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Two new isostructural two-dimensional (2D) coordination polymers exhibiting spin crossover (SCO) behavior of formulation [Fe(4,4'-bipy)(2)(NCX)(2)]·4CHCl(3) (4,4'-bipy = 4,4'-bipyridine; X = S [1·4CHCl(3)], Se [2·4CHCl(3)]) have been synthesized and characterized, and both undergo cooperative spin transitions (ST). For 1·4CHCl(3) the ST takes place in two steps with critical temperatures of T(c1)(down) = 143.1 K, T(c2)(down) = 91.2 K, T(c1)(up) = 150.7 K, and T(c2)(up) = 112.2 K. 2·4CHCl(3) displays half ST characterized by T(c)(down) = 161.7 K and T(c)(up) = 168.3 K. The average enthalpy and entropy variations and cooperativity parameters associated with the ST have been estimated to be ΔH(1)(av) = 5.18 kJ mol(-1), ΔS(1)(av) = 35 J K(-1) mol(-1), and Γ(1) = 2.8 kJ mol(-1) and ΔH(2)(av) = 3.55 kJ mol(-1), ΔS(2)(av) = 35 J K(-1) mol(-1), and Γ(2) = 2.6 kJ mol(-1) for 1·4CHCl(3), and ΔH(av) = 6.25 kJ mol(-1), ΔS(av) = 38.1 J K(-1) mol(-1), and Γ = 3.2 kJ mol(-1) for 2·4CHCl(3). At T > [T(c1) (1·4CHCl(3)); T(c) (2·4CHCl(3))], both compounds are in the space group P2/c while at T < [T(c1) (1·4CHCl(3)); T(c) (2·4CHCl(3))] they change to the C2/c space group and display an ordered checkerboard-like arrangement of iron(II) sites where the high- and low-spin states coexist at 50%.

para-Phenylenediamine (ppda) may be ground together with metal chloride salts MCl2 to produce the coordination network compounds [{(ppda)MCl2}n] {M = Zn (2), Cd (4), Cu (6)}. Its dihydrochloride salt [H2ppda]Cl2 can be ground with MCl2 to produce the layered salt structures [H2ppda][MCl4] {M = Zn (1), Cd (3), Cu (5)}, which (when M = Zn or Cd) may then be converted into 2 or 4 respectively by grinding with solid KOH. Alternatively, [H2ppda][MCl4] will react directly with appropriate basic metal compounds (hydroxides and/or carbonates) to give 2 or 4, which can then be converted back to the salts by reaction with gaseous HCl. The interconversion of 5 and 6 is more complicated, with different combinations of starting material giving different products. The crystal structure of 2 has been solved ab initio from the powder-diffraction data, and is shown to consist of zigzag polymeric chains containing alternating ppda and MCl2 units.

Photolysis of THF solutions of 10-vertex [N(PPh3)2][6,6,6-(CO)3-closo-6,1-FeCB8H9] (1) in the presence of PEt3 results in [N(PPh3)2][6-CO-6,6-(PEt3)2-closo-6,1-FeCB8H9] (2), which readily oxidizes in air to form the neutral and paramagnetic, 17-electron Fe(III) species [6-CO-6,6-(PEt3)2-closo-6,1-FeCB8H9] (3). Substitution of one PEt3 ligand by cyanide occurs on addition of [NBun4][CN] and Me3NO to 3 in CH2Cl2, giving [NBun4][6-CO-6-CN-6-PEt3-closo-6,1-FeCB8H9] (4). When [IrCl(CO)(PPh3)2] and Tl[PF6] (1:1) are added to CH2Cl2 solutions of 4, the neutral, paramagnetic complex [6-{(μ-CN)Ir(CO)(PPh3)2}-6-CO-6-PEt3-closo-6,1-FeCB8H9] (5) is obtained. Results of X-ray diffraction studies carried out on 3 and 5 are presented herein.

The d4 halide complexes [MX(CO)(η-RCCR)Tp′] {R = Me, M = W, X = F; R = Ph, M = Mo or W, X = F or Cl; Tp′ = hydrotris(3,5-dimethylpyrazolyl)borate} undergo two-electron oxidation in the presence of a halide source to give the d2 monocations [MX1X2(η-PhCCPh)Tp′]+ (R = Me, M = W, X1 = X2 = F; R = Ph, M = Mo, X1 = X2 = F or Cl; M = W, X1 = X2 = F or Cl; X1 = F, X2 = Cl). Each monocation (R = Ph) shows two reversible one-electron reductions (the second process was not detected for R = Me) corresponding to the stepwise formation of the neutral d3 and monoanionic d4 analogues, [MX1X2(η-PhCCPh)Tp′] and [MX1X2(η-PhCCPh)Tp′]− respectively; the potentials for the two processes can be ‘tuned’ over a range of ca. 1.0 V by varying M and X. Chemical one-electron reduction of [MX2(η-PhCCPh)Tp′]+ gave [MX2(η-PhCCPh)Tp′] (M = Mo or W, X = F or Cl). X-Ray structural studies on the redox pairs [WX2(η-PhCCPh)Tp′]z (X = F and Cl, z = 0 and 1+) show the alkyne to bisect the X–W–X angle in the d2 cations but align more closely with one M–X bond in the neutral d3 molecules, consistent with the anisotropic ESR spectra of the latter; the solution ESR spectrum of [MoF2(η-PhCCPh)Tp′] showed equivalent fluorine atoms, i.e the alkyne oscillates at room temperature. The successful isolation of [MX2(η-PhCCPh)Tp′]+ and [MX2(η-PhCCPh)Tp′] completes a series in which d6 to d2alkyne complexes are linked in a redox family tree by sequential one-electron transfer and substitution reactions. The implications for such trees in the production of new species and the selective synthesis of paramagnetic complexes acting as synthetically useful ‘alkyne radicals’ are discussed.

The photophysical and electrochemical properties of a platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2'-diacetylide (tda), Pt(dbbpy)(tda) [dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine] (1), are compared with two reference compounds, Pt(dbbpy)(C[triple bond]CPh)(2) (2) and Pt(dppp)tda [dppp = 1,3-bis(diphenylphosphino)propane] (3), respectively. The X-ray crystal structure of 1 is reported, which illustrates the nearly perfect square planarity exhibited by this metallacycle. Chromophore 2 possesses low-lying charge-transfer excited states analogous to 1, whereas structure 3 lacks such excited states but features a low-lying platinum-perturbed tda intraligand triplet manifold. In CH(2)Cl(2), 1 exhibits a broad emission centered at 562 nm at ambient temperature, similar to 2, but with a higher photoluminescence quantum yield and longer excited-state lifetime. In both instances, the photoluminescence is consistent with triplet-charge-transfer excited-state parentage. The rigidity imposed by the cyclic diacetylide ligand in 1 leads to a reduction in nonradiative decay, which enhances its room-temperature photophysical properties. By comparison, 3 radiates highly structured tda-localized triplet-state phosphorescence at room temperature. The 77 K emission spectrum of 1 in 4:1 EtOH/MeOH becomes structured and is quantitatively similar to that measured for 3 under the same conditions. Because the 77 K spectra are nearly identical, the emissions are assigned as (3)tda in nature, implying that the charge-transfer states are raised in energy, relative to the (3)tda levels in 1 in the low-temperature glass. Nanosecond transient absorption spectrometry and ultrafast difference spectra were determined for 1-3 in CH(2)Cl(2) and DMF at ambient temperature. In 1 and 2, the major absorption transients are consistent with the one-electron reduced complexes, corroborated by reductive spectroelectrochemical measurements performed at room temperature. As 3 does not possess any charge-transfer character, excitation into the pipi* transitions of the tda ligand generated transient absorptions in the relaxed excited state assigned to the ligand-localized triplet state. In all three cases, the excited-state lifetimes measured by transient absorption are similar to those measured by time-resolved photoluminescence, suggesting that the same excited states giving rise to the photoluminescence are responsible for the absorption transients. ESR spectroscopy of the anions 1- and 2- and reductive spectroelectrochemistry of 1 and 2 revealed a LUMO based largely on the pi* orbital of the dbbpy ligand. Time-dependent density functional theory calculations performed on 1-3 both in vacuum and in a CH(2)Cl(2) continuum revealed the molecular orbitals, energies, dipole moments, and oscillator strengths for the various electronic transitions in these molecules. A DeltaSCF-method-derived shift applied to the calculated transition energies in the solvent continuum yielded good agreement between theory and experiment for each molecule in this study.

The d4 halide complexes [MX(CO)(η-RCCR)Tp′] {X = F, Cl, Br or I; R = Me or Ph; M = Mo or W; Tp′ = hydrotris(3,5-dimethylpyrazolyl)borate} undergo one-electron oxidation to the d3 monocations [MX(CO)(η-RCCR)Tp′]+, isolable for M = W, R = Me. X-Ray structural studies on the redox pairs [WX(CO)(η-MeCCMe)Tp′]z (X = Cl and Br, z = 0 and 1), the ESR spectra of the cations [WX(CO)(η-RCCR)Tp′]+ (X = F, Cl, Br or I; R = Me or Ph), and DFT calculations on [WX(CO)(η-MeCCMe)Tp′]z (X = F, Cl, Br and I; z = 0 and 1) are consistent with electron removal from a HOMO (of the d4 complexes) which is π-antibonding with respect to the W–X bond, π-bonding with respect to the W–C(O) bond, and δ-bonding with respect to the W–Calkyne bonds. The dependence of both oxidation potential and ν(CO) for [MX(CO)(η-RCCR)Tp′] shows an inverse halide order which is consistent with an ionic component to the M–X bond; the small size of fluorine and its closeness to the metal centre leads to the highest energy HOMO and the lowest oxidation potential. In the cations [MX(CO)(η-RCCR)Tp′]+ electronegativity effects become more important, leading to a conventional order for Cl, Br and I. However, high M–F π-donation is still facilitated by the short M–F distance.

Reduction of [M(CO)2(η-RCCR′)Tp′]X {Tp′ = hydrotris(3,5-dimethylpyrazolyl)borate, M = Mo, X = [PF6]−, R = R′ = Ph, C6H4OMe-4 or Me; R = Ph, R′ = H; M = W, X = [BF4]−, R = R′ = Ph or Me; R = Ph, R′ = H} with [Co(η-C5H5)2] gave paramagnetic [M(CO)2(η-RCCR′)Tp′], characterised by IR and ESR spectroscopy. X-Ray structural studies on the redox pair [Mo(CO)2(η-PhCCPh)Tp′] and [Mo(CO)2(η-PhCCPh)Tp′][PF6] showed that oxidation is accompanied by a lengthening of the CC bond and shortening of the Mo–Calkyne bonds, consistent with removal of an electron from an orbital antibonding with respect to the Mo–alkyne bond, and with conversion of the alkyne from a three- to a four-electron donor. Reduction of [Mo(CO)(NCMe)(η-MeCCMe)Tp′][PF6] with [Co(η-C5H5)2] in CH2Cl2 gives [MoCl(CO)(η-MeCCMe)Tp′], via nitrile substitution in [Mo(CO)(NCMe)(η-MeCCMe)Tp′], whereas a similar reaction with [M(CO){P(OCH2)3CEt}(η-MeCCMe)Tp′]+ (M = Mo or W) gives the phosphite-containing radicals [M(CO){P(OCH2)3CEt}(η-MeCCMe)Tp′]. ESR spectroscopic studies and DFT calculations on [M(CO)L(η-MeCCMe)Tp′] {M = Mo or W, L = CO or P(OCH2)3CEt} show the SOMO of the neutral d5 species (the LUMO of the d4 cations) to be largely dyz in character although much more delocalised in the W complexes. Non-coincidence effects between the g and metal hyperfine matrices in the Mo spectra indicate hybridisation of the metal d-orbitals in the SOMO, consistent with a rotation of the coordinated alkyne about the M–C2 axis.

A series of new crystal structures of salts containing [PtCl4]2- or [PdCl4]2- with organic cations containing pyridinium and piperidinium groups have been prepared: [4,4‘-H2bpe][PtCl4] (2), [4,4‘-H2bpethane][PtCl4] (3), [HNC5H4CO2H-4]2[PtCl4] (6a), [HNC5H4CONH2-3]2[PtCl4] (8), [H2NC5H9CO2H-4]2[PtCl4] (9), [H2NC5H9CO2H-3]2[PtCl4] (10), [H2NC5H9CO2H-4]Cl (11), [HNC5H4CO2H-4]Cl (12), [4,4‘-H2bpe][PdCl4] (13), [4,4‘-H2bipip][PdCl4] (14a, 14b, 14c), [piperazinium][PdCl4]·2H2O (15), and [HNC5H4CO2H-4]2[PdCl4]·2H2O (16). The molecular recognition motifs formed in these and related structures are identified and discussed. The robustness of these supramolecular synthons and their applicability in synthetic crystallography are analyzed. Cases of structural mimicry of a molecule by a supramolecular dication (1 and 6a), isomorphism (2 and 3; 4 and 14a; 6 and 16), polymorphism (14a−c), and “latent” polymorphism (2 and 13) are identified.

The radical cation [1,2-B2{1,2-(MeN)2C6H4}2]˙(+) has been synthesised and its structure and bonding have been probed using a combination of X-ray crystallography, EPR spectroscopy and DFT calculations which show that it represents a new type of radical centred primarily on two N-heterocyclic units joined by a B2 linker but with only a minor contribution from boron-based orbitals.

Cationic nitrile complexes and neutral halide and cyanide complexes, with the general formula [MnL1L2(NO)(eta-C5H4Me)]z, undergo one-electron oxidation at a Pt electrode in CH2Cl2. Linear plots of oxidation potential, Eo', vs. nu(NO) or the Lever parameters, EL, for L1 and L2, allow Eo' to be estimated for unknown analogues. In the presence of TlPF6, [MnIL'(NO)(eta-C5H4Me)] reacts with [Mn(CN)L(NO)(eta-C5H4Me)] to give [(eta5-C5H4Me)(ON)LMn(mu-CN)MnL'(NO)(eta5-C5H4Me)][PF6] which undergoes two reversible one-electron oxidations; DeltaE, the difference between the potentials for the two processes, differs significantly for stable cyanide-bridged linkage isomers. Novel pentametallic complexes such as [Mn[(mu-NC)Mn(CNBut)(NO)(eta5-C5H4Me)]4(OEt2)][PF6]2 and [Mn[(mu-NC)Mn(CNXyl)(NO)(eta5-C5H4Me)]4(NO3-O,O')][PF6], containing a trigonal bipyramidal and a distorted octahedral Mn(II) centre, respectively, result either from slow decomposition of the binuclear cyanide-bridged species or from the reaction of anhydrous MnI2 with four equivalents of [Mn(CN)L(NO)(eta5-C5H4Me)] in the presence of TlPF6.

The complex [Rh(CO)2{HC(pz′)3}][PF6], 1+[PF6]− {HC(pz′)3 = tris(3,5-dimethylpyrazolyl)methane}, prepared by reacting [{Rh(CO)2(μ-Cl)}2] with HC(pz′)3 in the presence of Tl[PF6], has a distorted square pyramidal structure with a κ3-HC(pz′)3 ligand. Carbonyl substitution with Lewis bases gives [Rh(CO)L{HC(pz′)3}][PF6] {L = PPh3, 2+[PF6]−; L = AsPh3, 3+[PF6]−; L = P(o-tolyl)3, 4+[PF6]−}, which have square planar κ2 structures, confirmed by X-ray crystallography for 2+[PF6]−. The cations 2+ and 3+ have the third pyrazolyl ring orientated pseudo-parallel to the square planar metal whereas 4+ more likely has the third ring orientated exo to that plane. One-electron oxidation of 2+ and 3+ gives the Rh(II) dications [Rh(CO)(PPh3){HC(pz′)3}]2+, 22+, and [Rh(CO)(AsPh3){HC(pz′)3}]2+, 32+, characterised by ESR spectroscopy. Complex 1+[PF6]−reacts with PhCCPh to give [Rh(CO)(η2-PhCCPh){HC(pz′)3}][PF6], 5+[PF6]−, in which the two-electron donor alkyne occupies an equatorial position in a trigonal bipyramidal κ3 structure. With MeCCR (R = Me or Et), 1+[PF6]− gives the κ2 square planar complexes [Rh{η4-C4Me2R2C(O)}{HC(pz′)3}][PF6] (R = Me, 6+[PF6]−; R = Et, 7+[PF6]−) in which the cyclopentadienone ligands are coordinated via two Rh–monoalkene bonds; the structurally characterised form of 7+ has the two alkyne units linked head-to-head with the CEt termini bound to the ketonic CO group. With HCCPh or HCCH, 1+ gives the octahedral, κ3 rhodium(III) metallacyclopentadienes [Rh(CO)(η1:η1′-CHCRCHCR){HC(pz′)3}][PF6] (R = Ph, 8+[PF6]−; R = H, 9+[PF6]−) with the two alkynes linked head-to-tail in 8+. The reaction of 1+ with HCCH also gives the cycloheptatrienone (tropone) derivative [Rh{η4-C6H6C(O)}{HC(pz′)3}][PF6], 10+[PF6]−, with a κ3 ligand and the cycloheptatrienone ligand bound to the metal via two Rh–C σ-bonds and one Rh–monoalkene interaction.

X-Ray structural studies on the redox pair [Cr(CO)2(η-PhCCPh)(η-C6Me5H)]z (z = 0 and 1) show that one-electron oxidation of the neutral complex results in a shortening of the Cr–Calkyne bonds and a lengthening of the Cr–C(O) bonds, consistent with depopulation of a HOMO antibonding with respect to the metal–alkyne interaction. Oxidation leads to an increase in the substitutional lability of the Cr–CO bonds so that [Cr(CO)2(η-RCCR)(η-C6Me6)]+ (R = Ph or C6H4OMe-p) reacts with Lewis bases to give [Cr(CO)L(η-RCCR)(η-C6Me6)]+ {L = CNXyl, P(OMe)3 and P(OCH2)3CEt}, X-ray studies on which show a rotation of the alkyne to align with the remaining Cr–CO bond. ESR spectroscopic studies on [Cr(CO)L(η-RCCR)(η-C6Me6)]+ show delocalisation of the unpaired electron onto the alkyne ligand, consistent with its description as a three-electron donor. The cations [Cr(CO)L(η-RCCR)(η-C6Me6)]+ undergo both one-electron reduction and oxidation, and chemical oxidation of [Cr(CO){P(OCH2)3CEt}(η-p-MeOC6H4CCC6H4OMe-p)(η-C6Me6)]+ with AgPF6 gives the dication [Cr(CO){P(OCH2)3CEt}(η-p-MeOC6H4CCC6H4OMe-p)(η-C6Me6)]2+. Thus the two-electron alkyne of [Cr(CO)2(η-RCCR)(η-C6Me6)] is converted into the four-electron alkyne of [Cr(CO)L(η-RCCR)(η-C6Me6)]2+ by an ECE (E = electrochemical, C = chemical) process in which all of the intermediates have been fully characterised.

Reaction of (4,4′–bis–tert–butyl–2,2′–dipyridyl) platinum bis–alkynyl [(tBu2bipy)Pt(CCR)2] (R=C6H4Me 1a, SiMe3 1b) with Group 11 metal thiocyanate salts (M=Cu, Ag) affords 1:1 mixed-metal complexes [(tBu2bipy)Pt(CCR)2M(SCN)] (M=Cu, R=C6H4Me 2a, SiMe3 2b; M=Ag, R=C6H4Me 3a, SiMe3 3b). X-ray analyses of the complexes 2a and 3b show that the group 11 metal is bonded in an η2 fashion to two carbon–carbon triple bonds so that the co-ordination geometry is trigonal planar. The Pt atom geometry in both complexes is square planar. An electrochemical study of the copper complexes 2a and 2b reveals one fully reversible one electron reduction that is consistent with the first reduction of the co-ordinated bipyridyl ligand. There is also an irreversible one electron oxidation that corresponds to the CuI to CuII transition.

Reaction of the dicarbon-containing complex Ru5(µ5-C2)(µ-SMe)2(µ-PPh2)2(CO)11 1 with diphenylethyne gave as major products Ru5(µ5-CCCPhCPh)(µ-SMe)2(µ-PPh2)2(CO)10 2 and Ru5(µ5-CCPhCPh)(µ3-SMe)(µ-SMe)(µ-PPh2)2(CO)9 3. The only product from the reaction between 1 and but-2-yne was identified as Ru5(µ5-CCCMeCMe)(µ3-SMe)(µ-SMe)(µ-PPh2)2(CO)9 4. Pyrolysis of 2 gave 3. Carbonylation of 3 yields the complex Ru5(CCCPhCPh)(µ-SMe)2(µ-PPh2)2(CO)11 5, further heating of which regenerated a mixture of 2 and 3. The structures of 2 and 3 were determined from single crystal X-ray studies. The Ru5 clusters in both complexes adopt the open-envelope conformation, the Ru4 rhombus being planar in 2, but bent across the Ru(3)· · ·Ru(5) diagonal by 39.6° in 3. The organic ligand is formed by coupling of the C2 group in 1 with the alkyne and is attached by three of the four carbons in 2 and by all four in 3, atom C(1) being strongly attached to the Ru4 rhombus. In 3, atoms C(1,2,3,4) have an η4 interaction with Ru(4).

A highly crystalline powder sample of NaP with a Si/Al ratio of 1.0 was synthesized and ion-exchanged against Ca, yielding a monophasic sample of a CaP zeolite, Ca 4 Al 8 Si 8 O 32 ·18.9H 2 O. The crystal structure of CaP was determined from X-ray (synchrotron) data in the monoclinic crystal system, space group P2 1 / c ( a =10.02415 A, b =10.6130 A, c =9.8333 A, β =92.292°, R p =0.0677, w R P =0.0648). It is found to be very similar to the structure of the natural occuring zeolite, gismondine. The close structural relationship between the synthetic group of P zeolites and natural zeolites with gismondine framework (gismondine, garronite, amicite and gobbinsite) is discussed.

The reaction between [Ru 5 (µ 5 -C 2 )(µ-SMe) 2 ( µ-PPh 2 ) 2 (CO) 11 ] 1 and CO (30 atm) yielded [Ru 5 (µ 4 -C 2 )(µ-SMe) 2 ( µ-PPh 2 ) 2 (CO) 13 ] 2 and [Ru 4 (µ 4 -C 2 )(µ-SMe) 2 ( µ-PPh 2 ) 2 (CO) 10 ] 3, both characterised by single-crystal X-ray crystallography. In 2, addition of 2CO results in the net cleavage of two Ru–Ru bonds and expansion of the resulting Ru 3 cluster. The C 2 ligand bridges one edge of the Ru 3 core and the isolated Ru–Ru bonded fragment in a µ,µ-η 1 ,η 2 mode, albeit with asymmetric Ru–C 2 π interactions. In 3, one Ru atom has been excised from the cluster present in 1. One Ru–Ru bond is bridged by two SMe groups as a result of migration of one of these. Although the C 2 ligand bridges all four metal atoms, only two Ru – Ru bonds are present, with the non-bonded Ru · · · Ru vector being bridged by PPh 2 . Extended-Huckel molecular orbital calculations have been used to rationalise the observed structures.

The reaction between [Ru 5 (µ 5 -C 2 PPh 2 )(µ- PPh 2 )(CO) 13 ] and Me 2 S 2 yielded [Ru 5 (µ 5 -C 2 PPh 2 )(µ- SMe) 2 (µ-PPh 2 )(CO) 13 ] as the major product. When heated the latter yielded the dicarbon complexes [Ru 5 (µ 5 -C 2 )(µ-SMe) 2 ( µ-PPh 2 ) 2 (CO) 12 ] and [Ru 5 (µ 5 -C 2 )(µ-SMe) 2 ( µ-PPh 2 ) 2 (CO) 11 ]. In large-scale preparations of the latter four minor products were isolated: two isomers of [Ru 5 (µ 5 -C 2 PPh 2 )(µ- SMe) 2 (µ-PPh 2 )(CO) 12 ], the tetranuclear complex [Ru 4 (µ 4 -C 2 PPh 2 )(µ- SMe) 2 (µ-PPh 2 )(CO) 10 ] and [Ru 5 (µ 5 -C 2 )(µ-SMe) 4 ( µ-PPh 2 ) 2 (CO) 10 ]. The latter is also formed by direct reaction of [Ru 5 (µ 5 -C 2 )(µ-SMe) 2 ( µ-PPh 2 ) 2 (CO) 11 ] with Me 2 S 2 . All new complexes have been fully characterised by single-crystal X-ray studies. In the three Ru 5 (C 2 PPh 2 ) complexes the C 2 PPh 2 ligand acts as a seven-electron donor, whereas in the Ru 4 complex it donates only five electrons to the cluster. In the C 2 complexes, the different C–C separations [between 1.26(2) and 1.305(5) A] suggest a variable degree of interaction with the metal core (electron donation and back-bonding), the ligand formally donating either six or four electrons to the cluster. This is borne out by the Ru–Ru separations, average values of which range between 2.791 and 2.916 A. The conversion of [Ru 5 (µ 5 -C 2 PPh 2 )(µ- PPh 2 )(CO) 13 ] into [Ru 5 (µ 5 -C 2 )(µ-SMe) 2 ( µ-PPh 2 ) 2 (CO) 11 ] involves sequential formation of several of these complexes, which reactions are discussed.

Reaction of Ru5(μ5-C2PPh2)(μ-PPh2)(CO)13 (I) with 5-chloro-4-chloromethyl-2,4-dimethylpent-1-ene in refluxing CHCl3 affords Ru5(μ5-C2)(μ-PPh2)2(μ-Cl)2(CO)11 (3) and Ru5(μ-H){μ5-CC(PPh2)}(μ-Cl)(μ-PPh2(CO) (4). The crystal structures of 3 and 4 were determined by X-ray crstallography. Complex 3 is the second example of a cluster containing a C2 ligand sitting on top of a partially disordered puckered pentagonal Ru5 cluster, with one carbon strongly bonded (σ) to one Ru atom (RuC, 1.937 (9) A) with the C2 moiety interacting in π fashion with the other four metal atoms. Complex 4 retains the C2PPh2 ligand of the precursor, sitting on an “open-envelope” Ru5 cluster; one carbon is strongly bonded to four Ru atoms of a pseudosquare Ru4 array.

Reactions of [Co2(CO)8] with [{Mn(CO)11}2(µ-bdpp)][Mn Ru3, Os3, Re3(µ-H)3 or Ru4(µ-H)4; bdpp PPh2C2C2PPh2] afforded [{Mn(CO)11}2{µ-PPh2[C2Co2(CO)6]C2 PPh2}][Mn Ru31, Os32, Re3(µ-H)33 or Ru4(µ-H)44] in which the Co2(CO)6 moiety bonds to one of the CC triple bonds of the bridging bdpp ligand. Pyrolysis of 1 yielded [{Ru3(CO)11}{µ-PPh2[C2Co2(CO)6]C2}{Ru2(µ-PPh2)(CO)6}]5, which is formed by concomitant addition of a P–C(sp) bond to one Ru3 cluster and elimination of a Ru(CO)4 fragment. In [{Os3(CO)11}(µ-PPh2C2C2){Co2Os3(µ-PPh2)(CO)13}]8, obtained by heating 2, the Co2Os3 cluster consists of three edge-sharing triangles; the C2 fragment interacts with all five metal atoms. Reaction of the mixed-metal complex [{Os3(CO)11}(µ-bdpp){Re3(µ-H)3(CO)11}]10 with [Co2(CO)8] yielded a 1:1 isomeric mixture of [{Os3(CO)11}{µ-PPh2[C2Co2(CO)6]C2PPh2}{Re3(µ-H)3(CO)11}]11a and [{Re3(µ-H)3(CO)11}{µ-PPh2[C2Co2(CO)6]C2PPh2}{Os3(CO)11}]11b. Pyrolysis of 11a afforded [Co2Os3Re{µ6-C2CCH(PPh 2)}(µ-PPh2)(µ-CO)2(CO)14]12 in which all three transition metals form a cluster about the C4P fragment of the original bdpp ligand, which has also added one H atom to the carbon adjacent to the PPh2 group. The second PPh2 group bridges an Os–Os bond. Molecular structures of 5, 8 and 12 were determined by X-ray crystallography.

Several complexes of the acetylenic ditertiary phosphine, Ph2PC2C2PPh2, containing Mo, W, Fe, Ru or Au have been prepared; one CC triple bond in the Mo, W or Fe derivatives has been co-ordinated to Co2(CO)6 or Pt(PPh3)2 groups. Crystal structure determinations of [{Fe(CO)4}2(µ-PPh2C2C2PPh2)]3 and [Co2{µ-η2-[(OC)5W(PPh2)]CC [C2(PPh2)W(CO)5]}(CO)6]7 show that the P-bonded M(CO)n groups take up transoid positions; in 3, the PCCCCP chain, which is situated about a centre of inversion, is nearly linear [P–C–C, 173.2(5); C–C–C 179.7(6) for molecule a and 174.7(5) and 177.6(6)°, respectively, for molecule b] with CC distances of 1.192(7)A[1.201(6)A, molecule b]. In 7, co-ordination of the Co2(CO)6 group to one CC bond lengthens that bond by 0.13 A, compared with the unco-ordinated CC bond, and induces bend-back of the substituents of 141–143(1)°(PPh2) and 145–146(1)°(C2PPh2). Crystals of 3 are triclinic, space group P, a= 11.261(1), b= 12.456(2), c= 13.061(2)A, α= 79.23(2), β= 75.73(1), γ= 78.75(2)°, Z= 2; 2870 data were refined to R= 0.042, R′= 0.046. Crystals of 7 are triclinic, space group P, a= 17.940(4), b= 19.695(4), c= 16.449(2)A, α= 111.92(1), β= 108.83(1), γ= 100.29(2)°, Z= 4; 5942 data were refined to R= 0.055, R′= 0.056.

Monometallic complexes of the tetrakis(pyrazolyl)borate ligand [ML(2){B(pz)(4)}] {M = Rh, Ir; L(2) = eta-cod, eta-nbd, (CO)(2), (CO)(PPh(3))} have two free pyrazolyl rings which can be coordinated to a second ML(2) unit to give the dimeric compounds [L(2)M{mu-B(pz)(4)}ML(2)](+), and to a metal halide to give heterobimetallic species [L(2)M{mu-B(pz)(4)}M'Cl(2)]. (1)H NMR spectroscopy shows that [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-cod)](+) 1(+), [(eta-nbd)Rh{mu-B(pz)(4)}Rh(eta-nbd)](+) 2(+), [(eta-cod)Ir{mu-B(pz)(4)}Ir(eta-cod)](+) 3(+) and [(CO)(2)Rh{mu-B(pz)(4)}Rh(CO)(2)](+) 4(+) are fluxional at room temperature. Cooling a solution of [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-cod)](+) 1(+) to -90 degrees C slows the fluxional process, which involves inversion of the two B-(N-N)(2)-M six-membered rings. Attempts to synthesise the asymmetric complexes [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-nbd)](+) 7(+), [(eta-cod)Rh{mu-B(pz)(4)}Ir(eta-cod)](+) 8(+) and [(eta-cod)Rh{mu-B(pz)(4)}Rh(CO)(2)](+) 9(+) produced a mixture of [L(2)M{mu-B(pz)(4)}ML(2)](+), [L'(2)M'{mu-B(pz)(4)}M'L'(2)](+) and the desired species. The heterobimetallic complexes [L(2)Rh{mu-B(pz)(4)}M'Cl(2)] (M' = Co, L(2) = eta-cod 10; M' = Co, L(2) = eta-nbd 11; M' = Co, L = CO 12; M' = Co, L(2) = (CO)(PPh(3)) 13; M' = Zn, L(2) = eta-cod 14; M' = Zn, L(2) = eta-nbd 15; M' = Pd, L(2) = eta-cod 16) possess square planar Rh(I) linked to square planar Pd(II) or tetrahedral Zn(II) and Co(II) centres. The paramagnetic Co(II) complexes give (1)H NMR spectra with signals shifted over a range of 75 ppm. The UV-Vis spectra of 10-13 show four bands, one MLCT at Rh and three d-d transitions arising from the splitting of the (4)T(1)(P) excited state due to approximate C(2v) symmetry at Co.

Reaction of the labile triosmium cluster [Os3(CO)10(NCMe)2] with the thienyl substituted diyne [(C4H3S)C2C2(C4H3S)] affords [Os3(CO)10{μ3-η2-(C4H3S)C2C2(C4H3S)}] 1 and the novel co-linear cluster [Os3(CO)11{μ3-η4-(C4H3S)C2C2(C4H3S)}] 2 in reasonable yield; the X-ray structure of 2 shows that the diyne is coordinated to an ‘open’ triosmium unit as a 1,2,3-triene-1,4-diyl unit with essentially equal CC bond distances.

The compounds [Pt(MesBIAN)(C[triple bond]CR)2] (R = C6H4-CN-p, 1; SiMe3, 2; C6H4-CF3-p, 3; C6H5, 4; C6H4-CH3-p 5) {MesBIAN = bis(mesitylimino)acenaphthene} have been synthesized; the X-ray crystal structure determinations of 4 and 5 and the starting material [Pt(MesBIAN)Cl2] are reported. Chemical oxidation of 4 with diiodine leads to generation of an intermediate platinum(IV) bis(acetylide) diiodide complex, which then couples and reductively eliminates the acetylide ligands as a diyne, leading to the generation of [Pt(MesBIAN)I2] 6. Compound 2 readily forms an adduct 2a with copper(I) chloride, in which the copper atom is bonded to the two acetylide triple bonds. 1-5 each undergo an irreversible oxidation, and a reversible one-electron reduction to generate a stable anion. ESR studies of 1(-)-5(-) show that the unpaired electron is localized mainly on the pi* orbital of the coordinated MesBIAN ligand, with about 10% platinum contribution to the singly occupied molecular orbital (SOMO). The compounds show a strong absorption at around 500 nm in the UV/visible spectrum, which is assigned to a "mixed metal-ligand to ligand charge transfer" (MMLL'CT) transition; this assignment is supported by time-dependent density-functional theory (TD-DFT) calculations on 5. 1-5 emit in the near-infrared region from a (3)MMLL'CT excited state, with lifetimes ranging from 8 to 36 ns. Picosecond and nanosecond time-resolved infrared (TRIR) spectroscopy has been used to probe directly the nature and dynamics of the excited state of 5. The TRIR data show a decrease of the energy of the C[triple bond]C vibration upon excitation, by about 90 cm(-1) in comparison to the ground state, and formation of a new, very intense, and very broad band at 1820 cm(-1). We propose that the excited-state structure contains some contribution from a pseudo-cumulenic form of the platinum-acetylide moiety, which is supported by TD-DFT calculations. Picosecond TRIR allowed determination of the rate of vibrational relaxation (14 ps) of the vibrationally "hot" electronic excited state of 5 formed upon initial laser excitation.

The structures adopted by a range of poly(pyrazolyl)borate complexes [ML2Tp(x)] [M = Rh, Ir; L2 = diene; Tp(x) = Bp' {dihydrobis(3,5-dimethylpyrazolyl)borate}, Tp' {hydrotris(3,5-dimethylpyrazolyl)borate}, Tp {hydrotris(pyrazolyl)borate}, B(pz)4 {tetrakis(pyrazolyl)borate}] have been investigated. Low steric hindrance between ligands in [Rh(eta-nbd)Tp] (nbd = norbornadiene), [Rh(eta-cod)Tp] (cod = cycloocta-1,5-diene) and [Rh(eta-nbd)Tp'] results in K3 coordination of the pyrazolylborate but [M(eta-cod)Tp'] (M = Rh, Ir) are kappa2 coordinated with the free pyrazolyl ring positioned above and approximately parallel to the square plane about the metal. All but the most sterically hindered Tp(x) complexes undergo fast exchange of the coordinated and uncoordinated pyrazolyl rings on the NMR spectroscopic timescale. For [Rh(eta-cod){B(pz)4}], [Rh(eta-dmbd)Tp'] (dmbd = 2,3-dimethylbuta-1,3-diene) and [Rh(eta-cod)Tp(Ph)] {Tp(Ph) = hydrotris(3-phenylpyrazolyl)borate} the fluxional process is slowed at low temperatures so that inequivalent pyrazolyl rings are observed. The bonding modes of the Tp' ligand (but not of other pyrazolylborate ligands) can be determined by 11B NMR and IR spectroscopy. The 11B chemical shifts (for a series of Tp' complexes) show the general pattern, kappa3-7.5 ppmkappa2 and the nu(BH) stretch kappa32500 cm(-1)kappa2. The electrochemical behaviour of the pyrazolylborate complexes is related to the degree of structural change which occurs on electron transfer. One-electron oxidation of complexes with Tp', Tp and B(pz)4 ligands is generally reversible although that of [Ir(etacod)Tp] is only reversible at higher scan rates and that of [Ir(eta-cod){B(pz)4}] is irreversible. Of the complexes with the more sterically hindered Tp(Ph) ligand, only [Rh(eta-nbd)Tp(Ph)] shows any degree of reversible oxidation. The ESR spectra of a range of Rh(II) complexes show coupling to both 14N and 103Rh nuclei in most cases but what appears to be coupling to rhodium and one hydrogen atom, possibly a hydride ligand, for the oxidation product of [Rh(eta-nbd)Tp(Ph)].

An optimized procedure for the selective dimetalation of [V(eta (6)-C 6H 6) 2] by BuLi/tmeda allowed for the isolation and characterization of [V(eta (6)-C 6H 5Li) 2].tmeda. X-ray diffraction of its thf solvate [V(eta (6)-C 6H 5Li) 2].(thf) 7 revealed an unsymmetrical, dimeric composition in the solid state, in which both subunits are connected by three bridging lithium atoms. Treatment with several element dihalides facilitated the isolation of [ n]vanadoarenophanes ( n = 1, 2) with boron and silicon in the bridging positions. In agreement with the number and covalent radii of the bridging elements, these derivatives exhibit molecular ring strain to a greater or lesser extent. The B-B bond of the [2]bora species [V(eta (6)-C 6H 5) 2B 2(NMe 2) 2] was readily cleaved by [Pt(PEt 3) 3] to afford the corresponding oxidative addition product. Subsequently, [V(eta (6)-C 6H 5) 2B 2(NMe 2) 2] was employed as a diborane(4) precursor in the diboration of 2-butyne under stoichiometric, homogeneous, and heterogeneous catalysis conditions. This transformation is facilitated by the reduction of molecular ring strain, which was confirmed by a decrease of the tilt angle alpha observed in the corresponding solid-state structures. EPR spectroscopy was used to probe the electronic structure of strained [ n]vanadoarenophanes and revealed an obvious correlation between the degree of molecular distortion and the observed hyperfine coupling constant a iso. State-of-the-art DFT calculations were able to reproduce the measured isotropic vanadium hyperfine couplings and the coupling anisotropies. The calculations confirmed the decrease of the absolute isotropic hyperfine couplings with increasing tilt angle. Closer analysis showed that this is mainly due to increased positive contributions to the spin density at the vanadium nucleus from the spin polarization of doubly occupied valence orbitals of vanadium-ligand sigma-antibonding character. The latter are destabilized and thus made more polarizable in the bent structures.

The coordination chemistry of the tetradentate pyridyl-thiazole (py-tz) N-donor ligand 6,6'-bis(4-phenylthiazol-2-yl)-2,2'-bipyridine (L1) has been investigated. Reaction of L1 with equimolar copper(II) ions results in the formation of the single-stranded mononuclear complex [Cu(L1)(ClO4)2] (1), whereas reaction with copper(I) ions results in the double-stranded dinuclear helicate [Cu2(L1)2][PF6]2 (2). Both complexes were characterized by X-ray crystallography, UV-vis spectroscopy, and electrospray ionization mass spectroscopy (as well as 1H NMR spectroscopy for diamagnetic 2). Complex 2 is redox-active and, upon one-electron oxidation, forms the stable tricationic mixed-valence helicate [Cu2(L1)2]3+ (3). This species can also be prepared in situ by combining [Cu(MeCN)4][BF4], [Cu(H2O)6][BF4]2, and L1 in a 1:1:2 ratio in nitromethane. X-ray crystallographic analysis of 3 provides structural evidence for the presence of an internuclear Cu-Cu bond, with an even distribution of spin density across the two Cu centers. Room-temperature UV-vis spectroscopy is consistent with this finding; however, frozen-glass EPR spectroscopic investigations suggest solvatochromic behavior at 110 K, with the [Cu2]3+ core varying from localized to delocalized depending on the solvent polarity.

The crystal structure of di-μ(3)-chlorido-tetra-μ(2)-chlorido-dichloridoocta-(imidazole-κN)tetra-manganese(II) ethanol 1.234 solvate, [Mn(4)Cl(8)(C(3)H(4)N(2))(8)]·1.234C(2)H(5)O or [Mn(4)Cl(8)(Him)(8)]·1.234EtOH, where Him is imidazole (C(3)H(4)N(2)), is based upon two Mn(4)Cl(4) cubes which share one face, and which each lack one manganese vertex, giving a Mn(4)Cl(6) unit. This contains two different octa-hedral coordination environments for the Mn atoms. Mn1 is coordinated by four bridging chlorido ligands and two imidazole N atoms, whereas Mn2 is coordinated by three bridging and one terminal Cl and two imidazole N atoms. The remaining two Mn centres are generated by inversion symmetry. A partial occupancy solvent mol-ecule (ethanol) is present. The crystal structure displays several N-H⋯Cl and N-H⋯O hydrogen bonds.

The asymmetric unit of the title compound, (C4H5N2O)2[Cu2Cl6(C4H4N2O)2]·2H2O, consists of one cation, one half of a centrosymmetric dianion and one water molecule. The centrosymmetric dianion formed by dimerization in the crystal structure has neutral pyrimidin-2-one ligands coordinated to each copper(II) centre through Cu—N bonds. The Cu atoms each have a distorted trigonal bipyramidal geometry, with the N atom of the pyrimidin-2-one ligand in an axial position, and dimerize by sharing two equatorial Cl atoms. N—H...Cl, O—H...Cl and N—H...O hydrogen bonds connect the anions, cations and water molecules, forming a three-dimensional network.

Kara, Hülya (Balikesir Author), A series of crystalline salts based on the complex dianion [Fe(dto)(2)(NO)](2-) (dto = 1,2-dithiooxalate) with hydrogen-bond donor cations have been synthesised. The preparation and structural characterisation of the new crystalline phases [4,4'-H(2)bipy][Fe(dto)(2)(NO)]center dot H2O (1), [3,3'-H(2)bipy][Fe (dto)(2)(NO)] (2) and [H(2)Me(4)bipyz][Fe(dto)(2)(NO)]center dot 2H(2)O (3) (Me(4)bipyz = 3,3',5,5'-tetramethyl-4,4'-bipyrazole) are reported, and show that a charge-assisted NH center dot center dot center dot dto synthon is formed in each of compounds 1-3. In compound 1 the anion forms a dimer in the solid-state, and variable temperature magnetic susceptibility measurements reveal a weak antiferromagnetic interaction with a best fit superexchange parameter J = -3.18 (2) cm(-1), where H = -2JS(1)S(2)., TUBITAK TBAG - 108T431 Royal Society EPSRC University of Bristol

A number of different compounds have been synthesised by reaction of solutions containing Fe(NCE)2 (E = S, Se) with solutions containing 3,3′-bipyridine. When the solvent used is methanol, the products are the monomeric compounds trans-{Fe(NCS)2(3,3′-bipy)2(MeOH)2} 1 or trans-{Fe(NCSe)2(3,3′-bipy)2(MeOH)2} 2, but when acetonitrile is used the layered coordination network {Fe(NCS)2(3,3′-bipy)2} 3 or doubly interpenetrated coordination network {Fe(NCSe)2(3,3′-bipy)2} 4 is formed instead. Using methanol to dissolve the Fe(NCE)2 and CHX3 (X = Cl, Br) to dissolve the 3,3′-bipyridine yields solvated coordination networks of stoichiometry {Fe(NCE)2(3,3′-bipy)2}·2CHX3. The crystal structures of all of these compounds except 4 are presented.

Variable temperature NMR and EPR spectroscopic studies provide rates and activation parameters for alkyne rotation and oscillation, respectively, in the fluxional redox pair [Mo{P(OMe)3}2(MeCCMe)Cp][BF4] (diamagnetic) and [Mo{P(OMe)3}2(MeCCMe)Cp] (paramagnetic).

In the title compound (C(17)H(17)N(2))(2)[Fe(2)Cl(6)O], obtained from the solid-state reaction of FeCl(2) and N,N'-dibenzyl-imidazolium chloride, the complex anion has approximate D(3d) symmetry with crystallographically imposed inversion symmetry coincident with the bridging μ-O atom. The stereochemistry about each FeCl(3)O centre is distorted tetra-hedral [Fe-Cl = 2.2176 (5)-2.2427 (5) Å and Fe-O = 1.7545 (2) Å]. The Cl atoms are involved in weak anion-cation C-H⋯Cl inter-actions, giving a network structure.

The crystal structures of eight solvates of {Fe(4,4′-bipyridine)2(NCS)2}n have been determined. All of them contain a layered iron–bipyridine–thiocyanate framework formed from approximately square infinite two-dimensional (4,4) iron–bipyridine grids, with the solvent molecules hosted between adjacent layers. All the structures contain the iron(II) centres in the high-spin electronic configuration, and magnetic susceptibility measurements on the toluene and nitrobenzene solvates do not reveal any spin-crossover behaviour.

[{(4,4′-bipy)ZnCl2}n] (4) is known in three different polymorphs, in the space groups C2/c (4a), Pnma (4b) and Pban (4c). Solution synthesis produces a mixture of 4a and 4b, but solid-state synthesis, either by grinding together 4,4′-bipy and ZnCl2 or by heating [4,4′-H2bipy][ZnCl4] 3 to thermally eliminate HCl, generates only the 4b form, demonstrating that solid-state synthesis can exert control over polymorph formation; other solid-state preparations of 4 such as reaction of basic zinc carbonate with [4,4′-H2bipy]Cl2 or reaction of [4,4′-H2bipy][ZnCl4] 3 with KOH also increase the amount of 4b generated relative to the solution synthesis. It is also possible to form the mixed-metal phases [{(4,4′-bipy)Co1−xZnxCl2}n] 4x as effectively homogeneous solid-solutions by the same techniques, and when x 0.5, the amount of this polymorph is still greater than would be expected for a predominantly zinc-containing phase.

The new square-planar platinum–diimine–dithiolate compounds [Pt(mesBIAN)SS] have been synthesised {mesBIAN = bis(mesityl)biazanaphthenequinone; SS = 1,2-dithiooxalate (dto) 1, maleonitriledithiolate (mnt) 2, 1,2-benzenedithiolate (bdt) 3, 3,4-toluenedithiolate (tdt) 4 and 1,3-dithia-2-thione-4,5-dithiolate (dmit) 5}, and the X-ray crystal structures of 3 and 5 determined. Cyclic voltammetry reveals that all the compounds form stable anions, and ESR spectroscopy of these anions shows that the SOMO is based upon the mesBIAN ligand; compounds 2–5 also show a reversible oxidation wave in their CV. Computational studies reveal that charge-transfer processes from orbitals that are combinations of metal and dithiolate ligand to a mesBIAN π*-based LUMO are responsible for the low energy absorptions seen in the UV/visible spectra of these compounds, and that the reverse process is responsible for the observed room-temperature solution luminescence of [Pt(mesBIAN)Cl2] and 1, 2 and 5. Compounds 3 and 4, containing aromatic thiolates, were not found to luminesce under the same conditions. Resonance Raman experiments have shown the origin of band-broadening of the lowest-energy absorption band in the absorption spectra of 2–5 to be due to vibronic structure within one electronic transition.

The reaction of [Mn(CN)L'(NO)(eta(5)-C(5)R(4)Me)] with cis- or trans-[MnBrL(CO)(2)(dppm)], in the presence of Tl[PF(6)], gives homobinuclear cyanomanganese(i) complexes cis- or trans-[(dppm)(CO)(2)LMn(micro-NC)MnL'(NO)(eta(5)-C(5)R(4)Me)](+), linkage isomers of which, cis- or trans-[(dppm)(CO)(2)LMn(micro-CN)MnL'(NO)(eta(5)-C(5)R(4)Me)](+), are synthesised by reacting cis- or trans-[Mn(CN)L(CO)(2)(dppm)] with [MnIL'(NO)(eta(5)-C(5)R(4)Me)] in the presence of Tl[PF(6)]. X-Ray structural studies on the isomers trans-[(dppm)(CO)(2){(EtO)(3)P}Mn(micro-NC)Mn(CNBu(t))(NO)(eta(5)-C(5)H(4)Me)](+) and trans-[(dppm)(CO)(2){(EtO)(3)P}Mn(micro-CN)Mn(CNBu(t))(NO)(eta(5)-C(5)H(4)Me)](+) show nearly identical molecular structures whereas cis-[(dppm)(CO)(2){(PhO)(3)P}Mn(micro-NC)Mn{P(OPh)(3)}(NO)(eta(5)-C(5)H(4)Me)](+) and cis-[(dppm)(CO)(2){(PhO)(3)P}Mn(micro-CN)Mn{P(OPh)(3)}(NO)(eta(5)-C(5)H(4)Me)](+) differ, effectively in the N- and C-coordination respectively of two different optical isomers of the pseudo-tetrahedral units (NC)Mn{P(OPh)(3)}(NO)(eta(5)-C(5)H(4)Me) and (CN)Mn{P(OPh)(3)}(NO)(eta(5)-C(5)H(4)Me) to the octahedral manganese centre. Electrochemical and spectroscopic studies on [(dppm)(CO)(2)LMn(micro-XY)MnL'(NO)(eta(5)-C(5)R(4)Me)](+) show that systematic variation of the ligands L and L', of the cyclopentadienyl ring substituents R, and of the micro-CN orientation (XY = CN or NC) allows control of the order of oxidation of the two metal centres and hence the direction and energy of metal-metal charge-transfer (MMCT) through the cyanide bridge in the mixed-valence dications. Chemical one-electron oxidation of cis- or trans-[(dppm)(CO)(2)LMn(micro-NC)MnL'(NO)(eta(5)-C(5)R(4)Me)](+) with [NO][PF(6)] gives the mixed-valence dications trans-[(dppm)(CO)(2)LMn(II)(micro-NC)Mn(I)L'(NO)(eta(5)-C(5)R(4)Me)](2+) which show solvatochromic absorptions in the electronic spectrum, assigned to optically induced Mn(I)-to-Mn(II) electron transfer via the cyanide bridge.

A series of salts of pyridinium boronic acids: [HNC5H4B(OH)2-4]2[M(S2C2O2)2]·2H2O (M = Cu 1, Ni 2, Pd 3, Pt 4), [HNC5H4B(OH)2-4]2[Pt(O2C2O2)2] (5); [HNC5H4B(OH)2-3]2 [M(S2C2O2)2] (M = Cu 6, Ni 7, Pd 8, Pt 9) and [HNC5H4B(OH)2-3]2[Pt(O2C2O2)2] (10) have been prepared and characterized by X-ray diffraction methods. Salts 2, 3 and 4 are isostructural and isomorphous and contain hydrogen-bonded supermolecules of form [pyridinium]2[M(S2C2O2)2] linked by BOH⋯OB and B(OH)–water hydrogen bonds into a three-dimensional network. Anhydrous salt 5 has a different structure in which the ions are linked by R(2,2)8 B(OH)2⋯carboxylate and pyridinium⋯carboxylate interactions to form a planar hydrogen-bonded ribbon. Salts 6, 7, 8 and 10 are all isostructural and isomorphous and contain hydrogen-bonded supermolecules of form [pyridinium]2[M(S2C2O2)2] linked by B(OH)2⋯carboxylate synthons to form a stepped chain. These chains pack in layers superimposed so as to afford short metal⋯metal contacts of length 3.6–4 A between layers. The structure of 5 is isomorphous with that of salts 6–8 and 10 but with a different pattern of NH hydrogen bonding as a result of the different isomer of pyridinium boronic acid present.

The crystal structures of both a symmetric and an unsymmetric platinum--alkynyl compound with terminal iodophenyl functionalities have been determined, and found to exhibit an attractive interaction between the iodine atom and the carbon-carbon triple bond of the alkynyl ligand.

Addition of ButNC to [Ru5(µ5-C2)(µ-SMe)2(µ-PPh2)2(CO)10] 1 results in expansion of the Ru5 polygon and flattening of the C2Ru5 cluster so that in the product 2 one carbon atom acquires a planar tetracoordinate configuration; reversible loss of CO from 2 affords a CNBut derivative of 1.

Addition of PhCCR (R = H, Ph)to [Ru5(µ5-C2)(µ-SMe)2(µ-PPh2)2-(CO)10] 1 results in the formation of [Ru5(µ5-CCCPhCR)(µ-SMe)2(µ-PPh2)2-(CO)10](R = H 2, Ph 3), the µ5-CCCPhCR ligand being formed by coupling of the alkyne with the C2 ligand of 1; in 2 the pentagonal Ru5 cluster of 1 is retained while 3 an extra Ru–Ru bond is formed, yielding an envelope-type structure; corresponding differences in the attachment of the organic ligand to the Ru5 cluster are found.

The reaction between [Ru5(µ3-CCH2)(µ3-SMe)2(µ-PPh2)2(CO)10] and [Fe2(CO)9] afforded the electron-rich mixed-metal cluster [FeRu5(µ4-CCH2)(µ3-SMe)(µ-SMe)(µ-PPh2)2(CO)13], with a symmetrical µ4-vinylidene ligand; the metal core consists of an Ru5 bow-tie, the central and two wing-tip atoms of which are attached to the Fe atom.