Hydrogen bonding and cation ordering in Magnet Cove pectolite

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Abstract
The crystal structure of Mn-bearing pectolite has been refined to R = 2.1% using crystals from Magnet Cove, Arkansas, U.S.A.: HNaCa1.969Mno.045Fe0.014-Si3O9, a = 7.980(1) Å, b = 7.023(1) Å, c = 7.018(1) Å, α = 90.54(1)°, β = 95.14(1)°, γ = 102.55(1)°, P[unk], Z = 2, D x = 2.906 gem−3. The result has established that hydrogen bonds occur between pairs of oxygen atoms, O(3) and O(4), in each silicate chain, the distance between the paired oxygen atoms being 2.473(2) Å. The difference Fourier peak showing the hydrogen atom assumes the following random model rather than a symmetrical bond: The hydrogen atom is mainly associated with O(3) giving the O(3)–H bond length of 1.06(5) Å, and an angle of 171(1)° subtended at the hydrogen atom. There is between O(3) and O(4) another position for hydrogen associated with O(4); the occupancy of hydrogen atom at this position is smaller than that of the other position. The manganese atoms, including Fe, are fully concentrated at the M(2) position.

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