TTF charge transfer salts containing cyanometallate anions [M(phen)(CN)4] (M = Cr or Fe; phen = 1,10-phenanthroline)

Two new charge transfer salts of TTF with the counter anions [M(phen)(CN)₄]⁻ (phen = 1,10-phenanthroline, M = Cr (I) and Fe (II)) are described. The structures consist of alternating stacks of dimerised TTF⁺ cations and [M(phen)(CN)₄]⁻ anions and they are linked together by many short S?S contacts and hydrogen bonds. Within the organic stack, two dimerised TTF⁺ cations are arranged in a slipped face-to-face mode with short intra-dimer and long inter-dimer S?S distances. Strong antiferromagnetic exchange was found in the TTF⁺ dimers. Conductivity measurements show that compound I is a semiconductor.     

Synthesis and characterization of deuterium-labelled (fulvene)M(CO)3 complexes (M = Cr, Mo)

The preparation and characterization of a series of deuterium-labelled (fulvene)M(CO)₃ (M = Cr, Mo) complexes is reported. (η⁵-6-Dimethylaminofulvene-d₂)Cr(CO)₃ and (η⁵-6-dimethylaminofulvene-d₂)Mo(CO)₃ were obtained in high yields by reacting the deuterated fulvene ligands with (MeCN)₃M(CO)₃ (M = Cr, Mo). In addition, syntheses of 6,6-diphenylfulvene-d₁₀ and 6,6-diphenyl-1,2-benzofulvene-d₁₀ as well as the corresponding tricarbonylchromium complexes are described.     

Synthesis and characterization of [Fe(III)(qsal)2][M(III)(pds)2] (M = Cu, Au)

Salts of the Fe(III) spin crossover cation [Fe^III(qsal)₂]⁺ (qsalH = N-(8-quinolyl)salicylaldimine) and monoanions [M^III(pds)₂]⁻ (M = Cu, Au; pds = pirazine-2,3-diselenolate) with formula [Fe^III(qsal)₂][M^III(pds)₂] were prepared and characterized by single crystal X-ray diffraction and magnetic measurements. These two salts present magnetic properties essentially due to the Fe^III centres in the high-spin state (S = 5/2), and do not have any spin transition.     

Searching for switchable molecular conductors: Salts of [M(dcbdt)2] (M = Ni, Au) anions with [Fe(sal2-trien)] and [Fe(phen)3]

Salts of [Fe^III(sal₂-trien)]⁺and [Fe^II(phen)₃]²⁺ cations and M[(dcbdt)₂]⁻ anions with M = Ni and Au (dcbdt = dicyanobenzenedithiolate) with formula [Fe(sal₂-trien)] [M(dcbdt)₂] and [Fe(phen)₃] [M(dcbdt)₂]₂ were obtained and characterized by single X-ray diffraction and magnetic measurements. None of these salts shows a clear spin crossover behaviour and their magnetic properties are due essentially to the cations in a high spin S = 5/2 and low spin states for the Fe^III and Fe^II salts respectively. The magnetic Ni sublattices in both compounds appear to have a negligible direct contribution to the magnetization but enhance the AF interactions in the cation sublattice.     

Dioxouranium complexes as ligand. Synthesis and characterization of sandwich-type polyoxometalates [X2W18(UO2)2{(H2O)3M}2O68] (X = As and P) (M = Co, Cu, Mn, Ni and Zn)

The title complexes are synthesized by the reaction of an unusual ligand of [K₂P₂W₁₈(UO₂)₂O₆₈]¹²⁻ (1) and [KAs₂W₁₈(UO₂)₂O₆₈]¹³⁻ (2) with divalent metal ions of Co^II, Cu^II, Mn^II, Ni^II and Zn^II in 1:2 mole ratio and are characterized by elemental analysis, IR, ³¹P NMR, UV-Vis spectroscopy, TGA, and single crystal structure analysis. Crystals of [P₂W₁₈(UO₂)₂{(H₂O)₃Co}₂O₆₈]¹⁰⁻ (1a) and [As₂W₁₈(UO₂)₂{(H₂O)₃Cu}₂O₆₈]¹⁰⁻ (2b) are orthorhombic space group Cmca. Both 1a and 2b have structures in which two [M(H₂O)₃] (M = Co^II, Cu^II) and two UO₂ groups are sandwiched between two symmetry equivalent (XW₉) (X = P, As) units in a virtual C_i symmetry. In solution, 1a and [P₂W₁₈(UO₂)₂{(H₂O)₃Zn}₂O₆₈]¹⁰⁻ (1d) give two-line P NMR spectra that are consistent with a C_s symmetry structures so, are not consistent with the solid-state structures. The sodium salts of them give one-line P NMR spectra and are consistent with the C_i symmetry of solid-state structures. The uranium atoms have pentagonal-bipyramidal coordination, achieved by three equatorial bonds to the one XW₉ and two bonds to the other. The M atoms have octahedral or square pyramidal coordination, but only one bond to the one XW₉ and one bond to the other.     

Syntheses and crystal structures of cyano-bridged cluster-metal layered coordination polymers [Cu(dien)]3[W4Te4(CN)12] · 9H2O and [Ni(en)(NH3)]3[W4Se4(CN)12] · 7.5H2O

Two new tetrahedral tungsten cyanide cluster compounds, [Cu(dien)]₃[W₄Te₄(CN)₁₂] · 9H₂O (1) (dien=diethylenetriamine) and [Ni(en)(NH₃)]₃[W₄Se₄(CN)₁₂] · 7.5H₂O (2) (en=ethylenediamine), were synthesized by treating aqueous solutions of the saltlike cluster compound K₆[W₄Te₄(CN)₁₂] · 5H₂O/K₆[W₄Se₄(CN)₁₂] · 6H₂O with copper(II)/nickel(II) chloride in aqueous ammonia containing dien/en. The cyano-bridged layered coordination polymeric compounds were characterized by single-crystal X-ray diffraction analysis: monoclinic, space group P2₁ for 1; trigonal, space group for 2. Structures of 1 and 2 consist of infinite neutral layers of cluster components {W₄Te₄(CN)₁₂}/{W₄Se₄(CN)₁₂} connected, one another by {Cu(dien)} or {Ni(en)(NH₃)} fragments, respectively.     

Synthesis, magnetism and X-ray structures of [Cu(2-aminopyrimidine)2(μ-OH)(CF3SO3)]2(2-aminopyrimidine)2, a new hydroxo-bridged dinuclear Cu(II) compound generating extremely small antiferromagnetism

The synthesis, optical and magnetic properties and X-ray crystal structure of [Cu(2-aminopyrimidine)₂(OH)(CF₃SO₃)]₂(2-aminopyrimidine)₂, a new dinuclear hydroxo-bridged copper(II) compound with a CuOCu angle of 97.96° and a very small antiferromagnetic interaction for which the singlet-triplet exchange parameter J, is described. The magnetic exchange coupling is almost negligible and, depending on the actual sample, varies from −1.8 to −7.2 cm⁻¹.     

Synthesis, structure and properties of TTF-carboxylate bridged paddlewheel dirhodium complexes, Rh2(BuCO2)3(TTFCO2) and Rh2(BuCO2)2(TTFCO2)2

Reaction of tetrathiafulvalene carboxylic acid (TTFCO₂H) with paddlewheel dirhodium complex Rh₂(Bu^tCO₂)₄ yielded TTFCO₂-bridged complexes Rh₂(Bu^tCO₂)₃(TTFCO₂) (1) and cis- and trans-Rh₂(Bu^tCO₂)₂(TTFCO₂)₂ (cis- and trans-2). Their triethylamine adducts [1(NEt₃)₂] and cis-[2(NEt₃)₂] were purified and isolated with chromatographic separation, and characterized with single crystal X-ray analysis. Trans-[2(NEt₃)₂] is not completely separated from a mixture of cis- and trans-[2(NEt₃)₂], but its single crystals were obtained from a solution of the mixture. A three-step quasi-reversible oxidation process was observed for 1 in MeCN. The first two steps correspond to the oxidation of the TTFCO₂ moiety and the last one is the oxidation of the Rh₂ core. The oxidation of cis-2 is observed as a two-step process with very similar E_1/2 values to those of the first two processes for 1. Both 1⁺ and cis-2²⁺ in MeCN at room temperature show isotropic ESR spectra with a g value of 2.008 and a_H = 0.135 mT for two equivalent H atoms and a_H = 0.068 mT for one H atom. The redox and ESR data of cis-2 suggest that the intramolecular interaction between the TTF moieties is very small.     

Reaction of [MCl2(CH3CN)2] (M = Pd(II), Pt(II)) compounds with N1-alkylpyridylpyrazole-derived ligands

Palladium(II) and platinum(II) complexes with N-alkylpyridylpyrazole-derived ligands, 2-(1-ethyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L¹) and 2-(1-octyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L²), cis-[MCl₂(L)] (M = Pd(II), Pt(II)), have been synthesised. Treatment of [PdCl₂(L)] (L = L¹, L²) with excess of ligand (L¹, L²), pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ and NaBPh₄ produced the following complexes: [Pd(L)₂](BPh₄)₂, [Pd(L)(py)₂](BPh₄)₂ and [Pd(L)(PPh₃)₂](BPh₄)₂. All complexes have been characterised by elemental analyses, conductivity, IR and NMR spectroscopies. The crystal structures of cis-[PdCl₂(L²)] (2) and cis-[PtCl₂(L¹)] (3) were determined by a single crystal X-ray diffraction method. In both complexes, the metal atom is coordinated by one pyrazole nitrogen, one pyridine nitrogen and two chlorine atoms in a distorted square-planar geometry. In complex 3, π-π stacking between pairs of molecules is observed.     

Raman and infrared spectroscopic and theoretical studies of dinuclear rhenium and osmium complexes, M2(O2CCH3)4X2 (M = Re, Os; X = Cl, Br)

Infrared, far-infrared and Raman spectra of Re₂(O₂CCH₃)₄X₂ (X = Cl, Br) and Re₂(O₂CCD₃)₄Cl₂ have been recorded. Assignments of the vibrational spectra of Os₂(O₂CCH₃)₄Cl₂ and its deuterated derivative have been completed together with the Re complexes on the basis of normal-coordinate analysis. Force constant calculation was made for the acetate ion as well as for a four-atomic unit (with the CH₃ and CD₃ groups considered as point masses) using optimized masses of 16.7, 17.8, 20.5 and 21.6 for ¹²CH₃, ¹³CH₃, ¹²CD₃ and ¹³CD₃ groups, respectively. The force constants of the acetate ion have been adopted to the starting force field of the M₂(O₂CCH₃)₄X₂ type complexes. The metal-halide (0.889, 0.997 and 1.286 N cm⁻¹) and metal-metal stretching (3.32, 3.34 and 3.57 N cm⁻¹) force constants were obtained for Re₂(O₂CCH₃)₄Cl₂Re₂(O₂CCH₃)₄Br₂ and Os₂(O₂CCH₃)₄Cl₂ complexes, respectively. It was shown that the so-called diatomic approximation in most cases overestimates the M-M stretching force constants by 30-40%. Much better correlation has been obtained to fit these force constants, which produced values very close to those obtained by full normal-coordinate calculations. The Re-Re stretching force constants showed a reasonable correlation with the Re-Re bond distances for 18 rhenium complexes.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).     

Mn(II) complexes of monoanionic bidentate chelators: X-ray crystal structures of Mn(dha)2(CH3OH)2 (Hdha = dehydroacetic acid) and [Mn(ema)2(H2O)]2 · 2H2O (Hema = 2-ethyl-3-hydroxy-4-pyrone)

This report describes synthesis and characterization of bis-ligand Mn(II) complexes of bidentate chelators: maltol (3-hydroxy-2-methyl-4-pyrone), ethylmaltol (2-ethyl-3-hydroxy-4-pyrone), 1,2-dimethyl-3-hydroxy-4-pyridinone (DMHP) and dehydroacetic acid. All four Mn(II) complexes were characterized by elemental analysis, IR, UV/Vis, EPR, cyclic voltammetry, and X-ray crystallography in cases of Mn(dha)₂(CH₃OH)₂ and [Mn(ema)₂(H₂O)]₂ · 2H₂O. The bidentate chelator plays a significant role in the solid state structure of its Mn(II) complex. For example, dha forms the monomeric complex Mn(dha)₂(CH₃OH)₂ while ethylmaltol forms the dimeric complex [Mn(ema)₂(H₂O)]₂. Because of smaller size, maltol ligands in Mn(ma)₂ are able to bridge adjacent Mn(II) centers to give a polymeric structure in solid state. Despite of the difference in their solid state structures, both Mn(ema)₂ and Mn(ma)₂ exist in solution as monomeric Mn(II) species, Mn(ema)₂(H₂O)₂ and Mn(ma)₂(H₂O)₂. This assumption is supported by the similarity in their UV/Vis spectra, EPR data and electrochemical properties. Replacing maltol with DMHP results in a decrease (by ∼100 mV) in the redox potential for the Mn(II)/Mn(III) couple, suggesting that DMHP stabilizes Mn(III) better than maltol. Since Mn(DMHP)₂(H₂O)₂ is readily oxidized to form the more stable Mn(III) complex Mn(DMHP)₃, DMHP has the potential as a chelator for removal of excess Mn(II) from patients with chronic Mn toxicity.     

3D hydrogen bonded metal-organic frameworks constructed from [M(H2O)6][M′(dipicolinate)2] · mH2O (M/M′ = Zn/Ni or Ni/Ni). Identification of intercalated acyclic (H2O)6/(H2O)10 clusters

New heterodinuclear Zn^II/Ni^II (1) and homodinuclear Ni^II/Ni^II (2) water-soluble and air stable compounds of general formula [M(H₂O)₆][M′(dipic)₂] · mH₂O have been easily prepared by self-assembly of the corresponding metal(II) nitrates with dipicolinic acid (H₂dipic) in water solution at room temperature.  The compounds have been characterized by IR, UV/Vis and atomic absorption spectroscopies, elemental and X-ray single crystal diffraction (for 1 · 4H₂O and 2 · 5H₂O) analyses.  3D infinite polymeric networks are formed via extensive hydrogen bonding interactions involving all coordinated and crystallization water molecules, and all dipicolinate oxygens, thus contributing to additional stabilization of dimeric units, metal-organic chains and 2D layers.  In 1 · 4H₂O, the latter represent a rectangular-grid 2D framework with multiple channels if viewed along the c crystallographic axis, while in 2 · 5H₂O intercalated crystallization water molecules are associated to form acyclic nonplanar hexameric water clusters and water dimers which occupy voids in the host metal-organic matrix, with a structure stabilizing effect via host-guest interactions.  The hexameric cluster extends to the larger (H₂O)₁₀ one with an unusual geometry (acyclic helical octamer with two pendent water molecules) by taking into account the hydrogen bonds to water ligands in [Ni(H₂O)₆]²⁺.  The obtained Zn/Ni compound 1 relates to the recently reported family of heterodimetallic complexes [M(H₂O)₅M′(dipic)₂] · mH₂O (M/M′ = Cu/Co, Cu/Ni, Cu/Zn, Zn/Co, Ni/Co, m = 2, 3), what now allows to establish the orders of the metal affinity towards the formation of chelates with dipicolinic acid (Co^II > Ni^II > Zn^II > Cu^II) or aqua species (Co^II < Ni^II < Zn^II < Cu^II).     

The structural definition of adducts of stoichiometry MX:dpex (2:3)(∞), M = Cu, Ag, X = simple anion, dpex = Ph2E(CH2)xEPh2, E = P, As

Single crystal X-ray structural characterizations are recorded for a number of adducts of MX:dpex (2:3) stoichiometry (MX = simple univalent copper or silver salt; dpex = Ph₂E(CH₂)_xEPh₂ (E = P, As)). CuX:dppe (2:3) (X = Cl, Br, I, CN) are binuclear [(dppe-P,P′)CuX(P-dppe-P′)CuX(P,P′-dppe)], all centrosymmetric. AgX:dpex (2:3) (dpex = ‘dpae’ (Ph₂As(CH₂)₂AsPh₂), X = Br, F₃CCO₂ (= ‘tfa’), F₃CSO₃ (≡ ‘tfs’); dpex = ‘dpape’ (Ph₂As(CH₂)₂PPh₂), X = CN, SCN, OClO₃) are one-dimensional polymers ?-E′)₁AgX(E-dpex-E′)₂-AgX(E-dpex-E′)₁AgX?, P, As sites scrambled in the latter. AgNO₃:dpam (2:3) is also a one-dimensional polymer, ?AgO·NO·OAg(As-dpam-As)AgO·NO·OAg? (‘dpam’ ≡ Ph₂As(CH₂)₂AsPh₂). AgX:dpae (2:3) (X = I, CN, ClO₄, NO₃) and AgX:dpape (2:3) (X = Br, I, NO₃) are two-dimensional polymers with large 30-membered macrocyclic rings; similar webs are found for dppx ligands in AgOH:dppb (2:3) and AgNCO, Agtfa:dpph (2:3) with 42- and 54-membered rings. Complexes AgX:dpape (1:3) (X = Cl, Br) are defined as mono-nuclear [XAg(Ph₂P(CH₂)₂AsPh₂)₃] arrays, the unidentate ligands predominantly P-bound. Synthetic procedures for the adducts are reported, selected compounds being characterized both in solution (¹H, ³¹P NMR, ESI MS) and in the solid state (IR).     

Transition metal halide salts of 8-methylquinolinium: Synthesis and structures of (8-methylquinolinium)2 MX4·nH2O (M = Cu, Co, Zn; X = Cl, Br; n = 0, 1)

The reactions of metal(II) chlorides and bromides with 8-methylquinoline (8-mequin) in neutral and acidic solutions were investigated. The reaction with ZnCl₂, ZnBr₂, CoCl₂, CoBr₂, CuCl₂ or CuBr₂ with the appropriate HX in water or aqueous ethanol gave complexes of the formula (8-mequin)₂MX₄ (1, M = Cu, X = Cl; 2, M = Cu, X = Br; 3, M = Co, X = Cl; 4, M = Co, X = Br) or (8-mequin)₂ZnX₄·nH₂O (5, X = Cl, n = 0; 6, X = Br, n = 0; 7, X = Cl, n = 1; 8, X = Br, n = 1). Crystals of 1, 2 and 4-8 suitable for single crystal X-ray diffraction were obtained and the structures reported. Compounds 1 and 2 crystallize in the monoclinic space group C2/c, while 4-8 crystallize in the triclinic space group, . Variable temperature magnetic susceptibility data indicate very weak interactions for the copper compounds 1 and 2, while the magnetic behavior of 3 and 4 is dominated by single ion anisotropy, with weaker antiferromagnetic interactions.     

Long-range superexchanged magnetic interaction observed in heterometallic complex: {[Fe(Tpms)(CN)3][Mn(H2O)2(DMF)2]} · DMF

A new tri-cyanometalate building block for heterometallic complexes, [PPh₄]₂[Fe^II(Tpms)(CN)₃] (2) (PPh₄ = tetraphenylphosphonium; Tpms = tris(pyrazolyl) methanesulfonate), has been prepared. Using it as a building block, a one-dimensional chain compound, {[Fe^II(Tpms)(CN)₃][Mn^II(H₂O)₂( DMF)₂]} · DMF (3), has been synthesized and structurally characterized. The magnetic properties of 3 correspond to a ferromagnetic chain with weak long-range superexchanged magnetic interaction between the high-spin manganese(II) ions.     

Investigation of the MSO4 · xH2O (M = Zn, x = 7; M = Cd, x = 8/3)/methyl 2-pyridyl ketone oxime reaction system: A novel Cd(II) coordination polymer versus mononuclear and dinuclear Zn(II) complexes

The reactions of methyl 2-pyridyl ketone oxime, (py)C(Me)NOH, with MSO₄ · xH₂O (M = Zn, x = 7; M = Cd, x = 8/3), in the absence of an external base, have been investigated. The synthetic study has led to the two new complexes [Zn(SO₄){(py)C(Me)NOH}(H₂O)₃] · H₂O (1 · H₂O) and [Zn₂(SO₄)₂{(py)C(Me)NOH}₄] · (py)C(Me)NOH [2 · (py)C(Me)NOH], and the coordination polymer [Cd(SO₄){(py)C(Me)NOH}(H₂O)]_n · [Cd(SO₄){(py)C(Me)NOH}(H₂O)₂]_n (3). In the three complexes the organic ligand chelates through its nitrogen atoms. The sulfate anion in 1 · H₂O is monodentate; the complex molecule is the mer isomer considering the positions of the aqua ligands. The Zn^II centers in 2 · (py)C(Me)NOH are bridged by two syn, anti η¹:η¹:μ₂ ligands; each metal ion has the cis-cis-trans disposition of the coordinated sulfate oxygen, pyridyl nitrogen and oxime nitrogens, respectively. The molecular structure of 3 is unique consisting of two different linear and ladder - type chains. π-π stacking interactions and/or hydrogen bonds lead to the formation of interesting supramolecular architectures in the three complexes. The thermal decomposition of complex 3 has been studied. Characteristic vibrational (IR, Raman) bands are discussed in terms of the nature of bonding and the structures of the three complexes.     

Hydrogen bond supramolecular self-assembly in nickel(II) dithiophosphates, Ni[S2P(OR)2]2, R = sec-Bu, iso-Bu, and their bis(pyrazole) adducts

The reaction between nickel(II) nitrate and potassium phosphorus-1,1-dithiolates (di-sec-butyl and di-iso-butyl) in methanol yields 2:1 complexes which were characterized by FT-IR and NMR spectroscopy. 2:1 pyrazole adducts of both compounds were also obtained.The X-ray diffraction analysis of the compounds reveals square planar, four-coordination geometry for the homoleptic compounds and a six-coordinated distorted octahedral geometry for the adducts. In Ni[S₂P(OBu^s)₂]₂ the molecules are associated through C-H?O hydrogen bonds (2.652 Å), and in Ni[S₂P(OBuⁱ)₂]₂ the molecules are associated through C-H?S hydrogen bonds (2.948 Å). The pyrazole adducts are associated through N-H?O bonds and N-H?S bonds from the pyrazole nitrogen atoms, to form supramolecular assemblies. Thus, Ni[S₂P(OBu^s)₂(Pz)₂]₂ (Pz = pyrazole) forms bi-dimensional layers through N-H?O and N-H?S bonds (2.502 and 2.965 Å, respectively), whereas Ni[S₂P(OBuⁱ)₂(Pz)₂]₂ forms linear chains with N-H?S bonds 2.728 Å. The dithiophosphato groups behave as isobidentate chelating ligands.     

Functionalised dithiocarbamate complexes: Synthesis and molecular structures of bis(2-methoxyethyl)dithiocarbamate complexes [M{S2CN(CH2CH2OMe)2}2] (M = Ni, Cu, Zn) and [Cu{S2CN(CH2CH2OMe)2}2][ClO4]

The bis(2-methoxyethyl)dithiocarbamate complexes [M{S₂CN(CH₂CH₂OMe)₂}₂] (M = Ni, Cu, Zn, Pd) are readily prepared and the three lighter complexes have been crystallographically characterised. Disproportionation of [Cu{S₂CN(CH₂CH₂OMe)₂}₂] upon addition of Cu(ClO₄)₂ · 6H₂O affords the copper(III) complex [Cu{S₂CN(CH₂CH₂OMe)₂}₂][ClO₄] which has also been crystallographically characterised. Unlike other copper(III) dithiocarbamate salts, there are no intermolecular cation-cation or cation-anion interactions.     

Structure of [Ni(dippe)(μ-S)]2 and its reaction products. The nucleophilicity of the Ni2S2 fragment

The dimer [(dippe)Ni(μ-S)]₂ reacts with organic electrophiles to give the alkylated species [(dippe)₂Ni₂(μ-S)(μ-SR)]⁺. Stronger alkylating agents lead to double alkylation and cleavage of the dimer. Protonation similarly occurs with strong acids. The structures of several of these species have been determined.