叶绿矾矿物中的新超结构

A New Superstructure in Copiapite

叶绿矾是具有岛状基本结构的硫酸盐类矿物,对产于新疆东天山北部红山矿区硫化物矿床氧化带中的叶绿矾进行单晶衍射实验发现,该叶绿矾具有明显的超结构弱衍射点,利用包括弱衍射点在内的全部可观察点求得的超晶胞参数为:a=1.49441(7)nm,b=1.83429(9)nm,c=1.14507(6)nm,α=93.2390(10)°,β=112.0330(10)°,γ=98.2800(10)°,V=2.8583(2)nm3,空间群为P1,Z=3。去掉弱衍射点后利用强衍射点得到的最小亚晶胞参数是a=0.737121(4)nm,b=1.83079(11)nm,c=0.73106(4)nm,α=93.9250(10)°,β=102.7252(10)°,γ=98.9463(10)°,V=0.947321(2)nm3,空间群为P1,Z=1。超晶胞与亚晶胞相比体积增加了2倍,其b轴的方向和大小基本不变,a和c轴产生了差异。该叶绿矾的晶体化学式为Fe0.656Fe4(SO4)6(OH)2·19.4H2O,属高铁叶绿矾。结构中,部分Fe-O八面体和SO4四面体联合形成的复合链,并沿[102]方向分布,形成一种稳定的骨干结构;部分孤立Fe-O八面体,位于链间,阳离子相当于晶体化学式中A位置的离子,通常有缺失。链和孤立八面体的分布均平行(010)面网,分别构成链层和八面体层,并按2∶1的比例堆垛,结构单元之间全部由氢键相连。超结构产生的原因是电价补偿机制造成的孔道中Fe的位置分离和占位差异造成。

A new superstructure was found in a copiapite from Dongtianshan Xingjiang.The occurrence of the superstructure reflections were observed by using X-ray area-detector CCD Single Crystal diffraction.Cell parameters of all the diffraction points were a = 1.49441（7）nm,b = 1.83429（9）nm,c = 1.14507（6） nm,α = 93.2390（10）°,β = 112.0330（10）°,γ = 98.2800（10）°,V = 2.8583（2）nm^3,space group P 1 and Z = 3.Subcell parameters of obliterated weakness points were a = 0.737121（4） nm,b = 1.83079（11） nm c = 0.73106（4） nm,α = 93.9250（10）°,β =102.7252（10）°,γ = 98.9463（10）°,V = 0.947321（2）nm^3,space group P 1 and Z = 1.The cell volume in supercell was treble the volume of the subcell,and b was the same as both cell,but a and c were different.The chemical formulae implied ferrian copiapite with Fe0.656 Fe4（SO4）6（OH）2 ·20H2O.The superstructure was solved with direct methods and Fourier methods and refined to an R value of 0.044 for 11596 independent observed reflections.The structure was built by the chains formed by SO4 tetrahedra and Fe-（OH）,（H2O） or O octahedra,as well as isolated Fe-（H2O） octahedra coordinated A sites at the origin of the cell.Both structure units were connected with hydrogen bonds.The reason for the formation of superstructure was that A position Fe^3 ＋ split two sites and different occupancies,0.954 and 0.062,respectively.Total occupancy was statistically 2 /3.