Cobalt ( II ) , iron ( II ) , zinc ( II ) and palladium ( II ) complexes of ditopic 4 ʹ-{ 4-[ Bis ( 2-pyridyl ) aminomethyl ] phenyl }-2 , 2 ′ : 6 ′ , 2 ′ ′-terpyridine . Synthetic and X-ray structural studies †

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Introduction
Di-, tri-and poly-pyridyl based ligands systems have been widely used as components in metallo-supramolecular chemistry, reflecting the coordination versatility of this heterocyclic amine ligand class. 1,2For example, the metal ion chemistry of 2,2′:6′,2′′-terpyridine (terpy) and its derivatives has received a great deal of attention over many decades [3][4][5][6] as has 2,2′-dipyridylamine (dpa) and its extended (secondary amine-substituted) derivatives. 7,8Thus, in the latter case a range of bridging groups have been employed to connect from two to four dpa units via their respective secondary amine sites for use in metal coordination/metallo-supramolecular studies and a variety of such systems have now been investigated in some detail. 7,8As an example, in previous studies we have investigated the interaction of copper(II), 9 palladium(II) 9 and silver(I) 10,11 with such linked dpa ligands, with our focus being on the supramolecular aspects of the resulting solid state structures.As an extension of these studies we now report the synthesis of the new linked "hybrid" ligand 4′-{4-[di- (2-pyridyl)aminomethyl]phenyl}-2,2′:6′,2′′-terpyridine (L) incorporating both dpa and 2,2′:6′,2′′-terpyridine domains together with an investigation of its interaction with selected metal ions.

Experimental
NMR spectra were recorded on a Bruker Avance DPX200 or DPX300 spectrometer.Electrospray mass spectra (ESI-MS) were obtained on a Finnigan LCQ-8 spectrometer.FTIR spectra were determined on a Bio-Rad FTS-40 spectrometer.All commercially available reagents were used as received.

Crystal structure determinations
Data were collected on either a Bruker-Nonius APEX2-X8-FR591 diffractometer employing graphite-monochromated Mo-Kα generated from a rotating anode (0.71073 Å) with ω and ψ scans to approximately 56°2θ or a Bruker SMART 1000 diffractometer employing graphite-monochromated Mo-Kα generated from a sealed tube (0.71073 Å) with ω scans to approximately 56°2θ.Data integration and reduction were undertaken with SAINT and XPREP 12 and subsequent computations were carried out using the WinGX-32 graphical user interface. 13Multiscan empirical absorption corrections were applied to the data using the program SADABS. 14Gaussian absorption corrections were applied using XPREP. 12Structures were solved by direct methods using SIR97 15 then refined and extended with SHELXL-97. 16Unless otherwise stated, ordered non-hydrogen atoms were refined anisotropically while partial occupancy non-hydrogen atoms were refined isotropically.Hydrogen atoms attached to carbon atoms were included in idealised positions and a riding model was used for their refinement.Hydrogen atoms bound to solvent water molecules that could not be located in the difference Fourier map were not included in the model.CCDC 988029-988033.
The reaction of L with cobalt(II) chloride in acetonitrile/ dichloromethane resulted in dark green crystals of [CoLCl 2 ]•0.25DCM•0.5H 2 O whose X-ray structure (Fig. 1) showed that the cobalt cation coordinates at the terpy site (in a second experiment a similar product showing the absence of coordination at the dpa site was also obtained even when a several-fold excess of CoCl 2 was employed for the reaction).The cobalt(II) centre is five-coordinate, adopting a distorted trigonal bipyramidal geometry (Addison τ parameter 18  . 19djacent complexes are involved in a complex web of intermolecular interactions forming an infinite three dimensional network; the close to planar "tolylterpy" sections of the molecule undergo a series of offset face-to-face arene-arene interactions indicated by ring centroid-ring centroid separations of 3.5-3.7 Å forming a one-dimensional stack that extends parallel to the crystallographic āb vector (Fig. 2).This arrangement is further stabilised by a series of hydrogen bonds between aromatic protons and coordinated chloride ions (CH⋯Cl distances of between 3.0 and 3.2 Å).More of these bonds (CH⋯Cl distances of between 2.81 and 2.86 Å) and further arene-arene interactions bridge these one-dimensional chains resulting in two-dimensional sheets.Each of these sheets is further bridged by interactions involving the dpa part of the ligand.The N(5)-containing dpa pyridine acts as a hydrogen bond acceptor from an adjacent terpy pyridyl hydrogen donor (C( 14)H⋯N(5) = 2.6 Å) and is also involved in edge-to-face π stacking, forming a threedimensional network of interactions.
Interaction of zinc(II) chloride with L under similar conditions to those employed for the cobalt(II) complex (with methanol substituted for acetonitrile) resulted in formation of a pale yellow species of type [ZnLCl 2 ].This 5-coordinate zinc(II) complex is isostructural (Fig. 3) with the cobalt(II) complex described above and forms the same three-dimensional network of interactions consisting of arene-stacking and both CH⋯Cl and CH⋯N hydrogen bonding.Indeed, interactions of this type appear to dominate the crystal packing of each of [M(L′)Cl 2 ] (where L′ is any ligand incorporating the "tolylterpy" motif); similar crystal packing arrangements to those found in the present study for both the zinc(II) and cobalt(II) complexes of L are present in each of the eight other [M(L′)Cl 2 ] structures in the literature. 20eaction of zinc acetate in acetonitrile with L in dichloromethane resulted in yellow crystals whose X-ray structure is shown in Fig. 4. The zinc centre again has a distorted trigonal bipyramidal geometry with the metal bound to the terpy domain of L; the remaining two coordination sites are occupied by oxygens from monodentate acetate ions.Once again two pyridyl group occupy the axial positions, with the third and the anions in the equatorial plane, an arrangement that   has been observed in two other [Zn(terpyR)(OAc) 2 ] structures reported previously. 21Unlike the two chloride-bound complexes above, [ZnL(CH 3 CO 2 ) 2 ] crystallises with two chemically identical but crystallographically distinct molecules in the asymmetric unit.
The dpa site is again not coordinated to a metal ion.In a similar fashion to the two chloride complexes, the relatively planar "tolylterpy" sections of the ligands lie closely above and below each other forming infinite one-dimensional chains which are further stabilised by CH⋯O hydrogen bonds.These chains interact with adjacent stacks through further dpa pyridyl H⋯O hydrogen bonds.
Reaction of ferrous ammonium sulfate with L followed by addition of ammonium hexafluorophosphate led to isolation of a purple product of type [Fe(L) 2 (PF 6 ) 2 ].The nature of this compound was investigated by mass spectrometry, NMR and IR spectroscopy as well as by an X-ray structure determination (Fig. 5).The ESI mass spectrum of this product showed a parent peak corresponding to [Fe(L) 2 (PF 6 )] + and the X-ray structure determination showed that the iron(II) is six coordinate with the two terpy units of two molecules of L coordinated in the commonly observed bis-terpy octahedral motif.The dpa units are, once again, not coordinated.The crystal packing of the complex is dominated by arene-arene interactions and aromatic CH⋯F hydrogen bonds resulting in a three-dimensional array, with the uncoordinated dpa groups participating in a series of edge-to-face and offset face-to-face arene-arene stacking.The "tolylterpy" parts of the molecule interact with each other in a 'terpy embrace' motif similar to that observed previously in the iron(II) and ruthenium(II) complexes of 4′-phenylterpy 22 and 4′-pyridylterpy. 23he strong coordination of palladium(II) to both dpa 9,24,25 and terpy 26 has been well documented and this provided a motivation for investigating the interaction of this metal ion with L. Reaction of L in dichloromethane/methanol (1 : 1) with palladium(II) chloride in 2 M hydrochloric acid resulted in a pale yellow precipitate.Elemental analysis of the isolated solid gave a Pd : L ratio of 2 : 1.The mass spectrum also revealed a parent peak corresponding to two palladium and one L in solution, in accord with formation of a homodinuclear species of type 1. Unfortunately crystals of 1 suitable for an X-ray diffraction study were not obtained.
In view of the above result bis(acetonitrile)dichloropalladium(II) in acetonitrile was added to [Fe(L) 2 ](PF 6 ) 2 in acetonitrile and the warm solution stirred for 30 minutes.The solution remained dark purple.Ether vapour was then diffused into the reaction mixture to yield a dark purple precipitate.The 1 H NMR spectrum of this product exhibited a noticeable shift of the (single) methylene proton signal relative to the starting complex (in keeping with the occurrence of palladium coordination at both dpa sites).The mass spectrum revealed a parent peak corresponding to [FePd 2 L 2 Cl 4 PF 6 ] + ; such a stoichiometry corresponds to a structure of type 2. Further, the isotopic distribution of this ion (Fig. 6) is in agreement with a trinuclear structure and the elemental analysis of the isolated product also corresponded to the proposed stoichiometry.Unfortunately, crystals suitable for an X-ray structure determination were again not obtained; however, on the basis of the above evidence the product was assigned the trinuclear structure 2.  Based on the success of this study in forming a heterometallic complex we investigated the possibility of using [Fe(L) 2 ](PF 6 ) 2 as a metallo-ligand for the formation a heterometallic coordination polymer in conjunction with silver(I).Our choice of silver was based on our previous success in coordinating silver(I) with dpa ligands 11 and the well established propensity for silver(I) to form coordination complexes with nitrogen donor ligands when other metal ions have not been successful. 27Accordingly, an acetonitrile solution of [Fe(L) 2 ](PF 6 ) 2 was mixed with one equivalent of AgClO 4 •H 2 O in methanol to yield a small number of purple crystals suitable for diffraction studies, following diffusion of ether vapour into the resulting purple solution.X-ray analysis revealed a mixed-anion complex of composition [Fe(L)(HL)](PF 6 ) 0.5 (ClO 4 ) 2.5 •H 2 O•1.5MeOH (Fig. 7).
In this complex, the iron(II) centre adopts the expected octahedral geometry, bound to one terpyridine domains from each ligand, one dpa moiety is protonated and both of these remain uncoordinated.The crystal packing is again dominated by π-interactions.In this case the bis-terpyridine groups form a classical one-dimensional terpyridine embrace motif 28 with the network again extended to three dimensions by further π-stacking involving the dpa groups.

Conclusions
A new di-functional hybrid terpy/dpa ligand L along with five crystal structures of its metal derivatives are reported.In each complex the metal ion preferentially binds to the terpyridine moiety, with the dpa site remaining uncoordinated and the crystal packing dominated by extensive π-interactions.Contrasting with the above, reaction of palladium(II) with L gives a complex for which the evidence indicates that this metal ion binds at both the terpy and dpa domains.Based on this result, addition of [Pd(CH 3 CN) 2 Cl 2 ] to [Fe(L) 2 ](PF 6 ) in acetonitrile yielded a heterometallic Fe/Pd (1 : 2) complex in which the evidence indicates that both non-metal bound dpa sites of [Fe(L) 2 ](PF 6 ) are now occupied by palladium ions to form a species of type [FePd 2 (L) 2 Cl 4 ](PF 6 ) 2 •1.5CH 3 CN.An initial attempt to form a related Fe(II)/Ag(I) species led instead to a silver-free [FeL 2 H] 3+ species in which protonation of one of the two unoccupied dpa sites of dpa has occurred.Further studies involving L directed towards the synthesis of other heteronuclear species are planned for the future.

Fig. 1 X
Fig. 1 X-ray structure of [CoLCl 2 ]•0.25DCM•0.5H 2 O. Solvent molecules have been removed for clarity.Thermal ellipsoids are shown at the 50 percent probability level.

Fig. 2
Fig. 2 Representation of the one-dimensional stack that propagates parallel to the crystallographic āb vector in [CoLCl 2 ]•0.25DCM•0.5H 2 O. Double headed arrows indicate the presence of arene-arene interactions.

Fig. 3 X
Fig. 3 X-ray structure of [ZnLCl 2 ]•0.7MeOH•0.3H 2 O. Solvent molecules and protons have been removed for clarity.Thermal ellipsoids are shown at the 50 percent probability level.The pyridyl group comprising N(4) exhibits minor positional disorder and was modelled over two sites.For clarity only one of these is shown.

Fig. 4 X
Fig. 4 X-ray structure of [ZnL(CH 3 CO 2 ) 2 ].Only one of the two chemically identical but crystallographically unique complexes in the asymmetric unit are shown for clarity.Thermal ellipsoids are at the 50 percent probability level.

Fig. 5
Fig. 5 X-ray structure of [Fe(L) 2 (PF 6 ) 2 ]•2.5H 2 O. Solvent water molecules and protons have been removed for clarity.Thermal ellipsoids are shown at the 30 percent probability level.