“Brown‐Ring”‐Related Coordination Polymers of the Quartet‐{FeNO}7Chromophore

Georg Monsch,Peter Klüfers,Areenan In‐Iam,Xaver Kästele

doi:10.1002/zaac.201900352

Georg Monsch, Peter Klüfers + Show 2 more

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https://doi.org/10.1002/zaac.201900352

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Abstract

A conspicuous detail of the so‐called brown‐ring test (the analytical test on nitrate) is the reddish color of the bottom layer of concentrated sulfuric acid, which develops upon the bleeding of the brown layer into the acid. Crystals of the same color form from a solution of ferrous sulfate in concentrated sulfuric acid on saturation with gaseous nitric oxide. The structure of this H3O[{Fe(NO)(μ4‐SO4)(μ2‐SO4)0.5}n/n] (1a) is made up from infinite chessboard‐type layers with sulfur on the field junctions and Fe(NO) moieties below the black and above the white fields. An Fe–N–O angle of about 160° causes disorder in the tetragonal space groupI4/mmm. A similar crystal pathology was found in the related [{Fe(MeOH)(NO)(μ4‐SO4)}n/n] (1b) in the same crystal class. A one‐dimensional coordination polymer is formed in crystals of a third compound that comprises the Fe(NO)O5coordination pattern, namely the brown oxalato species [{Fe(H2O)(NO)(μ2‐ox)}n/n·H2O] (2). A still larger NO tilt of about 156° is not obscured by disorder in the triclinic crystals of2.

Highlights

In a first intense period of research on the reaction products of iron(II)-containing solutions and gaseous nitric oxide, the competing groups of Manchot and Kohlschütter discovered experimental conditions for the preparation of the parent chromophore [Fe(H2O)5(NO)]2+ as well as variants thereof.[1]
Manchot claimed two solids: a brown to black 2FeSO4·NO·13H2O, which precipitated from aqueous solutions of the components on ethanol addition, and red crystals of an FeSO4·NO, which grew from red solutions of ferrous sulfate in concentrated sulfuric acid after exposure to nitric oxide.[1e]. Schlesinger and Salathe reproduced
The formation of red crystals from concentrated sulfuric acid reliably occurred as described by Manchot

Summary

Introduction

In a first intense period of research on the reaction products of iron(II)-containing solutions and gaseous nitric oxide, the competing groups of Manchot and Kohlschütter discovered experimental conditions for the preparation of the parent chromophore [Fe(H2O)5(NO)]2+ as well as variants thereof.[1]. In a first intense period of research on the reaction products of iron(II)-containing solutions and gaseous nitric oxide, the competing groups of Manchot and Kohlschütter discovered experimental conditions for the preparation of the parent chromophore [Fe(H2O)5(NO)]2+ as well as variants thereof.[1] In terms of color, weakly acidic FeII/NO solutions containing this ion resemble the brown part of the layer, which is obtained in the course of a positive nitrate test in the classical “brown-ring”

Results

Conclusion