INTRODUCTION:

The design and synthesis organic and inorganic homo and hetero-metallic coordination polymers is one of the most interesting topics in current coordination chemistry and crystal engineering. Thanks to unique structures, properties and reactivity a lot of hybrid coordination polymers has been employed in catalysis, molecular adsorption, molecular magnetism, non-linear optics, luminescence or model bioinorganic chemistry^1-6. Nair et al.⁷ have also reported synthesis and characterization of transition metal complexes of Cu(II), Ni(II) and Zn(II). Heterobimetallic bridged complexes can be formed in step-wise fashion from a mononuclear compound which contain a dangling ligand. The first spin crossover complexes were reported by Brewer.⁸ These complexes are also of interest in bioinorganic chemistry due to the importance of the structurally similar porphyrin complexes with unsymmetrical axial ligation.^9-11 Bridged bis-(2-amino benzophenone)malonyidihydrazone complexes form a family of molecules with a remarkable potential for binding to additional species. Their chemical importance and reactions are controlled by the nature of the metal ion and the substituent groups. In this view we have started a systematic study involving the synthesis, chazation and toxicity of heterobinuclear complexes.

MATERIAL AND METHODS:

Hydrated Mn(II), Co(II), Ni(II), Cu(II) chlorides(BDH), 5-nitroindazole (Fluka), diethyl malonate, hydrazine, 2-amino benzophenone (Merck) were used as received. The transition metal complexes of 5-nitroindazole³⁰ and bis-(2-amino benzophenone)malonyldihydrazone^31,32were prepared by the method reported earlier.

Preparation of [NiL₁Cl₂Cu(L₂)₂]:

The solution of [Cu(L₂)₂Cl₂] (1mole) in dry DMF (25 ml) was treated with a methanolic solution (20ml) of [NiL₁]Cl₂(1mole). The pale-green solution of [Cu(L₂)₂Cl₂] changed to blue after addition of the solution of [NiL₁]Cl₂. The mixture was refluxed for ca. 8h. The crystalline solid which was separated out on cooling the mixture was filtered, washed with alcohol ether and dried in vacuo.

Preparation of [CuL₁Cl₂Ni(L₂)₂]:

The solution of [Ni (L₂)₂Cl₂] (1mole) in dry DMF (20 ml) was treated with a methanolic solution (20ml) of [CuL₁]Cl₂(1mole). The light green solution of [Ni (L₁)₂Cl₂] changed to dark green on mixing the solution of [Ni(L₂)₂Cl₂] with [CuL₁]Cl₂. The mixture was refluxed for ca. 12h. The green crystals were separated on keeping the solution in a refrigerator overnight at 0-5 C. The crystals were filtered, washed with ethanol, ether and dried in vacuo.

Preparation of [NiL₁Cl₂Mn(L₂)₂]:

The solution of [Mn(L₂)₂Cl₂] (1mole) in dry DMF (20 ml) was treated with a methanolic solution (20ml) of [NiL₁]Cl₂(1mole) and refluxed for 10h and then kept in a refrigerator overnight. A cream coloured product was formed. It was filtered, washed with ethanol, ether and dried in vacuo.

Preparation of [CuL₁Cl₂Mn(L₂)₂]:

This complex was prepared by the same procedure as above.

Preparation of [NiL₁Cl₂Co(L₂)₂]:

The solution of [Co(L₂)₂Cl₂] (1mole) in dry DMF (20ml) was treated with a methanolic solution (20ml) of [NiL₁]Cl₂(1mole). The purple solution of [Co(L₂)₂Cl₂] changed to blue after addition of the solution of [NiL₁]Cl₂. A yellow coloured product was precipitated on refluxing for 6 h.The compound was filtered, washed with alcohol ether and dried in vacuo.

Preparation of [CuL₁Cl₂Co(L₂)₂]:

This complex was prepared by the same procedure as above.

Toxicity and Probit Analysis:

To investigate the toxicity of the complexes in terms of LD₅₀ the graphical method has been evaluated.³³

The toxicity of a substance in terms of Probit analysis is determined against the stimuli of living organisms. Usually, the stimulus is applied to a set of experiments and the reaction of each set is determined.

Varying concentrations of the compound are prepared and a set of insects are exposed (or fed) to each set of insects, counts were made at the total number df insects (n) and number killed (r). The result may be expressed either as a proportion (r/n) or as a percentage 100 (r/n) where n = 10. Such data may then be applied for Probit analysis in assessing the various toxic substances and lethal doses.

Practical Application of Probit Analysis:

Since we expect to get a straight line when Probits are plotted against dosage, the methods of linear regression are suggested.

To measure the potency of a preparation it has been found that the dose giving a 50% kill is statistically the most instructive one and is referred to as LD₅₀ (median lethal dose). In the experiments where the response is not death, we referred to the ED₅₀ (median effective dose). Whatever practical advantages there may be in knowing the LD₉₀ or some similar value, the fact is that much greater precision can be obtained in the measure of LD₅₀ which is corresponding to a Profit value of 5.

Another factor to be measured is the range of the dosage required for a given range of percentage kill. This might be referred to us the sensitivity of the preparation tested. Obviously, if small change in concentrations give a wide range in the percentage kill, the sensitivity is high and this is represented by the slope of the line. The greater the slope of narrower the range in dosage for a given range in the percentage kill. The geometry of the line would seem to give, therefore, the required measure potency and sensitivity. Taking two points, X₁ and X₂, representing the dosage on the abscissa of the graph and finding the corresponding points Y₁ and Y₂ on the Probit scale, will the slope of the line. If b represents the slope, then

Y₂-Y₁

b= -------------

X₂-X₁

This makes it possible to set up a regression equation of the type

Y= a + bx

Where, a =Y₁-bx₁, or Y₂-bx₂.

Toxicity experiments were done on cockroaches, equal number of individuals in five steps were taken and allowed to feed on heterobinuclear complexes in different concentrations ranging from 8-12ppm (w/w).A control set was also run simultaneously and the set insects were kept under observation. The % mortality was recorded after 24h.

RESULTS AND DISCUSSIONS:

The complexes were prepared according to the following equations,

Table I. Analytical Data, Melting Points and % Yields of Heterobinuclear Complexes

Complexes	Empirical Formula	Colour	m.p. (^OC) ± 2	Yield (%)	Calcd (Founds) %
Complexes	(Formula Weights)	Colour	m.p. (^OC) ± 2	Yield (%)	C	H	N	Cl
[NiL₁Cl₂Cu(L₂)₂]	C₄₃H₃₄Cl₂NiN₁₂O₆Cu (1008.047)	Light Green	300	30	51.23 (51.26)	3.39 (3.41)	16.67 (16.68)	7.04 (7.05)
[CuL₁Cl₂Ni(L₂)₂]	C₄₃H₃₄Cl₂CuN₁₂O₆Ni (1008.047)	Pale Green	310	25	51.23 (51.25)	3.39 (3.40)	16.67 (16.68)	7.04 (7.04)
[NiL₁Cl₂Mn(L₂)₂]	C₄₃H₃₄Cl₂NiN₁₂O₆Mn (999.439)	Cream	320	28	51.67 (51.69)	3.42 (3.44)	16.81 (16.83)	7.10 (7.12)
[CuL₁Cl₂Mn(L₂)₂]	C₄₃H₃₄Cl₂CuN₁₂O₆Mn (1004.285)	Brown	335	35	51.42 (51.44)	3.41 (3.42)	16.73 (16.74)	7.06 (7.08)
[NiL₁Cl₂Co(L₂)₂]	C₄₃H₃₄Cl₂NiN₁₂O₆Co (1003.434)	Yellow	325	30	51.47 (51.49)	3.41 (3.42)	16.75 (16.76)	7.07 (7.08)
[CuL₁Cl₂Co(L₂)₂]	C₄₃H₃₄Cl₂CuN₁₂O₆Co (1008.280)	Dirty Yellow	295	40	51.22 (51.24)	3.39 (3.41)	16.67 (16.69)	7.04 (7.05)

All the complexes are soluble in DMSO or DMF in the range^12,13of nonelectrolytes for the heterobinuclear complexes. As a consequence, bis-(2-amino benzophenone)malonyldihydrazone Cu(II))/Ni(II) chloride with dichlorobis(5-nitroindazole)M₂(II) form a covalent bond in the inner sphere of the binuclear complexes.

Table II. Important IR Spectral Data (cm^-1) of the Heterobinuclear Complexes

Complexes	ν(NH₂)	ν(N-H)	Ring Stretching	ν(NO₂)(Asym/Sym)	ν(C=N)	ν(M-N)	ν(M-Cl)
[NiL₁Cl₂Cu(L₂)₂]	3435b	3336m	1511s	1559s/1350s	1403S	460m	321m
[CuL₁Cl₂Ni(L₂)₂]	3430b	3329m	1628s	1566s/1348s	1405S	460m	334m
[NiL₁Cl₂Mn(L₂)₂]	3449b	3320m	1614s	1534s/1390s	1461S	460m	321m
[CuL₁Cl₂Mn(L₂)₂]	3448b	3332m	1618s	1533s/1398s	1460S	460m	329m
[NiL₁Cl₂Co(L₂)₂]	3445b	3327m	1623s	1533s/1390s	1477S	460m	321m
[CuL₁Cl₂Co(L₂)₂]	3449b	3330m	1629s	1537s/1381s	1461S	460m	337m

IR Spectra of the heterobinuclear complexes:

The relevant IR bands and their assignments are cited in Table II.

The IR spectra of the binuclear complexes under investigation show several bands belonging to 5-nitroindazole. They are considerable changed compared with the relevant bands of the ligands and monometallic complexes.¹⁴

The band centered at 1623cm^-1 assigned to ν(C-N) vibrations^15,16is shifted in the binuclear complexes to the higher energy (123 cm^-1) indicating that nitrogen takes part in the coordination. Strong bands at 1460 and 3332 cm^-1 due to ν(C-N) and v(N-H), respectively, remain unaltered in the binuclear complexes. New bands due to the NH₂ group of the [M₁L₁]Cl₂ complexes in the range 3420-3470 cm^-1 appear confirming binuclear complexation. The far-IR spectral data with assignments of ν(M-N) (440-490 cm^-1), ν(M-Cl) (310-350 cm^-1) and ν(Cu-N) and ν(Ni-N) (405-435 cm^-1) bands are given in Table II. Our results are consistent with the results reported earlier.^17-22

Electronic Spectra and Magnetic Moments:

In Table III are listed the magnetic moment values, EPR parameter and UV-Vis, spectral data of the heterobinuclear complexes. The µ_effvalues of the binuclear complexes deviate from their calculated values due to change in the environment²³ on the central metal atom. The binuclear complexes possess antiferromagnetic properties at room temperature by intramolecular spin exchange interaction between M₁ and M₂ metal ions.²⁴The electronic spectra of the complexes contain mixed transitions due to two different metal ions in different oxidation states and different coordination numbers. M₁ is associated with square planar geometry while M₂ is octahedral environment.^25,26

The peak at 554nm due to [NiL₁]Cl₂ disappears, indicating a change in oxidation of Ni(II) to Ni(0) and Mn(II) to Mn(IV). This is unique redox reaction in the series. The heterobinuclear complexes of [CuL₁Cl₂] have low magnetic moment values which is due to weak antifarromagnetic interaction. While with [NiL₁Cl₂] the magnetic moment value is high due to a large diamagnetic group attached to the central metal ion. Our results are consistent with the heterobinuclear Ni(II)-Gd(II) complexes.²⁷

EPR Spectra:

The EPR spectra of heterobinuclear complexes were recorded at room temperature. The spectra of [Cu(II)L₁Cl₂Co(II)(L₂)₂] shows g_II= 1.93, g_┴ =1.86 which are relatively lower than the characteristic values of octahedral Cu(II) in a octahedral environment. The signals of two different metals are merged together and new signals are obtained. The heterobinuclear compounds exhibit a slightly higher g_┴ values and a higher g_II values than Co(II) in a square-planar environment. This might be expected if the interaction changes the geometry of the central metal ion.²⁸

Complexes	Transition(cm-¹) (values,cm^-1M^-1)	Assignments	EPR (Value) µeff(B.M.) g_II /g_┴
[CuL₂Cl₂Ni(L₂)₂]	14,390 (540) 17,250 (324) 21,270 (2.4)	²B_1g→²A_1g ²E_g→²T_2g ¹A_g→¹B_1g ¹A_g→¹B_2g	1.78	2.13/ 2.23
[NiL₂Cl₂Cu(L₂)₂]	15,670 (210) 23,315 (6.4) 15,500 (5.9)	²A_2g→³T_1g (F) ³A_2g→³T_1g(P) ²A_1g←²B_1g	2.85	----
[MnL₂Cl₂Ni(L₂)₂]	20,000 (300) 18,181 (265) 12,500 (45)	⁴A_2g→⁴T_1g(P) ⁴A_2g→³A_1g ⁴A_2g→⁴T_2g	3.90	----
[MnL₂Cl₂Cu(L₂)₂]	38,310 (54) 25,440 (425) 20,400 (8.4) 16,594 (410)	C.T. ⁴A_1g(G) ←⁶A_1g ⁴T_2g(G) ←⁶A_1g ²E_g←²B_1g ⁴T_1g(G) →⁶A_1g	5.10	2.03
[CoL₂Cl₂Ni(L₂)₂]	6,568 (3.2) 14,410 (4.2) 21,270 (3.5) 16,389 (2.5)	⁴T_2g(F) ←⁴T_1g(F) ⁴A_g(F) →⁴T_1g(F) ¹A_1g→¹B_1g ¹A_1g→¹B_2g	----	----
[CoL₂Cl₂Cu(L₂)₂]	6,568 (3.2) 14,410 (5.2) 18,235 (5.3) 15,500 (6.4) 20,300 (9)	⁴T_2g(F) ←⁴T_1g(F) ⁴A_2g(F) ←⁴A_1g(F) ⁴T_1g(P) ←⁴T_1g(F ²A_1g←¹B_1g ²E_1g→²B_1g	1.93	1.86

Table-IV. % Mortality of Cockroaches at Different Concentration of Heterobinuclear Complexes

Long Conc. (In ppm x 100)	% Mortality [NiL₁Co(L₂)₂Cl₂/CuL₁Co(L₂)₂Cl₂	Probit Values	LD₅₀ Ni or Cu Complexes
2.9	30/20	4.45750/4.1584
2.95	50/30	5.000/4.4750
3	60/50	5.2533/5.000	8.94/10.00
3.04	60/80	5.8416/5.2833
3.07	80/100	5.8416/-

The EPR spectra of the complex [Cu(II)L₁Cl₂Mn(II)(L₂)₂] at room temperature show a broad signal due to spin crossover of one unpaired electron of the Cu(II) ion in the binuclear complex. The values of g_II and g_┴ for copper are suppressed by Mn(II) spin-spin interaction, which is further supported by the µ_eff value which is lower than the calculated value.

TOXICITY:

The toxicity of two representative heterobinuclear complexes (Table IV) (Ni with Co and Cu with Co) was tested by the standard method.²⁹

Experiments were done on cockroaches, % mortality of the insects was plotted against the concentration of the compound in ppm (w/w) which gave a sigmoid curve. Since it was not a straight line, the data pertaining to percentage kill were transferred into Probit and were plotted against log concentration (in ppm x 100). The LD₅₀ values were calculated at Probit 5. It is evident from LD₅₀ values that the Ni-containing compounds are more toxic than Cu ones.

This may be due to the biological significance of Cu ion which is more than the Ni metal ion.

Physical Measurements:

The IR and far-IR spectra (4000-200cm^-1) were recorded on a Perkin Elmer 621 spectrophotometer in KBr and Nujol, respectively. UV-Vis spectra were run on a Systronic 119 spectrophotometer in DMF. Magnetic susceptibility measurements were made on a Gouy balance using Hg[Co(NCS)₄] as calibrating agent, χ_g = 16.44 x 10^-6 cgs units. The NMR and EPR spectra were recorded on Bruker 500 MHz and Bruker ESP-300X band spectrometers, respectively. The conductivity measurements were made in DMF on a type CM-82T Elico conductivity bridge. Elemental analysis done on a model 1106 Carlo Erba microanalyzer. Determinations of chloride ions were done by a standard gravimetric method and metals were determined by atomic absorption using a portable digital voltmeter (PDV-2000). Chemotronics Ltd., Bentley-6102, Perth, Western Australia.

CONCLUSION:

On the basis of above studies, we can say that figure-1 shows the product of all six heterobinuclear complexes separately.

Figure 1. Heterobinuclear complex of the type [M₁L₁Cl₂M₂(L₂)₂]

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Received on 13.12.2010 Modified on 17.01.2010

Asian J. Research Chem. 4(5): May, 2011; Page 700-704