Aug 6, 2003 - ethylenediammonium chromate and ethylenediammonium dichromate. B R Srinivasan* .... The reaction of ammonium chromate \\ ith. 'en' also.
Indian Jo urnal of Che mi stry Vo l. 42A. Nove mbe r 2003, pp. 2735-2741
Synthesis, spectroscopic and X-ray structure characterization of ethylenediammonium chromate and ethylenediammonium dichromate B R Srin iv asan*, Sunder N Dhuri , Christian Nathert & Wolfgang Benschi * Departme nt of Chemi stry, Goa Unive rsity, Taleigao Plateau, Goa 403 206, Indi a Email: srini go uri @rediffm ail. com t lnstitut fUr Anorga ni sche Chemie, Christian-Albrechts-Universitat Ki el, Ol shau se n stra~e 40. 0-24098 Ki el. Ge rm an y Email: wbensc h @ac. uni -kiel.de
Received /2 /h November 2002; revised 6 August 2003 Th e reacti on of e th ylenediammo nium chl oride (enH 2)C I2 with potass ium chromate o r dichromate in a I: I mole ratio result s in th e fo rmation of the titl e co mpl exes ethylenediammonium c hromate (enH 2)[Cr04] 1 and eth y le nediammonium dic hromate (en H2) [C r207] 2 in good yields. The two co mplexes have bee n characterized by [R, UV-V is. IH NMR spectroscopy and me ta l a nalysis and their struc tures have been determined by sing le crystal X-ray crysta ll og raph y. Eth yle nedi amm onium chromate 1 cry stalli zes in th e o rth orhombic space g roup P2 12 121 (IT-Nr. :19) with the unit ce ll dime nsio ns a = 6.656( I) A, b = 8.869( I) A, c = 11 .83 1(2) A, V = 698.4(2) A J , Z = 4. The struc ture o f 1 co nsists or tetrahed ra l tetraoxoc hroma te di ani ons, with the Cr at the center of the te trahedron. Ethy lenediammonium dichromat e 2 c rys talli zes in th e mo noc lini c space group C2/c (IT-Nr. : 15 ) with the unit ce ll dime nsio ns (/ = 13.464(2) A. b = 7.79 1( I ) A. 3 (' = 8.639( I) A.. ~= I 08.97( I V = 857.0(2) A , Z = 4. [n both the co mpo und s, sho rt H-bo ndin g co ntacts are obsc r\'cd betwee n the oxygen atom s bound to the Cr co ntaining di an ion and the H attached to the N atom of the o rgani c d icat io n.
t.
C hro mium(VI) based reagents are an important class of co mpounds. which are extensively used in organic sy ntheses to effect a variety of synthetic transformations !.2. The commonly used Cr(VI) reagents are chromium tlioxide (crO)) in combination with a vari ety of organic compounds like acetic acid or acetic anhydride or pyridine etc., a mixture of sodi um di chromate and concentrated sulphuric acid and pyridinium chlorochromate3.4. In the last two decades, chromium(VI) reagents in combination with amines have been widely used for the oxidation of alcohol s to 5 the corresponding carbony l compounds . It has been show n that the nature of the amine determines the oxid izing power of the chromate ion and this is in versely rel ated to the donor strength of the associated amin e Ii gand.'i·6. Tetra methylethylenediammonium 7 d ichro mate and piperazinium dichromate 8 , which co ntain tetrameth ylethylenediamine and the cyclic diallline piperazine in the ir diproto nated form have bee n recently introduced as reagents in organic syn th eses as mi Id oxi dants. The [M0 4],,- tetrahedron can be used as a n acentric building bl ock to create non-ce ntrosy mmetric mat eria ls. Based o n thi s strategy, Poeppe lmei er9 and cowo rkers have reported the synthes is of novel c1 ich romates having formula [M (PY)4]Cr20 7 (M=Cu , Zn or Cd). Of these, th e Zn and Cu dichromates
exhibit interesting structural features like neutra l nOflintersecting one-dimensional chains of M(pyLCr:O i and nonlinear optical properties. Altho ug h a number of chromates and dichromates containing in o rganic cations have been structurally characterised')-17. relatively few structures of Cr(V l) comp0uflds containing organic cations have been determi fl ed I '-:' I . An important aspect of the reported struc tures of th e organic salts of Cr(VI) co mpo und s I S thL' identification of an extended H-bondin g net work ill these systems. In view of the importance of o rganic salts of chromate and dichromate in sy nthetic o rga nic chemistry, and also their emerging importan ce a~ useful material s, it is desirabl e to develop ne\\' synthetic methodologies for the pre paration o f s uch salts and also to determine th e three dime nsio na l structures. Hence, the study of Cr(V I) compounds arc of current interest. As part of an o ngo in g prog ra mm l' aimed at the sy nthesis of Mo/W-S compo un cl~ contallllllg organ ic dication s, the structures of (enH z)[M 'S4] (en=ethy le nedi amine M' = Mo or W ) 21 have already been reported by us recent li 2. . We have extended thi s chemistry to th e correspo ndin g oxochromates and devel o ped a conveni ent syntheti c route for the preparation of the e thyl e nedi alllJll oniulll sa lts of chromate and dichromate. The res ults or th c~l' investigation s are described in this pape r.
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INDIAN 1 CHEM, SEC A, NOVEMBER 2003
Materials and Methods Solvents and reagents were used as obtained from co mmercial sources in this investigation. Infrared spectra in the 4000-400 cm" region were recorded on a Shimadzu (Model 8101 A) FrIR instrument. The samples were pressed as KBr diluted pellets in the so lid state and the infrared signals referenced to po lystyrene bands. UV-Vis spectra were recorded on a Shimadzu UV-1601 instrument using matched quartz cells. The 'H NMR spectra of (enH 2 )[Cr04] 1 and (enH 2)[Cr2 0 7] 2 were recorded in DMSO-d6 and D2 0 o n a Bruker 300 MHz instrument at the National In stitute of Oceanography (NIO), Goa. Chromium anal yses were performed gravimetrically following a 24 . Iandard procedure . Single crystal X-ray structure determin atio n was performed on a AED2 four-circle di ffractometer.
Preparation of ethylell.ediamllloniu/11 chromate 1 KJCr04] (1.94 g, 0 .01 mol) was dissolved in water (20 ml ) and (enH 2)CI 2 (1.33 g, 0.01 mol) in water (5 1111) was slowly added at room temperature. The ye ll ow coloured solution thus obtained was filtered and kept in the refrigerator for crystallisation. After 2 days ye llow block-like crystals were obtained. The crystalline product was filtered and washed with iceco ld water (- 5 ml) and air-dried . Yield (54 %). IR Data: 2971-2365(br), 2081 (w), 1607 (m), 1526 (m), 1466 (m) , 1412 (w) , 1327 (w), 1256 (w), 1098 (m), 1067 (m) , 1021 (s), 924 (s) , 80 1 (br) , 777 (m) cnf' . UV-V is. Data: 373 nm (£=2500), 270 nm (£=2480) An al. Found (caled.): Cr 29.1. % (29 .2 %). Preparation of ethylen ediammoniwn dichrolllate 2 K2[Cr20 7] (2.94 g, 0 .0 I mol) was dissolved III water (25 ml) and (enH 2)Ch (1.33 g, 0.01 mol) in water ( 10 ml) was slowly added at room temperature. The oran ge coloured so luti on thu s obtained was fi !tered and kept aside for crystallization. After 2-3 day s orange crystalline blocks were obtained. The crysta lline product was fi ltered and washed with icecold water (-10 ml) and air-dried . Yield (65 %). IR Data: 3063-2512 (br), 1615 (m), 1556 (m), 1501 (m), 1470 (m) , 1360 (m), 1333 (w), 1065 (m), 1022 (m), 930 (s), 878 (m), 787 (w) cm", UV-vis. data: 353 nm (£=2770), 260nm (£=3700) Anal. Found (caled.): Cr 37,3 % (37.4%).
Results and Discussion The reaction of an aqueous (enH 2)CI 2 solution with K2 lCr04] or KACr20 7] in a 1: 1 mole ratio readily
affords the title compounds in good yield s and till' product formation can be represe nted as :-. IH)\\ ' 11 below: K2 [Cr04] + (enH 2)CI 2 ------?
(enH2)[CI'O~ ]
,!,
.2 KCI .. , ( I )
K 2 [Cr20 7] + (enH 2)Ch ------? (enH2) [Cr20 7] (2) + :2 KC I .. , (2)
where 'en' stands for ethyl enediam ine The more soluble KCI remains in solution and till' organi c chromates crystalli se out from th c re4
