The chemical reagents (Ni(NO₃)₂· 6H₂O, dimethylsulfoxide, levofloxacin, lomefloxacin, nalidixic acid, oxolonic acid, pipemidic acid, and pefloxacin mesylate) received in this study were of analytical grade and used without further purifications. These chemicals were purchased from Aldrich-Sigma chemical company.

The microanalytical and spectroscopic analysis that used to discussed the chemical formula of nickel(Ⅱ ) quinolone complexes can be summarized in Table 2.

Table 2

Table 2

Table 2 The type of analysis and the model of instrument Type of analysis Models Elemental analyses Perkin Elmer CHN 2400 Molar Conductance Jenway 4010 conductivity meter FTIR spectra Bruker FTIR Spectrophotometer Electronic spectra UV2 Unicam UV/Vis Spectrophotometer Magnetic moment Magnetic Susceptibility Balance

Table 2 The type of analysis and the model of instrument

The six solid nickel(Ⅱ ) quinolone complexes were synthesized by mixing 2.0 mmol HLEV, HLOM, HNAL, HOXO, HPIP or HPEF drugs in 50 mL of methanol solvent with 1.0 mmol of Ni(NO₃)₂· 6H₂O in 20 mL of distilled water. The reaction mixtures were adjust the pH value between 8~9 using ammonia solution (5%), then the mixtures were refluxed on the hotplate for three hours till the precipitate appeared. After cooling to room temperature, the green solid complexes were filtered off and washed with a hot methanol and little amount of distilled water in order to remove the un-reacted chemicals. The clean precipitates were dried and stored in a glass desiccators over anhydrous CaCl₂. The yield of the isolated products was ranged between 77%~74%. The melting points of synthesized nickel(Ⅱ ) complexes have a higher m.p over > 250 ℃.

The elemental analysis (calculated/Found) and physical values of the six new nickel(Ⅱ ) quinolone complexes are listed in Table 3. The experimental percentage (%) of each elements C, H, N and nickel metal in situ synthesized complexes were matched with the theoretical values, which confirmed the speculated structures of the six nickel(Ⅱ ) complexes (Fig.1). The synthesized Ni(Ⅱ ) complexes were stable in air and insoluble in most organic solvent but soluble in dimethylsulfoxide (DMSO) and dimethylformamide (DMF) with warming. The molar conductivities (Λ _m) values are located within 9~12 ohm^-1· cm²· mol^-1, which were considered as non-electrolytes nature^[29].

Table 3

Table 3

Table 3 Microanalytical and physical data of Ni(Ⅱ ) quinolone complexes Complex Color Magnetic moment (BM) Conductance/ (ohm-1· cm2· mol-1) Element Calc. Found Ⅰ Light Green 3.32 12 %C 50.78 50.34 %H 5.45 5.32 %N 9.87 9.80 %Ni 6.89 6.82 Ⅱ Green 3.12 17 %C 49.12 49.06 %H 5.33 5.26 %N 10.11 10.04 %Ni 7.06 7.05 Ⅲ Green 3.36 11 %C 48.59 48.49 %H 5.10 5.09 %N 9.44 9.41 %Ni 9.89 9.88 Ⅳ Green 3.42 14 %C 45.44 45.34 %H 4.69 4.64 %N 4.08 4.02 %Ni 8.54 8.48 Ⅴ Green 3.47 16 %C 43.60 43.45 %H 5.75 5.72 %N 18.16 18.07 %Ni 7.61 7.54 Ⅵ Green 3.28 9 %C 51.34 51.26 %H 5.83 5.78 %N 10.57 10.34 %Ni 7.38 7.29

Table 3 Microanalytical and physical data of Ni(Ⅱ ) quinolone complexes

Fig.1

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	Fig.1 Speculated structures of Ni(Ⅱ ) quinolone complexes

The infrared spectra of free quinolone drugs (HLEV, HLOM, HNAL, HOXO, HPIP, and HPEF) and corresponding nickel(Ⅱ ) complexes (Fig.2) have been assigned to identify the site of coordination and speculated structures (Table 4). Regarding the six Ni(Ⅱ ) complexes, the stretching vibration bands of ν (C& #61; O)_COOH carboxylic group which are existed at 1 708~1 728 cm^-1 in the spectra of the free HLEV, HLOM, HNAL, HOXO, HPIP, and HPEF ligands are disappeared as well as the frequencies take place at 1 618~1 639 cm^-1 due to ν (C& #61; O)_pyridone are shifted to lower wavenumbers after complexation. These results confirm that nickel(Ⅱ ) metal ions is coordinated to chelate molecule through oxygen atoms of deprotonated carboxylic group and oxygen of pyridine ring. Table 4 includes the frequencies data of the vibrations of carboxylate anion for the nickel(Ⅱ ) complexes as well as differences in the values of these vibrations Δ (COO). According to Nakamoto, this allows the assessment of the metal-acid coordination mode^[30]. In the case of LEV (Ⅰ ), LOM (Ⅱ ), NAL (Ⅲ ), OXO (Ⅳ ), PIP (Ⅴ ), and PEF (Ⅵ ) nickel(Ⅱ ) complexes, the difference in wavenumbers of stretching vibrations of asymmetric ν _as(COO) and asymmetric ν _s(COO) carboxylate anions (Δ ν =ν _asCOO-ν _sCOO) for all nickel(Ⅱ ) complexes is higher than for sodium salts (304~328 cm^-1) indicates a mono-dentate chelate of metal-to-ligand coordination by a carboxyl group. The broad band at 3 433 cm^-1 is attributed to the stretching vibrations of coordinated and uncoordinated water molecules. The three distinguish motions of water molecules, δ _r(H₂O), δ _w(H₂O), and δ _t(H₂O) are observed at 766, 550, 710 cm^-1, respectively with agreement with aquo-complexes^[30]. The presence of new stretching vibration bands within 500~400 cm^-1 range are assigned to the frequencies of ν (Ni— O) vibrations in case of nickel(Ⅱ ) complexes (Ⅰ — Ⅵ )^[30].

Fig.2

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	Fig.2 Infrared spectra of Ni(Ⅱ ) quinolone complexes (Ⅰ — Ⅵ )

Table 4

Table 4

Table 4 FTIR assignments of Ni(Ⅱ ) quinolone complexes (Ⅰ — Ⅵ ) Compounds Assignments/cm-1 ν (O— H) ν (C& #61; O)COOH ν (C& #61; O)pyridone ν (C& #61; N)pyridine δ (C— R)pyridine ν as(COO) ν s(COO) Δ (COO) HLEV 3 429 1 722 1 618 1 451 - - - Ⅰ 3 433 - 1 610 1 448 1 580 1 271 309 HLOM 3 440 1 728 1 624 - - - - Ⅱ 3 414 - 1 617 - 1 580 1 253 327 HNAL 3 425 1 708 1 624 - - - - Ⅲ 3 367 - 1 610 - 1 571 1 263 308 HOXO 3 438 1 711 1 639 1 461 - - - Ⅳ 3 396 - 1 590 1 487 1 590 1 263 327 HPIP 3 459 1 710 1 633 - - - - Ⅴ 3 422 - 1 602 - 1 549 1 245 304 HPEF 3 444 1 721 1 637 1 486 - - - Ⅵ 3 414 - 1 600 1 477 1 553 1 225 328

Table 4 FTIR assignments of Ni(Ⅱ ) quinolone complexes (Ⅰ — Ⅵ )

The electronic spectra of six nickel(Ⅱ ) quinolone complexes contains three absortion bands exhibited at three regions as 13 333~14 388, 14 535~15 674, and 24 390~25 707 cm^-1, these electronic transition bands are assigned to ³A_2g→ ³T_2g (F), (ν ₁); ³A_2g→ ³T_1g (F), (ν ₂) and ³A_2g→ ³T_2g (P), (ν ₃) transitions, respectively. The divide data of ν ₂/ν ₁ ratios concerning the synthesized nickel(Ⅱ ) complexes are presence at 1.04~1.16, this results located within the range of an octahedral geometry for the Ni(Ⅱ ) complexes (Table 5)^[31]. The low values of ν ₂/ν ₁ are due to the strong interaction between ³T_1g (P) and ³T_1g (F) states. The Racah inter-electronic repulsion (B), ligand field splitting energy (10 Dq), covalency factor (β ) and ligand field stabilization energy (LFSE) as a physical spectroscopic parameters have been estimated according to the electronic spectra. The B parameter is low in comparison with free nickel(Ⅱ ) ion (1 038 cm^-1), this meaning that nickel(Ⅱ ) complexes have a covalent character. The covalency factor (β ) of the six nickel(Ⅱ ) complexes has data within 0.04~0.17 region and the percentage lowering of energy in free gaseous ion (β ° ) has data within 82%~96% which their assigned to the covalency nature of complexes.

Table 5

Table 5

Table 5 Ligand field parameters of the Ni(Ⅱ ) quinolone complexes (Ⅰ — Ⅵ ) Ligand Field parameters Complexes Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ Ⅵ 3A2g→ 3T2g (F), (ν 1)/cm-1 13 333 13 850 14 006 14 184 14 084 14 388 3A2g→ 3T1g (F), (ν 2)/cm-1 15 408 14 903 14 535 14 992 14 925 15 674 3A2g→ 3T2g (P), (ν 3)/cm-1 25 707 24 390 24 691 24 331 25 316 25 641 Dq/cm-1 1 333 1 385 1 401 1 418 1 408 1 439 ν 2/ν 1 1.16 1.08 1.04 1.06 1.06 1.09 B/cm-1 181 90 45 68 71 109 β 0.17 0.09 0.04 0.065 0.068 0.11 β ° /% 82 91 96 93 93 89 LFSE/(kcal· mol-1) 15 999 16 620 16 807 17 021 16 901 17 266

Table 5 Ligand field parameters of the Ni(Ⅱ ) quinolone complexes (Ⅰ — Ⅵ )

The experimental effective magnetic moment of the nickel(Ⅱ ) quinoloe complexes (Ⅰ — Ⅵ ) are presence within 3.12~347 BM that agreement with the high spin octahedral geometry (3.00~3.50 BM)^{[31, 32]}. The high spin values may be assigned to the quenched of ³A_2g ground state regarding the Ni(Ⅱ ) ion in an octahedral structure^{[31, 32]}.