红外与拉曼光谱案例教学

1、 FT-IR和Raman光谱在硼酸盐化学研究中的应用 1、 FT-IR和Raman光谱表征硼氧酸盐的结构 振动光谱法(Vibrational Spectroscopy)主要包括红外光谱法(Infrared Spectroscopy, IR)和拉曼光谱法(Raman Spectroscopy)，是现代实验技术中广泛应用的物理分析方法，不但可以用于分子组成的分析和结构的研究，而且还可以用于动态的物理行为和化学反应的研究。从量子力学的观点来看，如果振动时，分子的偶极矩发生变化，则该振动是红外活性的；如果振动时，分子的极化率发生变化，则该振动是拉曼活性的。一般来说，极性基团的振动和分子非对称振动使分子

2、偶极矩发生变化；非极性基团和分子的全对称振动使分子的极化率发生变化。利用群论的观点，从对称性出发，对照特征标表，可以预示在IR光谱或Raman光谱中可能出现的对应于简正振动模式的谱带数。1. 固体无机硼氧酸盐的振动光谱由硼氧酸盐晶体结构研究可知，BO键的强度比MO键(M=Metal)强度大得多，而MO振动也多在远红外区。因此，硼氧酸盐中硼氧配阴离子基团的内模振动可看作是硼氧酸盐的主要特征振动，且主要集中在中红外区(4000cm-1400 cm-1)。但由于硼氧酸盐结构的复杂多变性使得其振动光谱特别是IR光谱也表现出相当的复杂性。1.1 硼氧酸盐振动光谱的理论分析(1) 孤立BO3基团的正则坐标

3、分析BO3的最高对称点群为D3h，但实际晶体中位置群要低得多，为便于计算，假设它处于C3v对称条件下。内振动模式vib = 2A1(IR, R) + 2E(IR, R)，表1.1给出C3v对称条件下孤立BO3的正则坐标分析结果及IR光谱实验观测值。表1.1 C3v对称孤立BO3的正则坐标分析结果及实验观测值ModesFrequencies (cm-1)Calculateda 1Observedb2A11(sym. str.)9449392(out-of-plane bend)754740E3(asym. str.)1247 13304(in-plane bend)594606a By usin

4、g a general valence force field (GVFF)； b IR spectrum of LaBO3(2) 孤立BO4基团的正则坐标分析S. D. Ross2曾假定BO45-对BO33-的力常数比值与BF4-对BF3的相似，进而利用广义力价场模型(GVFF)计算了Td对称的BO4基团的振动模式，vib = A1(R) + E(R) + 2T2(IR, R)，与Weir等人3的IR光谱实验观测值一同列于表1.2中。表1.2 Td对称孤立BO4的正则坐标分析结果及实验观测值ModesFrequencies (cm-1)Calculateda2Observedb3Combin

5、ation or 1200wshovertone bend 1160wshA11(sym. str.)854 1037m927vbE2(bend)481470sT23(asym. str.) 1050 1082svb4(bend)702717sa By using a general valence force field (GVFF)；b IR spectrum of Zn4O(BO2)6 which was known to contain only tetrahedrally coordinated boron. s-strong, m-middle, w-weak, b-broad,

6、v-very, sh-shoulder显然，实际上BO4的对称性要比Td低，因此，Weir等人3对Zn4O(BO2)6的IR光谱的实验归属是基于C3v对称性展开的。(3) C3h对称的B(OH)3的理论分析B(OH)3在C3h对称条件下，内振动模式为vib = 3A'(R) + 2A''(IR) + 4E'(IR, R) + E'' (R)4。已有很多人进行过B(OH)3的IR光谱或Raman光谱的研究工作5。L. Andrews6和K. Zaki等人7分别从自洽场理论(SCF)和二级Moller-Plesset微扰理论(MP2)出发对B(OH)

7、3的振动模式作了计算，并与不同介质中B(OH)3的IR光谱实验观测数据进行了比较，现将他们的计算结果和B(OH)3的IR光谱和Raman光谱实验数据列于表1.3中。表1.3 C3h对称B(OH)3振动模式的理论计算结果及在不同介质中的实验观测值ModesFrequencies (cm-1)CalculatedObserved6SCF 6MP2 7SolidN2matrixArmatrixVaporRaman8 of solidA'1(sym OH str)420739483172370531642(sym BOH bend)111510451065(1015) a10203(sym B

8、O str)925886880866882A''4(sym BO def)7416826486756675(sym BOH def)477445824514436E'6(antisym OH str)42053949320036683689370632407(antisym BO str)1555150914501426(1421) b14298(antisym BOH bend)1108104411971010(1012) b101711709(antisym OBO bend)464428540449432E''10(antisym BOH def)

9、557547(577)(520) a502a Fundamentals deduced from mixed H/D isotopic bands.b Estimate of unperturbed fundamental without Fermi resonance.K. Zaki等人对A' 模所作的非谐性修正未列于表1.3中；另外，也未列出B(OH)3晶体IR光谱在2700cm-11950cm-1间的合频峰和倍频峰，可参见Broadhead等人9对此所作的讨论。从表1.3中可以看出，二级Moller-Plesset微扰理论拟合的结果与实验观测值更为接近；同时可以看到，原来在孤立状

10、态下非红外活性的A' 模振动，在晶体状态下被激活，这与晶体状态下B(OH)3对称性降低以及受到氢键影响等因素有关。而Raman光谱中的情况却恰恰相反。Lutz等人10对理论计算结果和实验观测值之间在活性和位移上存在差异的原因曾作过较详尽的论述。(4) B(OH)4-的正则坐标分析D2d对称和S4对称的B(OH)4-的内振动模式分别为：vib = 4A1(R) + 2B1(R) + 4B2(IR, R) + 5E(IR, R) (A2无活性)vib = 5A(R) + 6B(IR, R) + 5E(IR, R)V. Devarajan等人11对D2d对称和S4对称的B(OH)4-都作了正

11、则分析，并与Na2B(OH)4Cl的IR光谱和Raman光谱数据进行了比较，对振动频率给出了初步归属。在两种对称性下所得的计算结果相差不大，但以D2d对称性拟合的结果要稍好些。另外，V. Devarajan等人12对KB5O8·4H2O中(B5O8)基团也作过正则坐标分析，振动模式相当复杂。由以上对四种比较简单的硼氧基团振动模式的理论计算可见，引入H后，硼氧基团的振动模式会大量增加，加之在晶体中对称性降低等因素，水合硼氧配阴离子的振动模式一般都很复杂。因此，目前对比较复杂的水合硼氧配阴离子的振动模式进行理论分析，常常是非常困难的。1.2 硼氧酸盐的振动光谱特征IR光谱和Raman光谱

12、对无机化合物结构是非常重要的物理表征手段。半个世纪以来，在国内外各种科学期刊上关于无机盐振动光谱的研究报道屡见不鲜。Miller等人13, 14曾系统收集了上百种无机盐的红外光谱数据，并归纳了部分常见阴离子基团的特征吸收范围。但相应的Raman光谱的收集和频率归属目前仍未完成。(1) 无水硼氧酸盐无水硼氧酸盐大部分为合成化合物，主要有以下几类15：正硼氧酸盐(BO33-, orthoborate)、偏硼氧酸盐(BO2-, metaborate)、焦 (二)硼氧酸盐(B2O54-, pyroborate/ diborate)、三硼氧酸盐(B3O5-, triborate)、四硼氧酸盐(

13、B4O72-, tetraborate)、五硼氧酸盐(B5O8-, pentaborate)、六硼氧酸盐(B6O102-, hexaborate)和高聚硼氧酸盐(Higher Borate )。其中单体和部分低聚硼氧酸盐的振动光谱比较简单，易于识别和解析。早期的研究主要集中在IR光谱方面。因为晶体的基频振动和大部分强泛频及合频吸收峰都不会超过2000cm-1，所以，研究的波数范围多集中在2000cm-1400cm-1的中红外区域。Weir4, 16, Ross2和Seshadri17等对无水硼氧酸盐的IR光谱都有过研究和报道。其中Weir的研究工作最为全面和系统，曾先后报道了近百种无水硼氧酸盐

14、的IR光谱，并利用硼同位素替代方法研究了其中部分具有代表性的无水硼氧酸盐的IR光谱。根据研究结果，Weir3认为，对于正硼氧酸盐、焦硼氧酸盐和部分偏硼氧酸盐红外吸收频率的解析和归属是令人满意的；并且根据特征吸收峰，特别是伸缩振动峰位置的差别，可以区分三配位硼(1100cm-11300cm-1, strong, broad stretching oscillation)和四配位硼(800cm-11100cm-1, strong, broad stretching oscill ation)；但是对于比较复杂的具有硼氧六元环结构的无水硼氧酸盐的IR光谱还不能给予充分而可信的解析。继Weir之后，S

15、. D. Ross2和J. H. Denning18研究了SmYb (包括Y)正硼氧酸盐的IR光谱和Raman光谱，并通过正则分析认为其结构中并不含有孤立的BO33-基团，具有伪Vaterite的结构，由三个四配位硼通过O原子相连，形成一个B3O9六元环 (G. Chadeyron等19对YBO3结构的研究表明，它确实具有伪Vaterite的结构，属于P63/m空间群，硼为四配位，但是没有形成硼氧六元环结构，而是通过2个O原子分别与2个BO4相连，通过另2个O原子分别与2个YO8相连，形成三维网状结构)。Seshadri等人17分析了碱金属偏硼氧酸盐的IR光谱特征，不同阳离子对BO2-振动并没

16、有特别明显的影响。后来，Chryssikos等人20依据Raman光谱特征将碱金属和碱土金属偏硼氧酸盐分为以下三类：D3h环类，C3h环类和长链类。Shepherd21在研究磁性材料FeBO3不同温度的Raman光谱时发现，在接近居里温度时，其特征峰的强度会下降。近些年来，无水硼氧酸盐紫外非线性光学材料越来越受到人们的关注。对于无水硼氧酸盐振动光谱的研究也更多的集中到了这些材料上。表1.4列出几种常见的无水硼氧酸盐紫外非线性光学材料的基本结构参数及主要的振动光谱特征。表1.4 几种无水硼氧酸盐紫外非线性光学材料的基本结构参数及主要的振动光谱特征BoratesSpace groupof crys

17、talPolyborate anionsFrequencies /cm-1-BaB2O422-25R3cCB3O63-s-B(3)Oext. :IR 15001400; Raman 1545,1525LiB3O525, 26Pna21CB3O75-s-B(3)O: IR 999, 973, 959s-B(3)O: Raman 763s-B(4)O: Raman 550CsB3O527P212121DB3O75-Raman: s-B(3)O: 758; s-B(4)O: 550CsLiB6O1028I 2dDB3O75-Raman: ring: 620; s-B(4)O: 500Li2B4O72

18、9,30I41cdCB4O72-=2B3O6Raman: s-B(4)O: 720, 780 (2) 水合硼氧酸盐对于水合硼氧酸盐振动光谱的早期研究是从对硼氧酸盐矿物的IR光谱开始的，Weir31，Kessler32, 33，Heller34和Valyashko等人35都曾从事过这方面的研究工作。其中以Weir的工作最具代表性，报道了四十多种天然和合成水合硼氧酸盐的IR光谱。但是，由于水合硼氧酸盐晶体结构大多都相当复杂，因此在其IR光谱中含有大量未知的结构细节暂时无法作出进一步可信的解析。同时，由于受到当时实验条件和技术的限制，导致不同学者对同一种水合硼氧酸盐得到并不完全一致的光谱结果。据此，

19、Weir曾对水合硼氧酸盐IR光谱的可信性提出质疑。但是，Valyashko等人35通过研究认为通过对谱图的比较研究，解析未知硼氧酸盐的结构是可能的。1974年，Ross5在综合前人研究工作的基础上，总结了硼氧酸盐矿物(包括无水硼氧酸盐)的IR光谱，并且给出了它们的特征吸收范围，见表1.5。但是，Ross对于硼氧基团的特征吸收范围的归属仍然是比较宽泛的。表1.5 硼氧酸盐矿物的IR光谱吸收范围Region (cm-1)Cause of absorption36003000OH stretching or free H2O16601600Free H2O (bending mode)1500130

20、0Asymmetric stretching, trigonal boron13001000OH in-plane bending1100 850Asymmetric stretching, tetrahedral boron 950 850Symmetric stretching, trigonal boron 850 700Symmetric stretching, tetrahedral boron;OH out of plane bending 700 400Bending modes of trigonal and tetrahedral boron在Raman光谱中，水合硼氧酸盐的

21、特征峰一般比IR光谱少，但谱带却较窄，更具特征性。Janda和Heller36采用硼同位素替代法研究了硼酸、四硼酸铵及部分碱金属硼氧酸盐的IR光谱和Raman光谱，确定了多聚硼氧配阴离子的对称脉冲振动峰，并且对硼氧基团的特征振动频率给出了更为详尽和可信的归属，见表1.6。Kloprogge和Frost37对钠硼解石，四水硼砂和多水硼镁石的Raman光谱进行过报道，对硼氧基团Raman振动频率的归属与Ross给出的结果相同。另外V. Bermanec等人38对NaCaB5O8(OH)2·3H2O的振动光谱也有过报道。国内此项研究的起步较晚，谢先德，查福标对硼酸盐矿物的振动光谱做过专门著

22、述39，对不同温度下加热过的硼酸盐矿物的IR光谱40的研究中发现，观测不同温度下热分解样品的谱带特征有助于谱带的归属。王继扬、李丽霞等人41, 42从群论的观点出发研究了KB5O8·4H2O 和K2B4O7·4H2O的Raman光谱，认为其中的最强峰属畸变BO4四面体的内模振动。李军、高世扬、朱黎霞等43系统地完成了三十多种水合硼氧酸盐振动光谱的测定工作，并尝试对其振动频率进行了归属，为进一步深入开展水合硼氧酸盐及其水溶液振动光谱的研究，建立硼氧酸盐振动光谱库，奠定了良好的基础。目前，水合硼氧酸盐振动光谱的表征性已经普遍为人们所认可，且可以提供重要的结构信息。对一些未知结构

23、的硼氧酸盐，通过与已知结构的硼氧酸盐振动光谱特征谱带对比，可以对其结构作出比较可靠的预测。表1.6 BO基团在IR光谱和Raman光谱中的振动频率归属75Wave number (cm-1)Oscillation 490540s-B(4)O(IR, R) 500s-B(3)O(R) 520550s-B(3)O(IR) 529560p-B5O6(OH)4- (R*) 567590p-B4O5(OH)42-(R*) 613p-B3O3(OH)4- (R) 620700-B(3)O(IR) 720750-B(3)O(IR) 738785s-B(4)O(IR, R) 877950s-B(3)O(IR,

24、 R) 933980as-B(4)O(IR, R) 9951150as-B(4)O(IR, R) 1193 1370as-B(3)O(IR, R)* Predominant IR = IR active R = Raman active1.3 稀碱金属硼酸盐及其复盐的振动光谱研究1.3.1 合成 根据文献制备得到如表 所示的稀碱金属硼酸盐及其复盐。Table 1.7 Chemical Composition of borates (mass fraction)BoratesStructural formulaChemical CompositionM2OMOB2O3H2ORef.Rb2B4O7

25、·5.6H2ORb2B4O5(OH)4·3.6H2O43.8632.6223.5244Cs2B4O7·5H2OCs2B4O5(OH)4·3H2O57.1228.2614.6445Rb2CaB8O14·12H2ORb2CaB4O5(OH)42·8H2O25.42 7.5837.8129.4046Cs2CaB8O14·12H2OCa2CaB4O5(OH)42·8H2O33.79 6.7633.4525.7547K2SrB8O14·14H2OK2SrB4O5(OH)42·10H2O12.9114.17

26、38.2134.7148RbB5O8·4H2ORbB5O6(OH)4·2H2O27.6651.2020.9349CsB5O8·4H2OCsB5O6(OH)4·2H2O36.4544.9418.6550KBO2·4/3H2OK3B3O4(OH)4·2H2O44.5132.9522.5451K2CoB12O20·10H2OK2CoB6O7(OH)62·4H2O12.29 9.7654.5523.4052Rb2CoB12O20·10H2ORb2CoB6O7(OH)62·4H2O21.93 8.5748

27、.4021.10531.3.2. TetraborateInfrared and Raman spectra of two hydrated alkali tetraborates and three alkali double tetraborates are shown in Fig.1 and 2. and the data are tabulated in Table.2. The structure of those compounds contain isolated B4O5(OH)42- which is constructed from two BO3(OH) tetrahe

28、dron groups and two BO2(OH) triangular groups joined at common oxygen atoms. The two BO3(OH) tetrahedron groups are further linked by means of an oxygen bridge across the ring. The double borate Rb2CaB4O5(OH)42·8H2O is isotypic with Cs2CaB4O5(OH)42·8H2O and is homeotypic with the K2SrB4O5(

29、OH)42·10H2O, however, Rb2B4O5(OH)42·3.6H2O is also isotypic with Cs2B4O5(OH)42·2H2O. Infrared and Raman spectra of Rb2CaB4O5(OH)42·8H2O are similar to those of Cs2CaB4O5(OH)42·8H2O. For each band found in the spectra of Rb2CaB4O5(OH)42·8H2O a corresponding band is obser

30、ved in the Cs2CaB4O5(OH)42·8H2O with frequencies differing at most by -2cm-1. In the range 1050 to 938cm-1 three major IR absorptions are characteristic peaks of borates containing B4O5(OH)42-, and attributed to the asymmetric stretching mode of B4-O and the symmetric stretching mode of B3-O re

31、spectively. In the Raman spectra, the very sharp band observed at around 570cm-1 is attributed to the pulse vibration of tetraborate anion B4O5(OH)42- according to the work of Janda and Heller36, and middle intensity bands at around 770 and 460cm-1 are attributed to the symmetric stretching and the

32、bending mode of B4-O. The weak bands at near 1350cm-1 can be asymmetric stretching mode of B3-O.In comparison with the previous various spectra study , all hydrated borates containing the basic B4O5(OH)42- anion with differing degrees of hydration and polymerization show similar infrared and Raman s

33、pectra. Raman shift(cm-1)Fig.1.2 Raman spectra of tetraboratesA: Cs2B4O5(OH)4·3H2O B: Rb2B4O5(OH)4·3.6H2OC: Cs2CaB4O5(OH)42·8H2OD: Rb2CaB4O5(OH)42·8H2OE: K2SrB4O5(OH)42·10H2OWavenumber(cm-1)Fig.1.1 FT-IR spectra of tetraboratesA: Cs2B4O5(OH)4·3H2O B: Rb2B4O5(OH)4·3

34、.6H2OC: Cs2CaB4O5(OH)42·8H2OD: Rb2CaB4O5(OH)42·8H2OE: K2SrB4O5(OH)42·10H2O8Table 1.8 Results for FT-IR and Raman spectra of hydrated alkali tetraborates (cm-1) Rb2CaB4O5(OH)42·8H2OFT-IR RamanCs2CaB4O5(OH)42·8H2OFT-IR RamanK2SrB4O5(OH)42·10H2O FT-IR RamanRb2B4O5(OH)4

35、3;3.6H2OFT-IR Raman Cs2B4O5(OH)4·3H2OFT-IR RamanAssignment3614.72s3611.71s3614.28s3611.90s3488.89bw3588.32s3598.33m3593.65m3608.41m3603.61m3439.92w3443.02bw3439.22w3465.40bw3293.33bm3434.93s3362.13bw3533.16m3358.55bvw3549.97m3319.61vw3275.19vw3296.30vw3293.58vw3207.41bw3185.72bvw3200.00bw3348.8

36、9bw(O-H)3200.00vw3210.47vw3185.19vw3200.23vw3147.69bw2607.41vw2597.95vw2592.20m2585.19w2437.04vw2442.35vw2406.00bvw2429.63bvw2432.65bw2359.95vw2363.63vw1680.45m1669.76m1653.55m1678.52w(H-O-H)1632.61m1629.02m1645.47w1646.75bm1453.70bw1432.58bw1423.00bm1453.94bvw1457.50m1344.38bwas(B3-O)1345.45m1349.6

37、8m1343.71m1350.89m1348.42m1341.42m1342.51m1290.39w1282.68w1249.83bw1232.63bm1220.35bm1264.67w1229.34w1152.03m1147.94bm1143.37bm(BO-H)1157.98bm1148.61bm1125.39w1120.55w1067.94w1063.55w1052.35bvw1050.35bvw1050.80was(B4-O)1001.76m1021.45bw1001.57m1004.08bw 999.93s1000.50s 998.45m 998.64m1002.54m 945.22

38、s 943.11w 943.04s 940.45w 943.55vs 940.55vs 941.71w 939.30vs 938.83ws(B3-O) 833.08m 831.06m 828.30s 825.33s 830.55bw 819.42s 772.68m 770.95m 781.08m 771.38m 771.10ms(B4-O) 707.90m 703.00m 707.69m 706.70w 712.39 659.06bm 661.92bw 680.83w 668.53m(B3-O) 606.93bw 653.56w 640.18w 590.92bm 576.47vw 586.47

39、bw 576.71vw 572.26bw 573.45s 566.28w 568.26vs 572.03vsp(tetraborate anion) 532.05m 530.06m 518.22w 519.33m 518.24w 464.09m 461.75m 464.20m 576.71vw 459.66m 458.12m 462.84m 459.83m(B4-O)b=broad m=middle s=strong v=very w=weak, B(3)-O means three coordinate boron; B(4)-O means four coordinate boron121

40、.3.3. Pentaborate Infrared and Raman spectra of RbB5O6(OH)42H2O and CsB5O6(OH)42H2O are shown in Fig.3 and 4, respectively, and the band assignments are listed in Table 3. The B5O6(OH)4- consists of a central BO4 tetrahedral with two opposite tetrahedral edges shared with B2O3(OH)2 groups. A series

41、of borate compounds MB5O6(OH)4xH2O(M=Li,Na,K,Rb,Cs and NH4) reported are isotypic or homeotypic. IR and Raman spectra of RbB5O6(OH)42H2O and CsB5O6(OH)42H2O are similar to those of MB5O6(OH)4xH2O(M=Li,Na,K and NH4). The characteristic peaks of infrared spectra of borates containing pentaborate anion

42、 B5O6(OH)4- exhibit at around 1090,1025,925,780 and 690cm-1. In the Raman spectra, the very sharp strong band observed at 550cm-1 is assigned to the pulse vibration of pentaborate anion B5O6(OH)4- according to the work of Janda and Heller9. The middle band at 914.81(905.76) and 764.57(767.48)cm-1 is

43、 characteristic for the symmetric stretching modes of B3-O and B4-O, respectively. Two weak bands observed at 507.51(503.57) and 454.61(459.59)cm-1 are attributed to the bending modes of B4-O.Raman shift(cm-1)Fig.1.4 Raman spectra of pentaboratesA: CsB5O6(OH)4·2H2O B: RbB5O6(OH)4·2H2OWaven

44、umber(cm-1)Fig.1.3 FT-IR spectra of pentaboratesA: CsB5O6(OH)4·2H2O B: RbB5O6(OH)4·2H2OTable 1.9 Results for FT-IR and Raman spectra of hydrated pentaborates (cm-1)RbB5O6(OH)42H2OFT-IR Raman CsB5O6(OH)42H2OFT-IR RamanAssignment3442.07s3441.74s 3390.06s3083.99s3075.05m3131.00s3121.61s(O-H)2

45、454.80m2420.88m2167.79w2189.15w1647.77m1642.71m(H-O-H)1427.25bvw1488.15w1430.95bvw1474.28was(B3-O)1357.62bvw1363.61bvw1238.18m1219.35m(BO-H)1087.40s 1085.69w1077.64m1063.57was(B4-O)1023.38m1023.57m 922.95s 914.81m 925.11s 905.76ms(B3-O) 780.82s 785.69w 779.64ss(B4-O) 745.50w 764.57m 747.51m 767.48m

46、691.05s 691.66s 639.94m 637.85w(B3-O) 597.00w 609.00w 553.31vs 542.84m 547.81vsp(hexaborate anion) 501.24m 507.51w 501.12m 503.57w(B4-O) 457.94m 454.61w 457.94m 459.59wb=broad m=middle s=strong v=very w=weak, B3-O means three coordinate boron; B4-O means four coordinate boron1.3.4. Hexaborate and tr

47、iborateInfrared and Raman spectra of two alkali cobalt hexaborates and one triborate are shown in Fig.5 and 6, respectively, and the band assignments are listed in Table 4.The B6O7(OH)62- ion contains three triangular and three tetrahedral boron group and is unique in that one oxygen atom is common

48、to all three rings. The hexaborate K2CoB6O7(OH)62·4H2O is isotypic with Rb2CoB6O7(OH)62·4H2O and their vibrational spectra show very similar. For each band found in the spectrum of K2CoB6O7(OH)62·4H2O a corresponding band is observed in the Rb2CoB6O7(OH)62·4H2O with frequencies d

49、iffering at most by +4cm-1. Infrared spectra of alkali cobalt hexaborate occur in range 3500 to 3100cm-1 because of hydrogen bonding, with decreasing strength going towards lower frequencies, and the middle band at 1641.66(1639.51)cm-1 is related to H-O-H bonding mode. The three weak peaks at 1443.7

50、5(1443.35), 1412.87(1412.18) and 1363.89(1362.77)cm-1 are attributed to the asymmetric stretching modes of B3-O. Two alkali cobalt hexaborates show two sharp characteristic bands at 947.61(945.28) and 809.39(805.15) cm-1, and those peaks are assigned as the symmetric stretching modes of B3-O and B4-

51、O, respectively. In the Raman spectra, the strong band observed at 620.19(616.79)cm-1 are assigned to the symmetric pulse vibration of hexaborate anion. Compared with alkaline-earth metal borates reported by Li Jun, infrared and Raman spectra of alkali cobalt hexaborates show a resemblance to those

52、of alkaline-earth metal borates and the difference lies in the shifting of bands.The triborate K3B3O4(OH)42·2H2O was built up from six-membered rings formed from alternate boron and oxygen by concern sharing among two BO4 tetrahedral and one BO3 triangle. Infrared and Raman spectra of this compound is similar