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This review describes the switching behaviors of the electronic structure, which were observed in iron(III) porphyrinoids, by the addition of external stimuli. The combined analysis by various methods, such as EPR, Mossbauer, SQUID, single crystal X-ray structure analysis, revealed a wide variety of electronic structures of the heme related complexes. This paper focuses in particular on the spin-crossover phenomenon in the solid state. An overview of spin-crossover phenomena found in iron(III) porphyrinoids between (i) S = 5/2 and S = 1/2, (ii) S = 3/2 and S = 1/2, (iii) S = 5/2 and S = 3/2, will be described.

Four novel Mo(II) and Rh(II) complexes with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (cis-dbe) or closed-dbe were synthesized and characterized. Employing [M(O2CCF3)4] (M = Mo, Rh) with cis-dbe or closed-dbe afforded complex [Mo2(O2CCF3)4(cis-dbe)](benzene) (1), [Rh2(O2CCF3)4(cis-dbe)](benzene) (2), [{Mo2(O2CCF3)4}2(closed-dbe)] (3), and [Rh2(O2CCF3)4(closed-dbe)](p-xylene) (4). The structures of four metal complexes were revealed by X-ray crystallographic analyses and the correlation between the crystal structures and the photochromic performance was discussed. In all complexes, two cyano groups of the ligand bridged two dimetal carboxylates to give a 1-D zigzag infinite chain structure. Upon irradiation with 405 nm light, complex 1 turned into reddish purple from yellow, and the color reverted to initial yellow on exposure to 563 nm light, indicating the reversible cyclization/ring-opening reaction in the crystalline phase. However, the Rh(II) complex 2 did not display similarities in reaction induced by light, which is attributable to the lower ratio of photoactive anti-parallel conformers compared with complex 1 and coordination effect of metal ions on photochromism of diarylethenes. The complexes of Rh(II) ions did not exhibit the expected reversible photoinduced behavior.

Four novel mononuclear Rh–Cp* and Ir–Cp* complexes with polycyclic aromatic hydrocarbons (PAHs), [M(Cp*)(η6-PAHs)](BF4)2 (M = Rh and Ir; Cp* = η5-C5Me5; PAHs = phenanthrene (phn), pyrene (pyr) and triphenylene (triph)), were prepared by the reactions of the intermediate [M(Cp*)(Me2CO)3]2+ with appreciable PAHs. Their structures were characterized by a single crystal X-ray analysis, 1H, 13C {1H} NMR and 2D NMR techniques. The X-ray crystallographic studies showed that the [M(Cp*)]2+ fragment is η6-coordinated to one terminal benzene ring in each PAH. In particular, it is interesting to note that the partial π/π/π/π interaction was formed in the Ir–pyr complex [Ir(Cp*)(η6-pyr)](BF4)2. The 1D and 2D NMR studies described that the Rh–Cp* and Ir–Cp* complexes with PAHs gave unique 1H and 13C {1H} NMR spectra with positive coordination shifts (Δδ(1H, 13C)) in (CD3)2CO at 23 °C, which are likely induced by the local effect and the non-local effect on the coordination of the [M(Cp*)]2+ fragment to PAHs. The decreasing of the coupling constants (3JH–H) in the η6-coordinated benzene ring is also induced, with no changes in the uncoordinated benzene rings. The time-course of 1H NMR spectra showed that Rh–Cp* and Ir–Cp* complexes with PAHs are partially dissociated to [M(Cp*)(Me2CO)3]2+ and metal-free PAHs in (CD3)2CO at 23 °C. It was demonstrated that their stabilities are in the order of Ir–triph, Ir–phn, Ir–pyr and Rh–triph complexes in (CD3)2CO.

Reaction of the precursor Ir complex [Ir(H) 2 (PPh 3 ) 2 (Me 2 CO) 2 ]PF 6 with 3,6-bis(2-pyridyl)tetrazine (bptz) in CH 2 Cl 2 gave a novel dinuclear Ir hydrido complex [Ir 2 (H) 4 (PPh 3 ) 4 (bptz)](PF 6 ) 2 · 4CH 2 Cl 2 . Crystallographic study described an interesting coordination environment having a π–π interaction and 1 H NMR study showed unique upfield shifts of pyridyl rings that are likely induced by the ring current effect of neighboring PPh 3 ligands.

Coordination polymers of [2.2]paracyclophane (pcp) with in situ silver(I) perfluoro-dicarboxylates characterized by single crystal X-ray analysis are described. Structures are found to strongly depend on the dicarboxylate spacer (n). With disilver(I) tetrafluorosuccinate ((CF2)n(COOAg)2, n = 2), 3D network with composition of [Ag4(pcp)(C2F4(CO2)2)2] (1) forms in which silver salts afford infinite double chains and pcp act as linkages between chains. Changing the silver salt to disilver hexafluoroglutarate ((CF2)n(COOAg)2, n = 3) produces 3D pillared-layer structure of composition of [Ag4(pcp)(C3F6(CO2)2)2] · THF (2) (THF = tetrahydrofuran), in which silver salts form 2D sheets and pcp act as pillars between the sheets. With silver octafluoroadipate (HO2C(CF2)nCO2Ag, n = 4), 2-fold interpenetrated diamond structure, [Ag2(pcp)2(HO2CC4F8CO2)2]2 · 2toluene (3), is obtained in which silver-anion chains and silver-pcp chains are connected with each other in the perpendicular manner. The three complexes represent unprecedented metal-organic networks of silver(I) multicarboxylates and polycyclic aromatic compounds. Additionally, the effects of the dicarboxylate conformations as well as the solvents on the resulting structures were discussed.

New five mono- and dinuclear Ir hydrido complexes with polydentate nitrogen ligands, [Ir(H) 2 (PPh 3 ) 2 (tptz)]PF 6 ( 1 ), [Ir 2 (H) 4 (PPh 3 ) 4 (tptz)](PF 6 ) 2 · 2H 2 O ( 2 · 2H 2 O), [Ir(H) 2 (PPh 3 ) 2 (tppz)]BF 4 ( 3 ), [Ir 2 (H) 4 (PPh 3 ) 4 (tppz)](BF 4 ) 2 ( 4 ) and [Ir 2 (H) 4 (PPh 3 ) 4 (bted)](BF 4 ) 2 · 6CHCl 3 ( 5 · 6CHCl 3 ), were systematically prepared by the reactions of the precursor Ir hydrido complex [Ir(H) 2 (PPh 3 ) 2 (Me 2 CO) 2 ]X (X=PF 6 and BF 4 ) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 1,4-bis(2,2 ′ :6 ′ ,2″-terpyridine-4 ′ -yl)benzene (bted), and their structures and properties were characterized in the solid state and in solution. Each of the Ir hydrido complexes with polydentate nitrogen ligands crystallographically described a unique coordination mode. Their 1 H NMR spectra demonstrated unusual 1 H NMR chemical shifts of pyridyl rings that are likely induced by the ring current effect of neighboring ligands.

Reaction of [2.2]paracyclophane (pcp) with silver(I) trifluoroacetate (AgCF(3)CO(2)) and silver(I) pentafluoroproprionate (AgC(2)F(5)CO(2)) has led to isolation of three novel intercalation polymers: [Ag(4)(pcp)(CF(3)CO(2))(4)](C(6)H(6)) (1), [Ag(4)(pcp)(CF(3)CO(2))(4)](C(6)H(3)Me(3)) (2), and [Ag(4)(pcp)(C(2)F(5)CO(2))(4)](pcp) (3). Structure studies using single crystal X-ray diffraction have shown that all compounds contain two-dimensional layered frameworks based on cation-pi interactions, in which pcp exhibits an unprecedented micro-tetra-eta(2) coordination mode. Guest molecules which weakly interact with the host pcp via C-H.pi interactions are intercalated between layers. The guest-eliminated complexes (1a and 2a) and guest-reincorporated ones (1b or 1c and 2b or 2c), accompanied by small structural changes, were confirmed by (1)H NMR, thermogravimetric analysis, mass spectra, and X-ray powder diffraction patterns. The structural changes from 1 --1a --1c (=1) can take place reversibly in the process of exposure of 1a to benzene vapor. The original framework of complex 2 is also completely recovered by immersing 2a in mesitylene as well as exposing it to mesitylene vapor.

As a continuation of the study on the construction of the multidecker aromatic compounds with pi-pi interactions, the anthracene derivatives 9,10-dimethylanthracene (dman), 9,10-diphenylanthracene (dpan), and 7,12-dimethylbenz[a]anthracene (dmban) have been studied toward complexation with the silver(I) ion. The crystal structures of [Ag(dman)(0.5)(p-xylene)(ClO(4))], [Ag(2)(dpan)(0.5)(C(6)H(6))(0.5)(CF(3)SO(3))(2)], and [Ag(2)(dmban)(2)(ClO(4))(2)](p-xylene), together with the metal-free ligand dpan, have been determined by single-crystal X-ray diffraction. These pi-electron-rich aromatic compounds are found to have great promise as an approach to the effective self-assembly of high nuclearity in a multilayer fashion.

A novel 2-D silver(I) coordination polymer of 1,8-diphenylocta-1,3,5,7-tetraene was synthesized, and characterized by X-ray single crystal analysis. Reaction of 1,8-diphenylocta-1,3,5,7-tetraene (dpot) with silver(I) perchlorate at 60 °C afforded [Ag2(dpot)(ClO4)2]n (1). In this structure, silver(I) adopts a distorted tetrahedral geometry and the dpot molecules link the silver(I) ions in a trans-μ-tetra-η2 manner to generate 1-D chains with metallocyclophane motifs. Further, the silver(I) ions between the two neighboring chains are bridged by perchlorate groups to give a novel 2-D (3,4)-connected polymeric network with (4,62)2(42,62,82) topology. Additionally, the main plane of the phenyl moiety makes an angle of 33.08° with the topology through the polyene portion in 1, and thus the coordination of silver(I) to dpot results in the distortion of the dpot molecule. To the best of our knowledge, this is the first example of a silver(I) complex with acyclic polyene.

Three novel silver(I) complexes with benzopyrene derivatives were synthesized and characterized in this paper. Treatment of AgClO4•H2O with 7-methylbenzo[a]pyrene (L1) afforded [Ag2(L1)(toluene)0.5(ClO4)2]n (1) which exhibits a 2-D sheet structure with double-stranded helical motifs. Reaction of AgCF3SO3 with dibenzo[b,def ]chrysene (L2) gave rise to an unprecedented cocrystallization structure, {[Ag2(L2)(CF3SO3)2][Ag2(toluene)2(CF3SO3)2]}n (2), formed by a 2-D neutral lamellar polymer and a 1-D neutral rodlike one. The ligand benzo[e]pyrene (L3) coordinated to silver(I) ions generating a closed triple-decker tetranuclear complex [Ag4(L3)4(p-xylene)(ClO4)4] (3) which can be regarded as a stacking polymer owing to existing intermolecular π−π stack interactions. The structural diversity of the silver(I) coordination polymers with polycyclic aromatic hydrocarbons is not only related to the stacking patterns of free polycyclic aromatic hydrocarbons in the crystalline state, but also the geometric shapes of th...

The title complex, [Ag4(C5F6O4)2(C14H8N2)(C4H8O)2]n, exhibits a one-dimensional chain structure propagated through inversion centres, with two crystallographically independent AgI atoms in the asymmetric unit. One of the Ag atoms has a distorted trigonal-pyramidal coordination, defined by two carboxyl O atoms from two hexafluoro­glutarate (HFG2−) anions, one N atom from 4,4′-biphenyl­dicarbonitrile and one apical O atom of tetrahydro­furan. The other Ag atom is coordinated by two O atoms from two HFG2− anions.

The title compound, {[Ag2(C16H16S2)2(C2H3N)4](C8F4O4)·2C8H2F4O4·4C2H3N}n, has been prepared from the reaction of 2,11-di­thia­[3.3]­paracyclo­phane (dtpcp) and in situ silver(I) tetrafluoroterephthalate (TFTP2−) using an interface method. In the solid state the title compound forms two infinite chains, which are parallel to one another. One chain consists of [Ag2(C16H16S2)2(C2H3N)4]n2n+, and the other is formed from TFTP2− and H2TFTP via Oc—H⋯Oc (c is carboxy) hydrogen- bonding interactions, with H⋯A distances of 1.72 (2) and 1.774 (19) A. The AgI ion is tetrahedrally coordinated by two aceto­nitrile N atoms and two dtpcp S atoms. The cyclo­phanes have inversion symmetry.

The title compound, [Mn2(mu-O)(C6H3NO3)2(C5H5N)4].H2O, was isolated from the reaction of 2,6-pyridinedicarboxylic acid with [Mn12O12(CH3COO)16(H2O)4] in pyridine. The dimanganese complex has twofold symmetry; the MnIII atoms are bridged by one oxo and two amidate ligands and show compressed octahedral Jahn-Teller distortion. The molecular packing comprises a three-dimensional structure constructed by means of extensive intermolecular interactions, including three kinds of hydrogen bonds and pi-pi interactions.

Reaction of [2.2]paracyclophane with silver(I) heptafluorobutyrate (AgC 3 F 7 CO 2 ) has isolated three novel networks: [Ag 4 (pcp)(C 3 F 7 CO 2 ) 4 ].pyrene (1), [Ag 4 (pcp)(C 3 F 7 CO 2 ) 4 ].phen (phen = phenanthrene) (2), and [Ag 4 (Pcp)(C 3 F 7 CO 2 ) 4 ]. fluorene (3), and an intercalation compound [Ag 4 (Pcp)(C 3 F 7 CO 2 ) 4 ].2benzene (4). All the four complexes exhibit two-dimensional (2D) sheet structures in which AgC 3 F 7 CO 2 form an infinite chain and pcp acts as linkage. 1, 2, and 3 show 2D flat sheets with cavities in which guest molecules are situated, whereas 4 exhibits 2D zigzag layers between which guest benzene molecules are intercalated. Pcp shows μ-di-η 1 -η 2 coordination mode in 1, μ-tetra-η 1 coordination mode in 2 and 3, and μ-tetra-η 2 coordination mode in 4. The reversible guest exchanges were observed between complex 1, 2, or 3 and intercalation compound 4. It is unprecedented for metal-organic inclusion complexes that the guest exchange occurs where the guest is the solute molecule. Furthermore, 4 can release the guest, and the original framework was completely recovered after reincorporation of benzene. It should be noted that 4 can incorporate pyrene, phen, and fluorene to give 1, 2, and 3, respectively, after desorption.

In the title complex, [Ag 2 (C 7 H 4 NO 4 ) 2 (C 16 H 16 S 2 )], each Ag I atom is trigonally coordinated by one S atom of a 2,11-dithia[3.3]paracyclophane (dtpcp) ligand, and by one N and one O atom of a 6-carboxypyridine-2-carboxylate ligand. Dtpcp acts as a bidentate ligand, bridging two inversion-related Ag I atoms to give a dinuclear silver(I) compound. The dinuclear moieties are interconnected via O-H...O hydrogen bonds to form a two-dimensional zigzag sheet. Two such sheets are interwoven via π-π interactions between pyridine rings, affording an interwoven bilayer network.

The preparation and physical characterization are reported for a novel single-molecule magnet [Mn(12)O(12)(OAc)(12)(dpp)(4)] (dppH = diphenyl phosphate) with no coordinating water molecules. The crystal structure analysis reveals that there are four five-coordinate Mn(III) ions with Mn.H approaches. Addition of water in CD(2)Cl(2) solution was monitored by (1)H NMR, which showed that H(2)O could coordinate to a vacant site of a five-coordinate Mn(III) ion in solution. The measurements and analyses of magnetization hysteresis and ac magnetic susceptibility indicate that the title complex is a single-molecule magnet with a quantum tunneling behavior, whose ground state was tentatively assigned to S = 10 with g = 1.78 and D = -0.60 K.

A novel 3-D silver(I) cationic coordination polymeric network, [Ag4(bcdt)4(CF3SO3)2]·(CF3SO3)2·acetone (bcdt = 4,5-bis(cyanoethylsulfanyl)-1,3-dithiole-2-thione) with double (3,4)-connected nodes a...