Divalent chromium, pentavalent chromium and tetravalent chromium compounds

Chromium can form many compounds with a low oxidation state, such as compounds with an oxidation state of 0, such as the bigroup complex Cr(CO) ₆ (white), and the benzene sandwich complex Cr(C ₆ H ₆ ) ₂ (brown-black)
.

1.
Divalent chromium compounds

Cr(II) anhydrous halides include CrF ₂ (blue-green), CrCl ₂ (white), CrBr ₂ (white), and Crl ₂ (red-brown), all of which are ionic compounds with melting points above 800°C
.

CrSO ₄ ·5H ₂ O(blue), [Cr(H ₂ O)4Cl ₂ ]·4H ₂ O(blue), Cr(C ₅ H ₅ ) ₂ (dark red, Mao sandwich complex), Cr( CH ₃ COO) 2·H ₂ O (red) and other dimers (as shown in Figure 16-2), containing a Cr-Cr quadruple bond
.

Figure 16-2 Cr(CH ₃ COO) ₂ ·H ₂ O dimer structure

2.
Compounds of pentavalent chromium and tetravalent chromium

The only stable compound of pentavalent chromium is fluoride CrF ₅ (red), which has low melting point (34°C) and boiling point (117°C), strong oxidizing property, and volatile
.

Among the tetravalent chromium halides, CrF _{4 is the} most stable, green solid, with a melting point (277°C) significantly higher than CrF5, and does not decompose when melted
.
CrCl ₄ exists only in gaseous form at high temperatures and decomposes above 600°C

Chromium dioxide CrO ₂ (brown-black) has the conductivity of metal
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The ferromagnetic properties of CrO ₂ make it used in magnetic tape manufacturing.