂O)]·2H₂O}_n (2) and {[Co₂(tbip)₂(bbi)₂]·2H₂O}_n (3), were prepared through hydrothermal reactions of Cu(II) and Co(II) acetate with H₂mip or H₂tbip (H₂mip = 5-methyl isophthalic acid and H₂tbip = 5-tert-butyl isophthalic acid) and the flexible ligand bbi (bbi = 1,1′-(1,4-butanediyl)bis(imidazole)). All these complexes were structurally characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Complex 1 exhibits a 3D network, which are constructed from 2D carboxylate layer and bbi pillar. Complex 2 possesses a 2D layer structure, and exists extensive hydrogen-bonding interactions, while complex 3 is constructed from 2D layers which consists of alternating left- and right-handed helical chains, and further assembled to form a 3D framework by hydrogen-bonding interactions. The thermal stabilities of the corresponding complexes have been briefly investigated. In addition, dominant antiferromagnetic coupling was observed in complex 1.     

Cleavage of a RNA analog containing uridine by a bifunctional dinuclear Zn(II) catalyst

The macrocyclic ligand, 1,4-bis((1-oxa-4,7,10-triazacyclododecan-7-yl)methyl)benzene (L1) is prepared. L1 binds two Zn(II) ions at neutral pH to form Zn₂(L1) as studied by using pH-potentiometric titrations. Zn₂(L1) binds two uridines at pH 7.0, I = 0.100 M (NaCl) and the mononuclear analog Zn(L2) (L2 = 1-oxa-4,7,10-triazacyclododecane) binds a single uridine; dissociation constants for both complexes are in the millimolar range. Both complexes promote the cleavage of a simple RNA analog lacking a nucleobase (HpPNP = 2-hydroxypropyl-4-nitrophenylphosphate), and a uridine containing RNA analog UpPNP (uridine-3′-4-nitrophenylphosphate). Plots of the first-order rate constant for cleavage of HpPNP as a function of Zn(L2) concentration from 0.5 mM to 20.0 mM are linear, consistent with weak complexation to substrate K_d > 20 mM. In contrast, first-order rate constants for cleavage of UpPNP by Zn(L2) or Zn₂(L1) over similar concentration ranges exhibit a downward curvature, consistent with the formation of a complex between catalyst and UpPNP. Comparison of second-order rate constants (k₂ = k_cat/K_d) shows that the dinuclear complex Zn₂(L1) is a better catalyst than Zn(L2) for both HpPNP and UpPNP cleavage.     

Construction of several d metal coordination polymers based on aromatic polycarboxylate and flexible triazole-based ligand

To investigate the effect of organic anions on the coordination frameworks, we synthesized five new complexes, namely, {[Zn₃(μ-OH₂)₂(btc)₂(btx)₃]·4H₂O}_n (1), [Zn(bdc)(btx)]_n (2), {[Ag₈(3,5-pydc)₄(btx)₄]·8H₂O}_n (3), [Ag(2,6-Hpydc)(btx)]_n (4) and [Cd₂(μ₂-OH₂)(2,6-pydc)₂(btx)]_n (5) (H₂bdc = 1,4-benzenedicarboxylic acid; H₃btc = 1,3,5-benzenetricarboxylate; 3,5-H₂pydc = pyridine-3,5-dicarboxylic acid; 2,6-H₂pydc = pyridine-2,6-dicarboxylic acid), which were obtained by the reactions of 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene (btx) as main ligand, and several aromatic polycarboxylate as organic anions with different d¹⁰ metal salts. Single crystal structure analysis shows that complexes 1, 3 and 5 possess 3D structures, 2 takes a 2D layer motif, and 4 displays a 1D chain structure. The distinct structures indicate that polycarboxylate anions with the diverse coordination modes and coordination groups can affect the topologies of metal-organic frameworks. In addition, the luminescence measurements reveal that the complexes 1, 2 and 5 exhibit strong fluorescent emissions in the solid state at room temperature.     

Two new 3D (3,8)-connected metal-organic frameworks based on zinc-triazole secondary building units and benzenetricarboxylate linkers

Two new zinc-triazole-carboxylate frameworks constructed from secondary building units (SBUs), [Zn₅(trz)₄(btc)₂(DMF)₂(H₂O)₂]·2H₂O·DMF (1) and [Zn₄(trz)₃(btc)₂(CH₃CN)(H₂O)]·5H₂O·(Bu₄N) (2), [Htrz = 1,2,4-triazole, H₃btc = 1,2,4-benzenetricarboxylate, Bu₄N = tetrabutylammonium], have been synthesized by solvothermal reactions and characterized by single-crystal X-ray diffraction analyses, X-ray power diffraction, elemental analyses, infrared spectra and thermogravimetric analyses. Both compounds 1 and 2 exhibit 3D (3,8)-connected tfz-d nets with {4³}₂{4⁶.6¹⁸.8⁴} topology symbol built from rod-shaped {[Zn₅(trz)₄]⁶⁺}_n SBUs (1) and {[Zn₄(trz)₃]⁵⁺}_n SBUs (2). In two compounds, rodlike units are connected by btc ligands via different modes. Additionally, solid state fluorescent emission spectra of two compounds show fluorescent properties at room temperature.     

Metal-organic open frameworks with one-dimension channels assembled with pyridine 2,6-dicarboxylic acid and N-containing auxiliary ligands: Syntheses, crystal structures, and physical characterization

Four new complexes, {[Mn(imH)₂(pdc)]·H₂O}_n (1), [Zn₂(pdc)₂(H₂O)₅]·2H₂O (2), [Zn(imH)₂(pdc)]·H₂O (3), {[Zn₂(pdc)₂(bpy)(H₂O)₂]·5H₂O}_n (4) [imH = imidazole pdc = pyridine 2,6-dicarboxylate, bpy = 4,4′-bipyridine] have been synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR, PXRD, single-crystal X-ray diffraction and thermogravimetric analyses. All the four complexes display a three-dimensional (3D) open framework with one-dimensional (1D) channels that are filled with lattice water molecules. Particularly, in 4, the lattice water molecules form an infinite water chain. Both 1 and 4 consist of 1D polymeric chains. While 2 contains a dinuclear Zn(II) unit, and 3 is a mononuclear complex. Further, the result of thermal analysis of 1 and 2 shows the robustness of the overall supramolecular three-dimensional architecture. Complexes 1, 3, and 4 exhibit strong fluorescent emissions in the solid state at room temperature and could be significant in the field of photoactive materials.     

Novel topological nets of lanthanide metal-organic frameworks based on dicarboxylate ligands

Four novel topological nets of lanthanide metal-organic frameworks: [Sm₂(op)₃(H₂O)]_n (1), {Ln₂(op)₂(ox)(H₂O)₄] · H₂O}_n (Ln = La, 2; Sm, 3), {[La₂(mp)₂(ox)(H₂O)₄] · 2H₂O}_n (4), [La₂(op)₂(mp)(H₂O)₄]_n (5) (op = o-phthalate, mp = m-phthalate, and ox = oxalate), have been hydrothermally synthesized and characterized. Compound 1 exhibits novel (3,4,5,6)-connected five-nodal two-dimensional net, compound 2 and 3 show the (3,4)-connected V₂O₅ topologies, compound 4 has the (4,5)-connected topological net, and compound 5 shows the (4,5)-connected four-nodal three-dimensional network. Photoluminescent analyses of 1 and 3 show strong blue emission in the solid state at room temperature.     

New pyridine-monoacylhydrazidate-coordinated transition-metal complexes

By applying the hydrothermal in situ acylation reactions between alkyl-substituted pyridine-2,3-dicarboxylic acids and hydrazine hydrate, six pyridine-monoacylhydrazidate-coordinated transition-metal complexes [Mn(MPDH)₂] 1, [M(MPDH)₂(H₂O)₂]·2H₂O (M²⁺ = Co²⁺2, Zn²⁺3), [Mn(EPDH)₂(H₂O)₂] 4 and [M(EPDH)₂(H₂O)₂] (M²⁺ = Zn²⁺5, Co²⁺6) (MPDH = 6-methylpyridine-2,3-dicarboxylhydrazidate; EPDH = 5-ethylpyridine-2,3-dicarboxylhydrazidate) were obtained. Although only compound 1 is a 1-D chained coordination polymer and the others are the mononuclear molecular entities, they all further self-assemble into the interesting supramolecular networks via hydrogen-bonded interactions between pyridine-monoacylhydrazidate ligands. Two Zn²⁺ compounds 3 and 5 possess the fluorescence properties with maximum emissions at 517 nm for 3 and 530 nm for 5 upon excitation, respectively. The magnetic analysis for compound 1 indicates there exists the antiferromagnetic interactions between the Mn(II) ions.     

Synthesis and characterization of a novel three-dimensional photoluminescent coordination polymer generated from unsymmetrically bridging ligand

A novel three-dimensional metal-organic coordination polymer, [Zn₂(HBTC)₂(H₂O)₃]_n (1) (BTC=1,2,4-benzenetricarboxylate), has been prepared by aqueous solution reaction of Zn(NO₃)₂ · 6H₂O and BTC at moderate temperature and characterized by IR, TGA and single-crystal X-ray diffraction analysis. The three-dimensional architecture of 1 not only possesses rectangular cavities but also has ordered one-dimensional straight channels. Furthermore, compound 1 shows intense photoluminescent property at room temperature.     

New butane-1,2,3,4-tetracarboxylato bridged cobalt(II) complexes

Four butane-1,2,3,4-tetracarboxylato bridged supramolecular complexes [Co₂(H₂O)₅(BTC)]·2H₂O 1, [Co₂(H₂O)₅(BTC)]·2H₂O 2, [Co₂(H₂O)₆(bpy)₂(BTC)]·4H₂O 3 and [Co₂(H₂O)₂(bpy)₂(BTC)] 4, (H₄BTC = butane-1,2,3,4-tetracarboxylic acid, 2,2-bpy = 2,2-bipydine) are synthesized and characterized by single-crystal X-ray diffraction. IR spectroscopy, TG-DTA analyses, elemental analyses, powder X-ray diffraction and magnetic measurements for 3 and 4 are carried out. The dinuclear Co unit in 2 is bridged by BTC⁴⁻ anions into 2D layers, which are assembled via interlayer hydrogen bonds into a 3D (4⁴·6²)(4⁵·6⁵)₂(4⁶·6⁸·8) topological supramolecular architecture. In 3, the [Co₂(H₂O)₆(bpy)₂(BTC)] molecules are aggregated to 2D layers via π-π stacking interactions, the resulting layers are engaged in hydrogen bonding leading to a novel 3D supramolecular architecture with the schläfli symbol of (10².12)₂(4.10²)₂(4².10².12²). The Co atoms in 4 are linked by BTC⁴⁻ anions into a 1D chain, then the hydrogen bonding and π-π stacking interactions result in formation of a 3D novel (4³.6².8)₂(4⁶.6⁶.8³)(6³)₂ topological networks. The variable temperature magnetic characterizations on 3 and 4 suggest weak antiferromagnetic or ferromagnetic coupling exchange via π···π stacking interactions (J = -0.03 cm⁻¹ for 3, J = 0.11 cm⁻¹ for 4).     

Construction of carbon chains on ruthenium and osmium carbonyl clusters

We have used the elimination of AuX(PR₃) (X = halide, R = Ph, tol) that occurs in reactions of alkynylgold(I)-phosphine complexes with M₃(μ-H)₃ (μ₃-CBr) (CO)₉ (M = Ru, Os) to prepare the complexes M₃(μ-H)₃(μ₃-CCCR)(CO)₉ [M = Ru, R = Ph 2, CCSiMe₃3, Fc 4, CCFc 6-Ru, CC[Ru(PPh₃)₂Cp] 8; M = Os, R = CCFc 6-Os, CCCCFc 7], Fc′{(μ₃-CCC)Ru₃(μ-H)₃(CO)₉}₂5, and bis-cluster-capped carbon chain complexes {M₃(μ-H)₃(CO)₉}₂{μ₃:μ₃-C(CC)_nC} (M = Ru, n = 2 9, 3 10-Ru; M = Os, n = 3 10-Os) and {(L)(OC)₈(μ-H)₃M₃}C(CC)_nC{Co₃(μ-dppm)(CO)₇} (n = 1, M = Ru, L = CO 11, PPh₃12-Ru/P; n = 2, L = CO 12-Ru, PPh₃13; M = Os, L = CO 12-Os) in good to excellent yields. X-ray structural determinations of 2-5, 6-Ru, 6-Os, 7, 9, 11, 12-Ru, 12-Os and 12-Ru/P are reported.     

Syntheses and characterization of 3D heterometallic (3d-4f) metal-organic frameworks: Reversible de- and rehydration performance and magnetic properties

By the “metalloligand” strategy, two new 3d-4f heterometallic metal-organic frameworks (MOFs), {[Ln₂Cu₃(IDA)₆] · 1.5H₂O}_n [Ln = Tb (1) and Dy (2); H₂IDA = iminodiacetate acid], had been prepared. X-ray crystal structure analyses show that 1 and 2 possess of 3D frameworks with highly ordered 1D channels along the c axis. The highly stable skeleton and reversible de- and rehydration performance of 1 are demonstrated by thermogravimetric and powder X-ray diffraction analyses, and a low temperature magnetic study of 2 reveals a weak ferromagnetic interaction between the metal ions.     

Calix[4]arene supported group 5 imido complexes

The reaction of imidoyl chlorides [V(NR)Cl₃] (R = Ph 1, Tol 2, tBu 3) and calix[4]arene methyl ether H₃Mecalix unexpectedly leads to the formation of the structurally characterized vanadium (IV) complex [VCl(Mecalix)] (4). Calix[4]arene methyl ether stabilized imido complexes of the type [V(NR)(Mecalix)] (R = Ph 7, Tol 8, tBu 9) were afforded from the reaction of [V(NR)Cl₃] (R = Ph 1, Tol 2, tBu 3) and the tris(lithium) or tris(sodium) salt of the calix[4]arene ether. The lithium salt [{Li₃(Mecalix)}₂] (5) is a dimer in the solid state, in which two monomeric trianions are bridged by lithium cations. Imido complexes [M(NR)(Mecalix)] (M = Nb: R = tBu, 12, R = Tol 13, R = Mes 14, R = Dipp 15; M = Ta: R = tBu 16, R = Tol 17) (Tol = 4-C₆H₄Me, Mes = 2,6-C₆H₃Me₂; Dipp = 2,6-C₆H₃iPr₂) have been prepared from structurally characterized [NbCl₂(Mecalix)] (10) and previously known [TaCl₂(Mecalix)] (11) via reaction with two equivalents of the appropriately metallated (Li, K) primary amine. The molecular structures of 13 and 15 confirm the mononuclear nature of these complexes.     

Syntheses, structures, and photoluminescent properties of four d metal-quinolinato coordination polymers with similar rod-like SBUs

Four M^II quinolinato complexes, [Zn₂(quin)₂(H₂O)₃]_n (1), [Zn(quin)(H₂O)₂]_n (2), [Zn(quin)(H₂O)]_n (3) and [Cd(quin)]_n (4) (H₂quin = 2,3-pyridinedicarboxylic acid or quinolinic acid), have been hydrothermally synthesized and structurally characterized. X-ray diffraction analyses reveal that all of these four complexes are constructed from similar rod-like SBUs, [M(quin)]_n (M = Zn or Cd). Complexes 1 and 2 have similar 1-D box-like chains but different packing structures; complex 3 has a 2-D grid-like network and complex 4 has an unusual 2-D bilayer structure. Due to the different structural features, these complexes exhibit different photoluminescent emissions: complex 1 at 439 nm (λ_ex = 345 nm), complex 2 at 428 nm (λ_ex = 360 nm), complex 3 at 508 nm (λ_ex = 304 nm) and complex 4 at 500 nm (λ_ex = 324 nm).     

Syntheses, structures, and magnetic properties of 3d-4f heterometallic complexes constructed from pyrazole-bridged CuLn dinuclear units

A series of pyrazole-bridged heterometallic 3d-4f complexes, [CuDy(ipdc)₂(H₂O)₄] · (2H₂O)(H₃O⁺) (1) and [CuLn(pdc)(ipdc)(H₂O)₄] · H₃O⁺ (Ln = Ho (2), Er (3), Yb (4); H₃ipdc = 4-iodo-3,5-pyrazoledicarboxylic acid; H₃pdc = 3,5-pyrazoledicarboxylic acid), {[Cu₃Ln₄(ipdc)₆(H₂O)₁₆] · xH₂O}_n (Ln = Sm (5), x = 8.5; Ln = Eu (6), x = 7; Ln = Gd (7), Tb (8), x = 9), have been synthesized and structurally characterized. Ligand H₃ipdc was in situ obtained by iodination of ligand H₃pdc. Complexes 1-4 are pyrazole-bridged heterometallic dinuclear complexes, and 2-4 are isostructural. Complexes 5-8 are isostructural and comprised of an unusual infinite one-dimensional tape-like chain based on pyrazole-bridged heterometallic dinuclear units. The magnetic properties of compounds 1-4, 7 and 8 have been investigated through the magnetic measurement over the temperature range of 1.8-300 K.     

Structural and spectroscopic comparison of five-coordinate cobalt(II) and nickel(II) thiolato complexes with the related four-coordinate complexes

Five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co and Ni) (L1 = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate anion and HSMeIm = 2-mercapto-1-methylimidazole), were synthesized. These complexes were compared with the corresponding Cu(II) and Zn(II) complexes with the same ligands and were also compared with the related four-coordinate complexes [L1M(SC₆F₅)] (HSC₆F₅ = pentafluorobenzenthiol). All the complexes were characterized by X-ray crystallography and UV-Vis absorption, IR, ¹H NMR, and other spectroscopic techniques. All five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co, Ni, and Cu), form a distorted square pyramidal structure with a high spin state, and only [L1Zn(SMeIm)] takes a four-coordinate structure with a distorted tetrahedral configuration. The N21-M-S bond angles of the obtained five-coordinate complexes were proportional to the corresponding d value, which comes from between the equatorial basal plane with N4S ligand donor sets and metal ion. These observations and M-S bond distances affect on UV-Vis and far-IR spectral behavior.     

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%.     

Synthesis and reactivity of osmium (VI) nitrido complexes containing pyridine-carboxylato ligands

A series of osmium(VI) nitrido complexes containing pyridine-carboxylato ligands Os^VI(N)(L)₂X (L = pyridine-2carboxylate (1), 2-quinaldinate (2) and X = Cl (a), Br (1b and 2c) or CH₃O (2b)) and [Os^VI(N)(L)X₃]⁻ (L = pyridine-2,6-dicarboxylate (3) and X = Cl (a) or Br (b)) have been synthesised. Complexes 1 and 2 are electrophilic and react readily with various nucleophiles such as phosphine, sulfide and azide. Reaction of Os^VI(N)(L)₂X (1 and 2) with triphenylphosphine produces the osmium(IV) phosphiniminato complexes Os^VI(NPPh₃)(L)₂X (4 and 5). The kinetics of nitrogen atom transfer from the complexes Os^VI(N)(L)₂Br (2c) (L = 2-quinaldinate) with triphenylphosphine have been studied in CH₃CN at 25.0 °C by stopped-flow spectrophotometric method. The following rate law is obtained: −d[Os(VI)]/dt = k₂[Os(VI)][PPh₃]. Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) reacts also with [PPN](N₃) to give an osmium(III) dichloro complex, trans-[PPN][Os^III(L)₂Cl₂] (6). Reaction of Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) with lithium sulfide produces an osmium(II) thionitrosyl complex Os^II(NS)(L)₂Cl (7). These complexes have been structurally characterised by X-ray crystallography.     

3D hydrogen bonded heteronuclear Co, Ni, Cu and Zn aqua complexes derived from dipicolinic acid

The heteronuclear water-soluble and air-stable compounds [M(H₂O)₅M′(dipic)₂] · mH₂O (M/M′ = Cu^II/Co^II (1), Cu^II/Ni^II (2), Cu^II/Zn^II (3), Zn^II/Co^II (4), Ni^II/Co^II (5), m = 2-3; H₂dipic = dipicolinic acid) have been prepared by self-assembly synthesis in aqueous solution at room temperature, and characterized by IR, UV-Vis and atomic absorption spectroscopies, elemental and X-ray diffraction single crystal (for 1 and 2) analyses. 1-5 represent the first examples of heteronuclear dipicolinate compounds with 3d metals. Extensive H-bonding interactions involving all aqua ligands, dipicolinate oxygens and lattice water molecules further stabilize the dimetallic units by linking them to form three-dimensional polymeric networks.