Synthesis and structure of chloro(ligand)bis(diphenylglyoximato)cobalt(III) complexes

The synthesis and characterization of trans-chloro- (ligand)bis(diphenylglyoximato)cobalt(III) complexes [ligand = pyridine (py), α-, β-, or γ-picoline (α-pic, β-pic, γ-pic), 3,5-lutidine (lut), p-toluidine (p-tol) and PPh₃] is presented. X-ray crystal structure determination of the pyridine (1) and p-toluidine (6) derivatives has been carried out. Compound 1 crystallizes in the monoclinic system, space group P2₁/n, with Z = 4 and unit cell parameters a = 23.124(4), b = 13.009(3) and c = 11.204(3) Å, and β= 93.14(2)°. Compound 6 crystallizes in the monoclinic system, space group P2₁/n, with Z = 4 and unit cell parameters a = 18.792(3), b = 12.540(2) and c = 15.346(3) Å, and β = 97.54(2)°.     

Synthesis of Fe(II) and Cu(II) building blocks for metal-organic frameworks

In situ reaction of the aminobenzoic acids 2-aminobenzoic acid and 3,5-diaminobenzoic acid with salicylaldehyde provide easy access to the ligands 2-[{(2-hydroxyphenyl)methylene}amino]benzoic acid (L1) and 3,5-bis[{(2-hydroxyphenyl)methylene}amino]benzoic acid (L2). Addition of a Fe(II) or Cu(II) salt to the solution of the ligand yields the corresponding Fe and Cu complexes. The species synthesized have been structurally characterized by single-crystal X-ray diffraction. The Fe(II) complex [Fe(L1)(MeOH)₃] (1) crystallizes in the triclinic space group . The Cu(II) complex [Cu(L1)] (2) is a one-dimensional chain and crystallizes in the monoclinic space group P2₁. The Cu(II) complex [Et₃NH]₂[Cu₂(L2)₂] (3) crystallizes in the monoclinic space group P2₁/n. The magnetic properties of 1, 2 and 3 have been studied, showing that the Cu(II) ions of 2 and 3 are ferromagnetically coupled. Complexes 1 and 3 have strong potential as metal-bearing building blocks for the synthesis of metal-organic frameworks.     

3D azido-bridged cobalt(II) complexes with diazines as coligands

Two new three-dimensional azido-bridged Co(II) compounds with formula [Co(N₃)₂(2,5-Me₂pyz)]_n (1) and [Co(N₃)₂(2-ampym)]_n (2) have been structurally and magnetically characterized. 2,5-Me₂pyz and 2-ampym are 2,5-dimethylpyrazine and 2-aminopyrimidine, respectively. Compound 1 crystallizes in the monoclinic system with space group P2₁/c and compound 2 in the orthorhombic system with space group Pnma. In 1 and 2 each cobalt atom is linked to the four nearest-neighbors by end-to-end (EE) azido bridges, forming square layers. These layers are further connected to 3D networks by the N,N′-bridging ligands 2,5-dimethylpyrazine or 2-aminopyrimidine. The magnetic properties of 1 and 2 are reported. The plots of χ_M or χ_MT for 1 and 2 show antiferromagnetic coupling.     

Three coordination modes of the pentadentate ligand 2,6-diacetylpyridinedisemicarbazone

The pentadentate ligand 2,6-diacetylpyridinedisemicarbazone, DAPSC, reacts with Cr(NO₃)₃·9H₂O and forms two kinds of complexes. At pH=3, the ligand is singly-deprotonated and crystals of [Cr- (DAPSCH)(H₂O)₂](NO₃)₂·H₂O (Ia) are obtained. Evaporation of a solution at pH=0, yields crystals of [Cr(DAPSC)(H₂O)₂](NO₃)₃·2H₂O (II) in which the ligand is fully protonated. The reaction of DAPSC with UO₂(O₂CCH₃)₂ in methanol, followed by crystallization of the product from DMSO yields crystals of [UO₂(DAPSC2H)(H₂O)]·2DMSO (III) in which the ligand is fully deprotonated. Compound Ia is monoclinic, space group P2₁/n with a=11.746(1), b=14.752(2), c=11.866(1) Å,β=105.53(2)°, V= 1981(1) ų and Z=4. Compound II is monoclinic, space group, P2₁/n with a=38.000(3), b= 14.939(2), c=8.233(1) Å, β=96.12(2)°, V= 4647(1) Å and Z=8. Compound III is monoclinic, space group P2₁/n with a=18.048(2), b=15.207(2), c=8.842(1) Å,β=97.72(2)°, V=2405(1) ų and Z=4. The structures were refined using 2084, 4169 and 2516 reflections to R values of 4.4%, 7.8% and 4.8% respectively.     

Syntheses and characterizations of a series of silver-carboxylate polymers

Self-assembly reaction of H₃btc (1,3,5-benzenetricarboxylic acid), H₂ta (1,4-benzenedicarboxylic acid) or 1,2,4,5-benzenetetracarboxylic dianhydride with Ag(NO₃) in mixed H₂O/MeOH solution at room temperature gave rise to four novel 3D polymeric silver(I) complexes, [{Ag(H₂btc)}{Ag₂(Hbtc)}]_n (1), [Ag(ta)_1/2]_n (2), [Ag₂(btec)_1/2]_n (3) and [{Ag₃(btec)_3/4}{Ag(H₂O)₂(btec)_1/4}]_n (4) (H₄btec=1,2,4,5-benzenetetracarboxylic acid). Complex 1 crystallizes in orthorhombic space group Fddd, with a=14.877(5), b=25.926(1), c=36.377(7) Å, Z=32. Complex 2 crystallizes in monoclinic space group P2₁/c, with a=7.257(6), b=8.949(8), c=6.346(5) Å, β=111.654(3)°, Z=4. Complex 3 crystallizes in orthorhombic space group P2₁/c, with a=8.333(8), b=6.335(5), c=10.964(9) Å, Z=4, whereas complex 4 crystallizes in triclinic space group , with a=7.509(1), b=9.351(1), c=10.307(7) Å, α=69.514(2), β=84.521(2), γ=83.638(2)°, Z=2. All compounds possess 3D framework and short Ag-Ag contacts are present in 1-4. In 1, the ligand unsupported Ag-Ag interactions play an important role in the formation of the complex, which is constructed by silver chains formed by Ag-Ag interactions and carboxylate spacers.     

Organolanthanide constrained geometry complexes modified for catalysis: synthesis, structure, and aminoalkene hydroamination properties of a pyrrolidine-substituted constrained geometry organolutetium complex

The reaction of the organolutetium complex (CGC′)LuCl₃Li₂(THF), (1; CGC′ = [Me₂Si(3-pyrrolidinyl-1-η⁵-indenyl)(^tBuN)]²⁻) with NaN(TMS)₂ provides a straightforward route to the halide-free organolutetium amido complex, (CGC′)LuN(TMS)₂(THF) (2). These new complexes were characterized by standard analytical methodology. The monomeric complex 2 crystallizes in the monoclinic space group P2₁/c with four molecules in a cell of dimensions a = 11.1566(6) Å, b = 14.9805(8) Å, c = 22.18007(12) Å, and β = 90.0620(10)°. Complex 2 is an active precatalyst for the intramolecular hydroamination/cyclization of representative aminoalkenes with turnover frequencies as high as 205 h⁻¹ at room temperature.     

Heavy metal ion interactions with deoxy nucleotides. X-ray crystal structures of orthorhombic and monoclinic forms of 2'-deoxy cytidine 5'-monophosphate complexed with Cd(II)

The crystal structures of two polymorphic complexes of Cd(II) with 2'-deoxy cytidine 5'-mono-phosphate (5'-dCMP) are reported and discussed The orthorhombic complex, [Cd(5'-dCMP) (H₂O)₂] (1), crystallizes in space group P2₁2₁2₁ with cell dimensions a = 8.422(2), b = 24.428(8), c = 7.292(2) Å, and Z = 4, the monoclinic complex, [Cd₂(5'-dCMP)₂(H₂O)₂]·3H₂O (2), crystallizes in space group C2 with a = 30.809(9), b = 5.369(2), c = 25.126(8) Å, β = 127.61(2)°, and Z = 4 Structure (1) has been solved by Patterson and Fourier methods, and structure (2) has been deduced from its isomorphous ribo-analog (J.K. Shiba and R. Bau, Inorg.Chem. 17, 3484 (1978)); and both have been refined by full-matrix least-squares methods to final R values of 0.052 for (1) and 0.103 for (2) using, respectively, 1273 and 2287 independent reflections. The orthorhombic complex (1) is three-dimensionally polymeric, with the Cd atom bound in a distorted octahedral arrangement to the cytosine base at N(3) and O(2) [Cd-N(3) 2.29(1) and Cd-O(2) 2.64(1) Å], to two phosphate oxygens of different nucleotide molecules, and to two water molecules, each phosphate group links two Cd atoms, thereby producing an infinite [-Cd-O-P-O-Cd-]_n spiraling column, which is additionally interconnected to neighboring columns via nucleotide bridges to give a layer-like polymeric structure. The monoclinic complex (2), which includes two crystallographically independent [Cd(5'-dCMP) (H2O)] units, is also three-dimensionally polymeric, with each Cd atom bound in a distorted pentagonal bipyramidal arrangement to N(3) and O(2) of the base [Cd-N(3) 2.35_av and Cd-O(2) 2.73_av Å], to four phosphate oxygens of three different nucleotide molecules, and to a water molecule, each phosphate group binds to three Cd atoms, thereby creating an infinite cross-linked spiral of sequences [-Cd-O-P-O-Cd-]_n and [-Cd-O-Cd-]_n that is further connected to adjacent spirals via nucleotide bridges to form large     

A novel one-dimensional acentric copper(I) coordination polymer with second-harmonic generation response

The reaction of N,N-(2-pyridyl)(4-pyridylmethyl)amine with [Cu(MeCN)₂(PPh₃)₂]ClO₄ in the presence of THF affords a novel one-dimensional copper(I) coordination polymer {[Cu(PPh₃)(N,N-(2-pyridyl)(4-pyridylmethyl)amine)](ClO₄)}_n (1), which crystallizes in an noncentrosymmetric space group and displays strong second-harmonic generation (SHG) response.     

The crystal and molecular structures of dichloro [N,O-(D,L)-diaminopropionic acid] platinum(II) and Dichloro [N,O-(L)-lysine] platinum(II) monohydrate

K₂PtCl₄ reacts with L-lysine and with D,L-diaminiopropionic acid (Dap) forming the neutral complexes [PtCl₂(N,O-Lys)]·H₂0 (1) and [PtCl₂(N,O-Dap)], (2) respectively.Compound 1 is monoclinic, space group P2₁ with a = 11.262(3), b = 11.041(2), c = 9.690(2) Å, β = 102.07(5)°, V = 1178(1) ų and Z = 4. Compound 2 is monoclinic, space group P2₁/n with a = 8.777(1), b = 10.615(2), c = 7.947(1) Å, β = 94.98(3)°, V = 738(1) ų and Z = 4. In both compounds, the zwitterionic ligands form an N,O-five membered chelate with the platinum atom. Structures 1 and 2 were refined to R values of 3.3% and 6.3% respectively.     

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.     

Mimicking the reduced, oxidized and azide inhibited form of manganese superoxide dismutase by mononuclear Mn compounds utilizing tridentate ligands

The manganese complexes [Mn^II(Hbmimpm)₂(NO₃)](NO₃) · Et₂O (1), [Mn^III(bmimpm)₂(OAc)] · 2CH₂Cl₂(2), and [Mn^III(bmiapm)₂(OAc)] · MeOH · H₂O · CH₂Cl₂(3) containing the new ligands Bis(1-methylimidazol-2-yl)-(4-methoxyphen-1-yl)methanol (Hbmimpm) and Bis[(1-methylimidazol-2-yl)](2-aminophenyl)methanol (Hbmiapm) were synthesized. They are good structural models for the reduced (1) and oxidized (2, 3) form of manganese superoxide dismutase. All complexes were characterized by spectroscopic methods and X-ray structure analysis. Compounds 1 and 2 crystallize in the monoclinic space group P2₁/c whereas complex 3 crystallizes in the monoclinic space group P2₁/n. The coordination sphere around the manganese cores is distorted octahedral with two corresponding tridentate ligands representing the protein ligands and one nitrate (1) or acetate (2, 3) ion occupying two cis positions. Similar to the enzyme the Mn(III) complex 2 reacts with sodium azide. The obtained microcrystalline azide adduct was characterized by UV-Vis and IR spectroscopy.     

The complexes with end-to-end dicyanamide bridges: syntheses, characterization and crystal structures of [Cu(μ1,5-dca)2(phen)]n and [Cd(μ1,5-dca)2(py)2]n (phen=phenanthroline; py=pyridine; dca=dicyanamide, N(CN)2 )

Two new dicyanamide (dicyanamide=[N(CN)₂]⁻, dca) bridged complexes, [Cu(μ_1,5-dca)₂(phen)]_n (1) and [Cd(μ_1,5-dca)₂(py)₂]_n (2) have been synthesized and their structures have been determined by X-ray crystallography diffraction. Complex 1 crystallizes in the monoclinic space group P2(1)/c with a=10.1502(3), b=10.9815(4), c=14.5839(4) Å and Z=4. The adjacent copper atoms are connected by single end-to-end dca bridges to form a chain structure along the b axis. The chains are linked via Cu?N weak interactions to give rise to a 2D layer structure, which furthermore into a 3D structure by the π-π interaction between aromatic rings of adjacent layers. Complex 2 crystallizes in the monoclinic space group C2/m with a=6.6849(10), b=17.476(2), c=13.231(2) Å and Z=4. The cadmium(II) center is six-coordinated with a distorted octahedral geometry, bounded to four N atoms of four dca ligands and two N atoms of two-chelated py ligands. Neighbor Cd(II) atoms are linked by the double end-to-end dca bridges to generate a chain structure, which result in a 2D layer structure through the π-π interactions between the adjacent chains with distances 3.641 Å. EPR and magnetic results of 1 suggest that the complex exhibits a weak ferromagnetic interaction through CuNCNCNCu pathways.     

Synthesis and characterization of 5,5′-dibromo-2,2′-dipyridyl disulfide and some of its derivatives: X-ray structure of 5,5′-dibromo-2,2′-dipyridyl disulfide and bis(5-bromopyridine-2-ylthio) methane

Synthesis and characterization of 5,5′-dibromo-2,2′-dipyridyl disulfide and some of its derivatives under mild reaction conditions is described. A series of some novel synthetically important symmetrical/unsymmetrical bromo substituted pyridyl alkyl/aryl sulfur compounds have been easily synthesized from a variety of alkyl halides, using NaBH₄ in moderate to good yields. The important features of this protocol are strong base-free, operational simplicity, short reaction time and high yield. The synthesized compounds are characterized with the help of elemental analysis, IR, ¹H NMR, ¹³C NMR and mass spectral data (in representative cases). X-ray crystal structure analysis of 5,5′-dibromo-2,2′-dipyridyl disulfide (1) and bis(5-bromopyridine-2-ylthio) methane (2a) have been carried out to establish their molecular structure. Compound (1) and (2a) are monoclinic and crystallizes into P2₁/n and C2/c space group, respectively.     

Crystal structure of six and seven coordinate manganese(II) complexes with penta and hexadentate pyridylmethyl ligands

Two six-coordinated manganese(II) complexes [Mn(pydien)Cl](ClO₄) · C₂H₅OH (1), [Mn(pydien)NCS](ClO₄) (2) and two seven-coordinated manganese(II) complexes [Mn(pydado)Cl](ClO₄) (3), [Mn(pydado)NCS](ClO₄) (4) have been obtained using linear penta and hexadentate ligands pydien and pydado (pydien: 1,7-bis(2-pyridylmethyl)-1,4,7-triazaheptane and pydado: 1,10-bis(pyridylmethyl)-1,10-diaza-4,7-dioxadecane). The crystal structures for all compounds have been determined. 1 and 3 crystallize in the triclinic space group , 2 crystallizes in the orthorhombic space group Pbca, whereas 4 crystallizes in the monoclinic space group P2₁/c. The bound anion (chloro or isothiocyanato) in complexes 1 and 2 has no influence on the geometry of six-coordinate manganese(II) complexes, whereas the geometry and the wrapping of the hexadentate ligand (pydado) around Mn²⁺ cation depend on the nature of the bound anion. The complex 3 has a capped octahedron geometry with the two pyridyl groups in trans position, while the geometry of complex 4 can be described as pentagonal bipyramid with one pyridyl group and a thiocyanate anion in the axial positions.     

Rhenium(IV) cyanate complexes: Synthesis, crystal structures and magnetic properties of NBu4[ReBr4(OCN)(DMF)] and (NBu4)2[ReBr(OCN)2(NCO)3]

Two new rhenium(IV) mononuclear compounds of formula NBu₄[ReBr₄(OCN)(DMF)] (1) and (NBu₄)₂[ReBr(OCN)₂(NCO)₃] (2) (NBu₄ = tetrabutylammonium cation, OCN = O-bonded cyanate anion, NCO = N-bonded cyanate anion and DMF = N,N-dimethylformamide) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 crystallizes in the monoclinic system with the space group P2₁/n, whereas 2 crystallizes in the triclinic one with as space group. In both complexes the rhenium atom is six-coordinated, in 1 by four Br atoms in the equatorial plane, and two trans-oxygen atoms, one of a DMF molecule and another one from a cyanato group, while in 2 by one bromide anion and five cyanate ligands, two of which are O-bonded and three N-bonded, forming a somewhat distorted octahedral surrounding. Magnetic susceptibility measurements on polycrystalline samples of 1 and 2 in the temperature range 1.9-300 K are interpreted in terms of magnetically isolated spin quartets with large values of the zero-field splitting (|2D| is ca. 41.6 and 39.2 cm⁻¹ for 1 and 2, respectively).     

Syntheses,structures and ligand dissociation kinetics of Vitamin B12 model compounds with exceptionally poor electron donating groups,LCo(DH)2CHX2 (X = Cl or Br)

The syntheses and ligand dissociation kinetics of vitamin B₁₂ model compounds LCo(DH)₂CHX₂ with X = Cl and Br and L = different neutral N- and P- ligands are reported together with the crystal structures of the CHCl₂ derivatives with L = py (1) and 1,5,6-trimethylbenzimidazole, Me₃Bzm (2). Compound 1 crystallizes in the space group P2₁/n with cell parameters a = 9.617(1), b = 12.601(2), c = 15.586(2) Å, β = 95.44(1)°; 2 crystallizes in the space group P1 with cell parameters a = 8.867(2), b = 10.719(2), c = 13.345(2) Å, α = 94.81(2), β = 90.89(1), γ = 105.63(2)°. The two structures were solved by Patterson and Fourier methods and refined by least-squares methods to final R values of 0.037 (1) and 0.036 (2), using 3474 (1) and 4435 (2) independent reflections.The axial NCoC fragment is characterized by CoN and CoC distances of 2.045(2) and 1.995(2) Å in 1 and 2.043(2) and 1.983(2) Å in 2, respectively. The CoC bond lengths have the smallest values so far reported in both py and Me₃Bzm alkylcobaloximes.The displacement of the L ligand followed SN1 LIM behaviour and the corresponding rate constants depend upon the nature of L and vary in CHCl₂ derivatives from 2.42 X 10⁻¹ s⁻¹ for 2-aminopyridine to 1.99 X 10⁻⁵ s⁻¹ for P(OMe)₃. For fewer CHBr₂ analogs the rate constants were smaller.Kinetic results confirm previous findings that the donating ability of CHBr₂ is less than that of CHCl₂, although the electronegativity of Cl and Br species would suggest an opposite trend. Some relationships between kinetic and structural properties are discussed.     

Four three-dimensional lanthanide coordination polymer constructed from benzene-1,4-dioxydiacetic acid

Four crystalline lanthanide(III) three-dimensional (3D) coordination polymers {[La(BDOA)_1.5(H₂O)] · H₂O}_n (1), {[Nd(BDOA)_1.5(H₂O)] · H₂O}_n (2), [Tm(BDOA)_1.5(H₂O)]_n (3), [Yb(BDOA)_1.5(H₂O)]_n (4) were obtained under hydrothermal conditions and characterized by elemental analysis, IR, as well as single-crystal X-ray diffraction. Compounds 1 and 2 crystallize in the monoclinic system, space group P2₁/c, they are isostructural and exhibit the same 3²¹.4⁵⁷.5¹³ topological network constructed from different coordination modes of two BDOA ligands, whereas isostructural 3 and 4 crystallizes in the triclinic system, space group , it holds 3⁹.4²⁰.5⁷ topological architecture based on another two different coordination modes BDOA ligands. Moreover, a computational method is applied to evaluate the potential porosity of complex 1.     

Novel cobalt(II) complexes with pyridyl/ether or pyridyl/thioether ligands. The conversion of pyridyl/thioether cobalt(II) complex to pyridyl/sulfinato cobalt(III) compound

Two new cobalt(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesized as perchlorate salts. The crystal structures show that [Co(pydado)](ClO₄)₂ · H₂O (1) crystallizes in the triclinic space group and [Co(pydadt)](ClO₄)₂ (2) crystallizes in the monoclinic space group P2_1/c. The cation [Co(pydado)]²⁺ is pseudo-octahedral with the two pyridyl groups in trans position. However, in [Co(pydadt)]²⁺ complex, the size of thioether sulfur atoms imposes a distorted octahedral geometry; the pyridyl groups and the sulfur atoms are in trans position. The reaction of the complex 2 and hydrogen peroxide resulted to the oxidation of Co^II into Co^III and the thioether groups of the ligand to sulfinate groups with elimination of the central ethylenic group of pydadt. Thus, complex 2 was converted to bis[3-(2-pyridylmethylamino)ethanesulfinate] cobalt(III) complex (3) {[Co(pynso)₂](ClO₄) · 0.5H₂O}. The X-ray crystal structure reveals that the compound 3 crystallizes in the triclinic space group with the same donor atoms (N_pyridyl, N_amine and S) belonging to the two ligands in cis-position. In aqueous solution, the stability constants of the Co(II) chelates with these two ligands, determined by potentiometry, show the formation of [Co(LH)]³⁺ and [CoL]²⁺ species in all cases. The chelating power of pydadt ligand is slightly greater than that of pydado.     

Hydrothermal synthesis and characterization of an unprecedented η-type octamolybdate: [{Ni(phen)2}2(Mo8O26)]

A new octamolybdate-supported transition metal complex [{Ni(phen)₂}₂(Mo₈O₂₆)] (1) has been hydrothermally synthesized and characterized by the elemental analyses, IR spectrum, XPS spectra, TG analysis and the single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group P2₁/c, a=10.446(2) Å, b=12.103(2) Å, c=21.956(4) Å, β=97.81(3)°, V=2750.0(10) ų, and Z=2. The single crystal X-ray diffraction analysis reveals that compound 1 is constructed from a novel unprecedented η-type octamolybdate cluster linked to two {Ni(phen)₂}₂ coordination complexes.