缩二脲钴配合物的合成.表征与热分解(英文)

　　摘要在甲醇溶液中，以乙酸钴、氯化钴、硝酸钴和缩二脲为原料合成了3种结构不同的缩二脲钴配合物.通过元素分析、红外光谱、X射线粉末衍射和热分析对产物进行了表征，其化学组成为[Co（bi）2（H2O）2]（Ac）2・H2O （1），[Co（bi）2Cl2] （2）和[Co（bi）3]（NO3）2・2.5H2O （3） （bi = NH2CONHCONH2）.配合物1中每个Co2+与2个缩二脲分子中的4个羰基氧原子和2个水分子中的氧原子配位，配合物2中每个Co2+与2个缩二脲分子中的4个羰基氧原子和2个氯原子配位，而配合物3中每个Co2+与6个全部来自缩二脲分子的羰基氧原子配位，均形成了配位数为6的配合物.配合物1和3的热分解过程包括失水和配体的分解，而配合物2的热分解过程只是配体的分解过程，最后完全分解形成氧化钴. 　　关键词缩二脲；钴配合物；表征；热分解 　　Biuret is a kind of important chelating ligand， and can act as an O，O′bidentate neutral ligand or N，N′bidentate anionic ligand binding to metal ions， such as scandium（Ⅲ）[1]， copper（Ⅱ）[2]， samarium（Ⅲ）[3]， thorium（IV）[4] and so on. In recent years the chemistry of biuret and related compounds attracts increasing attention. A novel biscyclometalated complex named [Ir2（mbiuretato N，N′：O，O′）（ptpy）4] was obtained and studied[5]. Whats more， a research in thermal degradation kinetics of biuretformaldehyde polymeric ligand was done lately[6]. In animal husbandry， biuret is an excellent feed additive for ruminants， it has the advantages of good palatability， low toxicity and easy to digest， and is safer than other non protein nitrogen feed additives， such as urea. In medicine， biuret can be used for the preparation of hypnotics and sedatives and it is also good at lowering the blood pressure. In chemical industry， biuret can be utilized as raw materials for synthesis of paints， lubricants， and coatings. At home， the complexes of biuret ligand have been rarely reported[79]， especially in the comparison of different anions in the synthesis of Co（Ⅱ） complexes. The biuret complexes of trace elements as feed additives for ruminants can play a dual role of essential trace elements and non protein nitrogen nutrition supplements. Here we report three Co（Ⅱ） complexes synthesized with biuret and three different cobalt salts. 　　1Experimental 　　1.1Materials and physical measurements 　　All chemicals purchased were of analytical reagent grade and used without further purification. Cobalt acetate tetrahydrate， cobalt chloride hexahydrate， cobalt nitrate hexahydrate and biuret were purchased from Sinopharm Chemical Reagent Co. Ltd. of Shanghai. 　　Elemental analyses for C， H and N in the complexes were measured on a Vario EL CUBE elemental analyzer， and the content of cobalt was determined by EDTA complexometric titration with murexide as indicator. IR spectra were obtained with KBr pellets on a Nicolet 5700 FTIR spectrophotometer in the range of 4 000～200 cm-1. The powder Xray diffraction measurements were recorded on a D/maxⅡ Xray diffractometer in the diffraction angle range of 3～80°. The thermogravimetric analysis data were obtained using a SDT Q600 thermogravimetry analyzer in the air atmosphere in the temperature range of 20～800 ℃ with a heating rate of 10 ℃ min-1. 　　1.2Synthesis of [Co（bi）2（H2O）2]（Ac）2・H2O （1） 　　湖南师范大学自然科学学报第38卷第5期王美玲等：缩二脲钴配合物的合成、表征与热分解Co（CH3COO）2・4H2O （2.49 g， 10 mmol） and biuret （2.06 g， 20 mmol） were weighed and dissolved in 100 mL methanol. The mixed solution was stirred on a magnetic stirrer for about 6 h under reflux reaction. After the solution cooling， the resultant was separated from the reaction mixture by filtration， and washed by methanol and dried in the phosphorus pentoxide desiccator for 1 week. The product was pink powder （3.38 g） and the yield was about 77%. 　　1.3Synthesis of [Co（bi）2Cl2] （2） 　　Complex 2 was synthesized by the same procedure as that for preparation of complex 1 except for using CoCl2・6H2O （2.38 g， 10 mmol） instead of Co（CH3COO）2・4H2O as the start reactant. The product was fuchsia powder （2.36 g） and the yield was about 70%. 　　1.4Synthesis of [Co（bi）3]（NO3）2・2.5H2O （3） 　　Complex 3 was synthesized by the same procedure as that for preparation of complex 1 except for using Co（NO3）2・6H2O （2.91g， 10 mmol） instead of Co（CH3COO）2・4H2O as the start material. The product was light red powder （3.20 g） and the yield was about 60%. 　　2Results and Discussion 　　2.1Composition and property 　　The results of elemental analyses for the complexes are shown in Tab.1. As shown in Tab.1， the composition formulae of the complexes are CoC8H22O11N6， CoC4H10O4N6Cl2 and CoC6H20O14.5N11， respectively. The three complexes are consistent with the target products [Co（bi）2（H2O）2]（Ac）2・H2O， [Co（bi）2Cl2]， and [Co（bi）3]（NO3）2・2.5H2O （bi = NH2CONHCONH2）. The water molecules in the complexes come from the crystal water in the raw materials of inorganic salts. In order to make sure whether chlorine atoms were coordinated or ionic， a qualitative test was conducted， namely， a few drops of AgNO3 solution was added into aqueous solution containing complex 2 and there was no deposition at first. This indicated that the chlorine atoms were coordinated. However， the transparent solution became turbid with the increasing amount of AgNO3 solution， and this showed that the coordination ability of chlorine atom was not very strong. The molar ratio of Co（Ⅱ） to biuret in complex 1 and 2 is 1∶2， while in complex 3 is 1∶3. The three solid complexes are stable in the air， easily dissolved in water， and not easy to absorb moisture. 　　Tab.1Elemental analysis results of the complexes （Calculated values are in brackets） 　　ComplexFormulaMrw（Co）/%w（C）/%w（H）/%w（O）/%w（N）/%1CoC8H22O11N6437.2313.31 （13.48）22.08 （22.14）5.20 （5.08）40.50 （40.25）19.09 （19.23）2CoC4H10O4N6Cl2335.9917.48 （17.54）14.43 （14.29）2.82 （2.98）18.83 （19.05）24.84 （25.00）3CoC6H20O14.5N11537.2010.79 （10.97）13.19 （13.40）3.69 （3.72）43.34 （43.19）28.79 （28.67）2.2IR spectroscopy analysis 　　The IR spectra of three complexes are shown in Fig.1， and the main infrared spectral data of biuret and its complexes are listed in Tab.2. Biuret exhibits two strong N―H stretching bands at 3 363 and 3 185 cm-1[10]. The wide absorption peaks in three complexes from the stretching vibrations of O―H and N―H appear in the region of 3 450～3 100 cm-1， which are due to hydrogen bond in ligands and water molecules in the complexes. There is absorption peak at 1 623 cm-1 for 1 and 1 609 cm-1 for 3， which can be attributed to the bending vibration of water molecules and consistent with the molecular formulae of the complexes. The carbonyl stretching frequencies in compounds containing the CO―NH―CO group is reported to give rise to two bands[1112]， the symmetric stretching vibration peak appears above 1 700 cm-1 and the asymmetric stretching vibration peak appears near 1 700 cm-1. When coordination occurs， it determines the amount of electron delocalization in the N―CO―N system， thus， coordination through the oxygen atom will produce a decrease in the double bond character of CO bond and a shift of the carbonyl stretching mode to lower frequencies[13]. As shown in the spectra， there is absorption peak near 1 697 cm-1， and the measured frequencies are a little lower than theoretical values， which accords with the molecular internal environment. There are the characteristic absorption peaks of carboxyl at 1 411 cm-1 and 1 684 cm-1， and this indicates the existence of COO- in complex 1. The absorptions peaks at 1 388 cm-1 and 819 cm-1 originate from the stretching vibrations and bending vibrations of N―O bond in NO-3， which is the evidence of the existence of NO-3 in complex 3， however， the NO-3 doesnt coordinate to Co（Ⅱ） ion. In the lowfrequency region， the absorption peak at 469 cm-1 in three complexes is assigned to the stretching vibration of Co―O bond[14]. 　　Wavenumber/cm-12θ/（°） 　　Fig.1IR spectra of three complexesFig.2XRD patterns of three complexes 　　（a）―complex 1， （b）―complex 2， （c）―complex 3（a）―complex 1， （b）―complex 2， （c）―complex 3 　　Tab.2Infrared spectra of the ligand and the complexes （cm-1） 　　bi[Co（bi）2（H2O）2]（Ac）2・H2O[Co（bi）2Cl2][Co（bi）3]（NO3）2・2.5H2Ovibration type3 4143 428， 3 3883 3953 422， 3 401νas（NH2）+ν（H2O）3 253， 3 0813 201， 3 1123 194， 3 0923 304， 3 207νs（NH2）1 726， 1 6901 6841 6971 697ν（CO）1 620， 1 5801 6231 5821 609δ（NH2）1 499， 1 4201 5121 4921 499ν（C―N）+ν（C―NH2）1 3301 3341 3341 334δ（N―H）1 1301 1291 1291 129ν（C―N）+δ（N―H）1 0801 0651 1081 059ν（C―N）[1**********]4ν（C―N）+ν（C―NH2）[1**********]5δ（C―NH2）[1**********]4δ（CO）2.3Xray powder diffraction analysis 　　The XRD patterns of the three complexes are shown in Fig.2. As shown in Fig.2， the background of the XRD patterns is small and the diffractive intensity is strong， and the results indicate that the complexes have fine crystalline state. Comparing with the reactants， the strong peak locations of three complexes are changed obviously. The three main strong peaks appear in 2θ=23.81°， 13.52° and 10.29° for complex 1， and in 2θ=21.8°， 28.6° and 23.5° for biuret， while in 2θ=12.84°， 20.08° and 21.03° for cobalt acetate （JCPDS 0250372）. The main strong peaks of complex 1 are different from the main strong peaks of the raw materials. Similarly， the three main strong peaks of complex 2 appear in 2θ=28.49°， 13.23° and 15.12°， while in 2θ=15.24°， 35.74° and 51.44° for cobalt chloride （JCPDS 0150381）. At the same time， the three main strong peaks of complex 3 appear in 2θ=27.91°， 17.19° and 13.37°， and they are distinct from the main strong peaks at 20.69°， 26.83° and 40.42° for cobalt nitrate （JCPDS 0190356）. In short， all these strong peaks of the reactants are disappeared in Xray powder diffraction patterns of the three complexes. The diffraction angle （2θ）， diffractive intensity and spacing （d） of the products are completely different from the reactive materials， which may illuminate that the resultants are new compounds instead of the reactant mixture[15]. 　　2.4Thermal analysis 　　Thermogravimetric analysis under air is determined with the samples to investigate the thermal stabilities of three complexes and the TGDTG curves are shown in Figs. 3～5. In Fig.3， there is a mass loss of 12.41% near 118 ℃ for complex 1， which is ascribed to the loss of three lattice water and coordinated water molecules and the measured value is in agreement with the calculated one （12.36%）. There is a large mass loss of 47.20% at 178 ℃， 220 ℃ and 242 ℃ in DTG curve， which can be interpreted as the decomposition of the biuret ligand， and it is close to the calculated result （47.15%）. In the last step， it is the process of decomposition of Co（CH3COO）2， and the mass loss of 23.27% is in agreement with the calculated one （23.35%）. The residual mass of complex 1 in the TG curve is 17.12%， which agrees with the theoretical value （17.14%）， and the final residue is CoO. 　　Fig.3TGDTG curves of the complex 1Fig.4TGDTG curves of the complex 2In Fig.4， it is not difficult to find that complex 2 is stable up to 223 ℃ comparing with complex 1， whereafter the compound begins to collapse. The complex undergos two mass losses of 34.40% and 26.69% near 267 ℃ and 367 ℃， which represent the oxidation and decomposition of the biuret ligand （calcd. 61.36%）. There is a mass loss of 16.25% in the last step， which is considered to be the decomposition of cobalt chloride （calcd. 1634%）， and the final residue is CoO （found 22.66%， calcd. 22.30%）. 　　Fig.5TGDTG curves of the complex 3As shown in Fig.5， the decomposition process of complex 3 is divided into three steps. The mass losses are 795%， 56.62% and 20.30% near 133 ℃， 261 ℃ and 452 ℃， respectively， which agree with the loss of 2.5H2O （calcd. 8.38%）， 3C2H5O2N3 （calcd. 57.57%）， and N2O5 （calcd. 20.11%）. The final residue is CoO （found 14.45%， calcd. 13.95%）. 　　3Conclusions 　　Three kinds of Co（Ⅱ） complexes， namely [Co（bi）2（H2O）2]（Ac）2・H2O （1）， [Co（bi）2Cl2] （2）， and [Co（bi）3]（NO3）2・2.5H2O （3）， were synthesized. The Co（Ⅱ） complexes were all hexacoordinated， and the Co（Ⅱ） was coordinated by all the carbonyl oxygen atoms from the biuret molecules， while the cobalt ion was too coordinated by two oxygen atoms from coordinated water molecules in complex 1 and two chloride atoms in complex 2. This may be the reason that the structures of three complexes were quite different. The thermal analysis results showed that the complexes of 1 and 3 were lost water molecules below 170 ℃， then the biuret ligand in the three complexes was oxidized and decomposed about 200 ℃， and finally inorganic salts of cobalt（Ⅱ） were decomposed into cobalt oxide. The biuret complexes of trace elements can play a dual role of essential trace elements and non protein nitrogen nutrition supplements. With the rapid development of animal industry in our country， the prospects of biuret complexes which are used as feed additives for ruminants are considerable. 　　References： 　　[1]HARRISON W T A. Two scandiumbiuret complexes： [Sc（C2H5N3O2）（H2O）5]Cl3・H2O and [Sc（C2H5N3O2）4]（NO3）3 [J]. Acta Crystallogr C， 2008，64（5）：205208. 　　[2]FREEMAN H C， SMITH J E W L. Crystallographic studies of the biuret reaction. Ⅱ. structure of bisbiuretcopper（Ⅱ） dichloride， Cu（NH2CONHCONH2）2C12[J]. Acta Crystallogr， 1966，20（2）：153159. 　　[3]HADDAD S F. Structure of tetrakis（biuret）samarium（ⅡI） nitrate， [Sm（NH2CONHCONH2）4]（NO3）[J]. Acta Crystallogr C， 1987，43（10）：18821885. 　　[4]TANG N， TAN M Y， ZHAI Y L， et al. Synthesis and characterization of the solid complex of thorium nitrate with biuret[J]. J Lanzhou Univ （Nat Sci）， 1986，22（1）：9094. 　　[5]GRAF M， SüNKEL K， CZERWIENIEC R， et al. Luminescent diiridium（Ⅲ） complex with a bridging biuretato ligand in unprecedented N，N′：O，O′ coordination[J]. J Organomet Chem， 2013，745746：341346. 　　[6]AHMAD N， ALAM M， ALOTAIBI M A N. Synthesis， Characterization， and Thermal degradation kinetics of biuretformaldehyde polymeric ligand and its polymer metal complexes[J]. J Therm Anal Calorim， 2015，119（2）：13811391.