Tetra-, Penta-and Hexa-Coordinated Transition Metal Complexes Constructed from Coumarin-Containing N 2 O 2 Ligand

Three newly designed complexes, [Cu(L)]·CHCl3 (1), [Co(L)(MeOH)]·CHCl3 (2) and [{Ni(L)(MeOH)(PhCOO)}2Ni] (3) a coumarin-containing Salamo-type chelating ligand (H2L) have been synthesized and characterized by elemental analyses, IR and UV-VIS spectra, and X-ray crystallography. Complex 1 includes one Cu(II) atom, one completely deprotonated (L)2− unit and one crystalling chloroform molecule, the Cu(II) atom shows a square-planar geometry. Complex 2 includes one Co(II) atom, one completely deprotonated (L)2− unit, one coordinated methanol molecule and one crystalling chloroform molecule. The Co(II) atom is a distorted trigonal-bipyramidal geometry. While complex 3 includes three Ni(II) atoms, two completely deprotonated (L)2− units, two benzoates and two coordinated methanol molecules. The complexes 1 and 2 are both possess three-dimensional supra-molecular structures by abundant noncovalent interactions. But, complex 3 formed a two-dimensional supra-molecular structure by intra-molecular hydrogen bonds. In addition, the antimicrobial and fluorescence properties of H2L and its complexes 1, 2 and 3 were also investigated.

The introduction of different substituted groups into Salamo-type compounds may give rise to novel structures and the uncoordinated crystalling molecule can also affect the spatial structures [34][35][36].Although these Salamo-type complexes have been in the process of development, the fluorescence and antimicrobial properties with coumarin-containing transition metal complexes are still unreported.In this study, three newly designed complexes [Cu(L)]•CHCl 3 (1), [Co(L)(MeOH)]•CHCl 3 (2) and [{NiL(MeOH)(PhCOO)} 2 Ni] (3) have been prepared with a coumarin-containing Salamo-type N 2 O 2 ligand, in particular the research on the Salamo-type complex contained benzoate ligands is reported firstly.

Materials and Methods
7-Hydroxyl-4-methyl-coumarin (98%) was obtained from Alfa Aesar (New York, NY, USA).C, H and N analyses were gained by a GmbH VarioEL V3.00 automatic elemental analysis instrument (Elementar, Berlin, Germany).Elemental analyses for metals were obtained using an IRIS ER/S-WP-ICP atomic emission spectrometer (Elementar, Berlin, Germany).Melting points were measured by the use of a microscopic melting point apparatus made by Beijing Taike Instrument Limited Company (Beijing, China) and were uncorrected.IR spectra were recorded on a Vertex70 FT-IR spectrophotometer, with samples prepared as KBr (400-4000 cm −1 ) pellets (Bruker AVANCE, Billerica, MA, USA).UV-VIS absorption spectra were measured on a Shimadzu UV-3900 spectrometer (Shimadzu, Tokyo, Japan).Luminescence spectra in solution were recorded on a Hitachi F-7000 spectrometer (Shimadzu, Tokyo, Japan). 1 H-NMR spectra were measured by a German Bruker AVANCE DRX-400 spectrometer (Bruker AVANCE, Billerica, MA, USA).X-ray single-crystal structures were determined by a SuperNova Dual (Cu at zero) and Bruker APEX-II CCD diffractometers (Bruker AVANCE, Billerica, MA, USA), respectively.

Materials and Methods
7-Hydroxyl-4-methyl-coumarin (98%) was obtained from Alfa Aesar (New York, NY, USA).C, H and N analyses were gained by a GmbH VarioEL V3.00 automatic elemental analysis instrument (Elementar, Berlin, Germany).Elemental analyses for metals were obtained using an IRIS ER/S-WP-ICP atomic emission spectrometer (Elementar, Berlin, Germany).Melting points were measured by the use of a microscopic melting point apparatus made by Beijing Taike Instrument Limited Company (Beijing, China) and were uncorrected.IR spectra were recorded on a Vertex70 FT-IR spectrophotometer, with samples prepared as KBr (400-4000 cm −1 ) pellets (Bruker AVANCE, Billerica, MA, USA).UV-VIS absorption spectra were measured on a Shimadzu UV-3900 spectrometer (Shimadzu, Tokyo, Japan).Luminescence spectra in solution were recorded on a Hitachi F-7000 spectrometer (Shimadzu, Tokyo, Japan). 1 H-NMR spectra were measured by a German Bruker AVANCE DRX-400 spectrometer (Bruker AVANCE, Billerica, MA, USA).X-ray single-crystal structures were determined by a SuperNova Dual (Cu at zero) and Bruker APEX-II CCD diffractometers (Bruker AVANCE, Billerica, MA, USA), respectively.

Synthesis of Complex 1
A chloroform solution (4 mL) of H2L (4.64 mg, 0.01 mmol) was added dropwise to a methanol solution (4 mL) of Cu(OAc)2•H2O (1.99 mg, 0.01 mmol), the color of the mixed solution changes immediately to dark green.The mixed solution was filtered, and the filtrate was kept undisturbed in the dark to avoid decomposition of the coumarin-containing building blocks.Single-crystals suitable for X-ray crystallography were grown up by partial solvent evaporation after about two weeks, and collected carefully by filtration, washed with n-hexane, and dried at room temperature.Yield, 3.01 mg, 0.0047 mmol (46

Synthesis of Complex 1
A chloroform solution (4 mL) of H 2 L (4.64 mg, 0.01 mmol) was added dropwise to a methanol solution (4 mL) of Cu(OAc) 2 •H 2 O (1.99 mg, 0.01 mmol), the color of the mixed solution changes immediately to dark green.The mixed solution was filtered, and the filtrate was kept undisturbed in the dark to avoid decomposition of the coumarin-containing building blocks.Single-crystals suitable for X-ray crystallography were grown up by partial solvent evaporation after about two weeks, and collected carefully by filtration, washed with n-hexane, and dried at room temperature.Yield, 3.01 mg, 0.0047 mmol (46

Synthesis of Complex 2
A solution of H 2 L (4.64 mg, 0.01 mmol) in 4 mL of chloroform was added dropwise to a methanol solution (6 mL) of Co(NO 3 ) 2 •6H 2 O (2.91 mg, 0.01 mmol).The color of the mixed solution changes immediately to brown.The mixed solution was filtered, and the filtrate kept undisturbed in the dark to avoid decomposition of the coumarin-containing building blocks.Single-crystals suitable for X-ray crystallography were grown up by partial solvent evaporation after about one week, and collected carefully by filtration, washed with n-hexane, and dried at room temperature.Yield, 3.32 mg, 0.0049 mmol (49.3 %)

Synthesis of Complex 3
A chloroform solution (4 mL) of H 2 L (4.64 mg, 0.01 mmol) was added dropwise to a methanol solution (2 mL) of Ni(NO 3 ) 2 •6H 2 O (2.90 mg, 0.01 mmol).Then, a methanol solution (5 mL) of sodium benzoic (1.22 mg, 0.01 mmol) was added, and the mixed sulution was kept stirring for 5 min at room temperature.The mixed solution was filtered, and the filtrate kept undisturbed in the dark to avoid decomposition of the coumarin-containing building blocks.Single-crystals suitable for X-ray crystallography were grown up by partial solvent evaporation after about three weeks, and collected carefully by filtration, washed with n-hexane, and dried at room temperature.Yield, 2.6.X-ray Crystal Structure Determinations for Complexes 1, 2 and 3 X-ray single crystal diffraction data of the complexes 1, 2 and 3 were recorded using a SuperNova Dual (Cu at zero) and Bruker APEX-II CCD diffractometers with a monochromated Mo-Kα radiation (λ = 0.71073 Å) source at 296(2), 173.00 (10) and 153(2) K, respectively.The LP corrections were applied to the SAINT program [41] and Semi-empirical correction were applied to the SADABS program [42].The single crystal structures were solved by the direct methods (SHELXS-2014) [43].All hydrogen atoms were added theoretically and difference-Fourier map exhibited the positions of the remaining atoms.The H atoms were included at the calculated positions and constrained to ride on their parent atoms.All non-hydrogen atoms were refined anisotropically by a full-matrix least-squares procedure on F 2 with SHELXL-2014 [43].Crystal data and refinement parameters involved the structure determinations are presented in Table 1.Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication, No. CCDC 1,816,001, 1,816,000 and 1,816,002 for complexes 1, 2 and 3, respectively.Copies of the data can be gained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (Telephone: (44) 01223 762910; Fax: +44-1223-336033; E-mail: deposit@ccdc.cam.ac.uk).These data can be also obtained free of charge at www.ccdc.cam.Ac.uk/ conts/retrieving.html.

Results and Discussion
Complexes 1, 2 and 3 a coumarin-containing Salamo-type ligand have been prepared, and characterized by IR, UV-VIS and X-ray crystallography methods.In addition, the fluorescence properties of complexes 1, 2 and 3 and antimicrobial activities of H 2 L and its complexes 1, 2 and 3 were also investigated.

IR Spectra
The FT-IR spectra of H 2 L with its corresponding complexes 1, 2 and 3 possess different bands in the 4000-400 cm −1 region (Figure 1  Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication, No. CCDC 1,816,001, 1,816,000 and 1,816,002 for complexes 1, 2 and 3, respectively.Copies of the data can be gained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (Telephone: (44) 01223 762910; Fax: +44-1223-336033; E-mail: deposit @ccdc.cam.ac.uk).These data can be also obtained free of charge at www.ccdc.cam.Ac.uk/conts/retrieving.html.

Results and Discussion
Complexes 1, 2 and 3 a coumarin-containing Salamo-type ligand have been prepared, and characterized by IR, UV-VIS and X-ray crystallography methods.In addition, the fluorescence properties of complexes 1, 2 and 3 and antimicrobial activities of H2L and its complexes 1, 2 and 3 were also investigated.

IR Spectra
The FT-IR spectra of H2L with its corresponding complexes 1, 2 and 3 possess different bands in the 4000-400 cm −1 region (Figure 1 and Table 2).The characteristic C=O stretching band at 1734 cm −1 of the ligand H 2 L, and those of the complexes 1, 2 and 3 emerge at 1722, 1726 and 1719 cm −1 , respectively [44].Meanwhile, a characteristic C=N stretching band of H 2 L emerges at 1616 cm −1 , and those of complexes 1, 2 and 3 show at 1601, 1597 and 1605 cm −1 , respectively [45].The characteristic C=N stretching frequencies are moved to low frequencies, which indicates that the metal(II) atoms are bonded by azomethine N atoms of the ligand (L) 2− moieties [46].H 2 L presents a characteristic Ar-O stretching frequency at 1282 cm -1 , while those of complexes 1, 2 and 3 emerge at 1242, 1238 and 1222 cm −1 , respectively.The characteristic Ar-O stretching frequencies are moved to low frequencies, which can be evidence for formation of Cu-O, Co-O and Ni-O bonds between Cu(II), Co(II) and Ni(II) atoms with O atoms of phenolic groups [47].

UV-VIS Spectra
The UV-VIS absorption spectra of H 2 L with its complexes 1, 2 and 3 in the dichloromethane solutions (2.0 × 10 −5 M) at 298 K are shown in Figure 2 and Table 3.The absorption peaks of H 2 L are different from its complexes 1, 2 and 3.The absorption spectrum of H 2 L comprises three relatively intense absorption peaks centered at 291, 330 and 345 nm, the first peak at 291 nm can be assigned to the π-π* transitions of the phenyl rings [48], the second peak at 330 nm can be assigned to the π-π* transitions of the oxime group [49], and the third peak at 345 nm can be assigned to the n-π* transitions of lactone carbonyl group [50].Upon coordination of H 2 L, the π-π* transitions of the phenyl rings in complexes 1 and 2 are bathochromically shifted to 299 and 297 nm, respectively, and the absorption peak at 291 nm vanishes from the UV-VIS spectrum of complex 3, indicating the coordination of Co(II), Cu(II) and Ni(II) atoms with the (L) 2− units [48].Compared with H 2 L, the absorption peak at 330 nm vanishes from the UV-VIS spectra of complexes 1, 2 and 3, indicating that the oxime N atoms are participated in coordination to the Cu(II), Co(II) and Ni(II) atoms [49].Meanwhile, the n-π* transitions of the lactone carbonyl group in complexes 1, 2 and 3 assumes a hypsochromic shift to 343, 347 and 338 nm exhibiting that the coordination of the (L) 2− units with Cu(II), Co(II) and Ni(II) atoms, respectively.Meanwhile, three weak broad absorption peaks are gained at 396, 399 and 391 nm for complexes 1, 2 and 3, respectively, these new absorption peaks can be attributed to L→M charge-transfer transitions (LMCT).This is characteristic of N 2 O 2 -donors sphere with the transition metal complexes [49].

Fluorescence Properties
The fluorescent properties of H 2 L and its complexes 1, 2 and 3 were measured at room temperature (Figure 3).The ligand H 2 L exhibits a strong and broad emission at 432 nm upon excitation at 351 nm, which should be assigned to intraligand π-π* transition [12].The complexes 1, 2 and 3 display weakened photoluminescence with maximum emission peaks at ca. 417, 462 and 469 nm upon excitation at 351 nm, respectively.The absorption peaks are bathochromically-shifted of complexes 1 and 2, and hypsochromically-shifted of complex 3, which could be attributed to LMCT [12].Table 3. Absorption maxima and molar extinction coefficients for H2L and its complexes 1, 2 and 3.

Crystal Structure Description of Complex 1
As presented in Figure 4 and Table 4, complex 1 crystallizes in the monoclinic system, space group P 21/c, which comprises one Cu(II) atom, one deprotonated (L) 2− unit and one crystalling chloroform molecule.Table 3. Absorption maxima and molar extinction coefficients for H 2 L and its complexes 1, 2 and 3.  Table 3. Absorption maxima and molar extinction coefficients for H2L and its complexes 1, 2 and 3.

Crystal Structure Description of Complex 1
As presented in Figure 4 and Table 4, complex 1 crystallizes in the monoclinic system, space group P 21/c, which comprises one Cu(II) atom, one deprotonated (L) 2− unit and one crystalling chloroform molecule.

Crystal Structure Description of complex 2
Complex 2 presents a symmetric mononuclear structure, crystallizes in the monoclinic system, space group P 21/c, composes one Co(II) atom, one deprotonated (L) 2− unit, one coordinated methanol molecule and one crystalling chloroform molecule.Selected bond lengths and angles are listed in Table 6.Complex 2 presents a symmetric mononuclear structure, crystallizes in the monoclinic system, space group P 2 1 /c, composes one Co(II) atom, one deprotonated (L) 2− unit, one coordinated methanol molecule and one crystalling chloroform molecule.Selected bond lengths and angles are listed in Table 6.As shown in Figure 7, the Co(II) atom is penta-coordinated by two oxime N (N1 and N2) and phenoxo O (O1 and O6) atoms from one deprotonated (L) 2− unit, and one O (O9) atom from the coordinated methanol molecule (Figure 7a).The coordination around the Co(II) atom is depicted as a trigonal bipyramid [54], and the τ value was estimated to be τ = 0.888 (Figure 7b) [55] As shown in Figure 7, the Co(II) atom is penta-coordinated by two oxime N (N1 and N2) and phenoxo O (O1 and O6) atoms from one deprotonated (L) 2− unit, and one O (O9) atom from the coordinated methanol molecule (Figure 7a).The coordination around the Co(II) atom is depicted as a trigonal bipyramid [54], and the τ value was estimated to be τ = 0.888 (Figure 7b) [55]   As shown in Figure 9 and Table 7, the three-dimensional supra-molecular network of complex 2  As shown in Figure 7, the Co(II) atom is penta-coordinated by two oxime N (N1 and N2) and phenoxo O (O1 and O6) atoms from one deprotonated (L) 2− unit, and one O (O9) atom from the coordinated methanol molecule (Figure 7a).The coordination around the Co(II) atom is depicted as a trigonal bipyramid [54], and the τ value was estimated to be τ = 0.888 (Figure 7b) [55]   As shown in Figure 9 and Table 7, the three-dimensional supra-molecular network of complex 2  As shown in Figure 9 and Table 7, the three-dimensional supra-molecular network of complex 2  Table 7. Hydrogen bondings (Å, °) for complex 2. Note: Cg6 = C15-C16-C17-C18-C20-C23; Cg4 = O7-C19-C23.

Crystal Structure Description of Complex 3
As illustrated in Figure 10 and Table 8, complex 3 exhibits a symmetric trinuclear structure, crystallizes in the triclinic system, space group P-1, includes two completely deprotonated (L) 2− units, three Ni(II) atoms, two benzoates and two coordinated methanol molecules.Table 7. Hydrogen bondings (Å, • ) for complex 2.

Crystal Structure Description of Complex 3
As illustrated in Figure 10 and Table 8, complex 3 exhibits a symmetric trinuclear structure, crystallizes in the triclinic system, space group P-1, includes two completely deprotonated (L) 2− units, three Ni(II) atoms, two benzoates and two coordinated methanol molecules.The terminal Ni2 atom is hexa-coordinated by two phenolic O (O3 and O9) and two oxime N (N1 and N2) atoms of the completely deprotonated (L) 2− moity, one O (O7) atom from the coordinated benzoate group and one O (O6) atom from the coordinated methanol molecule.The terminal Ni2 atom possesses a distorted octahedron geometry [59].The two oxime N (N1 and N2) and phenolic O (O3 and O9) atoms are in mutually cis-positions.Then, the central Ni1 atom is completed by double μ2-phenoxo O (O3 and O9) atoms from two (L) 2− moities and two O (O8 and O8#) atoms from two benzoate groups.Each of the benzoate groups bridges the central Ni1 and terminal Ni2 atoms in the syn-syn bridging mode, as a result the central Ni1 atom finally possesses an O2O2O2 coordination environment (Figure 10b) [59].The dihedral angles between the benzene rings of (L) 2− moities and the N2O2 basal plane are 32.87(2)° and 23.66(2)°, respectively, which defined as shown in Figure 11a.The dihedral angle between the planes of N1-Ni2-N2 and O3-Ni2-O9 is 6.50(2)° (Figure 11b) [59].8. Selected bond lengths (Å) and angles ( • ) for complex 3.

Bond
The terminal Ni2 atom is hexa-coordinated by two phenolic O (O3 and O9) and two oxime N (N1 and N2) atoms of the completely deprotonated (L) 2− moity, one O (O7) atom from the coordinated benzoate group and one O (O6) atom from the coordinated methanol molecule.The terminal Ni2 atom possesses a distorted octahedron geometry [59].The two oxime N (N1 and N2) and phenolic O (O3 and O9) atoms are in mutually cis-positions.Then, the central Ni1 atom is completed by double µ 2 -phenoxo O (O3 and O9) atoms from two (L) 2− moities and two O (O8 and O8#) atoms from two benzoate groups.Each of the benzoate groups bridges the central Ni1 and terminal Ni2 atoms in the syn-syn bridging mode, as a result the central Ni1 atom finally possesses an O 2 O 2 O 2 coordination environment (Figure 10b) [59].The dihedral angles between the benzene rings of (L) 2− moities and the N 2 O 2 basal plane are 32.87(2)• and 23.66(2) • , respectively, which defined as shown in Figure 11a.The dihedral angle between the planes of N1-Ni2-N2 and O3-Ni2-O9 is 6.50(2) • (Figure 11b) [59].9. Hydrogen bondings (Å, • ) for complex 3.

D-H•••A D•••A D-H•••A
C8-H8 As illustrated in Figure 13, two pairs of inter-molecular hydrogen bondings, O6-H6•••O1 and C12-H12A•••O11 are formed.The proton (-C12H12A) of the ((L) 2− moity forms hydrogen bondings with the O (O11) atom of four adjacent complex 3 molecules.Meanwhile, the proton (-O6H6) of the coordinated methanol molecule forms hydrogen bondings with the O (O1) atom from the (L) 2− moity of four adjacent complex 3 molecules.The space skeleton of complex 3 possesses a two-dimensional supra-molecular structure by the hydrogen bonding interactions [64].As illustrated in Figure 13, two pairs of inter-molecular hydrogen bondings, O6-H6•••O1 and C12-H12A•••O11 are formed.The proton (-C12H12A) of the ((L) 2− moity forms hydrogen bondings with the O (O11) atom of four adjacent complex 3 molecules.Meanwhile, the proton (-O6H6) of the coordinated methanol molecule forms hydrogen bondings with the O (O1) atom from the (L) 2− moity of four adjacent complex 3 molecules.The space skeleton of complex 3 possesses a two-dimensional supra-molecular structure by the hydrogen bonding interactions [64].Complexes 1, 2 and 3 with a coumarin-containing Salamo-type ligand H2L have been synthesized, and have different structures depending on the anions and cations used.In complexes 1, 2 and 3, the metal atom located at the Salamo N2O2 unit is tetra-, penta-and hexa-coordinated, respectively.As widely known, the coordination number of Cu(II) atom is generally four or five in Salamo-type Cu(II) complexes and the coordination geometry around Cu(II) atom is planar quadrilateral, tetrahedron or tetragonal pyramid [26,37,49,51].In complex 1, the coordination number of Cu(II) atom is four, the anions and the solvent molecules were not involved in the coordination.The coordination number of Co(II) atom is generally six, and the coordination geometry around Co(II) atom is octahedron [47,56,63,65].While in complex 2, the methanol molecule was involved in the coordination forming a mono-nuclear Co(II) complex.The coordination Complexes 1, 2 and 3 with a coumarin-containing Salamo-type ligand H 2 L have been synthesized, and have different structures depending on the anions and cations used.In complexes 1, 2 and 3, the metal atom located at the Salamo N 2 O 2 unit is tetra-, penta-and hexa-coordinated, respectively.As widely known, the coordination number of Cu(II) atom is generally four or five in Salamo-type Cu(II) complexes and the coordination geometry around Cu(II) atom is planar quadrilateral, tetrahedron or tetragonal pyramid [26,37,49,51].In complex 1, the coordination number of Cu(II) atom is four, the anions and the solvent molecules were not involved in the coordination.The coordination number of Co(II) atom is generally six, and the coordination geometry around Co(II) atom is octahedron [47,56,63,65].While in complex 2, the methanol molecule was involved in the coordination forming a mono-nuclear Co(II) complex.The coordination geometry around Co(II) atom is trigonal bipyramid, which is rare in the previously reported Salamo-type Co(II) complexes.In complex 3, both of the anions and the solvent molecules were involved in the coordination, this coordination pattern is frequently appeared in the Salamo-type trinuclear Ni(II) complexes, in which the three Ni(II) atoms are all hexa-coordinated with slightly distorted octahedral geometries [12,31,44,59], but the research on the Salamo-type trinuclear Ni(II) complex contained benzoate ligands is reported firstly.

Antimicobial Activities
Bacteriostasis tests on common bacteria, such as E. coli and S. aureus, were carried out by the punch method.A small amount (0.1 mL) of a fresh overnight bacterial suspension was added into autoclaved LB (lysogeny broth) agar, then the agar was poured into sterile dishes.The concentration of the test compounds were 0.6, 1.2 and 2.4 mg/mL.70 µL of samples were added into a burrowed hole measuring 5 mm in diameter with transfer liquid gun when the medium underwent solidification [65,66].
As shown in Figures 14 and 15, the zones of DMF, metal salts, H 2 L and complexes 1, 2 and 3 have apparent differences in antibacterial activity among two kinds of bacteria.The complexes 1, 2 and 3 displayed more enhanced antimicrobial activities than H 2 L under the same conditions (2.5 mg/mL), and the DMF and the metal salts also have a weak biological activity.Moreover, E. coli shows stronger antibacterial activity, whereas S. aureus possesses weaker antibacterial activity.This increase in the antibacterial activities of complexes 1, 2 and 3 were accompanied with an increase in concentration and can be explained on the basis of the chelation theory [65,66].Chelation reduces the polarity of the metal atom mainly due to partial share of positive charge of metal atom with donor groups and possible delocalization of π-electron within the whole chelate ring.Further, it enhances the lipophilic character of the central atom [66].
Crystals 2018, 8, x FOR PEER REVIEW 14 of 19 geometry around Co(II) atom is trigonal bipyramid, which is rare in the previously reported Salamo-type Co(II) complexes.In complex 3, both of the anions and the solvent molecules were involved in the coordination, this coordination pattern is frequently appeared in the Salamo-type trinuclear Ni(II) complexes, in which the three Ni(II) atoms are all hexa-coordinated with slightly distorted octahedral geometries [12,31,44,59], but the research on the Salamo-type trinuclear Ni(II) complex contained benzoate ligands is reported firstly.

Antimicobial Activities
Bacteriostasis tests on common bacteria, such as E. coli and S. aureus, were carried out by the punch method.A small amount (0.1 mL) of a fresh overnight bacterial suspension was added into autoclaved LB (lysogeny broth) agar, then the agar was poured into sterile dishes.The concentration of the test compounds were 0.6, 1.2 and 2.4 mg/mL.70 µL of samples were added into a burrowed hole measuring 5 mm in diameter with transfer liquid gun when the medium underwent solidification [65,66].
As shown in Figures 14 and 15, the zones of DMF, metal salts, H2L and complexes 1, 2 and 3 have apparent differences in antibacterial activity among two kinds of bacteria.The complexes 1, 2 and 3 displayed more enhanced antimicrobial activities than H2L under the same conditions (2.5 mg/mL), and the DMF and the metal salts also have a weak biological activity.Moreover, E. coli shows stronger antibacterial activity, whereas S. aureus possesses weaker antibacterial activity.This increase in the antibacterial activities of complexes 1, 2 and 3 were accompanied with an increase in concentration and can be explained on the basis of the chelation theory [65,66].Chelation reduces the polarity of the metal atom mainly due to partial share of positive charge of metal atom with donor groups and possible delocalization of π-electron within the whole chelate ring.Further, it enhances the lipophilic character of the central atom [66].3) derived from a Salamo-type coumarin-containing ligand (H2L) have been successfully prepared and well characterized.For the central metals, the Cu(II) atom of complex 1 is tetra-coordinated and the Co(II) atom of complex 2 is penta-coordinated with trigonal-bipyramidal geometry, and the Ni(II) atoms of complex 3 are hexa-coordinated possessing slightly distorted octahedral geometries.The complexes 1 and 2 are both possess the three-dimensional supra-molecular structures by abundant noncovalent interactions.But complex 3 is formed a two-dimensional supra-molecular structure by intra-molecular hydrogen bonds.Furthermore, the antimicrobial and fluorescence properties of H2L and complexes 1, 2 and 3 were also studied.

Figure 4 .
Figure 4. (a) X-ray crystal structure and atom numbering of complex 1 with 30% probability displacement ellipsoids; (b) Coordination polyhedron of Cu(II) atom of complex 1.

Figure 5 . 19 Figure 6 .
Figure 5. (a) View of the dihedral angles between the benzene rings and the N 2 O 2 basal plane of complex 1; (b) View of the dihedral angles between planes CuN 2 and CuO 2 of complex 1.

Figure 7 .
Figure 7. (a) X-ray crystal structure and atom numbering of complex 2 with 30% probability displacement ellipsoids; (b) Coordination polyhedron for Co(II) atom of complex 2.

Figure 8 .
Figure 8.(a) View of the dihedral angles between the benzene rings and the N2O2 basal plane of complex 2; (b) View of the dihedral angles between the planes CoN2 and CoO2 of complex 2.

Figure 7 .
Figure 7. (a) X-ray crystal structure and atom numbering of complex 2 with 30% probability displacement ellipsoids; (b) Coordination polyhedron for Co(II) atom of complex 2.

Figure 7 .
Figure 7. (a) X-ray crystal structure and atom numbering of complex 2 with 30% probability displacement ellipsoids; (b) Coordination polyhedron for Co(II) atom of complex 2.

Figure 8 .
Figure 8.(a) View of the dihedral angles between the benzene rings and the N2O2 basal plane of complex 2; (b) View of the dihedral angles between the planes CoN2 and CoO2 of complex 2.

Figure 8 .
Figure 8.(a) View of the dihedral angles between the benzene rings and the N 2 O 2 basal plane of complex 2; (b) View of the dihedral angles between the planes CoN 2 and CoO 2 of complex 2.

Figure 10 .
Figure 10.(a) X-ray crystal structure and atom numbering of complex 3 with 30% probability displacement ellipsoids; (b) Coordination polyhedrons for Ni(II) atoms of complex 3.

Figure 11 . 19 Figure 11 .
Figure 11.(a) View of the dihedral angles between the benzene rings and the N 2 O 2 basal plane of complex 3; (b) View of the dihedral angles between the planes NiN 2 and NiO 2 of complex 3.

Figure 13 .
Figure 13.View of the two-dimensional supra-molecular structure of complex 3 exhibiting the O-H•••O, C-H•••O hydrogen bonding interactions.

Figure 13 .
Figure 13.View of the two-dimensional supra-molecular structure of complex 3 exhibiting the O-H•••O, C-H•••O hydrogen bonding interactions.

Figure 14 .
Figure 14.The diameter of inhibition zones of E. coli in different concentrations.

Figure 14 .
Figure 14.The diameter of inhibition zones of E. coli in different concentrations.

Figure 15 .
Figure 15.The diameter of inhibition zones of S. aureus in different concentrations.